Thèses sur le sujet « Contingent capture of attention »

The environment is abundant with visual information. Each moment, this information competes for representation in the brain. From billboards and pop-up ads to smart phones and flat screens, in modern society our attention is constantly drawn from one salient object to the next. Learning how to focus on the objects that are most important for the current task is a major developmental hurdle. Fortunately, rewards help us to learn what is important by providing feedback signals to the brain. Sometimes, in adolescence for example, reward seeking can become the pre-potent response. This can ultimately lead to risky and impulsive behaviors that have devastating consequences. Until recently, little has been known about how rewards operate to influence the focus of attention. In this document, I first demonstrate the robustness of various behavioral paradigms designed to measure reward processing in vision. I found that even mundane rewards, such as images of money, are effective enough to prime the attentional system on the basis of value. Remarkably, this effect extended to images of Monopoly money. This observation suggests that whole classes of visual stimuli, such as food, pornography, commercial logos, corporate brands, or money, each with its own reward salience value, are likely vying for representation in the brain. This work has implications for the growing digital economy as it suggests that novel value systems, such as the digital currency Bitcoin, could eventually become as psychologically relevant as physical currency provided sufficient use and exposure. Likewise, this work has implications for gamification in the industrial setting. Next, I examined the sensitivity of the system to make optimal economic decisions. When faced with an economic choice normative theories of decision-making suggest that the economic actor will choose the response that affords the greatest expected utility. Contrary to this account, I developed a new behavioral paradigm (reward contingent capture) and reveal that the attentional homunculus is a fuzzy mathematician. Specifically, I found that low-level attentional processes conform to the same probability distortions observed in prospect theory. This finding supports a unified value learning mechanism across several domains of cognition and converges with evidence from monkey models. Then, I demonstrate the influence of rewards on high-order search parameters. I found that images of money can implicitly encourage observers to preferentially adopt one of two search strategies – one that values salience versus one that values goals. Together, my results expose two distinct ways in which the very same rewards can affect attentional behavior – by tuning the salience of specific features and by shaping global search mode settings. Lastly, I draw from my empirical results to present a unified model of the manifold role of rewards on visual attention. This model makes clear predictions for clinical applications of rewarded attention paradigms because it incorporates a dimension of complexity upon which learning processes can operate on attention. Thus, future work should acknowledge how individual traits such as developmental trajectory, impulsivity, and risk-seeking factors differentially interact with low- and high-level attentional processes. In sum, this document puts forward the notion that rewards serve a compelling role in visual awareness. The key point however is not that rewards can have an effect on attention but that due to the nature of visual processing, reward signals are likely always tuning attention. In this way we can consider reward salience an attentional currency. This means then that deciding where to attend is a matter of gains and losses.

Depuis une vingtaine d’années, la littérature scientifique traitant de la capture attentionnelle a mis en évidence, à l’aide de paradigmes expérimentaux testés en laboratoire, un certain nombre de processus attentionnels fondamentaux. Bien que les résultats obtenus « en laboratoire » à partir de stimuli visuellement « simples » méritent encore d’être investigués, depuis quelques années se pose la question de la « transposabilité » de ces observations à des objets et des situations issus du monde réel. Les phénomènes observés en laboratoire à partir d’un matériel visuellement simple sont-ils transposables à des situations, complexes, de la vie quotidienne ? Afin de répondre à cette question, nous avons créé et testé différentes conditions proches de celles du monde réel,notamment en expérimentant en situation de double-tâche, en utilisant un matériel visuellement complexe extrait du monde réel (c.-à-d. des photographies de conduite automobile), en faisant varier la fréquence d’apparition de l’élément distracteur ou bien encore en testant une nouvelle caractéristique du distracteur, la dimension sémantique. Nos résultats révèlent les conditions d’apparition du phénomène de capture attentionnelle dans des situations s’approchant de celles du monde réel. Nous avons tout particulièrement détaillé dans cet ouvrage le cas de l’effet de capture attentionnelle contingente, phénomène majeur et robuste de la capture attentionnelle, y compris dans des situations visuellement complexes
During the last two decades, studies about attentional capture revealed some major basic attentional processes by using several experimental paradigms. While further investigations need to be conducted by using simple visual stimuli, a raising question concerns the possibility to generalize laboratory findings to much more complex real-world situations. Indeed, basic attentional capture studies usually use simple stimuli while real-world displays are generally rich in visual information. To answer this issue, we conducted several experiments under close to real-world conditions, such as testingdual task situations, using complex visual stimuli from real-world situations (e.g. driving-scenes photographs), modulating the distractor frequency or testing attentional capture at a semantic and conceptual dimension. Our results revealed the conditions in which the attentional capture phenomenon occurs in close to real-world situations. We particularly discussed in our work the contingent attentional capture phenomenon which appears to be a strong and robust effect, in both laboratory and close to real-world situations

Being able to select relevant visual information from among irrelevant information is critical for the successful accomplishment of many day to day activities. However, the locus of attentional selection is not always under the control of the observer. Certain events and stimuli in the visual environment have been shown to control selection against observers’ intentions and goals. These are said to capture attention in an automatic and stimulus driven manner. The events and stimuli that capture attention can be static (colour, shape, size, etc.) or dynamic (motion, flicker, etc.). This thesis examines the effect of dynamic stimuli on attentional selection by using a visual search paradigm. The findings suggest that neither motion per se nor the onset of motion captures attention. They also suggest that when low refresh rate motion is used, capture occurs, but this effect cannot be attributed to capture by motion onset (Chapter 3). Further, the second study suggests that attention capture is observed using low refresh rate motion onsets because they are not masked as compared with the static items in the display. Thus capture is put down to a relatively better visual quality and stimulus encoding rather than motion (Chapter 4). The findings from this thesis also suggests that when back and forth oscillatory motion is used, capture re-emerges, but this effect is best attributed to a change in direction that happens to be temporally unique (Chapter 5). Another important finding is that in attention capture by abrupt onset, only one onset is prioritised in search (Chapter 6). The findings overall argue for a strong role of low level factors in attention capture by dynamic stimuli.

Recent research has suggested that music may enhance or reduce cognitive interference, depending on whether it is tonally consonant or dissonant. Tonal consonance is often described as being pleasant and agreeable, while tonal dissonance is often described as being unpleasant and harsh. However, the exact cognitive mechanisms underlying these effects remain unclear. We hypothesize that tonal dissonance may increase cognitive interference through its effects on attentional cueing. We predict that (a) consonant musical chords are attentionally demanding, but (b) dissonant musical chords are more attentionally demanding than consonant musical chords. Using a Posner cueing task, a standard measure of attention capture, we measured the differential effects of consonant chords, dissonant chords, and no music on attentional cueing. Musical chords were presented binaurally at the same time as a visual cue which correctly predicted the spatial location of a subsequent target in 80% of trials. As in previous studies, valid cues led to faster response times (RTs) compared to invalid cues; however, contrary to our predictions, both consonant and dissonant music chords produced faster RTs compared to the no music condition. Although inconsistent with our hypotheses, these results support previous research on cross-modal cueing, which suggests that non-predictive auditory cues enhance the effectiveness of visual cues. Our study further demonstrates that this effect is not influenced by auditory qualities such as tonal consonance and dissonance, suggesting that previously reported cognitive interference effects for tonal dissonance may depend on high-level changes in mood and arousal.

The main focus for this thesis was cross-modal attention capture by sudden and unexpected sounds and vibrations, known as deviants, presented in a stream the same to-be-ignored stimulus. More specifically, the thesis takes a multisensory perspective and examines the possible similarities and differences in how deviant vibrations and sounds affect visual task performance (Study I), and whether the deviant and standard stimuli have to be presented within the same modality to capture attention away from visual tasks (Study II). Furthermore, by presenting spatial deviants (changing the source of the stimuli from one side of the body to the other) in audiotactile (bimodal), tactile, and auditory to-be-ignored, it explores whether bimodal stimuli are more salient compared to unimodal (Study III). In addition, Study III tested the claims that short-term memory is domain-specific. In line with previous research, Study I found that both auditory and tactile deviants captured attention away from the visual task. However, the temporal dynamics between the two modalities seem to differ. That is, it seems like practice causes the effect of vibratory deviants to reduce, whereas this is not the case for auditory deviants. This suggests that there are central mechanisms (detection of the change) and sensory-specific mechanisms. Study II found that the deviant and standard stimuli must be presented within the same modality. If attention capture by deviants is produced by a mismatch within a neural model predicting upcoming stimuli, the neural model is likely built on stimuli within each modality separately. The results of Study III revealed that spatial and verbal short-term memory are negatively affected by a spatial change in to-be-ignored sequences, but only when the change is within a bimodal sequence. These results can be taken as evidence for a unitary account of short-term memory (verbal and spatial information stored in the same storage) and that bimodal stimuli may be integrated into a unitary percept that make any change in the stream more salient.

This study examined the attention capturing effect by one’s own name using a cross-modal oddball task. It was hypothesized that one’s own name would yield more distraction than a familiar name and a random name. Twenty-one participants (mean = 23.48 year) took part in the experiment. A standard sound and three deviant sounds were used (own name, a familiar name and a random name). The results revealed that the deviant sounds yielded longer response times than the standard sound (all p's<.05), a familiar name yielded longer response time than one's own name (p=.036), but, no difference in response latencies between the random name and the other names were found. It’s concluded that the own name may speed up responses due to arousal, while the familiar name on the other hand act more distracting. Lack of power can possibly explain some of the results, and a reaction time task may disentangle possible differences not shown in this study.

This study’s aim was to examine how attention is affected by action words. Twenty participants performed a cross‐modal oddball task with a standard sound (a sine wave tone) and two recorded speech sounds as novel sounds (stop and press). The result showed that novel sounds captured attention and increased response time compared to standard. There was a significant difference between “press” and standard and “stop” and standard but not between stop and press. This showed that the participants could not block out the sound and focus on the focal attention task. Even though not significant, the response time for “stop” was the slowest since it may inhibit the involuntary response. The results might be explained by the fact that not enough subjects participated, and because of that same reason the result might not be generalized either.

An effective alarm system is a critical part of many different types of jobs. It is also important that the alarm signal can capture human attention and convey appropriate urgency. In the current study the effect of siren sounds with or without unexpected, deviant sounds represented by a change of speed (a temporal deviant) were tested to evaluate if such change could successfully capture attention. The results showed that distraction was more pronounced when the deviant within the sound was a change from fast to slow as compared with slow to fast. Therefore, an alarm signal using a temporal deviant – changing from fast to slow—can be effective in capturing human attention and might be factored into the design of alarm systems.

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Master of Science
Psychological Sciences
Lester C. Loschky
A fundamental issue in visual attention is the relationship between the useful field of view (UFOV), the region of visual space where information is encoded within a single fixation, and eccentricity. A common assumption is that impairing attentional resources reduces the size of the UFOV (i.e. “tunnel vision”). However, most research has not accounted for eccentricity-dependent changes in spatial resolution, potentially conflating fixed visual properties with flexible changes in visual attention. Williams (1988; 1989) argued that foveal loads are necessary to reduce the size of the UFOV, producing "tunnel vision". Without a foveal load, it is argued that the attentional decrement is constant across the visual field (i.e. "general interference"). However, other research asserts that auditory working memory (WM) loads produce tunnel vision. To date, foveal versus auditory WM loads have not been compared to determine if they differentially change the size of the UFOV. In two experiments, we tested the effects of a foveal (rotated L vs. T discrimination) task, and an auditory WM (N-back) task on an extrafoveal (Gabor) discrimination task. Gabor patches were scaled for size and processing time to produce equal performance across the visual field under single task conditions, thus removing the confound of eccentricity-dependent differences in visual sensitivity. The results showed that while both foveal and auditory loads reduced Gabor orientation sensitivity, only the foveal load interacted with retinal eccentricity to produce tunnel vision, clearly demonstrating task-specific changes to the form of the UFOV. This has theoretical implications for understanding the UFOV.

Two Inattentional Blindness type experiments involving 446 participants were performed in order to examine how unexpected objects are noticed. Perception of these unexpected objects was measured using explicit and implicit measurements. Despite initial difficulty in determining implicit perception, results showed a dissociation between implicit measurements and explicit measurements, providing strong evidence for unconscious processing. Research into attention capture often emphasizes the role of either expectations or stimulus properties in attention capture; the current research examines both. Critical objects presented were either of a colour that participants were familiar with, or of a new colour. The different patterns of results for these two categories of objects provide evidence for two separate mechanisms of attention capture: a parallel process driven by the features of objects, and a serial process, driven by the intentions of the observer. Predications of the recent theoretical work produced by Most, Scholl, Clifford & Simons, (2005) are examined, and support is obtained for their theoretical formulation.

This study evaluated the effects of priming and contingent attention procedures on play variability in a child with autism. During baseline, numbers of novel play episodes, different play episodes, and actions occurred at low rates. Priming procedures did not produce desired change. When contingent attention was implemented, significant increases occurred in novel play episodes, different actions, and different play episodes. These results show that attention contingent on variable play episodes can increase the number of novel responses to play materials. The results are discussed within the context of treatment and future research.

In everyday life, we are constantly surrounded by a huge amount of information.Since our attentional resources are limited, we need to select just the stimuli that we want to process. Despite our voluntary attempt to select a precise information, it often occurs that a salient stimulus or event automatically captures our attention, regardless its irrelevance. The fact that we are immediately and unintentionally attracted by sudden visual onsets provides a clear advantage for our survival. However, in spite of that, the possibility to counteract visual distraction is fundamental for an efficient interaction with the environment, particularly when a salient but irrelevant stimulation repeatedly affects our visual system. And then, how can we resist from being continuously distracted by irrelevant repetitive onsets? The current work is aimed to explore the mechanisms that we use to filter irrelevant information, with a focus on habituation, an ancestral form of learning that has recently been associated to the decrement of attentional capture observed in several studies. This experience-dependent learning process is defined as a behavioral response decrement that results from repeated stimulation and that does not involve sensory or motor fatigue. I will first provide the reader with a general introduction (Chapter 1) concerning the visual attention field, with a particular emphasis on attentional capture and the filtering of irrelevant information. I will then (Chapter 2) try to disentangle the two main accounts concerning the nature of the distractor filtering, the first claiming that filtering is accomplished to shield target processing from interference (top-down inhibitory control hypothesis), and the second stating that the passive exposure to a repeating visual onset is sufficient to trigger learning-dependent mechanisms to filter the unwanted stimulation (habituation hypothesis). After providing strong evidence in favor of the latter account, I will then examine (Chapter 3) to what extent the filtering of irrelevant information that we achieve through the mechanisms underlying habituation is affected by contextual cues, showing that this kind of filtering is context-dependent. Finally (Chapter 4), motivated by the existence of a strong functional and anatomical link between attention and the oculomotor system, I will explore whether habituation affects also the oculomotor capture triggered by an onset distractor, showing that the execution of reflexive saccades is subject to habituation, while the programming component is not. Taken together, the results of the present work give a strong contribution to the attentional capture field in showing that both attentional and oculomotor capture are subject to habituation, that this form of learning is context-specific and that it occurs also when we are passively exposed to a visual irrelevant stimulus.

In everyday life, we are constantly surrounded by a huge amount of information.Since our attentional resources are limited, we need to select just the stimuli that we want to process. Despite our voluntary attempt to select a precise information, it often occurs that a salient stimulus or event automatically captures our attention, regardless its irrelevance. The fact that we are immediately and unintentionally attracted by sudden visual onsets provides a clear advantage for our survival. However, in spite of that, the possibility to counteract visual distraction is fundamental for an efficient interaction with the environment, particularly when a salient but irrelevant stimulation repeatedly affects our visual system. And then, how can we resist from being continuously distracted by irrelevant repetitive onsets? The current work is aimed to explore the mechanisms that we use to filter irrelevant information, with a focus on habituation, an ancestral form of learning that has recently been associated to the decrement of attentional capture observed in several studies. This experience-dependent learning process is defined as a behavioral response decrement that results from repeated stimulation and that does not involve sensory or motor fatigue. I will first provide the reader with a general introduction (Chapter 1) concerning the visual attention field, with a particular emphasis on attentional capture and the filtering of irrelevant information. I will then (Chapter 2) try to disentangle the two main accounts concerning the nature of the distractor filtering, the first claiming that filtering is accomplished to shield target processing from interference (top-down inhibitory control hypothesis), and the second stating that the passive exposure to a repeating visual onset is sufficient to trigger learning-dependent mechanisms to filter the unwanted stimulation (habituation hypothesis). After providing strong evidence in favor of the latter account, I will then examine (Chapter 3) to what extent the filtering of irrelevant information that we achieve through the mechanisms underlying habituation is affected by contextual cues, showing that this kind of filtering is context-dependent. Finally (Chapter 4), motivated by the existence of a strong functional and anatomical link between attention and the oculomotor system, I will explore whether habituation affects also the oculomotor capture triggered by an onset distractor, showing that the execution of reflexive saccades is subject to habituation, while the programming component is not. Taken together, the results of the present work give a strong contribution to the attentional capture field in showing that both attentional and oculomotor capture are subject to habituation, that this form of learning is context-specific and that it occurs also when we are passively exposed to a visual irrelevant stimulus.

Previous neurophysiological and behavioural studies have shown that attention can be guided by the contents of working memory (WM), and that such guidance can be involuntary even when it is detrimental to the task at hand. In three experiments, this thesis investigated whether the guidance of visual attention from WM could be generalized from a specific stimulus or a task to a category. Experiment 1 tested whether maintaining a set of stimuli of a specific category in WM would influence participants' deployment of visual attention to favour other stimuli that belonged to the same category. Experiment 2 further manipulated the interval between the onset of a critical prime (i.e., a stimulus in the same category as the stimuli held in WM) and the target to determine whether the results of Experiment 1 were associated with the lack of time for attention to be focused onto the critical prime. In both experiments, the stimuli held in WM never appeared in the prime display. In Experiment 3, the identity of the prime was manipulated so that it matched the stimuli held in WM on half of the trials. The results showed that when the stimuli held in WM never reappeared in the prime display (Experiments 1 and 2) there was no evidence that maintaining specific stimuli in WM biased the distribution of attention to other stimuli within the same category. However, when the stimuli held in WM could reappear in the prime display on some trials (Experiment 3), the participants whose reaction times were relatively fast showed evidence for category-based WM guidance of attention when the critical prime item was a new stimulus in the same category as the stimuli held in WM. In contrast, the participants whose reaction times were relatively slow showed a non-spatially specific cost when the critical prime was one of the WM items than when it was a new item in the same category. These results showed that category-based WM could guide the deployment of visual attention under certain conditions. It further suggests that the relationship between WM and attention is more complex than what is outlined by the biased competition theory and related theories of attention.

Australia has demonstrated an increasingly pharmaceuticalised response to ADHD, with per capita prescription rates growing 277 percent between 1995 and 2010. However, there have been large and inconsistent intertemporal variations between state jurisdictions. This thesis analyses key national, Western Australian and New South Wales ADHD policy and regulatory processes. It demonstrates that regulatory capture has been normal but is not inevitable and has been associated with rapidly increasing per capita ADHD child prescribing rates.

We live in a busy and complex world, so the ability to focus our attention on relevant information at the expense of the irrelevant is essential in allowing us to avoid distraction. However, it is also important that our attention be captured by external stimuli that, although irrelevant to the task at hand, may nevertheless provide information about important changes to our immediate environment. This capture/orienting of attention is an involuntary, fundamental, and biological mechanism necessary for survival. The present thesis employed event-related potentials (ERPs), the minute responses of the brains electrical activity, to examine how changes in the acoustic environment can lead to the capture of attention. Study 1 examined an ERP component, the P3a, which is associated with the processes that lead to the forced capture of attention by external stimuli. This intrusion into consciousness can be studied using an auditory sequence, the oddball paradigm, which consists of a frequently occurring and homogenous ‘standard’ stimulus. At times, a feature of the standard is changed to form a rarely occurring ‘deviant’. If the extent of change between standard and deviant is large enough, processes associated with attention capture may be activated. Study 1 of this thesis employed a more time-efficient multi-feature optimal paradigm, which allows for the presentation of numerous deviants in one auditory sequence. The standard stimulus was a pure tone. Four of the six deviants were created by changing a single feature of the standard (frequency, duration, increase and decrease in intensity), while the remaining two deviants varied on more than one feature from the standard (environmental sounds, white noise). Results revealed that only the environmental sounds (i.e. animal sounds, human voices, musical instruments) and white noise bursts, elicited the P3a, while the other four deviants did not. Studies 2 and 3 determined whether the attention capture processes associated with the P3a could be observed during the sleep onset and sleep periods, where awareness of the external environment is diminished. For sleep to be of benefit it needs to remain as undisturbed as possible, without constant awakenings by irrelevant external input, however, the sleeping organism must still have the ability to become conscious of possibly relevant input that requires immediate action. In Study 2, a P3a was elicited again following only the environmental sound and white noise deviants across wakefulness and the sleep onset period. Surprisingly, during definitive sleep, the environmental sounds continued to elicit a P3a suggesting that attention capture processes may still remain active during sleep. Nonetheless, only the first 30 minutes of sleep were examined. Study 3 was then conducted to examine the P3a across the entire night. Results revealed that the environmental sounds did, in fact, elicited a P3a during both NREM and REM sleep. The present thesis demonstrates that attention capture mechanisms, observed during wakefulness, are also active during sleep onset and sleep when awareness of the external environment is diminished. This is especially critical because the sleeping organism may be vulnerable to external danger, requiring the immediate ability to orient attention to incoming information, leading to awaking and conscious awareness.

Visual attentional capture is a form of visual attentional selection that is automatic and involuntary in nature, and is of high adaptive value as it allows visual attention to be oriented in a reflexive manner towards visual information without necessarily being guided by pre-existing knowledge, goals, and plans. According to the load-hypothesis (Lavie & De Fockert, 2005), attentional capture of salient stimuli increases under load on working memory due to disruption of stimulus-processing priorities. Moreover, it has been proposed that maintenance of task-irrelevant verbal information increases distractor interference in singleton search by increasing attentional capture of salient, but task-irrelevant, color singletons. This hypothesis was tested in the present study by having participants complete several succeeding trials of singleton search while simultaneously maintaining digits in working memory. The presence of task-irrelevant color singletons in the search array of a singleton search task led to increased response times, indicating attentional capture. However, the cost to response times associated with distractor presence did not increase under load on working memory, indicating that distractor interference may not be affected by load on working memory when task-irrelevant verbal information is maintained over an extended period of time. Individual differences in action video game playing and trait anxiety were considered and excluded as possible confounders.

The effects of graduated exposure, modeling and contingent social attention on tolerance to skincare products were evaluated with two boys with autism who displayed tactile defensiveness. Upon each presentation step of skincare products the number of positive and negative responses and successful step completion were measured. Procedures included modeling, presenting graduated opportunities, and providing social attention for step completion. Step advancement occurred if a child engaged in a step independently, without excessive refusals. A changing criterion design and a multiple baseline were employed to evaluate effects of this treatment package. Children demonstrated more positive and fewer negative responses as they completed the graduated steps. Effects maintained in follow-up observations.

This thesis focuses on the information processing in individuals with high levels of psychopathic traits. Part 1 reviews the research literature that has investigated whether individuals with psychopathy, or high levels of psychopathic traits, show deficits in the processing of punishment and/or reward information, and the extent to which the reported studies provide support for the two current competing theories of psychopathy. The review demonstrates that whilst there is strong evidence for intact processing of reward information, there is less conclusive evidence of a deficit in punishment processing. Furthermore, the literature reviewed was more supportive of an emotional dysfunction account of psychopathy, relative to an attention-based account. Part 2 presents an experimental study that investigates whether emotional face training is able to modify attentional capture by fearful faces in a community-based sample of individuals with high levels of psychopathic traits. The results showed that those who received the training were more captured by a task-irrelevant fearful face, and that this was the case, regardless of level of psychopathic traits. Part 3 considers some of the methodological and conceptual issues that arose while conducting the study reported in Part 2. Due to the specific nature of the research question, several decisions concerning the design and statistical analysis of the data needed to be made. This section discusses the advantages and disadvantages of those particular decisions.

Consistent high levels of physical activity are necessary for improved health in fitness in all individuals. Children are expected to engage in 60+ minutes a day of physical activity, but most do not meet this level (The Centers for Disease Control and Prevention, 2016). Methods to increase physical activity in these populations via social consequences and environmental manipulations have demonstrated efficacy in the past (Larson, Normand, Morley, and Miller, 2013) though primarily in a one-on-one setting. As most children’s opportunities for physical activity occur in group settings (i.e., recess) this study evaluates a possible observational learning approach to increasing physical activity among small play groups of young children via contingent delivery of praise. This study will evaluate the effects of contingent delivery of praise to one child on the physical activity of the entire group. The information obtained may be useful for the development of more effective methods of increasing physical activity in recess settings. Results, their implications, and potential future directions of research are discussed.

In the study of covert visual attention, two event-related potential (ERP) components have been identified by earlier research. The N2 posterior contralateral (N2pc) component has been suggested to index the enhancement of attention to a specific lateralized target item. The distractor positivity (PD) component has been suggested to index the suppression of distractors appearing in the same search array. Earlier studies have reported different latencies for the PD component depending on the task and experiment. Furthermore, the N2pc and the PD component are not always elicited in the same experiment. Relative target-to-difficult-distractor placement have been shown to affect the mean amplitude of the N2pc. Less is known about how different relative placements affect the PD component. The aim of the present study was to try and elicit both an N2pc and a PD component in the same visual search paradigm. The PD was recorded later time-window which previous studies have suggested to indicate the ending of attention to a previously attended target. Three relative placements were analysed, horizontally opposite, vertically opposite and diagonally opposite. When combining all three relative placements an N2pc component was elicited contralateral to the target. No PD component was found when combining all relative placements. A larger mean amplitude N2pc was measured for the vertically opposite condition. The results are not in line with previous research, that have found the N2pc to be smaller in conditions where both target and distractor are on the same side of the visual field. However, when comparing upper and lower visual field targets the N2pc was found to be larger for lower visual field stimuli, which is in line with previous research. A larger mean amplitude for the PD was found in the diagonally opposite condition. Earlier research has suggested that when difficult distractor and target are located on separate sides of the visual field, this leads to successful inhibition, indexed by the PD component. In contrast to earlier research a larger PD component was not found for upper visual field stimuli. The present study differs from previous studies in the way the target and difficult distractor were placed and analysed. By separating what has previously been called “opposite side” condition into two separate conditions diagonally opposite and horizontally opposite the results from the present study seem to suggest that these two conditions are not synonymous. However, the results should be regarded with caution due to the small sample size. Furthermore, the horizontally opposite side condition also differs from previous studies with regards to relative target and distractor distances, which could have had an effect on the results.

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2018-2019.
La présence de sons non pertinents est reconnue pour affecter le fonctionnement cognitif. Plus précisément, la présentation d’un son qui dévie du contexte auditif a le potentiel d’affecter la performance à une tâche réalisée simultanément. Plusieurs études s’intéressant à l’impact délétère des sons déviants sur la performance à une tâche montrent qu’il découle de la réorientation de l’attention déclenchée lorsqu’un son déviant est détecté par l’organisme. Cette capture attentionnelle (ou réponse d’orientation) est également reconnue pour engendrer plusieurs réponses physiologiques associées à l’état d’alerte. Ces réponses physiologiques, sous certaines conditions, sont considérées comme des indices psychophysiologiques de la capture attentionnelle auditive permettant de démontrer l’occurrence d’une réorientation de l’attention de la tâche en cours vers le son déviant. De récentes études suggèrent qu’il existe un lien entre ces indices et la réponse pupillaire, soit l’augmentation rapide du diamètre pupillaire. Quelques études ont tenté d’évaluer si cette réponse pouvait remplir les critères d’un indice valide de la réponse d’orientation; cependant, les résultats de ces études sont parfois contradictoires ou incomplets. La présente thèse propose donc une évaluation systématique de l’utilisation de la réponse pupillaire à titre d’indice psychophysiologique de la capture attentionnelle auditive. Les résultats de la première étude montrent que la réponse pupillaire respecte les critères d’un index valide de la réponse d’orientation, supportant ainsi la validité de cet index. L’Étude 2 montre que cet indice peut être utilisé dans des contextes dans lesquels les sujets effectuent simultanément à l’écoute des sons une tâche visuelle provoquant des changements systématiques de luminosité ou des mouvements oculaires qui affectent la taille de la pupille. Ces expériences appuient ainsi l’utilisabilité de cet index. Enfin, la dernière étude permet d’établir l’utilité de ce proxy puisque ce dernier permet de distinguer l’origine de deux phénomènes de distraction auditive différents. Dans l’ensemble, les résultats de la thèse révèlent que la réponse pupillaire représente un indice psychophysiologique adéquat qui pourrait être intégré aux études sur la distraction auditive ou dans des contextes plus appliqués où les mesures de la capture attentionnelle auditive peuvent s’avérer pertinentes.
The presence of task-irrelevant sound is known to impede cognitive functioning. More precisely, presenting a sound that deviates from the auditory background has been shown to disrupt performance on an ongoing task. Several studies regarding performance disruption by deviant sounds showed that this effect originates from the reorientation of attention triggered when the organism has detected the deviant sound. Such attentional capture (or orientation response) also elicits many physiological responses related to one’s state of alertness. These physiological responses, under certain conditions, are considered as psychophysiological indices of auditory attentional capture, permitting to show that attention has been reoriented from an ongoing task toward the deviant auditory stimulus. Recent work suggested a relationship between these indices and the pupillary dilation response, that is a rapid increase in the pupil size. A few studies have attempted to assess whether the pupillary dilation response could respect the criteria for an index to be considered as a proxy for attentional capture; yet, results of these studies either lack consistency or are incomplete. Hence, the current thesis proposes a systematic assessment of using the pupillary dilation response as a psychophysiological proxy for the auditory attentional capture. Results of the first study suggest that the pupillary dilation response respects criteria of a valid auditory attentional capture index, thus supporting the validity of this index. Study 2 shows that this index can be used in contexts in which participants are exposed to irrelevant deviant sound while concurrently performing a task inducing luminance changes or ocular movements, both influencing the pupil size. These experiments hence supported the usability of this index. The last study allows establishing the utility of this proxy since it can be used to dissociate the origin of two different auditory distraction phenomena. Overall, results of the current thesis reveal that the pupillary dilation response is a psychophysiological index that could be added to several auditory distraction paradigms or in applied contexts in which the occurrence of attention reorientation toward a sound may be relevant to assess.

The capacity of the visual system to process information about multiple objects at any given moment in time is limited. This is because not all information can be processed equally or in parallel and subsequently reach consciousness. Previous research has utilized behavioural experiments to explore visual attention. More recently research, however, has used electroencephalography (EEG) to measuring the electrical brain activity in the posterior scalp. By time locking visual stimulus events to fluctuations in scalp activity researchers have been able to estimate the time course of attentional changes by measuring changes in these event-related potentials (ERP). One component in particular (N2pc) has been a reliable tool in measuring either the suppression of, or the shift of attentional to, both ignored and attended items in the visual scene. The N2pc is measured by comparing the ERP activity contralateral and ipsilateral to the visual field of interest. More recently, evidence has been presented that the mechanisms of attention thought to be represented by the N2pc (suppression and attentional selection) could be separated into different ERP components (Pd: indexing attentional suppression of an ignored item; and Nt: indexing attentional selection of the target) and measured independently. In six experiments, using ERPs, this thesis employs these components to explore the mechanisms and strategies of the human attentional system. Additionally, this thesis focuses on the impact of different types of simultaneous processing load on the attentional system and how the mechanisms of this system are influenced. Experiment 1 explores the idea that the type or valence of information to be ignored may influence the ability to suppress it. Results of this experiment 4 show that neither the type nor valence of the irrelevant information modulated the amplitude of the distractor positivity (Pd), indicating suppression of the irrelevant distractor was not altered. Noted in experiment 1 was also the presence of an early negativity (Ne) that appeared to represent attentional capture of the ignored lateral stimulus. Experiment 2 demonstrated that the valence of the lateral target did not alter the target negativity (Nt), indicating a different pattern of results between the Nt and the N2pc reported in previous studies (e.g. Eimer & Kiss, 2007; Feldmann-Wüstefeld et al., 2010). Experiment 2 also showed a similarity of the target negativity (Nt) to the early negativity (Ne; the N2pc like component observed in exp 1) toward face and non-face stimuli. This comparison supported the idea that the early negativity (Ne) reflected attentional capture of the ignored lateral distractor and as a result was relabelled the distractor negativity (Nd) in subsequent experiments. Experiment 3 showed that the salience of the lateral image did not modulate the Pd as should be the case if the Pd reflected sensory-level processing. An early contralateral negativity (similar to the Nd observed in exp 1) was altered by the salience of the distractor which added support to the hypothesis that this reflects attentional capture of the lateral ignored image. Experiment 4 attempted to manipulate working memory (WM) to assess the effect of WM load on attentional capture and suppression. While the results did indicate modulation of suppression under WM load, the limitations of the design of experiment 4 made any definitive interpretation of the results unreliable. The results of experiment 5 showed that suppression, as indexed by the Pd, was not altered by cognitive load. However, reductions in attentional capture under high cognitive load, as indexed by the distractor negativity (Nd), were observed and contradict the results of previous experiments (c.f. Lavie & De Fockert, 2005) 5 where cognitive load resulted in an increase in attentional capture. Although, there appears to be some issue in the authors interpretation of the results of these experiments (see chapter 6 for discussion). The results of Experiment 6 show the opposite effect with a significant increase in the laterality of the Pd under high perceptual load. A similar increase in the laterality of the Pd was not reflected in terms of valence though, where suppression of threat related distractors was not altered under high perceptual load. The hypothesis that an increase in perceptual load will result in a decrease in attentional capture was generally supported by the results of experiment 6. Under high perceptual load angry face distractors captured attention, as indexed by the laterality of the Nd, with neutral face distractors showing a reduction in attentional capture. While under low perceptual load, both angry and neutral face distractors resulted in a significant (and similar) laterality of the Nd. The thesis concludes by discussing issues concerning Lavie’s Load Theory of attention and outlines some potential misinterpretations of previous data that have led to the proposal that cognitive load results in a decrease in attentional resources and therefore a decrease in attentional capture of ignored stimuli. It is argued in this thesis that the results of Lavie and de Fockert (2005), which concluded that the increase in cognitive load resulted in a decrease in attentional capture, are more likely to be due to changes in attentional capture (i.e. a reduction) and changes in RT (i.e. an increase), under cognitive load being separate responses to the availability of resources, one that focusses attention on the goal directed task and the other that results in extended processing time to carry out the more difficult task. In this case both ‘changes’ appear to work to prioritise resources in favour of the goal directed task.

Le but de cette étude était d'évaluer le rôle des boucles des ganglions de la base et des voies dopaminergiques sur les mécanismes « bottom-up » et « « top-down » du contrôle de l'attention visuelle (AV). Nous avons comparé les performances sur 3 tâches informatisés, appropriées à l'étude de la capture attentionnelle (CA), des mécanismes de sélection de la réponse motrice et d'initiation du mouvement, de deux groupes de patients avec maladie de Parkinson (MP) - un groupe étant évalué dans trois différentes conditions de stimulation électrique (sans stimulation, ou stimulation sélective de la partie sensorimotrice, SM, ou de la partie associative, AS, du noyau subthalamique, NST), l'autre groupe étant évalué dans deux différentes conditions de traitement médical (avec ou sans levodopa) - avec celles d'un groupe des sujets contrôles. Nos résultats suggèrent dans la MP un affaiblissement des mécanismes « top-down » de contrôle de l'AV, ce qui pourrait aussi expliquer indirectement l'augmentation de la CA. Le traitement dopaminergique est efficace dans le rétablissement des mécanismes « top-down » de l'AV, suggérant une implication des voies dopaminergiques dans ce domaine cognitif. Ces voies semblent aussi jouer un rôle dans les mécanismes « bottom-up » de l'attention, comme l'a suggéré le renforcement de la CA sous traitement dopaminergique. La stimulation du NST a montré un effet similaire à celui obtenu par un traitement dopaminergique, en favour d'une implication directe des boucles des ganglions de la base dans le contrôle de l'AV. Nos résultats ont mis en évidence une spécialisation fonctionnelle de différents sous-territoires du NST en ce qui concerne les mécanismes de « top-down ». La stimulation SM produit des effets marqués sur les processus d'initiation de mouvement et des effets positifs sur les mécanismes endogènes de l'AV, alors que la stimulation de la partie AS semble être plus particulièrement efficace dans l'amélioration des mécanismes de sélection de cible
We aimed to investigate the possible role of cortico-basal ganglia loops and dopaminergic pathways in the mechanisms of top-down and bottom-up control of visual attention (VA). We compared the performances on 3 computerized tasks, respectively suitable to study attentional capture (AC), motor response selection and movement initiation, of two groups of patients with Parkinson's disease (PD), one evaluated in different sets of electrical stimulation (without stimulation, or selective stimulation of the sensorimotor, SM, or associative, AS, parts of the subthalamic nucleus, STN), the other in different conditions of medication (with or without levodopa), with those of a group of controls. Our results showed that in PD there is a weakening of the mechanisms underlying the top-down control of VA, which also would account indirectly account for the enhancement of AC. Dopaminergic treatment proved to be effective in restoring the top-down mechanisms of VA, suggesting an involvement of dopaminergic pathways in this cognitive domain. These pathways seem to play a role also in the bottom-up mechanisms of attention, as suggested by the enhancement of AC under dopaminergic treatment. The STN-stimulation showed a similar effect to that obtained by dopaminergic treatment, establishing a direct involvement of the basal ganglia loops in VA control. Our results highlighted a functional specialization of different sub-territories of the STN in relation to the top-down mechanisms. SM stimulation produced marked effects on the movement initiation processes and appreciable positive effects on endogenous VA mechanisms, while AS stimulation seems to be especially effective in improving the mechanisms of target selection

There is more information in the visual environment than we can process at a given time, and as a result selective attention mechanisms have developed that allow us to focus on information that is relevant to us while ignoring information that is not. It is often assumed that our ability to overcome distraction by irrelevant information in the environment requires conscious, effortful processing, and traditional theories of selective attention have emphasized the role of an observer's explicit intentions in driving this control. At the same time, effortful control on the basis of explicit processes may be maladaptive when the behaviors to be executed are complex and dynamic, as is the case with many behaviors that we carry out on a daily basis. One way to increase the efficiency of this process would be to store information regarding past experiences with a distracting stimulus, and use this information to control distraction upon future encounters with that particular stimulus. The focus of the current thesis was to examine such a "learned control" view of distraction, where experience with particular stimuli is the critical factor determining whether or not a salient stimulus will capture attention and distract us in a given situation. In Chapters 2 through 4, I established a role for task-specific learning in the ability of observers to overcome attentional capture, showing that experience with particular attributes of distracting stimuli and the context in which the task was performed led to a predictable decrease in capture. In Chapter 5, I examined the neural basis of these learned control effects, and the results suggest that neocortical and medial temporal lobe learning mechanisms both contribute to the experience-dependent modulation of attentional capture observed in Chapters 2-4. Based on these results, a model of attentional capture was proposed in which experience with particular stimulus attributes and their context critically determine the ability of salient, task-irrelevant information to capture attention and cause distraction. I conclude that although explicit processes may play some role in this process under some conditions, much of our ability to overcome distraction results directly from past experience with the visual world.

Les mécanismes volontaires (V) et involontaires (I) de l’attention reposent sur les réseaux dorsal et ventral, convergeant dans le cortex préfrontal latéral (lPFC). La distractibilité accrue liée au vieillissement ou à une lésion frontale pourrait être due à une altération de l’équilibre entre ces mécanismes V et I, essentiel mais rarement étudié. Notre objectif est de tester, dans la modalité auditive, si (1) les oscillations alpha coordonnent l'activité du réseau dorsal, (2) les oscillations gamma celle du réseau ventral, (3) le couplage oscillatoire dans le lPFC maintient l’équilibre entre les deux réseaux. Ce travail vise également à étudier les corrélats oscillatoires de la distractibilité accrue liée au vieillissement ou à une atteinte frontale. Des données MEEG ont été enregistrées alors que des participants réalisaient le Competitive Attention Test, qui permet d’étudier simultanément les mécanismes V et I de l’attention. Nous avons montré que les oscillations alpha reflètent l’activation des mécanismes facilitateurs et suppresseurs de l’attention V, et la communication au sein du réseau dorsal ; alors que les oscillations gamma indexent l’activation du réseau ventral. De plus, le lPFC serait impliqué dans la communication au sein des deux réseaux, et le PFC médian dans l’équilibre attentionnel V/I. Nous avons également montré que la distractibilité accrue était liée à un déficit d’attention V au cours du vieillissement, et à une altération des processus V et I après lésion frontale. Ce travail de thèse offre donc une meilleure compréhension de la dynamique cérébrale oscillatoire sur laquelle repose l'équilibre attentionnel V/I, et donc la distractibilité
Top-down (TD) and bottom-up (BU) mechanisms of attention are supported by dorsal and ventral networks that mainly overlap in the lateral prefrontal cortex (lPFC). A balance between these mechanisms is essential, yet rarely investigated. Increased distractibility observed during ageing or after frontal damage could result from jeopardizing this balance. It has been proposed that distinct oscillatory frequencies support the activation of these two attention networks. Our main aim was to test, in the auditory modality, whether (1) alpha oscillations would coordinate activity within the dorsal TD network, (2) gamma activity would index the activation of the ventral BU network, (3) the lPFC would support the balance between these networks through oscillatory coupling. We also aimed to investigate the oscillatory correlates of the increased distractibility associated with ageing or frontal damage. MEEG data were recorded while participants performed the Competitive Attention Test, which enables simultaneous investigation of BU and TD attention mechanisms. We showed that alpha oscillations indexed facilitatory and suppressive mechanisms of TD attention, and communication within the dorsal network; while gamma oscillations indexed the ventral network activation. Moreover, the lPFC subtended communication in the two networks; with the TD/BU interaction occurring in the medial PFC. We also showed that ageing-related distractibility was of TD deficit origin. Finally, preliminary results suggest that lPFC damage can impact both TD and BU attention. This thesis provides novel insights into the brain oscillatory dynamics of the TD/BU attentional balance supporting distractibility

La maladie de Parkinson (MP) est la deuxième affection neurodégénérative la plus fréquente après la maladie d’Alzheimer. Elle se caractérise par un dysfonctionnement du système des ganglions de la base, en rapport avec une dégénérescence des neurones dopaminergiques de la substance noire compacte. A côté des symptômes moteurs, la MP s’accompagne de troubles cognitifs, en particulier une altération des capacités de sélectivité attentionnelle. Ce déficit attentionnel se traduit par des difficultés à sélectionner les informations pertinentes pour la conduite en cours et peut entraîner des troubles cognitifs légers. L’origine des troubles attentionnels reste imprécise : on ignore s'ils résultent d’une défaillance des mécanismes volontaires d’orientation de l’attention ou d'une perturbation des processus automatiques de capture attentionnelle. Le filtrage sensoriel permet de focaliser notre attention grâce à une sélection des informations pertinentes pour l’action en cours et une inhibition des informations non pertinentes. Il peut être exploré en neurophysiologie par le paradigme d’inhibition par le prepulse (PPI). Ce dernier correspond à l’atténuation de la réponse motrice et corticale suite à la présentation d’un stimulus sursautant (pulse) lorsque celui-ci est précédé de quelques millisecondes d’un stimulus non sursautant (prepulse). Le PPI est influencé par l’attention, son amplitude étant majorée lorsque l’attention est portée volontairement sur le prepulse. L’objectif général était donc de mieux identifier la nature des troubles de la sélectivité attentionnelle dans la MP par un paradigme actif de PPI au cours duquel la réponse corticale au pulse est enregistrée. Nous faisions l’hypothèse que les parkinsoniens présenteraient une inhibition plus faible que les témoins sains. En cas de défaillance de mobilisation volontaire des ressources attentionnelles, l'inhibition de la réponse corticale au pulse devrait être moins importante lorsque les ressources attentionnelles allouées au traitement du prepulse mettent en jeu la mobilisation volontaire de l’attention. A l’inverse, en cas de défaut de capture attentionnelle, l’inhibition de la réponse serait moins importante lorsque le traitement du prepulse implique les processus automatiques de capture.Pour répondre à cet objectif, nous avons dans un premier temps développé et validé un paradigme actif de PPI au cours duquel l’effet de la mobilisation volontaire de l’attention et de la capture attentionnelle sur le processus de filtrage sensoriel a été évalué. Pour ce faire, 26 témoins sains jeunes ont bénéficié d’un électroencéphalogramme à haute résolution tout en réalisant une tâche attentionnelle sur laquelle a été greffé un paradigme actif de PPI. Nous avons recueilli la réponse corticale évoquée et induite par la présentation du pulse. 16 témoins sains âgés, 16 patients parkinsoniens sans trouble cognitif et 16 patients avec troubles cognitifs légers ont bénéficié du même enregistrement au cours de la même tâche attentionnelle. Chez les témoins sains jeunes, nous avons montré que les processus de mobilisation volontaire de l’attention et de capture attentionnelle modulaient de façon différentielle la réponse évoquée et induite par la présentation du pulse. Au cours du vieillissement, nous avons observé une meilleure sensibilité de la réponse corticale induite, ce qui nous a conduit à choisir ce marqueur cortical pour évaluer le filtrage sensoriel dans la MP. Nos résultats montrent une réduction de l’inhibition de la réponse induite chez les parkinsoniens avec troubles cognitifs légers, confirmant la distractibilité. La MP s’accompagne aussi d’une altération dans la génération des oscillations corticales dans la bande de fréquence thêta quand la focalisation de l’attention est engagée
Parkinson’s disease (PD) is the most frequent neurodegenerative disorder after Alzheimer’s disease. It is characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta, causing a progressive loss of dopamine neurotransmission within the basal ganglia. Apart from motor symptoms, PD patients have cognitive disorders. Namely, focused attention is impaired and PD patients fail to select task-relevant information, leading sometimes to mild cognitive impairment (MCI). The origin of this impairment is still debated: PD-related selective attention deficit may be due either to a failure of goal-directed or stimulus-driven attention. Sensory gating helps the individuals to selectively allocate their attentional resources to salient stimuli and to inhibit irrelevant information. One of the physiological marker of this process is referred to as prepulse inhibition (PPI). It corresponds to the attenuation of the motor and cortical responses to a startling stimulus (pulse) when a non-startling stimulus (the prepulse) precedes the pulse by few milliseconds. PPI can be modulated by attention, its magnitude being greater after a to-be attended prepulse. Moreover, PPI is mediated by basal ganglia.The main aim of this work was to better identify the mechanisms involved in selective attention deficits in PD. We used an active PPI paradigm and recorded the cortical response to the pulse. We assumed that PD patients would exhibit a lower inhibition of the cortical response than healthy controls. If attention deficits in PD are related to an impairment of goal-directed attention, PD patients would exhibit lower inhibition after a to-be attended prepulse than in the other conditions. At the opposite, if it is due to a failure of stimulus-driven attention, inhibition would be lower after a prepulse which involuntarily captures attention than in the other conditions.In order to reach this objective, we have first developed and validated a new active PPI paradigm in order to investigate the role of goal-directed and stimulus-driven attention on sensory-cognitive gating. To this end, high resolution electroencephalogram was recorded in 26 young healthy subjects. They performed a selective attention task combined with an active PPI paradigm and the auditory-evoked and induced cortical response to the pulse was recorded. Then, the same procedure was administered in 16 elderly healthy subjects, 16 PD patients without MCI and 16 PD patients with MCI. In young healthy subjects, we found that stimulus-driven and goal-directed attention each had specific effects on the inhibition of the evoked and induced response to the pulse. The investigation of age-related changes on sensory gating revealed that the induced cortical response was more sensitive for assessing age-related changes than the evoked response. Then, we chose this cortical marker to investigate sensory gating in PD. Our results showed that PD patients with MCI exhibit lower inhibition of induced cortical response to the pulse than healthy controls. This finding confirms previous results showing a high distractibility in these patients. Moreover, PD patients exhibit impaired theta synchronization when focused attention was engaged

In this work I present several studies, which might appear rather heterogeneous for both experimental questions and methodological approaches, and yet are linked by a common leitmotiv: spatial attention. I will address issues related to the assessment of attentional asymmetries, in the healthy individual as in patients with neurological disorders, their role in various aspects of human cognition, and their neural underpinning, driven by the deep belief that spatial attention plays an important role in various mental processes that are not necessarily confined to perception. What follows is organized into two distinct sections. In the first I will focus on the evaluation of visuospatial asymmetries, starting from the description of a new paradigm particularly suitable for this purpose. In the first chapter I will describe the effects of multitasking in a spatial monitoring test; the main result shows a striking decreasing in detection performance as a function of the introduced memory load. In the second chapter I will apply the same paradigm to a clinical population characterized by a brain lesion affecting the left hemisphere. Despite a standard neuropsychological battery failed to highlight any lateralized attentional deficit, I will show that exploiting concurrent demands might lead to enhanced sensitivity of diagnostic tests and consequently positive effects on patients’ diagnostic and therapeutic management. Finally, in the third chapter I will suggest, in light of preliminary data, that attentional asymmetries also occur along the sagittal axis; I will argue, in particular, that more attentional resources appear to be allocated around peripersonal space, the resulting benefits extending to various tasks (i.e., discrimination tasks). Then, in the second section, I will follow a complementary approach: I will seek to induce attentional shifts in order to evaluate their role in different cognitive tasks. In the fourth and fifth chapters this will be pursued exploiting sensory stimulations: visual optokinetic stimulation and galvanic vestibular stimulation, respectively. In the fourth chapter I will show that spatial attention is highly involved in numerical cognition, this relationship being bidirectional. Specifically, I will show that optokinetic stimulation modulates the occurrence of procedural errors during mental arithmetics, and that calculation itself affects oculomotor behaviour in turn. In the fifth chapter I will examine the effects of galvanic vestibular stimulation, a particularly promising technique for the rehabilitation of lateralized attention disorders, on spatial representations. I will discuss critically a recent account for unilateral spatial neglect, suggesting that vestibular stimulations or disorders might indeed affect the metric representation of space, but not necessarily resulting in spatial unawareness. Finally, in the sixth chapter I will describe an attentional capture phenomenon by intrinsically rewarding distracters. I will seek, in particular, to predict the degree of attentional capture from resting-state functional magnetic resonance imaging data and the related brain connectivity pattern; I will report preliminary data focused on the importance of the cingulate-opercular network, and discuss the results through a parallel with clinical populations characterized by behavioural addictions.
In questo lavoro presenterò una serie di ricerche che possono sembrare piuttosto eterogenee per quesiti sperimentali e approcci metodologici, ma sono tuttavia legate da un filo conduttore comune: i costrutti di ragionamento e attenzione spaziale. Affronterò in particolare aspetti legati alla valutazione delle asimmetrie attenzionali, nell'individuo sano come nel paziente con disturbi neurologici, il loro ruolo in vari aspetti della cognizione umana, e i loro substrati neurali, guidato dalla convinzione che l’attenzione spaziale giochi un ruolo importante in svariati processi mentali non necessariamente limitati alla percezione. Quanto segue è stato dunque organizzato in due sezioni distinte. Nella prima mi soffermerò sulla valutazione delle asimmetrie visuospaziali, iniziando dalla descrizione di un nuovo paradigma particolarmente adatto a questo scopo. Nel primo capitolo descriverò gli effetti del doppio compito e del carico attenzionale su un test di monitoraggio spaziale; il risultato principale mostra un netto peggioramento nella prestazione al compito di detezione spaziale in funzione del carico di memoria introdotto. Nel secondo capitolo applicherò lo stesso paradigma ad una popolazione clinica contraddistinta da lesione cerebrale dell’emisfero sinistro. Nonostante una valutazione neuropsicologica standard non evidenziasse alcun deficit lateralizzato dell’attenzione, mostrerò che sfruttare un compito accessorio può portare ad una spiccata maggiore sensibilità dei test diagnostici, con evidenti ricadute benefiche sull'iter clinico e terapeutico dei pazienti. Infine, nel terzo capitolo suggerirò, tramite dati preliminari, che asimmetrie attenzionali possono essere individuate, nell'individuo sano, anche lungo l’asse sagittale; argomenterò, in particolare, che attorno allo spazio peripersonale sembrano essere generalmente concentrate più risorse attentive, e che i benefici conseguenti si estendono a compiti di varia natura (ad esempio compiti di discriminazione). Passerò dunque alla seconda sezione, in cui, seguendo una logica inversa, indurrò degli spostamenti nel focus attentivo in modo da valutarne il ruolo in compiti di varia natura. Nei capitoli quarto e quinto sfrutterò delle stimolazioni sensoriali: la stimolazione visiva optocinetica e la stimolazione galvanico vestibolare, rispettivamente. Nel quarto capitolo mostrerò che l’attenzione spaziale è coinvolta nella cognizione numerica, con cui intrattiene rapporti bidirezionali. Nello specifico mostrerò da un lato che la stimolazione optocinetica può modulare l’occorrenza di errori procedurali nel calcolo mentale, dall'altro che il calcolo stesso ha degli effetti sull'attenzione spaziale e in particolare sul comportamento oculomotorio. Nel quinto capitolo esaminerò gli effetti della stimolazione galvanica vestibolare, una tecnica particolarmente promettente per la riabilitazione dei disturbi attentivi lateralizzati, sulle rappresentazioni mentali dello spazio. Discuterò in modo critico un recente modello della negligenza spaziale unilaterale, suggerendo che stimolazioni e disturbi vestibolari possano sì avere ripercussioni sulle rappresentazioni metriche dello spazio, ma senza comportare necessariamente inattenzione per lo spazio stesso. Infine, nel sesto capitolo descriverò gli effetti di cattura dell’attenzione visuospaziale che stimoli distrattori intrinsecamente motivanti possono esercitare nell'adulto sano. Cercherò, in particolare, di predire l’entità di questa cattura attenzionale partendo da immagini di risonanza magnetica funzionale a riposo: riporterò dati preliminari focalizzati sull'importanza del circuito cingolo-opercolare, effettuando un parallelismo con popolazioni cliniche caratterizzate da comportamenti di dipendenza.

Task-irrelevant static emotional faces, pictures, and words are known to involuntarily receive or capture attention. Hand gestures, similar to faces, are biological stimuli that are often used to express emotion. This thesis examines attentional capture using static emotional hand gestures and dynamic emotional hand gestures and faces. The component processes model of emotion predicts that either positive or negative stimuli that are appraised as relevant will capture attention for further and deeper processing. Attentional capture and the resulting competition for resources to process emotional stimuli can cause interference with an ongoing implicit cognitive task. In a series of experiments, participants identified the gender of hand or face stimuli while neutral, positive, and negative valence of stimuli was manipulated. It was hypothesised that interference resulting from attentional capture would lead to greater gender identification accuracy for static neutral hand gestures than for static positive or negative hand gestures. Neutral and emotional static faces were used as comparison stimuli. The hypothesis was tested in six experiments using a novel Stroop-based experimental paradigm, specifically devised for future implementation in Magnetoencephalography (MEG) environment. Stimulus items were presented to the peripheral visual field in one of four quadrants for 100 ms (Experiments 1 and 4), 200 ms (Experiment 2), and 300 ms (Experiment 3) each, in trials of eight items with an inter-stimulus interval (ISI) that varied from 1800 to 2300 ms. As hypothesised, accuracy of identifying neutral hand gestures was significantly greater than accuracy of identifying gender of positive or negative hand gestures. The hypothesis was also supported for the case of negative faces but not for positive faces. The lack of an effect in response to positive faces is possibly due to the valence ambiguity of neutral faces capturing attention and interfering with gender identification. Experiment 5 examined attentional capture using emotional static hand gestures and faces presented to the central visual field. Only positive hand gestures and positive faces captured attention in this experiment. Experiment 6 tested two hypotheses using dynamic stimuli presented in the peripheral visual field for 300 ms. The hypothesis that greater gender identification accuracy would be found for neutral hand gestures/faces than for positive or negative hand gestures/faces was supported for positive hand gestures and negative faces, but not for negative hand gestures and positive faces. A second hypothesis was that greater attentional capture and resulting interference from dynamic stimuli would lead to poorer gender identification accuracy for emotional dynamic stimuli than for emotional static stimuli. The results of Experiment 6 did not support this hypothesis. These six experiments demonstrate that both static and dynamic positive and negative hand gestures and dynamic negative faces capture attention and interfere with an ongoing cognitive task when presented to the peripheral visual field. The experiments also demonstrate that static positive hand gestures and static positive faces capture attention when presented to the central visual field. Moreover, the novel Stroop-based experimental design appears to be a useful method for studying attentional capture using emotional pictorial stimuli and has already been implemented in a companion MEG experiment. A model explaining attentional capture and interference using emotional stimuli is proposed, based on the component processes model of emotion. In the model, the degree of attention recruited during the primary appraisal is proportional to the degree of interference with an implicit cognitive task.

Thesis (Ph.D.)--University of Western Sydney, 2008.
A thesis presented to the University of Western Sydney, College of Arts, MARCS Auditory Laboratories, in fulfilment of the requirements for the degree of Doctor of Philosophy. Includes bibliographies.

Complex behaviors require selectively attending to task-relevant items, and ignoring conspicuous, irrelevant items. For example, driving requires selectively attending to other cars on the road while ignoring flashing billboards. Dominant models of attentional control posit that we avoid distraction by biasing attention towards task-relevant items, and our ability to avoid distraction depends on the strength and specificity of this bias. I find that a strong, specific bias towards task-relevant items is insufficient for preventing distraction. Instead, preventing distraction also requires past experience ignoring distractors. I also find that long-term memory systems, rather than visual short-term memory or priming memory systems, maintain this experience. Based upon these findings, I propose that effective attentional control not only demands a strong, specific bias towards task-relevant items, but also requires that observers learn to ignore conspicuous, irrelevant items.

Au quotidien, notre attention sélective nous permet de sélectionner les informations pertinentes au regard de notre tâche et d'ignorer celles qui ne le sont pas, afin de maintenir un comportement cohérent avec nos buts. Néanmoins, dans certaines situations, un stimulus complètement non-pertinent peut capturer notre attention contre notre volonté et, de ce fait, produire un phénomène de distraction. La distraction a initialement été considérée comme essentiellement dépendante de la saillance perceptive des distracteurs. Cependant, de récentes études ont mis en évidence que les stimuli associés à l'obtention d'une récompense (i.e., disposant d'une histoire de récompense) sont également susceptibles de produire des effets de distraction particulièrement robustes et persistants (indépendamment de leur pertinence pour la tâche en cours et de leur saillance perceptive). Parallèlement, tout un autre champ de recherche a été consacré à l’étude du contrôle attentionnel qui peut être mis en place afin de prévenir une distraction par des stimuli visuellement saillants. Cependant, à ce jour, très peu de travaux ont tenté de manipuler la qualité du contrôle attentionnel qui peut être instauré pour éviter la distraction par des stimulus associés à une récompense. L'objectif de notre travail était donc de déterminer si, et si oui, dans quelles conditions, ces distracteurs pouvaient être ignorés efficacement ou, au contraire, pouvaient résister au contrôle attentionnel. Dans sept études, nous avons associé des stimuli visuels initialement neutres à une récompense (monétaire ou sociale) afin d’étudier leur impact sur les performances lorsqu’ils apparaissaient comme distracteurs dans des tâches recherche visuelle. Nous avons manipulé la qualité du contrôle attentionnel en faisant varier les contraintes perceptives (i.e., charge perceptive : Études 1 et 2), cognitives (i.e., charge cognitive : Étude 3) ou sensorielles (i.e., dégradation sensorielle : Études 4-7) imposées par la tâche. Nous avons mis en évidence que l'interférence provoquée par un distracteur associé à une forte récompense monétaire, contrairement à celle provoquée par des distracteurs uniquement saillants, peut résister à l'augmentation de la charge perceptive (Étude 1). L'analyse des potentiels cérébraux évoqués par ces distracteurs (Etude 2) suggère que cet effet puisse résulter d’une capture attentionnelle (N2pc) accrue en charge perceptive faible et d’une suppression attentionnelle (Pd) moins efficace en charge perceptive forte pour ces distracteurs. Contrairement à nos attentes, aucun effet de la récompense n'a été observé dans l’étude manipulant la charge cognitive (Étude 3), nous conduisant à proposer que notre manipulation ait pu drainer les ressources cognitives nécessaires à l'apprentissage de l’association distracteur-récompense. Ensuite, nous avons montré que l'augmentation de la pression temporelle (Étude 4-5), réputée pour favoriser la sélection précoce d'une cible, peut au contraire, dans certaines conditions, entrainer une plus grande difficulté à ignorer les distracteurs. Pour autant, dans ces conditions, le simple fait que des distracteurs récompensés puissent apparaître semble impacter encore plus négativement la sélection d'une cible que la pression temporelle elle-même. Enfin, nos deux dernières études (Études 6-7) ont mobilisé un cadre expérimental plus écologique, impliquant la recherche de cibles dans des photographies de scènes routières prises du point de vue d’un conducteur d’automobile et l’apparition de distracteurs récompensés sur l’écran d’un smartphone présent dans l’habitacle. Nous avons mis en évidence que la dégradation sensorielle de la cible (via une augmentation de l'intensité du brouillard) entraine une distraction plus importante pour des distracteurs associés à une récompense sociale, en particulier pour les personnes présentant un niveau élevé de FoMO (Fear of Missing Out ; peur de manquer une expérience sociale). [...]
In our daily activities, selective attention allow us to select task-relevant information among irrelevant ones, in order to maintain consistent, goal-directed behavior. However, sometimes, a completely irrelevant stimulus can capture our attention against our will and, as a result, produce a distraction phenomenon. Distraction was initially considered to be essentially dependent on the perceptual salience of the distractors. Nevertheless, recent studies have shown that stimuli associated with reward outcome (i.e., with a reward history) are also likely to produce particularly robust and persistent distraction effects (regardless of their relevance to the task at hand and their perceptual salience). Alongside, a large body of works has been devoted to the study of attentional control, which could prevent distraction by perceptually salient distractors. However, to date, very little work has attempted to manipulate the quality of the attentional control that could be implemented to avoid distraction by reward history. The objective of our work was therefore to determine whether, and if so, under what conditions, reward-distractors could be ignored or, on the contrary, could resist attentional control. Seven studies were conducted with neutral visual stimuli associated with (monetary or social) reward outcome, in order to investigate how they could affect task performance when they appeared as distractors in visual search tasks. Attentional control was manipulated by varying the perceptual (i.e., perceptual load: Studies 1 and 2), cognitive (i.e., cognitive load: Study 3) or sensory (i.e., sensory degradation: Studies 4-7) demands imposed by the task. We have shown that high-reward distractor interference resists to perceptual load increase, unlike that caused by only salient distractor (Study 1). Our event-related potentials study (Study 2) suggests that this effect may be due to an enhanced attentional capture (N2pc) under low perceptual load and by a less effective attentional suppression (Pd) under high perceptual load for high-reward distractors. Next, contrary to our expectations, no effect of reward history was observed when manipulating cognitive load (Study 3), leading us to propose that our manipulation could have drained the cognitive resources necessary to learn the distractor-reward association. Then, we have shown that the increase in time pressure (Studies 4-5), known to promote the early selection of relevant targets, could also enhanced the difficulty to ignore distractors under some circumstances. Nevertheless, in these conditions, the mere fact that rewarded distractors may appear seems to increase the difficulty to ignore the distractors, more than the time pressure itself. Finally, our last two studies (Studies 6-7) mobilized a more ecological visual search task, involving pictures of driving situations taken from a driver point-of-view, in which reward distractors were displayed on the screen of a smartphone in the vehicle cabin. The sensory degradation of the target (achieved by increasing the fog density outside the car) has led to greater distraction for distractors paired with a social reward, especially for people with a high level of FoMO (Fear of Missing Out; that is, the pervasive apprehension that others might be having rewarding social experiences from which one is absent). These results are discussed in the light of the literature on distraction by reward history and attentional control, in order to integrate the reward history into these models. Moreover, our observations are discussed under the scope of applied researches that focused on driver distraction, in which our work has a particular resonance

The movement of human beings appears to respond to a complex motor system that contains signals at different hierarchical levels. For example, an action such as ``grasping a glass on a table'' represents a high-level action, but to perform this task, the body needs several motor inputs that include the activation of different joints of the body (shoulder, arm, hand, fingers, etc.). Each of these different joints/muscles have a different size, responsiveness, and precision with a complex non-linearly stratified temporal dimension where every muscle has its temporal scale. Parts such as the fingers responds much faster to brain input than more voluminous body parts such as the shoulder. The cooperation we have when we perform an action produces smooth, effective, and expressive movement in a complex multiple temporal scale cognitive task. Following this layered structure, the human body can be described as a kinematic tree, consisting of joints connected. Although it is nowadays well known that human movement and its perception are characterised by multiple temporal scales, very few works in the literature are focused on studying this particular property. In this thesis, we will focus on the analysis of human movement using data-driven techniques. In particular, we will focus on the non-verbal aspects of human movement, with an emphasis on full-body movements. The data-driven methods can interpret the information in the data by searching for rules, associations or patterns that can represent the relationships between input (e.g. the human action acquired with sensors) and output (e.g. the type of action performed). Furthermore, these models may represent a new research frontier as they can analyse large masses of data and focus on aspects that even an expert user might miss. The literature on data-driven models proposes two families of methods that can process time series and human movement. The first family, called shallow models, extract features from the time series that can help the learning algorithm find associations in the data. These features are identified and designed by domain experts who can identify the best ones for the problem faced. On the other hand, the second family avoids this phase of extraction by the human expert since the models themselves can identify the best set of features to optimise the learning of the model. In this thesis, we will provide a method that can apply the multi-temporal scales property of the human motion domain to deep learning models, the only data-driven models that can be extended to handle this property. We will ask ourselves two questions: what happens if we apply knowledge about how human movements are performed to deep learning models? Can this knowledge improve current automatic recognition standards? In order to prove the validity of our study, we collected data and tested our hypothesis in specially designed experiments. Results support both the proposal and the need for the use of deep multi-scale models as a tool to better understand human movement and its multiple time-scale nature.

Contingent capture occurs when distractors that share distinguishing characteristics with a target capture attention and slow down target identification. Conventionally, this slowdown has been attributed to the time wasted by an inappropriate attentional shift to the location of a distractor. To examine this account, we obviated the spatial shift by presenting distractors at fixation, and measured contingent capture both directly by measuring response times and indirectly by estimating the duration for which the target remains vulnerable to backward masking. Contingent capture invariably occurred when a salient distractor was presented within about 600 ms before the target. Because spatial shifts were ruled out using our procedure, the conventional account is insufficient. We augment that account with a two-stage model in which stimuli must pass an input filter tuned to the target's distinguishing characteristic before gaining access to a high-level stage which is unavailable for targets while distractors are being processed.

碩士
國立中央大學
認知與神經科學研究所
96
The interaction between voluntary attentional control and stimulus-driven attentional control may result in the efficiency of the deployment of attention.. Nontarget items that are salient and match for the defining feature of the target can capture attention effectively. This phenomenon is so-called contingent attentional capture because the capture is contingent on that the features of the nontarget need to be consistent with the attentional set of the task. In the present study, we used contingent attentional capture task and repetitive transcranial magnetic stimulation (rTMS) to investigate the neural mechanism of attentional control. Previous studies showed that two neural networks are involved in two attentional control systems. The dorsal frontoparietal network generates and maintains voluntary control; the ventral frontoparietal network is modulated by attentional shifts to behaviorally relevant stimuli. We choose right frontal eye fields (rFEF) and right temporoparietal junction (rTPJ) as the representative sites of dorsal and ventral networks, respectively. In the first two TMS experiments, rTMS (10Hz, 200 ms) was applied over rFEF either 200 ms before, simultaneously with, or 200 ms after the onset of the visual search array. When rFEF and rTPJ were stimulated before the onset of search array, the overall reaction time was decreased. However, when rFEF were stimulated 200ms after the onset of the stimuli, the reaction time was increased. The results suggested that rFEF may play a causal role in deployment of attention. However, the two experiments did not observe selective modulation of TMS on contingent attentional capture. In the third set of TMS experiments, we applied some modifications to test the attentional shift caused by contingent capture and the results of compatibility effects for the verification that abrupt onset caused attentional shifting into the stage of motor preparation. The results also shown rTMS applied on the both regions would reduce the reaction time cost of incompatible onset regardless of any onset types. The present results demonstrate the causal relationship between rFEF and visual attention, however, several experiments derived from the current study are needed to be carried out for elucidating the functional roles of rTPJ and rFEF in the control of the contingent attentional capture.

碩士
國立中央大學
認知與神經科學研究所
104
Attention may be captured by salient stimuli, but this effect is determined by top-down control settings, a phenomenon called "contingent capture". Previous theoretical approaches claimed that anxiety impairs attentional control processing by disrupting the balance between top-down and bottom-up attentional control systems (Eysenck et al., 2007) resulting in anxious individuals having difficulty resisting distraction. The present study tests this assumption by investigating the relationship between individual differences in trait anxiety and attentional distraction by task-irrelevant stimuli in a rapid serial visual presentation (RSVP) paradigm while the electroencephalogram was recorded. Analysis of the behavioral and electrophysiological correlates of attentional control processing for three different distractors showed a larger capture effect in the target-relevant distractor condition than the non-target relevant distractor and the distractor absent condition both in high trait anxiety and low trait anxiety groups, states that capture effects appear to be contingent on top-down attention settings. Moreover, high trait anxiety participants generated a larger N2pc in the target-relevant distractor condition and their behavioral performance was worse when distractors presented in the left visual field. The findings in this study suggested that trait anxiety influence the balance between two hemispheres especially in hyperactivation of the right ventral attention network, resulting in a leftward attentional asymmetry effect in spatial orienting.

La capture contingente de l’attention est un phénomène dans lequel les mécanismes d’orientation endogène et exogène de l’attention interagissent, de sorte qu’une propriété qui est pertinente à la tâche en cours, et donc qui fait l’objet de contrôles attentionnels descendants, endogènes, capture l’attention de façon involontaire, exogène, vers sa position spatiale. Dans cette thèse, trois aspects de ce phénomène ont été étudiés. Premièrement, en explorant le décours temporel de la capture contingente de l’attention et la réponse électrophysiologique à des distracteurs capturant ainsi l’attention, il a été établi que le déficit comportemental symptomatique de cette forme de capture était lié à un déploiement de l’attention visuospatiale vers la position du distracteur, et que ce traitement spatialement sélectif pouvait être modulé par le partage d’autres propriétés entre le distracteur et la cible. Deuxièmement, l’utilisation des potentiels liés aux événements a permis de dissocier l’hypothèse de capture contingente de l’attention et l’hypothèse de capture pure de l’attention. Selon cette interprétation, un stimulus ne peut capturer l’attention aux stades préattentifs de traitement que s’il présente le plus fort signal ascendant parmi tous les stimuli présents. Les contrôles attentionnels descendants ne serviraient donc qu’à désengager l’attention d’un tel stimulus. Les résultats présentés ici vont à l’encontre d’une telle interprétation, puisqu’un déploiement de l’attention visuospatiale, indexé par la présence d’une N2pc, n’a été observé que lorsqu’un distracteur périphérique possédait une caractéristique pertinente à la tâche en cours, même lorsque ses propriétés de bas niveau n’étaient pas plus saillantes que celles des autres items présents. Finalement, en utilisant un paradigme où la cible était définie en fonction de son appartenance à une catégorie alphanumérique, il a été démontré que des contrôles attentionnels en faveur d’un attribut conceptuel pouvaient guider l’attention visuospatiale de façon involontaire, rejetant une nouvelle fois l’hypothèse de la capture pure de l’attention.
Contingent involuntary orienting is a phenomenon in which endogenous and exogenous attentional mechanisms interact, such that an item captures attention only if it shares an attribute that is relevant for the task at hand. Hence, top-down attentional control settings are established endogenously in favour of the relevant attribute, but stimuli sharing this attribute draw attention to their location involuntarily. The present thesis explores three aspects of this phenomenon. First, by studying the time course of this contingent capture effect, and by measuring event-related potentials (ERPs) to capturing distractors, it has been established that the performance deficits linked to contingent capture are in fact due to a deployment of visuospatial attention to the location of the distractor. Moreover, this spatially selective processing of the capturing distractor can be modulated if the distractor shares another target attribute, beside the target defining attribute. The ERP technique also permitted the dissociation of the contingent involuntary orienting hypothesis and the pure capture with brief attentional dwell time hypothesis. According to the latter interpretation, only salient singletons have the ability to capture attention at preattentive stages of processing. Therefore, top-down attentional control settings serve only to disengage attention from the location of such singletons when they do not share target features. The present results argue against this interpretation, because a deployment of visuospatial attention, indexed by the presence of the N2pc, was observed only in response to peripheral distractors sharing the target-defining attribute, even when all items in the stimulus displays were equated in terms of bottom-up salience. Lastly, when alphanumeric category was used to define the target, it was shown that top-down attentional control settings in favour of such conceptual attributes could be successfully implemented and used to guide visuospatial attention in an exogenous fashion, providing further evidence against the pure capture hypothesis.

L’estinzione visiva è un disturbo spazio-temporale di visual awareness. Pazienti con lesioni all’emisfero destro che presentano estinzione visiva spesso mostrano difficoltà nel rilevare lo stimolo controlesionale quando presentato contemporaneamente ad uno stimolo ipsilesionale (condizione di stimolazione bilaterale). In questi pazienti spesso inoltre lo stimolo di sinistra deve essere presentato con un vantaggio temporale per poter essere percepito come simultaneo a quello di destra. Nel presente lavoro, sono stati condotti tre esperimenti al fine di indagare le basi funzionali e neurali dei disturbi spazio-temporali di visual awareness. Attraverso il primo esperimento abbiamo indagato i correlati neurali di tali disturbi in pazienti con ictus in fase cronica con estinzione visiva. I deficit di visual awareness potrebbero in linea di principio dipendere da una disfunzione della corteccia parietale posteriore dovuta alla lesione della giunzione temporo-parietale, area tipicamente danneggiata nei pazienti con disturbi di visual awareness. Infatti la corteccia visiva ipsilesionale che risulta strutturalmente intatta potrebbe essere funzionalmente normale ma la sua attività viene modulata in maniera patologica a causa delle influenze top-down che derivano dalla corteccia parietale posteriore, e questo creerebbe asimmetria interemisferica. Tuttavia, non è ancora chiaro se l'effetto di una modulazione top-down disfunzionale influenzi esclusivamente le risposte del paziente o se induca cambiamenti neurali nelle aree visive. In questo esperimento, abbiamo cercato di indagare tale aspetto utilizzando la tomografia ad emissione di posizione (PET) a riposo in pazienti post-ictus. Nello specifico attraverso tale metodica abbiamo comparato il metabolismo corticale di un paziente che mostra estinzione visiva in fase cronica con quello di due pazienti che hanno recuperato il disturbo in fase acuta e che al momento dell’esame PET non evidenziavano deficit di visual awareness. Dai risultati si evidenzia che nel paziente con estinzione la corteccia visiva ipsilesionale, seppur strutturalmente intatta, risulta ipometabolica rispetto alla corteccia visiva controlesionale, mentre nessuna asimmetria interemisferica nelle aree visive è stata trovata nei pazienti senza estinzione. Questi dati suggeriscono che i cambiamenti neurali nelle aree occipitali strutturalmente intatte potrebbero essere cruciali per spiegare il disturbo di visual awareness per stimoli controlesionale in pazienti con estinzione in fase cronica. Nel secondo e nel terzo esperimento abbiamo studiato il possibile contributo dei meccanismi di cattura contingente dell’attenzione nell’elaborazione spazio-temporale delle informazioni visive, sia in pazienti con disturbi dell'attenzione (esperimento 2) sia in soggetti sani (esperimento 3). Dalla letteratura emerge che il deficit attentivo dei pazienti con lesioni parietali destre può essere determinato dalla difficoltà di disancorare l’attenzione da stimoli ipsilesionale per riorientarla verso stimoli controlesionali. È stato tuttavia dimostrato che il deficit di disancoraggio dipende della rilevanza che gli stimoli ipsilesionali assumono sulla base della richiesta del compito e/o delle aspettative del paziente. Anche studi su soggetti sani suggeriscono che l’aspettativa per una modalità sensoriale può accelerare la relativa percezione dello stimolo presentato in quella modalità piuttosto che in un’altra, riducendo il tempo necessario per la rilevazione dello stimolo stesso (ipotesi del “prior entry”). Il secondo esperimento si è concentrato sull’indagine delle basi funzionali dei disturbi spazio-temporali di visual awareness nei pazienti con estinzione visiva. Nello specifico abbiamo indagato se la richiesta del compito influenza l'elaborazione spazio-temporale delle informazioni visive in questi pazienti. Sono state valutate le prestazioni di un paziente con estinzione visiva in un compito di giudizio di ordine temporale. Il compito era eseguito in 2 diverse condizioni: in un caso s’istruiva il paziente ad eseguire il compito focalizzando la propria attenzione su un particolare stimolo (focused condition) mentre in un altro si chiedeva di eseguire il compito senza focalizzare l’attenzione su uno specifico stimolo (non-focused condition). Le prestazioni del paziente sono state confrontate con quelle di un paziente cerebroleso destro senza estinzione visiva e di quattro soggetti sani comparabili per età. Nella condizione non-focused il paziente con estinzione ha mostrato un bias spazio-temporale (PSS = -255), mentre si è evidenziata una riduzione importante di tale bias nella condizione focused (PSS = -44). Questi risultati indicano una chiara modulazione delle prestazioni del paziente sulla base del set attentivo utilizzato. Al contrario, nessuna modulazione è stata trovata sia nel paziente cerebroleso (condizione non-focused: PSS = -4, condizione focused: PSS = -2) che nei soggetti sani (condizione non-focused: PSS media = -16, condizione focused: media PSS = 3). Inoltre il paziente con estinzione ha mostrato una maggiore accuratezza nella discriminazione temporale di stimoli controlesionali, ma non di quelli ispilesionali, nella condizione focused (62,5%) rispetto alla condizione non-focused (46,7%). Lo scopo del terzo esperimento è stato quello di indagare le possibili influenze dei meccanismi di cattura contingente dell’attenzione sull’elaborazione spazio-temporale delle informazioni visive in soggetti sani. Diciotto soggetti sono stati testati attraverso un compito di giudizio di ordine temporale simile a quello utilizzato nell'esperimento 2. Nella condizione non-focused i soggetti non hanno mostrato alcun bias nel giudizio di ordine temporale (PSS = -3,6). Al contrario focalizzando l’attenzione su uno specifico stimolo (condizione focused) i soggetti mostravano un bias nel giudizio ordine temporale (PSS = -11) a favore di tale stimolo. Sulla base delle nostre conoscenze, questi sono i primi dati che dimostrano come la cattura dell’attenzione sia contingente al set attentivo anche in compiti di giudizio di ordine temporale.
Visual extinction is a spatial-temporal disorder of visual awareness. Right-hemisphere patients with visual extinction frequently miss the stimulus presented in their contralesional field on trials with bilateral presentation. They can also need the left stimulus to be presented with a temporal lead in order to be perceived as simultaneous to the right one. In the present work, three experiments were carried out in order to investigate functional and neural bases of spatial-temporal disorders of visual awareness. The first one focused on neural correlates of spatial-temporal disorders of visual awareness in patients with visual extinction at a chronic stage. An impairment of visual awareness is likely to depend upon unbalanced top-down modulation from dorsal fronto-parietal on occipital areas, typically intact in the ipsilesional hemisphere, biasing spatial-temporal processing of visual information towards the ipsilesional side. However, it is not clear yet whether the effect of a dysfunctional top-down modulation can only affect responses or, rather, induce neural changes in targeted visual areas. In this experiment, we addressed this issue by using position emission tomography (PET) at rest to measure possible differences between the cortical metabolism of one patient showing visual extinction at a chronic stage, and two patients who recovered from extinction, one at a chronic and another at a sub-acute stage. We found the structurally intact visual cortex of the extinction patient being hypometabolic in the right as compared to the left hemisphere, whereas no hemispheric asymmetry in the metabolism of visual cortex was found in the patients who recovered from extinction. Our data suggest that neural changes in structurally intact occipital areas might be crucial to explain the lack of visual awareness for contralesional stimuli in chronic extinction patients. In the second and third experiment we investigated the possible contribution of mechanisms of contingent attentional capture to spatial-temporal processing of visual information both in patients with attention disorders (experiment 2) and in healthy individuals (experiment 3). It was suggested that impairments of right parietal patients can be accounted for by a deficit in disengaging exogenous attention from ipsilesional stimuli and reorienting it towards contralesional events. It has been shown that the disengagement deficit depending on their behavioural relevance of ipsilesional stimuli (task demands and expectation of the patient). Also the results in the healthy subjects suggest that attending to a sensory modality can speed up the relative perception of stimulus presented in that rather than a different modality, reducing the time necessary for the stimulus to be perceived (“prior entry” hypothesis). The second experiment focused on functional basis of spatial-temporal disorders of visual awareness in patients with visual extinction, investigating whether task-set related factors can affect spatial-temporal processing of visual information in these patients. Specifically, we examined the performance of a visual extinction patient on a temporal order judgment (TOJ) task under conditions with different attentional set and compared his performance to that of one right-brain-damaged patient without visual extinction and four healthy subjects age matched. In the not focused condition the extinction patient shown spatial-temporal bias (PSS=-255), while he shown an important reduction of this bias under focused condition (PSS=-44). These findings indicate a clear modulation of patient’s performance with the attentional set, particularly for the PSS. On the contrary, no such a modulation was found both in the brain-damaged control patient (not focused condition: PSS=-4, focused condition: PSS=-2) and in healthy subjects (not focused condition: mean PSS=-16; focused condition: mean PSS=3). Furthermore the extinction patient showed higher accuracy of temporal discrimination for left-sided stimuli, but not for right-sides stimuli, in the focused (62,5%) as compared to the not focused (46,7%) condition. The aim of the third experiment was to investigate whether mechanisms of contingent attentional capture would also affect spatial-temporal processing of visual information in healthy subjects. Eighteen participants were tested on a similar TOJ paradigm as that used in experiment 2. In the not focused task-set condition subjects showed no bias in temporal order judgment (PSS=-3.6). On the contrary focusing subject’s attentional set onto one stimulus dimension yielded a clear-cut bias in temporal order judgment (PSS=-11). Present findings support evidence indicating that exogenous attention would affect sensitivity in a TOJ task and also extend this evidence, showing that in a TOJ task, as in other visual orienting tasks, capture of attention by external stimuli is contingent to the current attentional set.

The investigations contained in this thesis explore distraction during visual search, with particular attention to what eye movements can reveal about the processes involved in visual search. All the experiments make use of the oculomotor capture effect, whereby an eye movement is misdirected toward a sudden onset distractor before being redirected to a target object. Fundamental differences between eye movements and attention in general, and between eye movements and manual responses in particular, support the current view that oculomotor capture is distinct from the more general effect known as attentional capture. Like oculomotor capture, attentional capture involves interference with visual search for a target by distractors. Unlike oculomotor capture, this interference is expressed as a delayed correct manual response, rather than a misdirected eye movement. The first study shows that resolution of oculomotor conflict between target and distractor responses takes place at or above the level of the superior colliculus, a midbrain structure involved in eye movement control. The second study explores the timecourse of eye movement and manual localization responses to targets in the presence of sudden onsets, and suggests that for both response types, capture reflects the quality of information about the visual display at a given point in time. The final study expands the oculomotor capture effect to search among emotional faces and finds that the eyes are captured by emotional faces more than neutral distractors only if emotion is task-relevant. Together, the research suggests that oculomotor capture is a specific instance of the more general attentional capture effect. It is proposed that differences and similarities between the two types of capture can be explained by the critical idea that the quality of information in a visual display changes over time, and that different response systems tend to access the same information at different moments in time.
Arts, Faculty of
Psychology, Department of
Graduate