Dissertations / Theses on the topic 'Eye contact effect'

Theories of embodiment propose that our bodily states can influence affective processing. This thesis investigated the possibility that facial feedback (i.e., afferent signals from facial muscles) can influence the interpretation of affective stimuli. One study tested the effect of overt smiling and frowning on the interpretation of short descriptions of everyday events. Smiling, as compared to frowning, led to more positive evaluations, but only for participants who were aware of the emotional relevance of their expressions. A second study tested whether subtle changes in facial activation (elicited by unconsciously presented happy/angry facial expressions) led to changes in evaluations of ambiguous target symbols. While angry prime faces, as compared to happy prime faces, induced more frowning (as measured via electromyography), this change in facial activation did not translate into a behavioural effect on subsequent evaluations. A third study investigated the relation between naturally occurring facial reactions and interpretations of both clearly valenced and ambiguous facial expressions. Results indicate that facial reactivity predicts participants' self-reports of their own emotional reactions towards others' expressions (Experiment 1). A relation between facial reactions and interpretations of the expression senders' emotional states was only found in cases in which participants with high sensitivity towards their own bodily states (as measured with a test of interoceptive accuracy) tried to interpret ambiguous expressions (Experiment 2). In a last experiment, prolonged presentation of emotional prime faces led to expression-congruent facial reactions, but resulted in expression-incongruent behavioural reactions in both classification speed and interpretative tendency of emotional target faces. Overall, this thesis suggests that facial feedback is not generally involved in the interpretation of affective stimuli, but that it might contribute to evaluative processes only under special circumstances.

I nostri tre studi ci forniscono un progresso nella conoscenza dei diversi meccanismi in gioco nella percezione della direzione dello sguardo, nel comportamento di seguire lo sguardo e nell'attenzione congiunta, sia a livello comportamentale che neurofisiologico. In particolare, la presente tesi porta prove dell'interazione e del corso temporale dei meccanismi cognitivi e neurali (processi bottom-up e top-down) che vengono reclutati quando si vede lo sguardo di altre persone. Questo equilibrio è possibilmente mantenuto al fine di prendere giustamente in considerazione o ignorare le informazioni provenienti dagli occhi di un'altra persona a seconda dei nostri obiettivi, dell'intenzione e del comportamento corrente.
our three studies provide us with an advance in knowledge on the different mechanisms at play in the perception of gaze direction, gaze following behavior and joint attention, both at the behavioral and neurophysiological level. Specifically, the present thesis brings evidence of the interplay and time course of the cognitive and neural mechanisms (bottom-up and top-down processes) that are recruited when seeing other people’s gaze. This balance is possibly maintained in order to justifiably take into account or disregard information coming from another person’s eyes depending upon our goals, intention and current behavior.

Thesis (Ph.D.)--Indiana University, Dept. of Optometry, 2007.
Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4406. Adviser: Larry N. Thibos. Title from dissertation home page (viewed Apr. 21, 2008).

A healthy human would be expected to show periodic blinks, making a brief closure of the eyelids. Most blinks are spontaneous, occurring regularly with no external stimulus. However a reflex blink can occur in response to external stimuli such as a bright light, a sudden loud noise, or an object approaching toward the eyes. A voluntary or forced blink is another type of blink in which the person deliberately closes the eyes and the lower eyelid raises to meet the upper eyelid. A complete blink, in which the upper eyelid touches the lower eyelid, contributes to the health of ocular surface by providing a fresh layer of tears as well as maintaining optical integrity by providing a smooth tear film over the cornea. The rate of blinking and its completeness vary depending on the task undertaken during blink assessment, the direction of gaze, the emotional state of the subjects and the method under which the blink was measured. It is also well known that wearing contact lenses (both rigid and soft lenses) can induce significant changes in blink rate and completeness. It is been established that efficient blinking plays an important role in ocular surface health during contact lens wear and for improving contact lens performance and comfort. Inefficient blinking during contact lens wear may be related to a low blink rate or incomplete blinking and can often be a reason for dry eye symptoms or ocular surface staining. It has previously been shown that upward gaze can affect blink rate, causing it to become faster. In the first experiment, it was decided to expand on previous studies in this area by examining the effect of various gaze directions (i.e. upward gaze, primary gaze, downward gaze and lateral gaze) as well as head angle (recumbent position) on normal subjects’ blink rate and completeness through the use of filming with a high-speed camera. The results of this experiment showed that as the open palpebral aperture (and exposed ocular surface area) increased from downward gaze to upward gaze, the number of blinks significantly increased (p<0.04). Also, the size of closed palpebral aperture significantly increased from downward gaze to upward gaze (p<0.005). A weak positive correlation (R² = 0.18) between the blink rate and ocular surface area was found in this study. Also, it was found that the subjects showed 81% complete blinks, 19% incomplete blinks and 2% of twitch blinks in primary gaze, consistent with previous studies. The difference in the percentage of incomplete blinks between upward gaze and downward gaze was significant (p<0.004), showing more incomplete blinks in upward gaze. The findings of this experiment suggest that while blink rate becomes slower in downward gaze, the completeness of blinking is typically better, thereby potentially reducing the risk of tear instability. On the other hand, in upward gaze while the completeness of blinking becomes worse, this is potentially offset by increased blink frequency. In addition, blink rate and completeness were not affected by lateral gaze or head angle, possibly because these conditions have similar size of the open palpebral aperture compared with primary gaze. In the second experiment, an investigation into the changes in blink rate and completeness was carried out in primary gaze and downward gaze with soft and rigid contact lenses in unadapted wearers. Not surprisingly, rigid lens wear caused a significant increase in the blink rate in both primary (p<0.001) and downward gaze (p<0.02). After fitting rigid contact lenses, the closed palpebral aperture (blink completeness) did not show any changes but the open palpebral aperture showed a significant narrowing (p<0.04). This might occur from the subjects’ attempt to avoid interaction between the upper eyelid and the edge of the lens to minimize discomfort. After applying topical anaesthetic eye drops in the eye fitted with rigid lenses, the increased blink rate dropped to values similar to that before lens insertion and the open palpebral aperture returned to baseline values, suggesting that corneal and/or lid margin sensitivity was mediating the increased blink rate and narrowed palpebral aperture. We also investigated the changes in the blink rate and completeness with soft contact lenses including a soft sphere, double slab-off toric design and periballast toric design. Soft contact lenses did not cause any significant changes in the blink rate, closed palpebral aperture, open palpebral aperture and the percentage of incomplete blinks in either primary gaze or downward gaze. After applying anaesthetic eye drops, the blink rate reduced in both primary gaze and downward gaze, however this difference was not statistically significant. The size of the closed palpebral aperture and open palpebral aperture did not show any significant changes after applying anaesthetic eye drops. However it should be noted that the effects of rigid and soft contact lenses that we observed in these studies were only the immediate reaction to contact lenses and in the longer term, it is likely that these responses will vary as the eye adapts to the presence of the lenses.

Thesis (doctoral)--Technische Universiteit Eindhoven, 1999.
"SPIE digital library." Originally published: Knegsel : HV Press, 1999. Includes bibliographical references and index. Also available in print version.

Thesis (M.S.)--West Virginia University, 2003.
Title from document title page. Document formatted into pages; contains xi, 101 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 95-99).

The aim of this thesis is to study the effect that linguistic context exerts on the activation and processing of word meaning over time. Previous studies have demonstrated that a biasing context makes it possible to predict upcoming words. The context causes the pre-activation of expected words and facilitates their processing when they are encountered. The interaction of context and word meaning can be described in terms of feature overlap: as the context unfolds, the semantic features of the processed words are activated and words that match those features are pre-activated and thus processed more quickly when encountered. The aim of the experiments in this thesis is to test a key prediction of this account, viz., that the facilitation effect is additive and occurs together with the unfolding context. Our first contribution is to analyse the effect of an increasing amount of biasing context on the pre-activation of the meaning of a critical word. In a self-paced reading study, we investigate the amount of biasing information required to boost word processing: at least two biasing words are required to significantly reduce the time to read the critical word. In a complementary visual world experiment we study the effect of context as it unfolds over time. We identify a ceiling effect after the first biasing word: when the expected word has been pre-activated, an increasing amount of context does not produce any additional significant facilitation effect. Our second contribution is to model the activation effect observed in the previous experiments using a bag-of-words distributional semantic model. The similarity scores generated by the model significantly correlate with the association scores produced by humans. When we use point-wise multiplication to combine contextual word vectors, the model provides a computational implementation of feature overlap theory, successfully predicting reading times. Our third contribution is to analyse the effect of context on semantically similar words. In another visual world experiment, we show that words that are semantically similar generate similar eye-movements towards a related object depicted on the screen. A coherent context pre-activates the critical word and therefore increases the expectations towards it. This experiment also tested the cognitive validity of a distributional model of semantics by using this model to generate the critical words for the experimental materials used.

Considerable evidence indicates that visual sensitivity is reduced during saccadic eye movement. A central question has been whether saccadic suppression results from a non-visual central signal, or whether the obligate image motion that accompanies saccades is itself sufficient to mask vision. In the first of a series of experiments described here, the visual and non-visual effects of saccades were distinguished by measuring contrast sensitivity to luminance modulated low spatial frequency gratings, at 17 cd·m¯² and 0.17 cd·m¯², in saccade conditions and in conditions in which saccade-like image motion was produced by the rotation of a mirror but when observers’ eyes were kept still. The time course of suppression was examined by making measurements from well before image motion began until well after it had ended. A tenfold decrease in contrast sensitivity was found for luminance-modulated gratings with saccades, but little suppression was found with simulated saccades. Adding high contrast noise to the visual display increased the magnitude and the duration of the suppression during simulated saccades but had little effect on suppression produced by real saccades. At lower luminance, suppression was found to be reduced, and its course shallower than at higher luminance. Simulated saccades produced shallower suppression over a longer time course at both higher and lower luminance. In a second experiment the time course of contrast sensitivity to chromatically modulated gratings, at 17 cd·m¯², was examined. No suppression was found; rather there was some evidence of an enhancement of sensitivity, both before and after saccades, relative to fixation conditions. Differences in the effects of real and simulated saccades in the magnitude and time course of sensitivity loss with luminance modulated gratings suggest that saccadic suppression has an extraretinal component that acts on the magnocellular system; the pattern of enhancement found in the later experiment suggests a selective favouring of the parvocellular system both immediately prior to and immediately after saccades. The possibility that the degree of enhancement in sensitivity varies across the visual field was examined using spatially localized stimuli (either high spatial frequency chromatically modulated gratings or letter combinations). Sensitivity was found to decrease at the initial fixation point during the 75 ms prior to saccadic onset and simultaneously to improve at the saccadic target. In the immediate post-saccadic period, sensitivity at the saccadic target was found to exceed that which had been manifest at the initial fixation point prior to saccades, suggesting that post-saccadic enhancement may improve the temporal contrast between one fixation and the next. The final experiments investigated the possibility that our sense of continuity across saccades (as opposed to stability) is influenced by saccade-induced errors in locating events in time. The results of these experiments suggest that saccades can result in errors in judging (a) the time at which external events occur relative to saccadic onset, (b) the temporal order of visual events, and (c) the magnitude of temporal intervals. It is concluded that apparent time is generally foreshortened prior to saccades. This might be due to selective suppression of magnocellular activity and might function to hide saccades and their effects from our awareness. A speculative synthesis is presented based on the idea that recurrent feedback between the neocortical and cortical structures on the one hand, and the thalamic nuclei on the other, has special importance for perception around the time of saccades

During face-to-face meetings, humans use multimodal information, including verbal information, visual information, body language, facial expressions, and other non-verbal gestures. In contrast, during computer-mediated-communication (CMC), humans rely either on mono-modal information such as text-only, voice-only, or video-only or on bi-modal information by using audiovisual modalities such as video teleconferencing. Psychologically, the difference between the two lies in the level of the subjective experience of presence, where people perceive a reduced feeling of presence in the case of CMC. Despite the current advancements in CMC, it is still far from face-to-face communication, especially in terms of the experience of presence. This thesis aims to introduce new concepts, theories, and technologies for presence design where the core is actions for creating presence. Thus, the contribution of the thesis can be divided into a technical contribution and a knowledge contribution. Technically, this thesis details novel technologies for improving presence experience during mediated communication (video teleconferencing). The proposed technologies include action robots (including a telepresence mechatronic robot (TEBoT) and a face robot), embodied control techniques (head orientation modeling and virtual reality headset based collaboration), and face reconstruction/retrieval algorithms. The introduced technologies enable action possibilities and embodied interactions that improve the presence experience between the distantly located participants. The novel setups were put into real experimental scenarios, and the well-known social, spatial, and gaze related problems were analyzed. The developed technologies and the results of the experiments led to the knowledge contribution of this thesis. In terms of knowledge contribution, this thesis presents a more general theoretical conceptual framework for mediated communication technologies. This conceptual framework can guide telepresence researchers toward the development of appropriate technologies for mediated communication applications. Furthermore, this thesis also presents a novel strong concept – presence through actions - that brings in philosophical understandings for developing presence- related technologies. The strong concept - presence through actions is an intermediate-level knowledge that proposes a new way of creating and developing future 'presence artifacts'. Presence- through actions is an action-oriented phenomenological approach to presence that differs from traditional immersive presence approaches that are based (implicitly) on rationalist, internalist views.

Recent empirical studies about the neurological executive nature of reading in bilinguals differ in their evaluations of the degree of selective manifestation in lexical access as implicated by data from early and late reading measures in the eye-tracking paradigm. Currently two scenarios are plausible: (1) Lexical access in reading is fundamentally language non-selective and top-down effects from semantic context can influence the degree of selectivity in lexical access; (2) Cross-lingual lexical activation is actuated via bottom-up processes without being affected by top-down effects from sentence context. In an attempt to test these hypotheses empirically, this study analyzed reader-text events arising when cognate facilitation and semantic constraint interact in a 22 factorially designed experiment tracking the eye movements of 26 Swedish-English bilinguals reading in their L2. Stimulus conditions consisted of high- and low-constraint sentences embedded with either a cognate or a non-cognate control word. The results showed clear signs of cognate facilitation in both early and late reading measures and in either sentence conditions. This evidence in favour of the non-selective hypothesis indicates that the manifestation of non-selective lexical access in reading is not constrained by top-down effects from semantic context.
Dagens eye-trackingstudier över de neurologiska processer som styr läsning i tvåspråkiga är oeniga om graden av icke-selektiv aktivation som infinner sig inuti den tvåspråkiges mentala lexikon enligt kvantitativa data på tidiga och sena åtkomstsstadier. Två olika förhållningssätt till frågan finns: (1) Lexikal åtkomst är fundamentalt sett icke-selektiv, men top-down effekter från semantisk kontext kan influera den grad av selektiv åtkomst som påträffas i mentala lexikon; eller (2) Parallell aktivation av olika språkplan sker via bottom-up processer utan någon inverkan ifrån top-down effekter ifrån meningskontext. För att testa dessa hypoteser undersöktes läsprover framtagna genom att kontrollera kognatförenklingseffekten och kontextskapad ordförutsägbarhet i en 22 faktorial stimulusdesign. 26 tvåspråkiga (svenska L1, engelska L2) läste meningsstimuli på engelska. Stimulus bestod av meningar med hög eller låg grad av semantisk och lexikal priming som innehöll antingen ett kognat- eller ett ickekognatkontrollord. Resultaten visade klara tecken på kognatförenkling i tidiga såsom sena åtkomstsstadier för båda typers meningsstimuli. Dessa resultat förespråkar att icke-selektiv åtkomst  i läsning inte påverkas av top-down effekter ifrån meningskontext.

Författaren heter numer Mattias Bystedt.

People form impressions quickly and easily using stereotypical beliefs as well as information the social context provides. These impressions inform beliefs, and guide emotional reactions and behavioural responses to others. Research has examined the nature of beliefs based on the amount and type of food others consume, and has shown that people more favourably judge others who eat low fat foods in small amounts. Research in an independent tradition has examined beliefs based on physical activity levels, and shown that people more favourably judge exercisers. Both the diet- and exercise-based literatures have shown that beliefs are associated with gender roles as well as attractiveness and body-size ideals, and thus differ for women and men. However, previous researchers have not systematically examined these separate yet interrelated beliefs in combination, including how these variables in combination affect emotional responses and behavioural tendencies. It is important to establish the social consequences, particularly given society’s emphasis on healthy living. Thus, the studies in this thesis examined beliefs, emotional responses, and behavioural tendencies involving others, based on the dietary and activity behaviours of normal-weight women and men, in combination. In addition, presentation of body-size information was varied in explicitness through the use of verbal information and photographs. To extend previous research I utilised a unifying social psychological theoretical frame, the Stereotype Content Model (SCM) and its extension the Behaviours from Intergroup Affect and Stereotype (BIAS) model.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Applied Psychology
Griffith Health
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Tese de mestrado, Neurociências, Faculdade de Medicina, Universidade de Lisboa, 2012
A perceção de contacto ocular tem um efeito modulador em vários aspetos do processamento cognitivo, podendo facilitar o reconhecimento facial ou o acesso à memória semântica. Nesse sentido, realizaram-se duas experiências para analisar o efeito do contacto ocular na capacidade de nomeação de faces famosas e a sua variação dependentemente do tipo de tarefa. Na primeira experiência foi apresentado um conjunto de faces famosas masculinas a um grupo de participantes, com mais de 50 anos de idade, sem doença neurológica conhecida.. As faces foram apresentadas aleatoriamente em contacto ocular ou em olhar desviado e foi pedido aos participantes para realizarem uma tarefa de nomeação das faces. Numa segunda tarefa de controlo foi solicitado aos participantes para indicarem a presença ou ausência de contacto ocular, nos estímulos apresentados. Na segunda experiência, repetiram-se as tarefas de nomeação e identificação da direção do olhar, tendo sido acrescentadas um igual número de faces femininas aos estímulos e adicionada uma tarefa de descriminação de género. Em ambas as experiências foi encontrado um efeito facilitador do contacto ocular na nomeação das faces que pertenciam ao mesmo género do participante. Pelo contrário, na tarefa de direção do olhar (na segunda experiência) verificou-se um efeito facilitador do contacto ocular, mas apenas para faces do género oposto ao participante. Na tarefa de género, o contacto ocular conduziu a uma redução no número de acertos para faces do género oposto. Estes resultados mostram um efeito facilitador do contacto ocular na nomeação, e a sua dependência de fatores como o género. A existência de um efeito facilitador do contacto ocular está então, dependente do tipo de tarefa (nomeação, género e descriminação da direção do olhar) e da interação entre a tarefa e o género observador/estímulo. Assim o efeito modulador do contacto ocular, nas diferentes atividades cognitivas é complexo, podendo facilitar ou interferir dependendo da tarefa e da sua interação com outras variáveis. O efeito facilitador, a confirmar em situações patológicas, poderá ser utilizado na reabilitação das dificuldades de nomeação.
Awareness of eye contact has a modulatory effect on several cognitive tasks, enhancing facial recognition and encoding, as well as the access to semantic memory related to these faces. To analyse the effect of eye contact on proper name retrieval, and how it may depend upon type of task, two experiments using famous faces as stimuli were designed. In the first experiment a set of well-known public male faces was presented randomly in eye contact or averted gaze. Participants were asked to perform two tasks, one in which they had to name the presented faces and a control task in which they had to discriminate gaze direction. Since in this experiment all stimuli were male, a second experiment added an equal number of female and male faces. In this experiment a gender decision task was added. Participants were adult volunteers with fifty or more years, without known mental or neurological disease. Results from both experiments showed a facilitator effect of eye contact in naming faces of the same sex as the participant. In the gaze direction task of the second experiment, eye contact was easier to discriminate compared to averted gaze but only when the presented face was of the opposite sex than the participant’s. In the gender task, eye contact diminished accuracy but only with opposite-sex faces. These results show that eye contact facilitates proper name retrieval, but that this effect depends upon the sex of the perceiver and the perceived face. The existence of a facilitation effect due to eye contact was shown to be dependent both of task and of the interaction of sex of the stimuli and the participant. The modulator effect of eye contact in different cognitive tasks seems to be complex, either being a facilitator or causing interference depending on type of task and its interaction with other variables. Its facilitator effect, if confirmed in cases of pathology, may be used in rehabilitation settings of proper name retrieval.

Two experiments examined processing of "near-nonsense" noun-noun combinations (e.g., dictionary treatment, olive signals). In the first experiment, readers’ eye movements were monitored as they read sentences containing such combinations, or control sentences containing easy-to-interpret adjective-noun combinations. A preceding context sentence either did or did not support a specific interpretation of the critical noun-noun combination. The earliest measures of processing difficulty were not modulated by the context manipulation, but on later measures, the potentially helpful context did alleviate difficulty. In the second experiment, participants provided detailed interpretations of the critical combinations, with and without the potentially helpful context sentence; the results confirmed that the context sentences encouraged specific interpretations of these combinations. The results suggest that a noun-noun combination is initially interpreted without taking into account the immediate context, but that this context may ultimately play a critical role.

There is a difference between the raw sensory input to the brain and our stable perception of entities in the environment. A first approach to investigate perception is to study relationships between properties of currently presented stimuli and biological correlates of perceptual processes. However, it is known that such processes are not only dependent on the current stimulus. Sampling of information and the concurrent neuronal processing of stimulus content rely on contextual relationships in the environment, and between the environment and the body. Perceptual processes dynamically adjust to relevant context, such as the current task of the organism and its immediate history. To understand perception, we have to study how processing of current stimulus content is influenced by such contextual factors. This thesis investigates the influence of such factors on visual processing. In particular, it investigates effects of temporal context in early visual processing and the effect of task context in eye movement control. To investigate effects of contextual factors on early visual processing of current stimulus content, we study neuronal processing of visual information in the primary visual cortex. We use real-time optical imaging with voltage sensitive dyes to capture neuronal population activity in the millisecond range across several millimeters of cortical area. To characterize the cortical layout concerning the mapping of orientation, previous to further investigations, we use smoothly moving grating stimuli. Investigating responses to this stimulus type systematically, we find independent encoding of local contrast and orientation, and a direct mapping of current stimulus content onto cortical activity (Study 1). To investigate the influence of the previous stimulus as context on processing of current stimulus content, we use abrupt visual changes in sequences of modified natural images. In earlier studies, investigating relatively fast timescales, it was found that the primary visual cortex continuously represents current input (ongoing encoding), with little interference from past stimuli. We investigate whether this coding scheme generalizes to cases in which stimuli change more slowly, as frequently encountered in natural visual input. We use sequences of natural scene contours, comprised of vertically and horizontally filtered natural images, their superpositions, and a blank stimulus, presented with 10 or 33 Hz. We show that at the low temporal frequency, cortical activity patterns do not encode the present orientations but instead reflect their relative changes in time. For example, when a stimulus with horizontal orientation is followed by the superposition of both orientations, the pattern of cortical activity represents the newly added vertical orientations instead of the full sum of orientations. Correspondingly, contour removal from the superposition leads to the representation of orientations that have disappeared rather than those that remain. This is in sharp contrast to more rapid sequences for which we find an ongoing representation of present input, consistent with earlier studies. In summary, we find that for slow stimulus sequences, populations of neurons in the primary visual cortex are no longer tuned to orientations within individual stimuli but instead represent the difference between consecutive stimuli. Our results emphasize the influence of the temporal context on early visual processing and consequentially on information transmission to higher cortical areas (Study 2). To study effects of contextual factors on the sampling of visual information, we focus on human eye movement control. The eyes are actively moved to sample visual information from the environment. Some traditional approaches predict eye movements solely on simple stimulus properties, such as local contrasts (stimulus-driven factors). Recent arguments, however, emphasize the influence of tasks (task context) and bodily factors (spatial bias). To investigate how contextual factors affect eye movement control, we quantify the relative influences of the task context, spatial biases and stimulus-driven factors. Participants view and classify natural scenery and faces while their eye movements are recorded. The stimuli are composed of small image patches. For each of these patches we derive a measure that quantifies stimulus-driven factors, based on the image content of a patch, and spatial viewing biases, based on the location of the patch. Utilizing the participants’ classification responses, we additionally derive a measure, which reflects the information content of a patch in the context of a given task. We show that the effect of spatial biases is highest, that task context is a close runner-up, and that stimulus-driven factors have, on average, a smaller influence. Remarkably, all three factors make independent and significant contributions to the selection of viewed locations. Hence, in addition to stimulus-driven factors and spatial biases, the task context contributes to visual sampling behavior and has to be considered in a model of human eye movements. Visual processing of current stimulus content, in particular visual sampling behavior and early processing, is inherently dependent on context. We show that already in the first cortical stage, temporal context strongly affects the processing of new visual information and that visual sampling by eye movements is significantly influenced by the task context, independently of spatial factors and stimulus-driven factors. The empirical results presented provide foundations for an improved theoretical understanding of the role of context in perceptual processes.

The current dissertation investigates how pointing movements performed towards to-be- remembered target locations together with a task-partner influence visuo-spatial working memory (VSWM). Previous studies have shown that, under specific conditions, spatial arrays that have been pointed to during encoding are better recognized than passively viewed ones. The first experiment described here was aimed at replicating these results. Participants were presented with two spatial arrays, one of which was encoded through mere visual observation (the no-move array), while the other was encoded through observation accompanied by pointing movements towards target locations (the move array). The encoding was followed by a recognition test in which participants had to decide whether a probe array was equal or different from one of the arrays presented during the study phase. Results replicated the memory advantage of pointed-to arrays as compared to merely observed ones. Since a number of studies suggest that perceiving an action and executing it are functionally equivalent and activate common representational structures, we proceeded to investigate whether pointing movements performed by a task-partner could have similar effects. No memory advantage was found when participants passively observed the pointing movements performed by the task-partner. A joint condition of the task was thus tested where the participant and the task-partner took turns in performing the pointing movements towards the target locations in the move array (recognition was always performed by the participants). Results showed that in this joint-action condition the pointing movements performed by the task-partner benefited individual’s visuo-spatial working memory to the same extent as self-performed pointing movements. Further experiments were conducted to investigate the processes underlying the encoding of no-move and move arrays, either jointly pointed by the participant and the task-partner or pointed only by the task-partner. In two eye-tracking experiments, the eye movement patterns for the two types of arrays were recorded. The analysis of eye movements yielded results that are in line with the behavioral findings and showed that fixations to move arrays were higher in number and longer in duration than the fixations to no-move arrays but only when the participant and the task-partner alternate in making the pointing movements. No difference in eye movement patterns was found for the move and no-move arrays when the participant merely observed pointing movements performed by the task-partner. We propose that, in the joint-action condition, self and others’ actions are coded at the same representational level and their functional equivalency is reflected in a similar pattern of eye fixations. Behavioral experiments investigating the effects of a number of other factors on visuo-spatial working memory are also reported, including the partner’s involvement in the task or the animacy of the task-partner. Findings show that: a) in the joint-action condition, the infrequent execution of pointing movements by the participants (about 16%) is sufficient to successfully produce a social context which leads to the co-representation of partner’s actions; and b) a memory advantage occurs when the turn-taking task-partner is replaced by a moving cartoon hand, but only in the joint-action condition (there is no advantage when the movements were only carried out by the cartoon hand). The latter finding indicates that the mere presence of the cartoon hand is not sufficient to trigger the memory advantage. Altogether, the results suggest that the social context between the participant and the task-partner modulates the task co-representation process. Finally, event related potential (ERP) data were recorded in order to investigate the encoding processes involved in processing self and other’s pointing movements in the joint-action condition. In summary, the current dissertation investigates, from behavioral and physiological points of view, the question of how performing an action together with a partner influences individual’s encoding processes and suggests future directions for research investigating the influence of jointly performed tasks on individual’s memory.

BACKGROUND: Postural instability in older people is associated with an increased risk of falling. This experiment investigated the effects of different gaze strategies on postural stability in older people, when using distance single-vision compared with multifocal (progressive addition lens and bifocal) spectacles. METHODS: Eighteen healthy older habitual multifocal spectacle-wearers (mean age 72.1 +/- 4.0 years) participated in a randomised, cross-over study. Postural stability during quiet standing was assessed as the root mean square excursion in the centre of pressure (RMS-COP) in the antero-posterior direction. Ground reaction force data were collected (for 30 seconds), while subjects viewed one of two visual targets (one square metre) of different spatial frequencies and contrasts, while wearing either distance single-vision or multifocal (progressive addition and bifocal) spectacles. The visual targets were positioned either ahead at eye-level or on the ground (viewing distance 2.06 metres) and viewed under the following head-gaze conditions; 'head neutral-gaze forward', 'head flexed-gaze down' and 'head neutral-gaze down'. RESULTS: The type of spectacles worn or the target viewed had no significant effect on postural stability but postural stability deteriorated (antero-posterior RMS-COP excursion increased) in the 'head neutral-gaze down' compared with the 'head flexed-gaze down' and 'head neutral-gaze forward' conditions (5.9, 5.5 and 5.0 mm respectively, p < 0.001). CONCLUSIONS: Multifocal use had no effect on standing postural stability. Irrespective of spectacles worn, when fixating a visual target positioned at ground level, postural stability was better in the 'head flexed-gaze down' condition compared with the 'head neutral-gaze down' condition. A useful strategy to reduce falling in the older person might be to advise multifocal and distance single-vision spectacle-wearers to flex their heads rather than just lower their eyes when looking downwards.

The utilization of in vitro tests with a tiered testing strategy for detection of mild ocular irritants can reduce the use of animals for testing, provide mechanistic data on toxic effects, and reduce the uncertainty associated with dose selection for clinical trials. The first section of this thesis describes how in vitro methods can be used to improve the prediction of the toxicity of chemicals and ophthalmic products. The proper utilization of in vitro methods can accurately predict toxic threshold levels and reduce animal use in product development. Sections two, three and four describe the development of new sensitive in vitro methods for predicting ocular toxicity. Maintaining the barrier function of the cornea is critical for the prevention of the penetration of infections microorganisms and irritating chemicals into the eye. Chapter 2 describes the development of a method for assessing the effects of chemicals on tight junctions using a human corneal epithelial and canine kidney epithelial cell line. In Chapter 3 a method that uses a primary organ culture for assessing single instillation and multiple instillation toxic effects is described. The ScanTox system was shown to be an ideal system to monitor the toxic effects over time as multiple readings can be taken of treated bovine lenses using the nondestructive method of assessing for the lens optical quality. Confirmations of toxic effects were made with the utilization of the viability dye alamarBlue. Chapter 4 describes the development of sensitive in vitro assays for detecting ocular toxicity by measuring the effects of chemicals on the mitochondrial integrity of bovine cornea, bovine lens epithelium and corneal epithelial cells, using fluorescent dyes. The goal of this research was to develop an in vitro test battery that can be used to accurately predict the ocular toxicity of new chemicals and ophthalmic formulations. By comparing the toxicity seen in vivo animals and humans with the toxicity response in these new in vitro methods, it was demonstrated that these in vitro methods can be utilized in a tiered testing strategy in the development of new chemicals and ophthalmic formulations.