Tesi sul tema "Face perception"

Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed August 2, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

While previous studies of face perception have focused mainly on the understanding of the processing of individual face cues, such as gaze direction, emotional expressions or physical attractiveness, some more recent studies suggest that these different cues are integrated in face processing.  The findings from the first four experimental Chapters in this thesis present further evidence for complex interactions among different invariant physical cues and changeable social cues when processing faces.  Importantly, these studies also demonstrate sources of systematic variation that modulate the manner in which this integration occurs (e.g., effects of changes in women’s progesterone levels, or differences among individuals high and low in anxiety).  The final experiment Chapter reports a series of experiments showing that rapid transient pupil constrictions to faces are sensitive to parameters such as the species and orientation of face.  These latter findings reveal transient pupil constrictions as a useful non-invasive and involuntary measure of face processing.  Collectively, the findings reported in this thesis demonstrate that cues to the direction and valence of others’ social interest, in addition to physical cues to attractiveness, are integrated when processing faces, highlighting the complexity and sophistication of the integrative processes that underpin face perception.

I volti e i corpi veicolano gli indizi non-verbali più importanti per le interazioni sociali. Essi forniscono numerosi dettagli essenziali per il riconoscimento dell’identità, genere, intenzioni e stato emotivo. Tutti i volti e i corpi sono simmetrici e condividono la medesima struttura tridimensionale, ma gli esseri umani riescono ad identificare facilmente centinaia di persone diverse, facendo affidamento solo sulle informazioni fornite da volto e corpo. L’elaborazione del volto e del corpo è stata ampiamente studiata e diversi modelli cogntivi e neuroanatomici sono stati ideati per spiegare questi processi. Nonostante numerose differenze sostanziali, tutti questi modelli hanno riconosciuto diversi stadi di elaborazione, dalla codifica dello stimolo rapida e più grezza (corteccia visiva occipitale) fino a processi di livello più alto, finalizzati al riconoscimento di aspetti invarianti (es., identità) e mutevoli (es., sguardo, espressioni emotive) (sottesi da un vasto network fronto-temporo-parietale). È stato dimostrato che questi processi coinvolgono l’elaborazione configurale degli stimoli. Inoltre, le espressioni emotive sembrano influenzare la codifica di questi stimoli. Le espressioni emotive vengono elaborate ad uno stadio molto precoce e pare che coinvolgano l’attivazione di una via sottocorticale. Gli studi presentati in questa tesi hanno l’obiettivo di indagare la percezione visiva di volti e corpi, e come essa può essere modulata o manipolata, in alcuni studi anche attraverso l’elettroencefalografia (EEG). Mentre il primo Capitolo presenta il quadro teorico in cui è stato concepito questo lavoro di tesi, il secondo Capitolo presenta il primo studio (composto da due esperimenti), che ha l’obiettivo di indagare come può essere modulata la percezione di indizi sociali attraverso l’esclusione sociale. La ricerca era concentrata sulla percezione di due categorie di indizi facciali diversi, ma in interazione: le espressioni emotive e la direzione dello sguardo. In questo studio, abbiamo trovato che il riconoscimento della direzione dello sguardo veniva indebolita in modo specifico, mentre il riconoscimento delle espressioni emotive non era compromesso. I risultati di questo studio hanno portato a riflessioni importanti sull’importanza dello sguardo in quanto segnale di potenziale re-inclusione, e su come l’indebolimento dell’elaborazione dello sguardo potesse portare nuovamente all’esclusione sociale. Il terzo Capitolo presenta una meta-analisi sul body-inversion effect, una manipolazione che ha lo scopo di dimostrare l’elaborazione configurale dei corpi. Con la meta-analisi è stata indagata la coerenza e la dimensione di questo effetto, fondamentale nello studio della codifica strutturale dei corpi. Nel quarto capitolo, viene presentato uno studio sulle oscillazioni neurali coinvolte negli effetti di face- e body-inversion. Le oscillazioni sono state misurate nelle bande di attività theta e gamma attraverso l’EEG, dal momento che rappresentano un mezzo notevole per indagare l’attività psicofsiologica coinvolta in diversi processi. I risultati di questo studio hanno mostrato che l’elaborazione configurale di volti e corpi coinvolge meccanismi percettivi diversi. Nel quinto Capitolo viene presentato uno studio che indaga l’influenza dell’inversione e delle espressioni emotive nella codifica di volti e corpi. I correlati neurali di questi processi sono stati indagati attraverso i potenziali evento-correlati (ERPs). I risultati hanno evidenziato che sia l’inversione che l’espressione emotiva influenzavano l’elaborazione di questi stimoli, durante diversi stadi e attraverso diversi processi, ma queste due manipolazioni non interagivano. Pertanto, sembra che le informazioni configurali e le espressioni emotive siano elaborate attraverso processi percettivi indipendenti e che non interagiscono.
Human face and body convey the most important non-verbal cues for social interactions. Face and body provide numerous cues essential for recognition of other people’s identity, gender, age, intentions and emotional state. All faces and bodies are symmetrical and share a common 3D structure, but humans are able to easily identify hundreds of different people, just relying on facial and bodily information. Face and body processing have been widely studied and several cognitive and neuroanatomical models of these processes were hypothesized. Despite many critical differences, all these models recognized different stages of processing from early coarse stimulus encoding (occipital visual cortices) to higher-level processes aimed to identify invariant (e.g., identity) and changeable features (e.g., gaze, emotional expressions) (broad fronto-temporo-parietal network). It was demonstrated that these processes involve configural processing. Moreover, emotional expressions seem to influence the encoding of these stimuli. Processing of emotional expressions occurs at very early latencies and seems to involve the activation of a subcortical pathway. The studies presented in this thesis are aimed to investigate the visual perception of faces and bodies, and how it can be modulated or manipulated. EEG was used in some of the studies presented in this thesis to investigate the psychophysiological processes involved in face and body perception. While the first Chapter is aimed to present the theoretical background of the studies reported in the thesis, the second Chapter presents the first study (composed of two experiments), aimed to investigate how the perception of social cues can be modulated by social exclusion. The process investigated is the perception of two different, but interacting, facial cues: emotional expression and gaze direction. In this study, we found that the identification of gaze direction was specifically impaired by social exclusion, while no impairment was found for emotional expression recognition. The results of this study brought important insights concerning the relevance of gaze as a signal of potential re-inclusion, and how the impaired processing of gaze direction may reiterate social exclusion. The third Chapter presents a meta-analytic review on the body inversion effect, a manipulation aimed to demonstrate configural processing of bodies. This meta-analysis was aimed to investigate consistency and size of this effect, fundamental in studying structural encoding of body shapes. In the fourth Chapter, a study on the neural oscillations involved in face and body inversion effects is presented. Neural oscillations in theta and gamma bands were measured by means of the EEG since they are a very influential measure to investigate the psychophysiological activity involved in different processes. The results of this study showed that configural processing of faces and bodies involve different perceptual mechanisms. In the fifth Chapter, a study investigating the influence of inversion and emotional expression on the visual encoding of faces and bodies is presented. The neural correlates of these processes were investigated by means of event-related potentials (ERPs). Both inversion and emotional expressions were shown to influence the processing of these stimuli, during different stages and through different perceptual mechanisms, but results revealed that these two manipulations were not interacting. Therefore, configural information and emotional expressions seem to be processed through independent and non-interacting perceptual processes.

Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed Jan. 9, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Previous research has shown that deliberate disguise deteriorates human and automatic face recognition, with consequences for person identification in criminal situations. Common forms of deliberate disguise (e.g. balaclavas or hoodies) are easy to detect. When such disguises are used, viewer can distinguish between an unmasked individual - whose identity they knowingly can observe from facial appearance - and a masked individual - whose identity they knowingly cannot. Hyper-realistic silicone masks change this. Their recent use in criminal settings suggests that they effectively disguise identity and are difficult to detect. In this thesis, I first show that viewers are strikingly poor at distinguishing hyper-realistic masks from real faces under live and photographic test conditions, and are worse in other-race conditions. I also show large individual differences in discriminating realistic masks from real faces (5%-100% accuracy), and use an image analysis to isolate information that high performers use for effective categorisation. The analysis reveals an informative region directly below the eyes, which is used by high performers but not low performers. These findings point to selection and training as routes to improved mask detection. Second, I examine the reliability of estimates made of the person beneath the mask. Demographic profiling and social character estimates are poor, and results show that recognition rates were only just above chance, even for familiar viewers. This analysis highlights a systematic bias in these estimates: demographics, traits and social characteristics of the mask were attributed to those of the wearer. This bias has theoretical and applied consequences. First, it supports the automaticity with which viewers use a face to judge a person, even when they know the face is not that of the person. Second, it suggests that predictions of the person underneath the mask, by familiar and unfamiliar viewers alike, should be treated with great caution.

Thesis (Ph.D.)--Indiana University, Dept. of Psychology, 2006.
Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0570. Adviser: James Townsend. "Title from dissertation home page (viewed Feb. 22, 2007)."

Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed January 14, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references. Faces are central stimuli in our everyday life, hence, face processing is a sophisticated and highly specialized cognitive ability, at which adults are experts and children are proficient. Unlike other visuospatial abilities, face perception develops very slowly, becoming adult-like only well into adolescence. Some performance disparities between children and adults may reflect differences in general cognitive abilities, such as attention and memory. Alternatively, performance differences can be attributed to specific cognitive strategies implemented during face processing by different age groups; or to the interaction between the improvement of general abilities throughout development and the refinement of face specific cognitive strategies. The intent of the current studies was to further assess the development of and relationship between cognitive strategies in face processing. Specifically, we investigated the behavior and neurocorrelates associated with holistic face processing in children (8- to 11-year-olds), adolescents, and adults, utilizing the composite face effect. The task requires participants to engage in both holistic and featural processing, but certain trials (aligned-same) elicit a visual illusion called the composite face effect (CFE, calculated as difference between misaligned-same and aligned-same trials), which is considered an index of holistic processing. All age groups (adults, adolescents, 8- to 9-year-olds, 10- to 11-year-olds) showed a CFE, suggesting reliance on holistic processing. Notably, about half of the 8- to 11-year-old children displayed adult-like behavior and adult-like CFE, suggesting their reliance on holistic processing. However, the other half of the children performed below-chance on aligned-same trials, displayed an extremely large CFE, and a significant difference between different trials, suggesting reliance on a featural strategy. Thus child age groups were regrouped according to their accuracy performance on the hardest condition (aligned-same trials) into high performing and low performing children. We hypothesize that the aligned-same trials were too taxing for low-performing children, thus they fell back into relying on simpler strategies such as a difference-detection featural strategy. In order to further investigate the CFE behavioral differences between age and performance groups, we completed an imaging study. For the fMRI study children were grouped by performance rather than age following the results of our behavioral study. Overall, our imaging results for the CFE, thus for holistic processing, resembled behavioral results in that adult and high performing child groups revealed a similar (but not identical) whole-brain pattern of activation, whereas the low performing child group showed a distinctive pattern of activation for the composite face effect. Adults and high performing children showed a pattern of activation spanning frontal, parietal, temporal, and occipital lobes. In contrast, low performing children revealed a pattern of activation that spanned frontal, temporal, cingulate, and cerebellar regions. Brain areas typically associated with face processing, such as the right fusiform gyrus and right inferior temporal gyrus did not reach significance for the low performing child group. These differences may be attributable to the use of different cognitive strategies. However, the extent of frontal and cingulate cortex activation in low performing children may also suggest that because the task was especially difficult for them, working memory resources were particularly taxed, thus affecting the neural network engaged. Importantly, not only were performance differences associated with distinct neurocorrelates (i.e., differing profiles for low performing children vs. high performing children and adults), but age differences also had an appreciable effect. In fact, high performing children did not significantly differ from adults in the behavioral CFE, but did show differences in the neural CFE.

There has recently been much interest in how limitations in spatial frequency range affect face and object perception. This work has mainly focussed on determining which bands of frequencies are most useful for visual recognition. However, a fundamental question not yet addressed is how spatial frequency overlap (i.e., the range of spatial frequencies shared by two images) affects complex image recognition. Aside from the basic theoretical interest this question holds, it also bears on research about effects of display format (e.g., line-drawings, Mooney faces, etc.) and studies examining the nature of mnemonic representations of faces and objects. Examining the effects of spatial frequency overlap on face and object recognition is the main goal of this thesis.
A second question that is examined concerns the effect of calibration of stimuli on recognition of spatially filtered images. Past studies using non-calibrated presentation methods have inadvertently introduced aberrant frequency content to their stimuli. The effect this has on recognition performance has not been examined, leading to doubts about the comparability of older and newer studies. Examining the impact of calibration on recognition is an ancillary goal of this dissertation.
Seven experiments examining the above questions are reported here. Results suggest that spatial frequency overlap had a strong effect on face recognition and a lesser effect on object recognition. Indeed, contrary to much previous research it was found that the band of frequencies occupied by a face image had little effect on recognition, but that small variations in overlap had significant effects. This suggests that the overlap factor is important in understanding various phenomena in visual recognition. Overlap effects likely contribute to the apparent superiority of certain spatial bands for different recognition tasks, and to the inferiority of line drawings in face recognition. Results concerning the mnemonic representation of faces and objects suggest that these are both encoded in a format that retains spatial frequency information, and do not support certain proposed fundamental differences in how these two stimulus classes are stored. Data on calibration generally shows non-calibration having little impact on visual recognition, suggesting moderate confidence in results of older studies.

Advances in computer graphic and statistical methods have made it possible to visualise global face shape correlates of social judgments. The current thesis used a data-driven approach to investigate face shape correlates and perception of two traits, masculinity and strength, both of which are important in mate choice and social perception more generally. The studies presented defined the influences of body physique (height, body mass index, body fat and muscle mass) on facial shape, and their effects on the perception of masculinity, attractiveness and strength. Study 1 investigated the face shape correlates of actual and perceived masculinity. I found that perceived masculinity is not only driven by sexually dimorphic shape, but also by cues to body height and weight. Men with taller and heavier bodies were perceived to have more masculine-looking faces. Study 2 investigated women's perception of male attractiveness as a function of masculine face shape. As previously assumed but not explicitly tested, I found that masculinity preferences followed a quadratic relationship: attractiveness increased with increasing masculinity levels, but dropped o. at higher levels of masculinity. In addition, I showed that the relative costs and benefits of high and low masculinity are affected by individual differences in own condition, perceived financial harshness and pathogen disgust. In Study 3, I found that perception of strength from faces is driven by facial cues to body physique; individuals with higher body bulk were perceived to be stronger. In men, it proved possible to further dissociate facial cues to muscle and fat mass which both contributed to strength perception. The thesis demonstrates that facial cues used in the evaluation of masculinity and strength are linked to bodily characteristics associated with sex differences and actual strength, namely height, weight, muscularity and adiposity. My findings therefore support the hypothesis that perceptions have an adaptive origin.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005.
Includes bibliographical references.
Faces each have distinct pigmentation as well as shape, which suggests that both cues may play a role in the perception of faces. However, there is a common implicit assumption that pigmentation cues are relatively unimportant, and so the role pigmentation plays in face perception has gone largely unexplored. This thesis is a systematic investigation of the role of pigmentation in face recognition, facial sex classification, and facial attractiveness. The present studies present evidence that pigmentation cues are in fact quite important for face perception. For face recognition, pigmentation cues are about as important as shape cues. Male and female faces differ consistently in their pigmentation, with female faces having more luminance contrast between the eyes and lips and the rest of the face than do male faces. This sex difference in pigmentation is used as a cue for judgments of facial sex classification and facial attractiveness. Together, these results implicate an important role for pigmentation, and open new avenues of research in the perception of faces.
by Richard Russell.
Ph.D.

Sleep deprivation has been studied for over a century, providing knowledge about the benefits of sleep for many physiological, cognitive, and behavioural functions. However, there have only been anecdotal indications about what a tired or sleep-deprived person looks like, despite the fact that appearance influences not only how other people perceive a person but also how they evaluate them and behave towards them. How someone with sleep loss is perceived and evaluated by others is the focus of this thesis. Facial photographs of 48 participants were taken after normal sleep and after either one night of total sleep deprivation or two nights of partial sleep deprivation. The photographs were then evaluated in four different studies by a total of 288 raters recruited from universities and the general public in Stockholm, Sweden. The faces were rated on attractiveness, health, tiredness, sleepiness, sociability, trustworthiness, employability, and leadership ability. These factors were all adversely affected by sleep loss. Furthermore, looking tired was strongly related to being less attractive, looking less healthy and less trustworthy, and being perceived as a poorer employee and leader. One of the studies assessed facial features commonly associated with looking tired, showing that sleep deprivation results in eyes which appear more swollen and red, with dark circles and hanging eyelids, as well as paler skin with more fine lines and wrinkles. When sleep deprived, people were also perceived as more sad. In conclusion, the four studies show that sleep loss and a tired appearance affect how one is perceived by other people. These perceptions may lead to negative evaluations in interpersonal situations, both personal and professional. This thesis thus demonstrates social benefits of prioritizing sleep, adding to the physiological, cognitive, and behavioural research on sleep loss.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

An important issue in human cognition concerns face processing. Faces are incontestably one of the most important biological stimuli for humans. They convey crucial social cues, such as age, sex, emotion and identity information, and are the basis of verbal and non-verbal communication. Face processing and recognition have been extensively studied over the past years, through different methodology including neuroimaging and electrophysiology, mostly aimed at testing the extent to which faces can be considered a class of special visual stimuli (e. g. Farah, Wilson, Drain, & Tanaka, 1998; but see also Gauthier, Behrmann, & Tarr, 2004). Despite there is no complete agreement on this debated issue all authors concord on the fact that there are at least two reasons that make faces special: face recognition exhibit functional characteristics not found in the recognition of other visual stimuli and, second, the neural substrate that mediates face recognition is anatomically separated from the those mediating general object recognition (e.g. Farah, Rabinowitz, Quinn, & Liu, 2000). The majority of the literature on face processing was aimed primarily to investigate the ability to discriminate between faces and non-face like objects (e.g. Gauthier, Behrmann, & Tarr, 1999), as well as defining which kind of processing is involved (configural vs. featural processing) (e.g. Maurer, Grand, & Mondloch, 2002) and the ability to perceive the uniqueness of individual faces (e.g. Bruce & Young, 1986), thus focusing primarily on face-identity related aspects of recognition It has been claimed that the recognition of facial identity is based on invariant facial features, such as eyes, nose, mouth and their reciprocal configurational relations. As well as these invariant aspects, faces have another essential component: their changeable aspects, that carry a variety of socially important cues that are essential to social interaction. Indeed, since birth most face viewing occurs in the context of social interactions and faces provide a wealth of information, beyond identity, which facilitate social communication. Indeed, facial features can move, changing their reciprocal relations, generating for example facial expression, lip or eye movement. In fact, while these changeable aspects do not modify the identity of that particular face, they result constitute in different visual stimuli which convey different social signals. The ability to process such social relevant information may represent a more highly developed visual perceptual skill than the recognition of identity. Only recently however, the study of these aspects have started to be investigated. Among the different neuroanatomical - functional models proposed in literature, the Haxby and colleagues’s (2000) take into account both important components, invariant features and changeable aspects of a face. The network includes visual (“core”) regions, which process invariant facial features, as well as limbic and prefrontal (“extended”) regions that process changeable aspects of faces (Haxby, Hoffman, & Gobbini, 2000; Ishai, 2008). Starting from Haxby model, the attention of the present work has been focused on the role of the changeable aspect of a face within social interaction. More specifically, the aim of the current series of studies was to investigate how observer could process, use, interact and react to different social signals (i.e. gaze direction, head orientation, facial expressions). In experiment 1 we explored the perception of different gaze directions and the role of conflicting information in gaze following behaviour was investigated using ERPs. In experiment 2 we examined the effect of the combination between gaze direction and head positions on allocation of attentional resources and thus on the processing of subsequent target using fMRI. In experiment 3 we studied how non-emotional facial expressions could help recognition of identity in a clinical population (i.e. congenital prosopagnosia). It is well known that others’ gaze direction and body position attract our attention (Ricciardelli, Baylis, & Driver, 2000), and it also has been demonstrated the existence of an automatic tendency to follow the gaze of others, leading to joint attention (Ricciardelli, Bricolo, Aglioti, & Chelazzi, 2002). It is known that we can use those signals to modulate our attention, but it is still unclear the nature and the time course of control processes involved in this modulation. In the first part of the present study we investigate this issue on gaze by using different methodologies: electrophysiological method in order to investigate the time course of the gaze following behaviour (the fact that ultimately the observer’s look and attend where another person is looking); and neuroimaging method to explore what neural system is activated when a temporal allocation of resource is required and influenced by seeing actors with different gaze direction and head orientation. In experiment 1 we wanted to trace the time course of the processed involved in a gaze cueing task in which the effect was investigated in an overt paradigm. By combining eye movement and ERP recordings we investigate the involvement of conflict monitoring processes in various contexts and at different times with respect to the distracter’s eyes movement. We used ERP because they provide a measure of the timing of the elaboration of gaze observed and of the consequent planning of a saccadic response. Participants were instructed to saccade towards one of two lateral targets in a Posner like paradigm. Seventy-five milliseconds before, or after the instruction onset, a distracting face gazed towards a target (goal-directed), congruent or incongruent with the instructed direction, or towards an empty spatial location (non-goal-directed). We analyzed the N2 and Error-Related Negativity (ERN) measures, known to be involved in conflict monitoring processes (respectively in pre-response conflict and in error detection). Results interestingly showed that a certain degree of control over the gaze following response is possible, suggesting that tendency to follow the gaze of others is more flexible than previously believed, as it seems to depend not only on an early visuo-motor priming (Crostella, Carducci, & Aglioti, 2009), but also on the circumstances (i.e. context) associated with the seen gaze shift. In experiment 2 we explored activations in face neural system in order to verify whether social cues indicating mutual contact enhanced or reduced attention for subsequent events. More specifically it has been investigated how the processing of gaze direction (averted, directed) and head position (deviated, frontal) diminishes attentional blink (AB) for subsequent visual events. We used fMRI in order to measure the hemodynamic response (change in blood flow) related to neural activity in attentional and face processing systems when the temporal allocation of resource is linked to gaze direction and head position processing. Results showed that when the eyes and the head were oriented in the same direction (i.e., congruent conditions), attract attention and increase the processing of subsequent visual events, than when they were oriented in opposite directions (i.e., incongruent), In fact analysis showed that congruent gaze direction and head orientation increased activity within bilateral temporoparietal junction, an area that is strongly associated with mentalizing and understanding intentions of other’s (Redcay et al., 2010), as well as increased activity in regions of the face perception network, such as Occipital Face Area, Superior Temporal Sulcus and anterior insula (Ishai, 2008), but these responses were drastically diminished during AB. Moreover activity in bilateral Intraparietal Sulcus, a region involved in gaze perception (Calder et al., 2007) and attention (Marois, Chun, & Gore, 2000), decreased during AB in parallel to the decrease in recognition performance, thus when head and gaze were averted. These results show that head and gaze directions seem to be powerful social cues that are able to modulate the AB effect and, more generally, influence the observer's attention in reacting to subsequent visual stimuli. Together with the results from Experiment 1, these findings validate the issue that humans has a neural system to process other’s gaze direction and that this system is complexity linked with attentional networks both to allocate resource and to share the attention with someone else. Another important features connected with social signals in face perception are facial expressions which were investigated in the second part of the present work. The idea that facial identity and facial expressions are processed by separate visual route has well established in face research. The model proposed by Haxby and colleagues (2000) contain a separate route for facial identity but it is unknown if a single system supports the processing of emotional and non-emotional facial expressions whereas non emotional facial expressions are expressions that are not supported by an affective state. A previous study (Comparetti, Ricciardelli, & Daini, 2011) on normal subjects suggests that non-emotional facial expressions could be processed in a specific way dissociable from emotions and from other facial features. In perceiving emotional expressions congenital prosopagnosic individuals (people who are unable to recognize faces and maintain the disability lifelong in absence of any obvious brain damage) are indistinguishable from control but it’s still unknown if they could process non-emotional facial expressions. This hypothesis was tested in Experiment 3 by investigating whether and how CP participants could elaborate facial expressions that not convey an affective state (A. J. O'Toole, Roark, & Abdi, 2002). Using the Face inversion paradigm, as in Comparetti et al. (2011) we tested if non-emotional facial expressions could be processed by system, differentiated from identity recognition system and emotion processing in CP subjects with pathological score at standard face recognition tasks. We carried out a behavioural study in which we compared performance in a recognition task and in a same/different judgement task, using upright and inverted faces. In the experiment were manipulated respectively internal features, emotional and non-emotional facial expressions. Results demonstrated that in these subjects non emotional facial expressions are processed and facilitated the judgment in the upright orientation, while emotions and features manipulation did not. Overall, the present thesis has investigated issues from the current domain of processes associated with face perception and social information essential for adaptive behavior in a complex social environment. It provides further evidence that social signs are important and are processed even if they are not relevant for the task. For example gaze cueing is observed even when the participants are motivated to orient away from gaze direction because the target will be in an uncued location (experiment 1) or even if it is not relevant for the task (experiment 2) and facial expressions are elaborated even if only the identity of the face will be required (experiment 3). More specifically it has been investigated how people react to social signal and could plan their behaviours reacting to the social information given by a face. In fact in Experiment 1 has been demonstrated that other’s gaze is a strong trigger to allocate our attention to an important location in space but more deeply other’s gaze it’s really important when the two actors have something in common (i. e. the same peripheral targets); in fact, under certain conditions, the gaze following behaviour could be controlled and specifically when the context is not shared. Moreover the Experiment 2 has shown how people could allocate temporarily their attention responding to gaze direction and head orientation, and demonstrating that when the different signals are congruent it is possible to reallocate attentional resources to process subsequent event. Finally in Experiment 3 it has been demonstrated that a facial expression that does not convey an universal affective state could be processed by congenital prosopagnosic individuals and these expressions could be used as a cue to arrive to the identity.

A set of empirical studies is presented that examines the relationship between face perception, the modular hypothesis of cognitive function proposed by Fodor (1983), and attention. In the first study, two different manipulations were used to examine whether faces automatically trigger holistic processing operations as measured by the composite effect. The results support a modular account of face perception.
The second study introduces a novel rivalry phenomenon produced by overlapped upright tilted faces. The results indicate that this effect is dependent upon orientation with overlapped inverted faces being perceived as ambiguous in a majority of trials. The third study further examined the factors underlying this rivalry effect. It was found that contrast reversal did not influence the rivalry effect produced by overlapped upright faces and that overlapped houses did not produce rivalry. Results from both studies were taken as evidence that faces are more readily processed as Gestalts compared to other complex objects and therefore engage domain specific operations. The results also suggest that fast operations underlie perception of a face as a Gestalt. Finally, it was suggested that the rivalry effect produced by overlapped faces may illustrate informational encapsulation in face perception.
In the fourth study, faces were used to investigate the relationship between attention and modular functions. Three separate experiments showed that faces and houses compete for attention. This finding suggests that the face perception module does not have its own dedicated attentional resources but rather shares a common pool with other visual processes. Results from one experiment also suggested an advantage for faces in the allocation of attention at very short presentation times. This advantage was postulated to arise from two interacting mechanisms that is, faces capture attention over other objects and faces are more automatically encoded than other objects. Together, these studies indicate that a modular conceptualization of face processing is both appropriate and useful. They also demonstrate the utility of faces for investigating cognitive mechanisms that mediate modular functions.

What is meant by configural and holistic processing? The present project attempts to answer this question by formalizing configural and holistic processing as interactive processing of face parts. Four face images were created from one main face by varying the eye distance and nose length of the face to yield a 2x2 feature-complete factorial combination set of stimuli. Participants viewed each version of the face for 100 msecs, and then identified the face they saw. Their responses were subjected to multidimensional signal detection analysis to obtain estimates of different types of perceptual interactions defined by General Recognition Theory (Ashby & Townsend, 1986). It is shown here that perception of upright faces exhibits a number of interactions that are not present for inverted faces. The nature of these interactions are linked to concepts of holistic and configural face processing. A computational justification is forwarded for this interactivity account of face processing.

Given the importance of correctly perceiving and remembering faces for successful social interaction, face processing is one of the most widely studied cognitive domain in behavioral, neurophysiological and neuroimaging research, particularly, based on a group-mean approach. However, above mean differences, inter- and intra-individual variability in face processing provide valuable information for investigating the underlying mechanisms and binding the behavioral and neural substrates for better understanding of face processing.. In my dissertation I investigated the biological mechanisms underlying face cognition from an inter- and intra-individual variability perspective at the genetic, neural, and behavioral levels. The neural activities related to face processing are measured by event-related potentials (ERPs) and their trial-by-trial latency variability are estimated using a novel and well-established method, Residue Iteration Decomposition (RIDE).. Study 1 demonstrates the reliability of RIDE in extracting single-trial parameters of the P3b component, which is used in the investigation of the neural basis of intra-subject variability (ISV) in face processing speed in Study 2. In the Study 2, individual differences in ISV of face processing speed, measured at both behavioral and neural levels during a face processing task, are studied in their genetic variation. The results suggest that individual differences in ISV are related not only to the COMT Val158Met polymorphism, but also to the type of cognitive processing (e.g., memory domain). Moreover, we showed that ISV in reaction time can be partially explained by ISV in the speed of central cognitive processes.. Furthermore, the individual differences approach in Study 3, provided valuable and novel information beyond the common group-mean approach applied in the N1/N170-related research. Based on this approach, not only we could replicate previous findings that the N170 predicts individual differences in face cognition abilities, but also we could decompose individual differences in the N170 into a domain-general and a face-specific part with different predictive powers. Moreover, we showed that top-down modulations on the N170 have separable and qualitatively different relationships to face cognition abilities.. In summary, the integrated results from different studies in my dissertation demonstrate the psychological importance of the information provided by inter- and intra-individual variability in face processing in the investigation of its underlying biological mechanisms.

Face recognition is widely held to rely on 'configural processing', recently defined as an analysis of metric distances between features. Given that face recognition concerns those faces of people who we know, it is suggested that our unique representations of familiar faces contain information about these metric distances. The experiments in this thesis examine the hypothesis that face recognition relies on 'configural processing' by comparing performance between familiar and unfamiliar faces in a range of tasks. Experiments in the first half of the thesis investigate the effects of geometric distortions on different face tasks. Experiments in the second half examine familiarity advantages in rescaling distorted facial images. The main findings are that face recognition might not rely on simple measures of metric distances between features, and that observers show a surprising degree of tolerance to configural changes applied to familiar faces. This suggests that an operationalisation of configural processing will need to consider other measures that do not survive the image deformations tested in this thesis. The findings are discussed in relation to existing research on familiar face recognition as distinct from unfamiliar face perception.

Perception and recognition of faces are fundamental cognitive abilities that form a basis for our social interactions. Research has investigated face perception using a variety of methodologies across the lifespan. Habituation, novelty preference, and visual paired comparison paradigms are typically used to investigate face perception in young infants. Storybook recognition tasks and eyewitness lineup paradigms are generally used to investigate face perception in young children. These methodologies have introduced systematic differences including the use of linguistic information for children but not infants, greater memory load for children than infants, and longer exposure times to faces for infants than for older children, making comparisons across age difficult. Thus, research investigating infant and child perception of faces using common methods, measures, and stimuli is needed to better understand how face perception develops. According to predictions of the Intersensory Redundancy Hypothesis (IRH; Bahrick & Lickliter, 2000, 2002), in early development, perception of faces is enhanced in unimodal visual (i.e., silent dynamic face) rather than bimodal audiovisual (i.e., dynamic face with synchronous speech) stimulation. The current study investigated the development of face recognition across children of three ages: 5 – 6 months, 18 – 24 months, and 3.5 – 4 years, using the novelty preference paradigm and the same stimuli for all age groups. It also assessed the role of modality (unimodal visual versus bimodal audiovisual) and memory load (low versus high) on face recognition. It was hypothesized that face recognition would improve across age and would be enhanced in unimodal visual stimulation with a low memory load. Results demonstrated a developmental trend (F(2, 90) = 5.00, p = 0.009) with older children showing significantly better recognition of faces than younger children. In contrast to predictions, no differences were found as a function of modality of presentation (bimodal audiovisual versus unimodal visual) or memory load (low versus high). This study was the first to demonstrate a developmental improvement in face recognition from infancy through childhood using common methods, measures and stimuli consistent across age.

[Truncated abstract] Recent studies have provided evidence that face-coding mechanisms reference a norm or average face (Leopold, O`Toole, Vetter & Blanz, 2001; Rhodes & Jeffery, 2006). The central aim of this thesis was to establish whether distinct norms, and dissociable neural mechanisms code faces of different race and sex categories. Chapter 1 provides a brief introduction to norm based coding of faces, and reviews evidence for the existence of distinct norms for different races and sexes. Chapter 1 then introduces adaptation as a tool for investigating these ideas. Chapter 2 presents two adaptation studies that examined how faces of different races are coded. The aim of these studies was to determine whether dissociable neural mechanisms (or distinct face norms) code faces of different races. Chinese and Caucasian participants rated the normality of Caucasian and Chinese test faces, before and after adaptation to distorted faces of one race (e.g., 'contracted' Chinese faces; Experiment 1) or distorted faces of both races (e.g., 'contracted' Chinese faces and 'expanded' Caucasian faces; Experiment 2). Following adaptation to faces of one race, there were changes in perceived normality for faces of both races (i.e., perceptual aftereffects), indicating that common neural mechanisms code Chinese and Caucasian faces. However, aftereffects were significantly smaller in faces of the unadapted race suggesting some sensitivity to the race of faces. This sensitivity was also evident in Experiment 2. ... Some dissociability was also found in the coding of faces of different iv sexes. In Experiments 2 and 3, participants adapted to oppositely distorted faces of both sexes. Weak sex-selective aftereffects were found. Taken together, the findings suggest that male and female faces are coded by dissociable but not completely distinct neural populations. Chapter 4 examined whether the aftereffects reported for faces of different races or sexes reflected the adaptation of high-level neural mechanisms tuned to the social category information in faces, or earlier coding mechanisms tuned to simple physical differences between face groups. Chinese and Caucasian participants adapted to oppositely distorted face sets that were the same distance apart on a morph continua. The face sets were either from different race categories (e.g., contracted Chinese faces and expanded Caucasian faces), or from the same race category, (e.g., contracted Chinese faces and expanded caricatured Chinese faces). Larger opposite aftereffects were found when face sets were from different race categories, than when they were from the same race category suggesting that oppositely adapted neural mechanisms are tuned to social category differences rather than simple physical differences in faces. Together, these studies shed new light on how we code faces from different face categories. Specifically, the findings indicate that faces of different races and sexes are coded by both common and race- or sex-selective neural mechanisms. In addition, the findings are consistent with the possibility that race- and sex-selective norms and dimensions are used to code faces in face space. The implications of these findings and possible avenues for future research are discussed.

Le relationnalisme affirme que le caractère phénoménal de la perception est en partie constitué par les objets que l’on voit. Malgré son attrait intuitif, il est souvent rejeté en vertu de l'argument de l'hallucination. L'objectif de cette thèse est de défendre le relationnalisme. L'argument fait valoir que, puisque le relationnalisme ne peut être vrai pour les hallucinations, il doit forcément être faux pour les perceptions aussi. En cela, l'argument repose sur le principe de l’indiscernabilité (IND), affirmant que deux expériences qui sont introspectivement indiscernables les unes des autres ont le même caractère phénoménal. Je considère et rejette les autres versions de l'argument qui ne reposent pas sur l'IND. Bien que largement accepté, aucun support satisfaisant pour l'IND n'a encore été présenté. Dans cette thèse, je soutiens que la défense de l'IND requiert que l’on entende la notion d’indiscernabilité employée dans l'IND en un sens impersonnel. Ensuite, j’identifie ce qui motive l'IND : l'intuition que, en vertu de sa superficialité, la nature d'un caractère phénoménal doit être accessible par l'introspection, de concert avec l’idée qu’il est impossible de nier l'IND sans nier par là même la superficialité des caractères phénoménaux.Je soutiens que le relationnaliste peut nier l'IND tout en préservant la superficialité des caractères phénoménaux en adoptant une thèse négative de l'hallucination et en reconsidérant la nature de la relation entre le caractère phénoménal d’une expérience et l’accès introspectif qu'il peut y avoir
Relationalism claims that the phenomenal character of perception is constituted by the obtaining of a non-representational psychological relation to mind-independent objects. Although relationalism provides what seems to be the most straight forward and intuitive account of how experience strikes us introspectively, it is very often believed that the argument from hallucination shows that the view is untenable. The aim of this thesis is to defend relationalism against the argument from hallucination. The argument claims that the phenomenal character of hallucination and perception deserves the same account, and that relationalism cannot be true for hallucinations, therefore relationalism must be rejected. This argument relies on the Indistinguishability Principle (IND), the claim that two experiences that are introspectively indistinguishable from each other have the same phenomenal character. Before assessing the plausibility of this principle, I first consider and dismiss versions of the argument which wouldn’t depend on IND.Although widely accepted, no satisfactory support for IND has been presented yet. In this thesis I argue that defending IND requires that we understand the notion of ‘indiscriminability’ employed in IND in an impersonal sense. I then identify what underwrites IND: the intuition that, in virtue of its superficiality, the nature of a phenomenal character must be accessible through introspection, together with the claim that it is not possible to deny IND without denying the superficiality of phenomenal characters too.I argue that the relationalist can deny IND while preserving the superficiality of phenomenal characters. This can be done by adopting a negative view of hallucination and an account of introspection whereby the phenomenal character doesn’t exist independently of one’s introspective awareness of it and where having introspective access to our experience depends on our perceptual access to the world

As the world experiences increased international mobility, we encounter those from different racial, ethnic, and linguistic backgrounds. Therefore it is increasingly crucial to examine the ways we categorize and perceive other people. The main objective of this dissertation is to examine whether language is a dimension of social categorization, and whether this affects face perception. We also examined whether language categorization interacts with race categories, and whether this interaction affects the perception of other race faces. These issues were investigated in three studies. Firstly, we used behavioral and event-related potential techniques in an oddball paradigm to test whether language categorization affects visual face perception. We demonstrated that indeed, language is used as a social category, and this categorization affects the early stages of visual perception of faces. Secondly, we examined how language interacts with race in creating social categories. By using a popular psychological paradigm called the Memory Confusion Paradigm, we establish the robustness of language categorization, and the malleability of race categorization when crossed with different language contexts. In our final study, our aim was to understand whether native and foreign accents affect the perception and recognition of other-race faces. In summary, this dissertation has examined the effect of language on face perception, and has established that language categorization is a strong and robust effect that influences face perception.
Como resultado del incremento en la movilidad internacional que el mundo está experimentando, es común encontrar gente de otra raza y con orígenes étnicos y lingüísticos diferentes. Así pues, es cada vez más crucial examinar cómo categorizamos y percibimos a otros. El objetivo principal de la presente tesis es examinar si el lenguaje es una dimensión de social categorización y como afecta la percepción de la cara. Además, examinamos si la categorización lingüística interactúa con las categorías raciales y si esta interacción afecta la percepción de aquellas caras con raza diferente a la nuestra. Todas estas cuestiones se investigaron en tres estudios. Primero, mediante medidas conductuales y electrofisiológicas en un paradigma de detección del cambio (oddball paradigm) se investigó si el lenguaje se usa como categoría social y si tal categorización afecta estadios tempranos en la percepción visual de la cara. Segundo, se examinó como el lenguaje interacciona con la raza a la hora de crear categorías sociales. Por medio del paradigma psicológico de la confusión de memoria (Confusion Memory Paradigm), establecimos la robustez de la categorización lingüística y la maleabilidad de la categorización racial en diferentes contextos lingüísticos. Finalmente, el último estudio tenía por objetivo entender si acentos nativos y extranjeros pueden modular la percepción y el reconocimiento de caras de otra raza. En resumen, esta tesis ha examinado el efecto de lenguaje en la percepción de la cara y ha mostrado que la categorización lingüística es un efecto fuerte y robusto que influye la percepción de la cara.

It is a challenging task for researchers to determine how the brain solves multisensory perception, and the neural mechanisms involved remain subject to theoretical conjecture.  According to a hypothesised cortical model for natural audiovisual stimulation, phase synchronised communications between participating brain regions play a mechanistic role in natural audiovisual perception.  The purpose of this study was to test the hypothesis by investigating oscillatory dynamics from ongoing EEG recordings whilst participants passively viewed ecologically realistic face-speech interactions in film.  Lagged-phase synchronisation measures were computed for conditions of eye-closed rest (REST), speech-only (auditory-only, A), face-only (visual-only, V) and face-speech (audio-visual, AV) stimulation. Statistical contrasts examined AV > REST, AV > A, AV > V and AV-REST > sum(A,V)-REST effects.  Results indicated that cross-communications between the frontal lobes, intraparietal associative areas and primary auditory and occipital cortices are specifically enhanced during natural face-speech perception and that phase synchronisation mediates the functional exchange of information associated with face-speech processing between both sensory and associative regions in both hemispheres.  Furthermore, phase synchronisation between cortical regions was modulated in parallel within multiple frequency bands.

The distinctiveness of a face is a crucial factor for its ability to be discriminated, memorized, and identified correctly. In this thesis, we provided a contribution to face distinctiveness by examining the impact of socially relevant factors such as attractiveness, group and emotional expression on distinctiveness. We show that attractive faces are more similar to each other than unattractive faces, using female Caucasian faces and male faces of a Caucasian and heterogeneous Non-Caucasian group. We also show, using 3D face generated faces of photo-realistic quality, that attractive faces were closer to the prototype of only their specific group, and that hence typicality of attractive faces was group specific. Lastly, we show that assigning an emotional expression to a face that is evaluatively incongruent with its race makes it more psychologically distinctive, as revealed in perceptual discrimination and memory tasks.

Natural variability can make different instances of the same face appear remarkably dissimilar. Such variability rarely affects familiar face recognition. However, small differences in appearance between encounters can have really detrimental effects on identifying instances of unfamiliar faces as the same person. In typical face processing research, within-person variability is experimentally controlled, in order to explore the influences of between-person variability in face processing directly. That is, face stimuli are constrained so that differences between individual faces are restricted to identity-specific information; shape and texture. To this end, it remains unclear whether such natural variability plays a part in normal face processing. In this thesis, a series of experiments explore whether experiencing natural variability is beneficial in normal face processing. Specifically, the experiments described within this thesis address whether there is a role of within-person variability in face learning, with various manipulations, and also whether it has a role in improving unfamiliar face matching. The results suggest that experiencing variability is important in face learning – specifically in developing stable face representations. It was also found to be beneficial in improving unfamiliar face matching. Additional manipulations, such as the presence of additional person information, did not show any additional benefit to face learning – unlike previous studies. I suggest that the differences between the results observed here and previous studies highlight differences in measures of familiarity, and the importance of considering what different measures tell us about face processing. I discuss these findings in relation to previous face learning studies, in addition to face perception methodologies overall. Put simply, I suggest that in order to understand face identification processes comprehensively, it is important to consider both between- and within-person variability.

Schizophrenia is a psychiatric disorder characterized by social dysfunction. People with schizophrenia misinterpret social information and it is suggested that this difficulty may result from visual processing deficits. As faces are one of the most important sources of social information it is hypothesized that people suffering from the disorder have impairments in the visual face processing system. It is unclear which mechanism of the face processing system is impaired but two types of deficits are most often proposed: a deficit in face perception in general (i.e., processing of facial features as such) and a deficit in facial emotion processing (i.e., recognition of emotional facial expressions). Due to the contradictory evidence from behavioural, electrophysiological as well as neuroimaging studies offering support for the involvement of one or the other deficit in schizophrenia it is early to make any conclusive statements as to the nature and level of impairment. Further studies are needed for a better understanding of the key mechanism and abnormalities underlying social dysfunction in schizophrenia.

The effects of expertise, such as better recognition of own-race than other-race faces, have been attributed either to poor encoding of configural information (the dual-mode theory) or to representation of faces on dimensions attuned to own-race faces and, hence, inappropriate for coding of other-race faces (the ABC model). Neither framework alone has been able to account for the variety of past results. It is proposed that a composite account derived from the dual-mode theory and the ABC model may offer a more complete explanation of the effects of race. To evaluate the composite account, six experiments using perceptual paradigms were carried out. The structure of face space and the effects of expertise on configural processing were assessed in a dissimilarity perception task (Experiment 1). Caucasian and Chinese participants judged dissimilarity of own-race and other-race faces with various configural distortions relative to their unaltered versions. As predicted by the composite account, face spaces derived from the dissimilarity ratings for own-race and other-race faces were comparable. Consistent with the premise that expertise affects configural coding, Caucasian participants exhibited greater sensitivity to configural changes of own-race than other-race faces. The effects of expertise on configural encoding were further examined in a bizarreness perception paradigm (Experiments 2-4). Caucasian participants rated bizarreness of unaltered and distorted faces rotated from upright to inverted in 15� increments. The distortions involved either simple component alterations (i.e., whitened pupils and blackened teeth), global configural changes (i.e., inverted eyes and mouth), or more local configural transformations (e.g., moving the eyes closer together and upwards, and shifting the mouth down). Similar bizarreness ratings for all faces with component distortions confirmed that expertise does not affect processing of simple component information. Differences in the perceived bizarreness of own-race and other-race faces in the unaltered and global configural distortion conditions corroborated the hypothesis that expertise influences holistic configural encoding. Variations in the perceived bizarreness of faces with more local configural changes, however, indicated that expertise might also affect local configural coding. The effects of expertise on local configural processing were further examined in a discrimination paradigm (Experiments 5 and 6). Participants made same-different decisions with upright and inverted face pairs comprising either two identical faces (same trials) or unaltered and distorted versions of the same face (different trials). To distinguish between holistic and local processing of configural information, partial faces were created in addition to whole faces. Higher accuracy for own-race than other-race faces at both upright and inverted orientations in both whole and partial face conditions substantiated the argument that expertise modulates local configural encoding. Altogether, the present investigation offers direct evidence for the composite account of the effects of race. As ventured by the composite account, the own-race face bias in face perception was shown to be due to variations in configural processing. In addition, the reported experiments support the argument that configural information can be encoded both locally and holistically.

Matching unfamiliar faces is known to be a very difficult task. Yet, despite this, we frequently rely on this method to verify people's identity in high security situations, such as at the airport. Because of such security implications, recent research has focussed on investigating methods to improve our ability to match unfamiliar faces. This has involved methods for improving the document itself, such that photographic-ID presents a better representation of an individual, or training matchers to be better at the task. However, to date, no method has demonstrated significant improvements that would allow the technique to be put into practice in the real world. The experiments in this thesis therefore further explore methods to improve unfamiliar face matching. In the first two chapters both variability and feedback are examined to determine if these previously used techniques do produce reliable improvements. Results show that variability is only of use when training to learn a specific identity, and feedback only leads to improvements when the task is difficult. In the final chapter, collaboration is explored as a new method for improving unfamiliar face matching in general. Asking two people to perform the task together did produce consistent accuracy improvements, and importantly, also demonstrated individual training benefits. Overall, the results further demonstrate that unfamiliar face matching is difficult, and although finding methods to improve this is not straightforward, collaboration does appear to be successful and worth exploring further. The findings are discussed in relation to previous attempts at improving unfamiliar face matching, and the effect these may have on real world applications.

Whereas previous research has demonstrated that trait ratings of faces at encoding leads to enhanced recognition accuracy as compared to feature ratings, this set of experiments examines whether ratings given after encoding and just prior to recognition influence face recognition accuracy. In Experiment 1 subjects who made feature ratings just prior to recognition were significantly less accurate than subjects who made no ratings or trait ratings. In Experiment 2 ratings were manipulated at both encoding and retrieval. The retrieval effect was smaller and nonsignificant, but a combined probability analysis showed that it was significant when results from both experiments are considered jointly. In a third experiment exposure duration at retrieval, a potentially confounding factor in Experiments 1 and 2, had a nonsignificant effect on recognition accuracy, suggesting that it probably does not explain the results from Experiments 1 and 2. These experiments demonstrate that face recognition accuracy can be influenced by processing instructions at retrieval.

The pro-sociality of humans is manifested by the existence of cooperation in levels not common with any other species. Previous studies suggest that snap judgements of individuals are enough to determine if someone is a potential partner for cooperation. In addition to the often studied facial characteristics affecting cooperativeness and trustworthiness attribution (kin resemblance; attractiveness and emotional expression), the experimental work reported here examined the influence of head posture; gaze direction and skin colour on the attribution of trustworthiness and cooperation. A slightly tilted head (less than 3° downward) increased the perception of cooperativeness, especially for male and hostile looking faces. The importance of head tilt increased with decreased self-assessed dominance. Furthermore, even though some evidence that the effect of head posture is independent of gaze direction was found, gaze direction was also a strong indicator of cooperative intentions. Direct gaze and gaze slightly looking down (3°) were perceived as more cooperative than deviations of gaze outside this range (3° up or 6°- 9° down). Skin colour, a putative cue to current health status, was also found to impact on trustworthiness perception with a healthy skin colour increasing trustworthiness ratings. Additionally, as cooperative and trust decisions are vital for survival and social interactions, decisions based on facial appearance are made quickly and automatically as demonstrated by a trustworthiness modulation on an early face related component with 170 ms of exposure. Collectively, these findings suggest that facial characteristics employed to infer trust and cooperativeness help the observer to assess the motives and intentions of the individuals and assist the choice of partners that will lead to increased benefits and reduced costs in collaborative actions. Such considerations fit well with the evolutionary theory of cooperation as reciprocated social exchange.

Individuals with Williams syndrome (WS) have been characterised as hyper-sociable, showing an extreme compulsion to engage in communication with other people, whilst the opposite has been cited regarding autism. The most important social cue in our environment is the human face, which must be successfully recognised and interpreted for communicative signals. Although clear differences are apparent in social skills, individuals with WS and autism have been described as showing similarly atypical face processing styles. The present research addressed issues of face perception in Williams syndrome and autism to gain further insights into social abilities of individuals with these developmental disorders. Importantly, the research was grounded in typical face perception methods. The investigation began with a large-scale exploration of face skills, probing identity, eye gaze, expressions of emotion and lip reading to ask how these two disorders uniquely impact upon performance. Participants with WS and autism could be dissociated from those with general developmental delay and from each other primarily on the basis of eye gaze ability. Participants with WS showed strong eye gaze abilities whilst participants with autism had extreme difficulties. Although interpretation of expressions of emotion also showed a difference between groups, autism and WS did not uniquely impact upon the processing of identity or lip reading. The exploration also allowed the consideration of models of face perception; characterised by a typical modular structure in WS but a lack of modularity in autism. The second line of inquiry considered identity processing and firstly asked whether participants were more accurate at matching faces from internal or external features. Participants with WS showed an atypical use of internal features for matching unfamiliar faces, which may be linked to an atypical interaction style and exaggerated interest in unfamiliar people. Participants with autism used the same strategy to match faces of familiar and unfamiliar people and hence familiarity did not impact upon processing style. Subsequent chapters probed feature salience (eyes .v. mouth) and structural encoding. Across paradigms typically developing participants and those with WS showed greater accuracy using the eye than mouth region, a pattern not evident in autism. Regarding structural encoding, individuals with WS showed use of configural cues under the task demands implemented in this thesis, where individuals with autism were only able to interpret featural cues. Previous evidence of similar face processing styles in WS and autism were not supported. Taken together the findings provide further insights into face perception and social functioning in WS and autism. The research used the same participants across paradigms, considered level of functioning on the autistic spectrum and included investigations of WS and autism in the same research programme. Additional to the main experimental studies, pilot data is provided to open a new line of investigation into physiological arousal associated with holding eye contact in WS. Therefore, on the basis of the experiments conducted here, a number of suggestions are made to carry the research forward in future investigations. Throughout the thesis as a whole, comparisons are made between individuals with WS and autism that further our understanding of the links between face processing and social expertise.

Facial symmetry has been a central component in many studies on face perception. The relationship between bilateral symmetry and subjective judgments on faces is still arguable in the literature. In this study, a database of natural looking face images with different levels of symmetry is constructed using several digital preprocessing and morphing methods. Our aim is to investigate the correlations between quantified asymmetry, perceived symmetry and a subjective judgment: &lsquo
attractiveness&rsquo
. Images in the METU-Face Database are built to represent three levels of symmetry (original, intermediate, and symmetrical) within five classes which also represent the orientation of bilateral symmetry: left versus right. In addition, the asymmetry of original images is quantified using a landmark-based method. Based on the theory of holistic face perception, we introduce a novel method to quantify facial asymmetry wholesomely: Entropybased quantification. In Experiment 1 and 2, images were rated on attractiveness judgments and on perceived symmetry, respectively. Results indicate that landmark-based quantifications were not sufficient to account for perceived symmetry ratings (SRs), but they revealed that as the vertical deviation of the symmetry decreases, attractiveness rating (AR) collected from that face increases. Moreover, morphing classes and their relationship to both ARs and SRs were highly correlated. Consistent with the previously done research, symmetrical images were found more attractive. We found that although ARs were the same for left versus right composites, for SRs, there is a significant difference between left and right. Finally, a more elucidative quantification approach for subjective face perception is achieved through significant correlations of entropy scores with both ARs and SRs.

The neural mechanisms by which faces are processed are the subject of great interest. A key characteristic of human faces is the ability to induce emotion in the viewer, through expressed emotion or other more abstract constructs such as trustworthiness or attractiveness. In this thesis, five functional magnetic resonance imaging experiments that probe the neural systems underpinning the perception of such emotive characteristics are described. I show that perception of emotional expression and identity are doubly dissociable with fusiform cortex encoding identity and superior temporal sulcus (STS) encoding expression. In subsequent experiments I explore the parameters under which distinct brain regions involved in emotional face perception engage, in particular addressing whether responses are automatic or dependent upon a particular task. The issue of whether distinct emotions are processed by different brain regions is considered and the basic stimulus property of spatial frequency is manipulated to address the idea of a subcortical visual pathway carrying emotional information. I describe two further experiments that address the more complex social constructs of attractiveness and trustworthiness, and demonstrate that broadly similar cortical circuitry is invoked when processing these attributes compared to basic facial emotions. Ultimately, a network of brain regions including amygdala, fusiform cortex, STS, and orbital and medial prefrontal cortex (OMPFC) is characterised as the substrate for emotional face perception. In general, I found that amygdala and fusiform responses to emotive faces are automatic, whereas STS and OMPFC responses show a greater degree of task-dependence. I interpret the amygdala response as an emotional labelling process, whereas fusiform enhancements to emotive faces probably reflect feedback from amygdala to modulate early face processing. STS responses indicate the encoding of specific facial expressions in this region and a wider role in intention detection. The response profile of the OMPFC is complex and I suggest multiple roles for this region in mediating an interaction between cognition and emotion.

Current models of face perception suggest independent processing of identity and expression, though this distinction is still unclear. Using converging methods of psychophysics and functional magnetic resonance imaging (fMRI) in healthy and patient populations we assessed the relationship between these two perceptual processes. First, using perceptual aftereffects, we explored the neural representations underlying identity and expression. The expression aftereffect only partially transferred across different identities, suggesting adaptation within identity-invariant and identity-dependent expression representations. Contrarily, the identity aftereffect fully transferred across different expressions. This asymmetry cannot be explained through low-level adaptation. The identity-dependent component of the expression aftereffect relies on adaptation to a coherent expression, not low-level features, in the adapting face. Thus adaptation generating the expression aftereffect must occur within high-level representations of facial expression. Second, using fMRI adaptation, we examined identity and expression sensitivity in healthy controls. The fusiform face area and posterior superior temporal sulcus showed sensitivity for both identity and expression changes. Independent sensitivity for identity and expression changes was observed in the precuneus and middle superior temporal sulcus respectively. Finally, we explored identity and expression perception in a neuropsychological population. Selective identity impairments were associated with inferior occipitotemporal damage, not necessarily affecting the occipital or fusiform face areas. Impaired expression perception was associated with superior temporal sulcus damage, and also with deficits in the integration of identity and expression. In summary, psychophysics, neuroimaging and neuropsychological methods all provide converging evidence for the independent processing of identity and expression within the face network. However, these same methods also supply converging evidence for a partial dependence of these two perceptual processes: in the expression aftereffect, the functional sensitivities of the FFA and pSTS, and identity deficits observed in a patient with primarily impaired expression perception and a spared inferotemporal cortex. Thus, future models of face perception must incorporate representations or regions which independently process identity or expression as well as those which are involved in the perception of both identity and expression.