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.

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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.

Thesis (Ph. D.)--University of California, San Diego, 2008. / Title from first page of PDF file (viewed September 3, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Thesis (Ph.D.)--McMaster University, 2007. / Supervisor: D. Maurer. Includes bibliographical references (p. 177-193).

Thesis (Ph. D.)--University of Oregon, 2008. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 188-219). Also available online in ProQuest, free to University of Oregon users.

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains ix, 192 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 171-190).

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.

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.

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At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript.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