Similarity, being a psychological notion, involves the comparison of finite object representations. The specific nature and complexity of these representations is a matter of fierce theoretical debate traditionally, similarity research was dominated by the spatial and featural account. In the spatial account, similarity is determined by the distance between objects in a psychological space. Alternatively, the featural account proposes that similarity is determined by matching objects' features. Despite the empirical success of these accounts, the object representations they posit are regarded too simple and specific to deal with more complex objects. Therefore, two structural accounts have been developed: structural alignment (SA) and Representational Distortion (RD). This aim of this thesis was to further establish one particular structural account—RD—as a general framework for understanding the similarity between object representations. Specifically, RD measures similarity by the complexity of the transformation that "distorts" one representation into the other. This RD approach is investigated in detail by testing a detailed set of transformational predictions (coding scheme) within a rich stimulus domain. These predictions are tested through experiments and modelling that utilise both a) explicit measures (ratings, forced-choice), and, for the first time, b) implicit measures (reaction time, same-different errors & spontaneous categorisation). Moreover, RD is compared empirically with both traditional and alignment models of similarity. Overall, the results suggest that similarity can be best understood by transformational relationships in a number of contexts. The performance of RD in both explicit and implicit measures is made more compelling by the fact that rival accounts fundamentally struggle to describe the sorts of relationships that are easily captured by RD. Finally, it is emphasised that RD is actually compatible with supposedly rival approaches and can incorporate theoretically these accounts, both traditional and structural, under one general framework.

The face-space metaphor for the encoding and storage of faces in memory has received a great deal of theoretical and empirical support. This metaphor is applied to the development of face recognition here. Three versions of the immature face-space are presented: the constant-face-space presumes that the number of dimensions of the immature face-space is the same as the adult face-space and all that changes is the distribution of faces within face-space the expanding-face-space presumes that as more faces are encountered, new dimensions are added to the face-space to discriminate between highly similar faces the shrinking-face-space suggests that the immature face- space contains many more dimensions than the adult face-space and, through processes akin to perceptual narrowing, most become dormant, leaving a default set of dimensions. These dormant dimensions are still contained within the face-space and can be activated under certain circumstances leading to a more flexible and dynamic face-space in adulthood. Thirty-two experiments were conducted that aimed to discriminate between these three models of the immature face-space. The experiments presented in Chapter 2 explored the recognition and discrimination of: upright faces compared with inverted faces own- and other- race, gender, and age faces and faces with an ''unnatural" facial configuration in adults and children aged 5- to 15-years-old. Chapter 3 used recognition tests and manipulated participants, attentional focus to explore what happens to unattended dimensions of face-space. Chapter 4 used adaptation procedures to recalibrate the dimensions of face-space over short and longer timeframes. In Chapter 5, the lower-level perceptual nature of dimensions of face-space is explored indirectly. In Chapter 6, the data reported are incorporated into a developmental model of shrinking-face-space, leading to an adult flexible-face-space.

This thesis examines whether individual differences in implicit and explicit prejudice, and the interaction between them, influence perception of in-group and out-group facial emotion displays. Study One found that viewing dynamic displays of emotion resulted in an in-group advantage (see Elfenbein & Ambady, 2002a), with White participants faster at recognising in-group displays of happiness and anger, and more accurate at recognising in-group anger. Participants high in implicit and explicit prejudice were significantly more accurate at recognising out-group anger than other participants. Study Two examined participants' ability to correctly recognise racial in-group and out-group faces and found no effect of prejudice on recognition accuracy, suggesting that prejudice may influence emotion perception and face perception differentially. Study Three utilised a paradigm devised by Ackerman et al. (2006) to explore this divergence, presenting emotion displays in a face recognition test. High implicit prejudice led to poorer recognition of out-group displays of anger when the facial display was manipulated between learning and test. Study Four examined whether emotion displays would lead to differential arousal dependent upon race of target and found that participants high in explicit prejudice were aroused by negative in- group displays (anger and sadness) and by out-group displays of anger, and an interaction between implicit and explicit prejudice influenced perception of out- group happiness. Finally, Study Five examined perception of emotion displayed by ambiguous race targets and found that participants high in implicit prejudice were more likely to classify an ambiguous angry face as Black, and also reported anger displayed by targets classified as Black as being of greater intensity than those classified as White. Overall, findings suggest that individual differences in implicit and explicit prejudice play a role in the perception of facial emotion however, it is also important to examine the interaction between them.

When people first encounter a potential partner, they derive a wealth of objective and subjective impressions simply from their faces (e.g., age, gender, attractiveness, trustworthiness). Facial first impressions are consequential, for instance, impacting on decisions to approach a potential partner. Hence, it is relevant to have a solid theoretical understanding of how first impressions relate to ideal partner preferences, particularly as romantic relationship researchers primarily use verbal measures. The current research revealed that individuals can perceive traits and factors related to their ideal partner preferences in highly variable everyday face images, and these factors overlapped largely (although not completely) with those identified by face perception researchers. Partner preferences for face images were dominated by attractiveness-related concerns in both sexes. Further, a minimum-exposure paradigm revealed that, even in some non-romantic contexts, attractiveness is particularly salient in face images. Yet, these findings could not be attributed to an attractiveness halo effect, given that attractiveness did not dominate all non-romantic first impressions of face images (e.g., evaluations of faces in terms of occupations). There are multiple potential reasons why individuals might prioritise facial attractiveness (e.g., from an evolutionary perspective, attractiveness is a cue to fertility and resistance to environmental and genetic stressors). Of note, though, a verbal measure of partner preferences revealed that individuals prioritised warmth-trustworthiness, suggesting that face images and verbal measures may capture different elements of preferences. Therefore, these findings attest the relevance of using face images to complement verbal measures of partner preferences.

Matching unfamiliar faces is a difficult task. Despite this, ID checks are the primary screening method for individuals wishing to access countries, employment and a range of financial and medical services. Those we might consider experts, such as passport officers, are no better at the task than general population. Individuals with superior unfamiliar face matching have been identified, but the range of ability remains large across expert and general populations alike. Even individuals with superior face recognition skills have not been consistently found to have superior unfamiliar face matching abilities. This suggests that unfamiliar face matching ability may be highly specific. It may also suggest that the unfamiliar matching tasks carried out in the lab are different from ID checks in the applied context. It is the aim of this thesis to investigate the nature of unfamiliar face matching in the applied context and identify ways in which performance might be predicted. In Chapters 2 and 3 participants are required to match unfamiliar faces shown with a passport context and to check the validity of the accompanying biographical information. The presence of a passport context biases viewers to identify face pairs as the same and presence of a face pair biases and reduces accuracy when checking biographical information. These findings demonstrate that applied error rates in unfamiliar face matching may well have been underestimated. In Chapter 4, a battery of tasks is used to identify predictors of unfamiliar face matching ability. The results show that unfamiliar face matching is positively associated with other face identity tasks. However, same and different unfamiliar face matching also associate with more general measures of local processing and space perception. These findings are tested in Chapter 5 and the theoretical implications of these results and methods for optimising unfamiliar face matching performance are discussed.

The empirical work reported in the current thesis set out to explore the relationship between perceptual expertise, categorical perception (CP) and perceptual learning. Evidence to support the idea that the way people organise the world into categories can qualitatively affect their perception of it has been provided by CP research. Recent work indicates that categorisation experience can lead to enhanced sensitivity to diagnostic stimulus features and is consistent with the possibility that, as experts have learned to distinguish among objects, they have also acquired new ways of perceptually structuring the objects to be categorised. Nevertheless, there is debate about whether these effects are really perceptual and if so about the mechanisms and locus of learning. Here, experiments were designed to test whether the process of acquiring perceptual categories drives a perceptual learning process that enhances the discrimination of category relevant features thereby contributing to the development of perceptual expertise. The work therefore sought to test the possibility that category learning could drive changes to early stages of perceptual processing. Two classes of stimuli were used to address these issues. Initial experiments showed that learning to categorise Gabor patches can lead to learned CP effects that are specific to the trained spatial frequency, orientation and retinal location. Experiments using morphed cervical cell stimuli showed that expert cervical screeners have acquired heightened discrimination to cells that cross the normal/abnormal category boundary and that training novices to categorise cells as normal or abnormal can also lead to retinotopically specific learned CP effects. Taken together, the results reported in the current thesis support a general explanation of CP effects arising from categorisation driven perceptual learning at early stages of visual processing. Furthermore, the work speculated that modifications to intra-cortical connections at this stage of processing may underpin the learned CP effects observed.

When a serious crime has been committed, eyewitnesses may be required to assist a police investigation by constructing a facial composite of the perpetrator of the crime with the help of a police operator. A large body of research has investigated the utility of composite construction systems and the ways in which they are implemented with eyewitnesses. There has been less research conducted on individual differences which might have an impact on the accuracy of facial composites which eyewitnesses produce. The first aim of the research presented within this thesis was to investigate whether individual differences in stable cognitive style have an effect on the accuracy of the facial composites they produce. The second aim of the research was to investigate whether manipulating the temporary cognitive processing state of individuals during face encoding and prior to facial composite construction affects the accuracy of the facial composites they produce. These issues were investigated using two facial composite construction systems currently in widespread use by UK police forces, E-FIT and EFIT-V. Study One investigated, for the first time in the facial composite literature, individual differences in the cognitive style of field dependence/independence (Witkin, Oltman, Raskin & Karp, 1971). Results indicated that field independent individuals produced more accurate composites than field dependent individuals. Study Two investigated individual differences in holistic/analytic cognitive style (Riding & Cheema, 1991). Results indicated that individuals with a holistic cognitive style produced more accurate composites than individuals with an analytic cognitive style. Study Three manipulated the way in which faces were encoded by individuals, and introduced a Navon (1977) task into the composite construction process using E-FIT. Results showed that the Navon task had an effect on the accuracy of the facial composites that individuals produced which was mediated by the way in which the target face had been encoded. Study Four introduced a Navon task prior to composite construction using the EFIT-V system. In addition, the field dependence/independence cognitive style of the participants who created an EFIT-V was measured. Results showed that the Navon task had an effect on the accuracy of the EFIT-V composites that individuals produced, which was mediated both by the way in which the target face was encoded, and by the cognitive style of the individual. Overall, the findings indicated that there is a strong featural cognitive processing element to facial composite construction which is at odds with the way in which faces are processed and represented in memory. Collectively, the results indicate that featural cognitive processing prior to the composite construction process may lead to more accurate facial composites. In addition to this, if an individual does not have a natural featural processing cognitive style, then inducing a featural cognitive processing state may also lead to more accurate facial composites.

The studies reported here were intended to examine how affective and motivational factors influence attentional processing of goal objects, such as food, by exploiting modified versions of an Emotional Blink of Attention (EBA) task originally reported by Piech, Pastorino & Zald (2010). Attentional capture by food distractors presented within a rapid serial visual stream (RSVP) was measured by the extent to which they induced an attentional blink and prevented the correct identification of a subsequently presented, specific visual target. Initially, we explored temporal changes in attention to food images in relation to spontaneous changes in appetite that naturally occur before and after a sandwich lunch. Replicating earlier reports that fasting-induced hunger increases attention to food images, we found that attention to food depended on the level of appetite: increasing pre-prandially as hunger increased, and falling to a minimum after satiation. Moreover, changes in attention to food were seen to reflect subjective ratings of food pleasantness associated with the phenomenon of sensory-specific satiety. Notably, images of the consumed food became less distracting after lunch than images of non-consumed foods belonging to the same sandwich category or, more particularly, those representing very different food types. The EBA data also demonstrated that attentional bias for images of highly palatable, highcalorie desserts was largely immune to changing levels of appetite. Subsequent experiments confirmed that high palatability/high calorie foods with high intrinsic incentive value (cheesecake) potently capture attention even after being eaten to satiety. By contrast, satiation on palatable, sweet fruits did produce sensory-specific changes in attentional bias to fruit images in the EBA. These findings indicate that attention to food images is dependent, via separate processes, on the motivational salience and incentive value of food stimuli. It was noted that affective state (measured using PANAS) varied with appetite level: satiety was associated with a reduction in negative affect and increased positive affect. The relationship between affect, eating motivation and attention were explored further using an ‘Affective EBA’ paradigm, in which neutral filler images within the RSVP were substituted by images of faces displaying positive or negative emotions. Positive affective priming using this technique resulted in an enhancement of attentional bias to food distractors (but not to neutral or romantic distractors). Negative priming, by contrast had no effect. A final experiment explored whether the ability of positive affective priming to increase attentional bias to food might attenuate the previously noted, food-specific, postprandial decline in attentional capture by food stimuli. We found that in sated individuals, positive priming did produce a general increase in attention to food which was in opposition to the expected, satiety-related decline in attentional bias. Overall, the present findings strongly support a key role for attentional mechanisms in the processes that mediate the influence of motivational and incentive salience in energizing and directing goal-related behaviours, such as food seeking and consumption.

Individuals can employ different landmark-based wayfinding strategies to acquire spatial knowledge and support navigation. Allocentric strategy use is associated with a cognitive representation of a learned environment that allows flexible navigation, while egocentric strategy use is associated with uni-directional knowledge that only supports accurate navigation in tasks that involve reproducing learned behaviours. While many studies have investigated strategy use during navigation, how strategy use develops during spatial learning remains under- researched. Therefore, this thesis primarily investigated the processes underlying strategy selection. Participants’ strategy preference during various navigation tasks, including a novel strategy assessment paradigm developed specifically for this research, revealed that individuals adopt the most accurate strategy available – be it allocentric or egocentric – in accordance with the demands of the concurrent navigation task. Interestingly, when allocentric knowledge was required for accurate navigation, participants initially employed a suboptimal egocentric strategy before switching to an allocentric strategy, suggesting that egocentric knowledge precedes allocentric knowledge. Finally, participants were not subject to performance-related decrements associated with the effort of switching strategies. Interestingly, during spatial learning, participants acquired spatial knowledge related to alternative strategies, and selectively encoded landmarks that were compatible with the use of multiple strategies, which may explain why switching wayfinding strategies is cognitively efficient. This thesis also investigated the effects of aging on strategy selection. Strategy preference changes across the adult lifespan, with decreasing allocentric strategy use primarily attributed to reduced hippocampal function, and impaired egocentric strategy use associated with age-related learning and memory deficits. Analysis revealed that older adults exhibited a task-independent preference for egocentric strategy use, and therefore experienced difficulty with tasks that required allocentric knowledge. However, when egocentric strategy use most efficiently supported accurate navigation, younger and older adults performed similarly, suggesting that egocentric strategy use is largely unaffected by aging. Finally, age differences in strategy preference and spatial learning were observed when the most efficient route learning strategy differed between decision points, supporting findings of increasing susceptibility to switching costs with age. In summary, young adults flexibly employ a variety of strategies to optimise navigational efficacy, while older adults' strategy choices are affected by age-related difficulties with allocentric strategy use and increased vulnerability to strategy switching costs.

A range of research has shown an advantage for the perception of faces from same-race compared to other-races – the other race effect (ORE). Nevertheless, previous studies have focused on the ability to recognize facial identity. This thesis focuses on how information from the face that conveys expression is processed in own-race and other-race faces. First, the cross-cultural processing of facial expressions of basic emotions in Western Caucasian and Chinese observers was investigated. Perceptual judgments of facial expressions were quite similar between cultural groups, but facial expressions from own-race faces were categorized more accurately than expressions from other-race faces. This is explained by differences in the recognition of lower region of the face. Facial expressions were processed in a holistic way, but there was no difference in the engagement of holistic processing of own-race compared to other-race faces. Reliable own-group advantages were found in facial identity and expression processing with a free card-sorting task. However, there was also a large amount of cross-cultural consistency in response patterns. Two core face-selective regions, the FFA and the OFA, were sensitive to changes in facial identities and expressions, but there was no difference in the magnitude of response to own- and other-race faces. To summarize, this PhD thesis explored the cross-cultural processing of facial expression. Evidence showed significant differences in the perception of own-race and other-race faces, but these effects were generally small. The widely agreed opinion that the other-race effect is large is overstated.