hide
Free keywords:
-
Abstract:
A large body of behavioural and neuropsychological research, using static images of faces, has informed our understanding of the mechanisms underlying identity processing. Indeed, pioneering studies revealed dedicated modules for the processing of facial form in the human brain. Yet interactions with people in the real world are accompanied by a greater variety of sensory information beyond visual images, for example, people move and speak and are thus highly dynamic, multisensory stimuli. While these additional cues (e.g. facial motion, body motion and the voice) have received attention from researchers in the field, they have largely been studied in isolation, possibly driven by assumptions that each identity cue was processed independently. However, recent findings that facial form modules in the brain also respond to facial movement and to voice information (in the absence of a facial image) have sparked a re-examination of how these sensory cues may interact to support person perception. To date, assertions as to how these cues may interact have been largely based on observations from neurotypical younger adult studies (reviewed in detail in Chapter 1).
The aim of this thesis is to extend our understanding of how multiple sensory cues may interact in person perception through the study of three different cohorts: younger adults, older adults and developmental prosopagnosics (DP). This thesis argues that the unique approach of examining cohorts where there is a decline (older age) or a disorder (DP) in static face processing, may give rise to a more concrete understanding of how static and dynamic cues interact to support normal person perception. For example, it is poorly understood how impaired face processing, as found in cases of DP, may impact on the processing of other perceptual information e.g. perceiving the voice, or whether perception in an older person may benefit from multisensory cue combination, as processing in one modality declines. Such findings would clarify how the interactions between the senses may shape our ability to represent a person in memory. A number of behavioural studies, described in this thesis, examined this issue by centring on three main themes: 1) the interaction of form and motion cues in face perception; 2) the interaction of facial motion and the voice in person perception; and 3) the interaction between dynamic body cues and the voice in person perception.
The first theme involved studies which confirmed and expanded on previous findings of poorer static face processing in ageing and developmental prosopagnosia, using a battery of standardised face processing tests (Chapter 2). The tests revealed that older adults showed poor performance for recognising facial identity across changes in the visual appearance of the face; although this pattern was particularly exaggerated for the two cases of DP. Using a series of matching experiments reported in Chapter 3, the results demonstrated that learning a face in motion can lead to more accurate matching of facial identity across changes in the viewpoint and expression of the face, in older, relative to younger adults. This finding demonstrates that these two sensory cues, form and motion, are readily integrated and can, as a consequence, enhance the representation of the face in memory. The results of the experiments reported in Chapter 4 suggest evidence that certain types of facial motion resulted in poor matching of facial identity in the DP group, suggesting that motion may have distracted from the encoding of static form cues in faces. This finding adds support to the idea that the interactions between form and motion in face processing may be mandatory, as the ability to use motion cues may also be compromised in disorders of face recognition.
The second theme focused on interactions between the face and voice for person perception. Using a series of matching tasks, evidence reported in Chapter 5 revealed that relative to younger adults, older adults were poorer at matching identity from vocal cues alone. Interestingly, this pattern was exaggerated in one case of DP, suggesting that atypical face processing may impact on how the voice is processed to support identity. In addition, the results of Chapter 5 demonstrated that older adults’, and to some extent younger adults’, ability to represent the face and the voice as a single coherent percept, was likely mediated by the presence of dynamic, relative to static, cross-modal cues. These results support cross-modal sensory interactions for the purpose of representing identity.
The third theme concentrated on interactions between the voice and the body in person perception. Using a sex categorisation task reported in Chapter 6, the results demonstrated that sex cues present in the voice could modulate the perception of ‘gender-ambiguous’ biological motion displays in younger adults and in DP. However, in general older adults did not appear to benefit from voice information in the same way as younger adults, suggesting that sensory integration for less bound couplings e.g. the body and the voice, compared to the face and the voice, may be less likely to be observed in older age.
Taken together the main findings from this collection of studies support and inform emerging models of person perception and suggest that dynamic, cross-modal cues are integrated for the purpose of person perception at earlier stages of processing than previously assumed. As a consequence person perception can be enhanced or at least modulated by these interactions. The theoretical implications of these results are discussed in detail in Chapter 7.
