No abstract

Head and facial movements can provide valuable cues to identity in addition to their primary roles in communicating speech and expression [1-8]. Here we report experiments in which we have used recent motion capture and animation techniques to animate an average head [9]. These techniques have allowed the isolation of motion from other cues and have enabled us to separate rigid translations and rotations of the head from nonrigid facial motion. In particular, we tested whether human observers can judge sex and identity on the basis of this information. Results show that people can discriminate both between individuals and between males and females from motion-based information alone. Rigid head movements appear particularly useful for categorization on the basis of identity, while nonrigid motion is more useful for categorization on the basis of sex. Accuracy for both sex and identity judgements is reduced when faces are presented upside down, and this finding shows that performance is not based on low-level motion cues alone and suggests that the information is represented in an object-based motion-encoding system specialized for upright faces. Playing animations backward also reduced performance for sex judgements and emphasized the importance of direction specificity in admitting access to stored representations of characteristic male and female movements.

A series of experiments is reported that investigated the effects of variations in lighting and viewpoint on the recognition and matching of facial surfaces. In matching tasks, changing lighting reduced performance, as did changing view, but changing both did not further reduce performance. There were also differences between top and bottom lighting. Recognizing familiar surfaces and matching across changes in viewpoint were more accurate when lighting was from above than when it was from below the heads, and matching between different directions of top lighting was more accurate than between different directions of bottom lighting. Top lighting also benefited matching between views of unfamiliar objects (amoebae), though this benefit was not found for inverted faces. The results are difficult to explain if edge- or image-based representations mediate face processing and seem more consistent with an account in which lighting from above helps the derivation of 3-dimensional shape.

When information about three-dimensional shape obtained from shading and shadows is ambiguous, the visual system favours an interpretation of surface geometry which is consistent with illumination from above. If pictures of top-lit faces are rotated the resulting stimulus is both figurally inverted and illuminated from below. In this study the question of whether the effects of figural inversion and lighting orientation on face recognition are independent or interactive is addressed. Although there was a clear inversion effect for faces illuminated from the front and above, the inversion effect was found to be reduced or eliminated for faces illuminated from below. A strong inversion effect for photographic negatives was also found but in this case the effect was not dependent on the direction of illumination. These findings are interpreted as evidence to suggest that lighting faces from below disrupts the formation of surface-based representations of facial shape.

Two experiments are reported that assess how well the identity of highly familiar "famous# faces can be masked from short naturalistic television clips[ Recognition of identity was made more di.cult by either pixelating "Experiment 0# or blurring "Experiment 1# the viewed face[ Participants were asked to identify faces from both moving and static clips[ Results indicated that participants were still able to recognize some of the viewed faces\ despite these image degradations[ In addition\ moving images of faces were recognized better than static ones[ The practical and theoretical implications of these _ndings are discussed[ Copyright Þ 1990 John Wiley + Sons\ Ltd[ Correspondence to] Karen Lander\ Department of Psychology\ University of Stirling\ Stirling FK8 3LA\ UK[ E!mail] kl2Ýstir[ac[uk Contract grant sponsor] University of Stirling[ Contract grant sponsor] ESRC[ Contract grant number] R999 12 55 77[ 0 In both experiments reported\ famous faces rather than personally familiar ones have been used[ Personally familiar faces have typically been viewed in person on many occasions[ Famous face identity is much more likely to be learned from a small number of {stereotypical| instances[ Despite this di}erence\ a number of experimental studies have found no qualitative di}erence between the processing of personally familiar and famous faces "see Campbell and De Haan\ 0887^Roberts and Bruce\ 0878#[

Three experiments were conducted to investigate factors contributing to the 'hollow face' illusion. A novel method was employed in which the distance from the mask at which the illusion became apparent or disappeared, when retreating or approaching, respectively, was taken as a measure of the strength of the illusion. In all the experiments an effect of direction of observer's movement was found, demonstrating the stability of the initial percept. Upright orientations were compared with inverted ones to investigate if the illusion reflects a bias towards a familiar percept. The direction of lighting was also varied. Independent main effects of orientation and lighting were found to be consistent with preferences both for upright faces and for top lighting. However, inverted faces also produced the illusion to some extent, suggesting a general preference for convexity. The role of stereopsis in resolving the illusion was tested by comparing monocular with binocular viewing conditions. Monocular viewing conditions gave rise to shorter distances, suggesting that the retinal disparities available with binocular viewing are important in disambiguating the illusion at small distances. The results are interpreted within the framework of a 2 1/2-dimensional sketch derived from independent modular processing of visual information.

Speech perception provides compelling examples of a strong link between auditory and visual modalities. This link originates in the mechanics of speech production, which, in shaping the vocal tract, determine the movement of the face as well as the sound of the voice. In this paper, we present evidence that equivalent information about identity is available cross-modally from both the face and voice. Using a delayed matching to sample task, XAB, we show that people can match the video of an unfamiliar face, X, to an unfamiliar voice, A or B, and vice versa, but only when stimuli are moving and are played forward. The critical role of time-varying information is underlined by the ability to match faces to voices containing only the coarse spatial and temporal information provided by sine wave speech [5]. The effect of varying sentence content across modalities was small, showing that identity-specific information is not closely tied to particular utterances. We conclude that the physical constraints linking faces to voices result in bimodally available dynamic information, not only about what is being said, but also about who is saying it.

Humans are very good at perceiving each other's movements. In this article, we investigate the role of time-based information in the recognition of individuals from point light biological motion sequences. We report an experiment in which we used an exaggeration technique that changes temporal properties while keeping spatial information constant; differences in the durations of motion segments are exaggerated relative to average values. Participants first learned to recognize six individuals on the basis of a simple, unexaggerated arm movement. Subsequently, they recognized positively exaggerated versions of those movements better than the originals. Absolute duration did not appear to be the critical cue. The results show that time-based cues are used for the recognition of movements and that exaggerating temporal differences improves performance. The results suggest that exaggeration may reflect general principles of how diagnostic information is encoded for recognition in different domains.