Brain events related to normal and moderately scrambled faces

For more than 35 years, researchers have debated whether face recognition is carried out by face-specific mechanisms or whether it involves more general mechanisms that are also used for objects. Prosopagnosic patients have furnished powerful evidence for face-specific mechanisms. Yet for each case that has been tested there have always been several untested alternative explanations that could account for the case. As such, each of these individuals has not been sufficiently tested to provide conclusive evidence for face-specific processes. Here we make a stronger argument with a single case of severe developmental prosopagnosia by exhaustively addressing all extant alternatives. We reject each in turn and thus eliminate all alternative accounts. Because this case is developmental in etiology the results also indicate that face recognition involves developmental mechanisms different from those producing other visual recognition mechanisms.

/pdf/prosopagnosia-as-an-impairment-to-face-specific-mechanisms-4dl8jv9zvp.pdf

Prosopagnosia as an impairment to face-specific mechanisms: Elimination of the alternative hypotheses in a developmental case

This paper reports on current developments in the area of model-based video coding, a technique which shows promise of achieving very large bit-rate reductions for moving images. After an introduction and historical review, advances are summarized in several areas, among them improved 3D tracking of the human head and of facial expressions, the use of muscle-driven model animation with skin synthesis, techniques for luminance compensation, and switched coders. Bit rates ranging from 64 kb/s down to about 1 kb/s have been obtained using head-and-shoulder video sequences. Problems with model-based methods are identified and future developments in both CBR and VBR transmission discussed. >

Developments in model-based video coding

Inversion and photographic negation both impair face recognition. Inversion seems to disrupt processing of the spatial relationship between facial features ('relational' processing) which normally occurs with upright faces and which facilitates their recognition. It remains unclear why negation affects recognition. To find out if negation impairs relational processing, we investigated whether negative faces are subject to the 'chimeric-face effect'. Recognition of the top half of a composite face (constructed from top and bottom halves of different faces) is difficult when the face is upright, but not when it is inverted. To perform this task successfully, the bottom half of the face has to be disregarded, but the relational processing which normally occurs with upright faces makes this difficult. Inversion reduces relational processing and thus facilitates performance on this particular task. In our experiments, subjects saw pairs of chimeric faces and had to decide whether or not the top halves were identical. On half the trials the two chimeras had identical tops; on the remaining trials the top halves were different. (The bottom halves were always different.) All permutations of orientation (upright or inverted) and luminance (normal or negative) were used. In experiment 1, each pair of 'identical' top halves were the same in all respects. Experiment 2 used differently oriented views of the same person, to preclude matches being based on incidental features of the images rather than the faces displayed within them. In both experiments, similar chimeric-face effects were obtained with both positive and negative faces, implying that negative faces evoke some form of relational processing. It is argued that there may be more than one kind of relational processing involved in face recognition: the 'chimeric-face effect' may reflect an initial 'holistic' processing which binds facial features into a 'Gestalt', rather than being a demonstration of the configurational processing involved in individual recognition.

/pdf/evidence-for-holistic-processing-of-faces-viewed-as-v4wt9iu780.pdf

Evidence for holistic processing of faces viewed as photographic negatives.

Recognition of unfamiliar faces in prosopagnosia.

Three experiments are reported on the mental representation of faces with respect to the production of a face superiority effect. The effects of varying spatial position of the features and type of accompanying feature were investigated. Variations in attention to facial versus nonfacial features were considered by regression analyses, allowing an assessment of which was the more facelike of any two displays. Such regression analyses may have application to other recognition tasks if attention is divided between aspects of the display. Two further experiments explored the role of exposure duration in face superiority effects. The relationship of the results to models of face recognition is considered.

/pdf/the-mental-representation-of-faces-spatial-and-temporal-35zkpyshyn.pdf

J. Davidoff

Papers

The mental representation of faces: Spatial and temporal factors