Holistic processing of shape cues in face identification: Evidence from face inversion, composite faces, and acquired prosopagnosia

Abstract

Face recognition is based on two main sources of information: Three-dimensional (3-D) shape and two-dimensional surface reflectance (colour and texture). The respective contribution of these two sources of information in face identity matching task is usually equal, suggesting that there is no functional dissociation. However, there is recent evidence from electrophysiology and neuroimaging that contribution of shape and surface reflectance can be dissociated in time and neural localization. To understand the nature of a potential functional dissociation between shape and surface information during face individualization, we used a 3-D morphable model (Blanz & Vetter 1999) to generate pairs of face stimuli that differed selectively in shape, reflectance, or both. In three experiments, we provided evidence that the processing of shape and surface reflectance can be functionally dissociated. First, participants performed a delayed face matching task, in which discrimination between the sample and distractor faces with the same orientation (either upright or inverted) was possible based on shape information alone, reflectance information alone, or both. Inversion decreased performance for all conditions, but the effect was significantly larger when discrimination was based on shape information alone. Second, we found that participants' composite face effect, a marker of holistic processing, was caused primarily by the presence of interfering shape cues, with little interference from surface reflectance cues. Finally, contrary to normal observers, a well-known patient with acquired prosopagnosia suffering from holistic face perception impairment performed significantly better when discriminating faces based on reflectance than on shape cues. Altogether, these observations support the view that the diagnosticity of shape information for individualizing faces depends relatively more on holistic face processing than that of surface reflectance cues.