Abstract
Understanding the functional impairment in acquired prosopagnosia – a defect at face recognition following brain damage – may be important for understanding the neuro-functional basis of normal face processing. A long-standing view is that prosopagnosic patients have impaired holistic/configural processing (e.g., Levine & Calvanio, 1989), that is, an inability to integrate simultaneously different visual features into a coherent global representation. However, it is not clear whether this impairment in holistic processing is general or specific for faces, particularly because prosopagnosia can be embedded in general visual agnosia. Here we addressed this issue with three cases of acquired prosopagnosia, who do not complain of any object recognition difficulties: PS (Rossion et al., 2003), LR (Bukach et al., 2006) and GG (Busigny et al., 2010). These patients were tested with the Navon hierarchical letters, testing general holistic processing, and two tests measuring holistic face processing, the face inversion effect and the whole-part advantage. We show that the three patients present with an entirely normal response profile in the Navon task: they are as fast as controls and they have a normal global-to-local interference during identification of local letters. In contrast, the three patients do not present with the normal effects in the holistic face processing tasks: they have neither a face inversion effect, nor a whole-part face advantage. Thus, all three patients appear to encode facial information feature-by-feature, independently of the other features embedded in the whole facial context. These observations indicate that general holistic processing as measured with global/local interference in the Navon paradigm is functionally distinct from the ability to perceive an individual face holistically. We conclude that brain damage in adulthood may lead to selective recognition impairment for faces, because this is the only category of visual items for which holistic processing at a fine-grained (individual) level is necessary.
Belgian National Fund for Scientific Research (FNRS).