Vase or face? A neural correlate of shape-selective grouping processes in the human brain

Recent neuroimaging studies have described a differential activation patter n associated with specific object images (e.g., face-related and building-r elated activation) in human occipito-temporal cortex. However, it is as yet unclear to what extent this selectivity is Clue to differences in the stat istics of local object features present in the different object categories, and to what extent it reflects holistic grouping processes operating acros s the entire object image. To resolve this question it is essential to use images in which identical sets of local features elicit the perception of d ifferent object categories, The classic Rubin vase-face illusion provides a n excellent experimental set to test this question. In the illusion, the sa me local contours lead to the perception of different objects (vase or face ). Here we employed a modified Rubin vase-face illusion to explore to what extent the activation in face-related regions is attributable to the presen ce of local face features, or is due to a more holistic grouping process th at involves the entire face figure. Biasing cues (gratings and color) were used to control the perceptual state of the observer. We found enhanced act ivation in face-related regions during the "face profile" perceptual state compared to the "vase" perceptual state. Control images ruled out the invol vement of the biasing cues in the effect. Thus, object-selective activation in human face-related regions entails global grouping processes that go be yond the local processing of stimulus features.