Scale invariant adaptation in fusiform face-responsive regions.

Several functional neuroimaging studies have observed response adaptation in face-sensitive regions when repeating identical face stimuli. To address whether this was due to low-level stimulus properties or facial identity, we decomposed pictures of faces into pictures preserving only the lower or higher parts of the normal frequency spectrum. In an event-related functional neuroimaging study, pairs of such pictures were sequentially presented that showed the same or different persons in the same or different frequency bands. This factorial design allowed to separate effects related to repetition of personal identity from those related to identical stimulus properties. In a random effects group analysis, activation in the right fusiform region was affected by repetition of personal identity regardless of changing or constant spatial scale. Responses in the more medial and posterior fusiform and lingual regions adapted with repetition of the same frequency band. An analysis in regions of interest determined individually as face responsive showed that repetition decreases for the same faces in fusiform face-responsive regions generalized across spatial frequency bands. Our results therefore point to a role of this area in discriminating individual faces at a level of representation that is invariant to changes in low-level stimulus properties, as spatial scale. The same invariance could not be detected in more posterior occipital face-responsive regions.