Neural correlates of after-effects caused by adaptation to multiple face displays.

Adaptation to a given face leads to face-related, specific after-effects. Recently, this topic has attracted a lot of attention because it clearly shows that adaptation occurs even at the higher stages of visual cortical processing. However, during our every-day life, faces do not appear in isolation, rather they are usually surrounded by other stimuli. Here, we used psychophysical and fMRI adaptation methods to test whether humans adapt to the gender properties of a composite multiple face stimulus as well. As adaptors we used stimuli composed of eight different individual faces, positioned peripherally in a ring around a fixation mark. We found that the gender discrimination of a subsequent centrally presented target face is significantly biased as a result of long-term adaptation to either male or female multiple face stimuli. Similar to our previous results with single-face adaptors (Kovács et al. in Neuroimage 43(1):156-164, 2008), a concurrent functional magnetic resonance imaging adaptation experiment revealed the strongest blood oxygen level-dependent signal adaptation bilaterally in the fusiform face area. Our results suggest that humans extract the statistical features of the multiple face stimulus and this process occurs at the level of occipito-temporal face processing.