Poster E124, Monday, March 27, 2:30 – 4:30 pm, Pacific Concourse
Hemifield-split fMRI repetition effects using chimeric faces
Matthew Harrison1, Zhiheng Zhou1, Lars Strother1; 1University of Nevada, Reno
We used an fMRI repetition suppression paradigm to examine the effects of repeating versus changing an entire face or only half of it. Observers viewed chimeric faces split vertically at midline, under four conditions. Faces either (1) repeated in full, (2) changed in full, (3) changed in the right visual hemifield (RVF) and concurrently repeated to the left (LVF), or (4) repeated in the RVF and changed in the LVF. We observed widespread reduced fMRI responses (suppression) in ventral visual cortex as a result of full face and half-face repetitions. We observed maximal repetition suppression effects in bilateral face-selective areas—i.e. fusiform and occipital face areas (FFA and OFA respectively)—which we identified using a conventional independent localizer experiment; repetition suppression also occurred in other regions including retinotopic cortex (e.g. V4v). Bilateral FFA showed similar fMRI responses to half-face changes as whole-face changes, consistent with holistic processing with respect to hemifield-split face halves. Right and left OFA showed markedly different fMRI response patterns however. Right OFA showed similar fMRI responses to whole-face changes and contralateral half-face changes, but showed relatively reduced fMRI responses to ipsilateral half-face changes. Left OFA showed a reduced fMRI response to both contralateral and ipsilateral half-face changes compared to whole-face changes. Our results suggest that whereas anterior face areas (e.g. the FFA) in each hemisphere represent each half of a face equivalently, more posterior areas (e.g. the OFA) show different patterns of contralateral half-face sensitivity that may reflect differences in whole-face representation.
Topic Area: PERCEPTION & ACTION: Vision