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Kevin S. Weiner, Rory Sayres, Joakim Vinberg, Kalanit Grill-Spector; fMRI-Adaptation and category selectivity in human ventral temporal cortex: Evidence for the scaling and sharpening models. Journal of Vision 2009;9(8):466. doi: https://doi.org/10.1167/9.8.466.
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© ARVO (1962-2015); The Authors (2016-present)
Repeating object images produces stimulus-specific repetition suppression (or fMRI-adaptation, fMRI-A) in the ventral stream. However, the effects of stimulus repetition on functional selectivity are unknown. We investigated the effects of short-lagged (SL, 0–2 stimuli between repeats) and long-lagged (LL) repetition (∼ 20 stimuli between repeats) on category selectivity in the human ventral stream using high-resolution fMRI. Specifically, we examined whether repetition produces scaling, sharpening or additive offset of fMRI responses. We found that scaling best explained fMRI-A across the fusiform gyrus (FG) and occipito-temporal sulcus (OTS): fMRI-A was largest for the strongest stimulus, and there was linear relation between responses to repeated vs. nonrepeated stimuli, whereby the slope determined the scaling factor. Results were similar across SL and LL paradigms and regions selective to faces or limbs. However, a collateral sulcus (CoS) house-selective region showed differential effects across paradigms suggestive of differential repetition mechanisms at different time scales: it exhibited scaling for SL repetitions and sharpening for LL repetitions. Specifically, there was lesser fMRI-A to preferred than nonpreferred stimuli for LL repetitions. Finally, multi-voxel pattern analyses across lateral (FG and OTS) and medial (CoS) anatomical regions showed that distributed responses across ventral temporal cortex for object categories largely did not change when objects were repeated for both SL and LL repetitions, consistent with scaling. Nevertheless, in the medial region, repetition increased the decorrelation between distributed responses for inanimate stimuli during the LL experiment consistent with sharpening. Our results suggest differential repetition effects across medial (CoS) and lateral (FG and OTS) regions during LL repetitions, which highlight the possibility that interpretation of long-lagged fMRI-A experiments may vary across ventral subregions.
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