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Sonia Poltoratski, Kendrick Kay, Kalanit Grill-Spector; Population receptive field measurements of stimulus-driven effects in face-selective areas. Journal of Vision 2019;19(10):258c. doi: https://doi.org/10.1167/19.10.258c.
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Classic theories suggest that high-level visual recognition is largely invariant to the item’s position and size, but this is challenged by consistent reports of spatial biases and position information in high-level visual regions. Recent work in our lab (Kay, Weiner, and Grill-Spector, 2015; Gomez et al. 2018) has used population receptive field (pRF) models to computationally quantify spatial representations in face selective areas. However, it remains unknown how these spatial representations may contribute to face recognition behavior. Spatial integration of information is critical to two behavioral hallmarks of face processing: holistic processing, and competition between multiple items. In two experiments (Fig 1), we used 3T fMRI to map pRFs in 6 participants with stimuli thought to disrupt spatial processing enroute to face recognition: inverted faces (Experiment 1), and face pairs (Experiment 2), and compared these pRF properties to those measured with single, upright faces. To ensure fixation, participants performed a 1-back task on rapidly presented letters. Compared to upright faces, inverted faces yielded (1) a shift in the location of pRFs centers to the lower visual field, (2) lower variance explained by the pRF model, and (3) lower response amplitude (Fig 2). Further, these differences increased in magnitude from IOG-, to pFus-, to mFus-faces. Meanwhile, compared to a single upright face, presenting a face pair reduced pRF size and coverage across manipulations of the size of the single face, as predicted by classic theories of visual competition (Fig 3). In both experiments, we did not observe differences in pRFs or visual field coverage in V1 across varying mapping stimuli. Together, these results show for the first time that not only top-down attention, but also bottom-up stimulus driven properties can shift pRFs in face-selective regions. These data suggest that pRFs in high-level regions have complex properties that may constrain recognition behavior.
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