Parafoveal vision reveals qualitative differences between FFA and PPA

Abstract

The center-periphery visual field axis guides early visual system organization with enhanced resources devoted to central vision leading to reduced peripheral performance relative to that of central vision (i.e., behavioral eccentricity effect) for most visual functions. The center-periphery organization extends to high-order visual cortex where for example the well-studied face-sensitive fusiform face area (FFA) shows sensitivity to central vision and place-sensitive parahippocampal place area (PPA) shows sensitivity to peripheral vision. As we have recently found that face perception is more sensitive to eccentricity than place perception, here we examined whether these behavioral findings reflect differences in FFA and PPAs sensitivities to eccentricity. We assumed FFA would show higher sensitivity to eccentricity than PPA would, but that both regions modulation by eccentricity would be invariant to the viewed category. We parametrically investigated (fMRI, n=32) how FFAs and PPAs activations are modulated by eccentricity ([≤]8{degrees}) and category (upright/inverted faces/houses) while keeping stimulus size constant. As expected, FFA showed an overall higher sensitivity to eccentricity than PPA. However, both regions activation modulations by eccentricity were dependent on the viewed category. In FFA a reduction of activation with growing eccentricity ("BOLD eccentricity effect") was found (with different amplitudes) for all categories. In PPA however, there were qualitative modulations of the BOLD eccentricity effect with mild BOLD eccentricity effect for houses but a reverse BOLD eccentricity effect for faces and no modulation for inverted faces. Our results emphasize that peripheral vision investigations are critical to further our understanding of visual processing both quantitatively and qualitatively. Significance statementVisual perception significantly deteriorates with growing distance from central vision (behavioral eccentricity effect) with varying degrees according to visual function. For some functions (but not others) deterioration follows the reduction of resources devoted to peripheral vision at early visual processing stages. While early stages of visual processing reflect retinal spatial arrangement, here we found that activations in high-order visual areas that are less sensitive to visual field location show a BOLD fMRI activation eccentricity effect that mirrors the behavioral eccentricity effect. Importantly, the BOLD eccentricity effects we found varied across regions and were modulated quantitatively and qualitatively by the viewed visual categories. Our results emphasize that peripheral vision investigations are critical to further our understanding of visual processing.