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Masanori Kanazu, Hiroyuki Yamashiro, Hiroki Yamamoto, Nobukatsu Sawamoto, Hidenao Fukuyama, Jun Saiki; Population receptive field estimation of visuotopic areas in the human intraparietal sulcus. Journal of Vision 2012;12(9):378. doi: https://doi.org/10.1167/12.9.378.
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© ARVO (1962-2015); The Authors (2016-present)
The intraparietal sulcus (IPS) is known to have multiple visuotopic areas, but functional characteristics of these areas are not well understood. In the present study, we investigated differences in functional architecture across visuotopic IPS areas by population receptive field (pRF) analysis. In early visual areas, both electrophysiological studies and neuroimaging studies revealed that receptive field size is the smallest in V1 and increases through visual processing hierarchy. We are interested in whether this kind of hierarchical relationship also exists among the IPS areas. We first compared visual filed maps of the IPS based on phase-encoded analysis and pRF analysis. Participants observed rotating wedge or expanding rings, while performing spatial attention task to the stimulus. In the phase-encoded analysis, fMRI time series were Fourier transformed and response phase were plotted on the inflated cortical surface. In the pRF analysis, pRF parameters were estimated for each voxel, and receptive field position were plotted. Visual field maps produced by both methods were in good agreement. Based on these maps, five areas (IPS0, IPS1, IPS2, IPS3, and IPS4) were identified for each participant. Next, we investigated how pRF size changes as a function of eccentricity in visuotopic IPS areas. In all of identified areas, pRF expanded as visual field eccentricity become larger, as known in early visual areas. In contrast, pRF size in parafoveal region reached at maximum in the IPS1, and no difference was observed in more anterior areas. These results indicate that visuotopic areas in the IPS do not have hierarchical structure observed in early visual areas in terms of pRF organization. In monkey electrophysiological studies, the IPS is known to be divided into multiple functionally distinct areas. Similar functionally diverse organization in the human IPS is probably reflected in pRF structure, where information is processed in parallel, rather than hierarchical.
Meeting abstract presented at VSS 2012
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