Abstract
We introduce a functional magnetic resonance imaging (fMRI) method for estimating the neuronal population receptive field (pRF) in human visual cortex. This pRF method builds on conventional visual field mapping techniques but extracts additional information beyond the maps and generalizes both the traveling wave method and alternative mapping techniques. The pRF method computes a model of the pRF from responses to a wide range of stimuli. It produces estimates of the visual field map as well as other neuronal population properties, such as the pRF size ipsi and contralateral extent (laterality). The pRF method decouples the visual field map measurements from the conventional ring and wedge stimuli, thereby eliminating some of the difficulties with the conventional techniques. We describe four results with this method. First, we show that visual field maps obtained with the pRF method are more accurate than those obtained using conventional visual field mapping. Second, we delineate the visual field maps to the center of the foveal representation (foveal confluence). Third, we describe two visual field maps within human motion-sensitive cortex (MT+), located on the lateral surface at the temporal-occipital (TO) boundary. We adopt the neutral terms TO-1 and TO-2 for these maps because of primate homology uncertainties but they likely correspond to macaque areas MT and MST. TO-1/2 abut the LO-1/2 visual field maps and are part of a continuous sequence of visual field maps extending from medial to lateral occipital cortex. Fourth, we report quantitative estimates of pRF size in medial, lateral and ventral occipital regions of human visual cortex. Human pRF sizes vary systematically across visual field maps with pRF sizes about 5x larger in TO-1/2 than V1. Within each visual field map, the pRF sizes increase with increasing eccentricity. The human pRF size estimates in V1/2/3 agree well with monkey and human electrophysiological receptive field measurements in corresponding locations. The pRF method is non-invasive and can be applied to a wide range of conditions when it is useful to link fMRI signals in the visual pathways to neuronal population receptive fields.
Supported by NEI EY03164 to BW and LLHF 2005/2BB to SD.