Abstract
Decades of research have confirmed that all stages of processing within the visual system show retinotopic organization, from retinal ganglion cells to high-level visual areas, such as the parahippocampal place area (PPA). The parahippocampal cortex in particular has been shown to exhibit a peripheral field bias, which is commonly interpreted as leading to a lack of sensitivity to high spatial frequencies (Arcaro et al., 2009). However, neuroimaging studies have shown that the PPA is activated more strongly by high than low spatial frequencies (Rajimehr et al., 2011). How can this be the case if the PPA is not sensitive to high spatial frequencies? Using a stimulus that is known to activate high-level visual cortex, we sought to thoroughly map the population receptive fields (pRFs) in order to verify previous findings and explore the apparent contradiction regarding the representation of high spatial frequencies in the PPA. Here, we used the pRF scans from a subset of the participants in the Human Connectome Project database, obtained with high field strength (7T) fMRI. We estimated the eccentricity, angle, and pRF size using a nonlinear optimization model fitting procedure (Kay et al., 2013). Within the PPA, we find that pRFs range from small and foveal representations, to larger pRFs, which are located in the peripheral visual field regions. The anatomical location of voxels fitted for pRF eccentricity are significantly correlated along the anterior-posterior axis, with more foveal pRFs located closer to the anterior regions of the brain. In line with previous studies (Silson et al., 2015), there was a significant contralateral hemifield bias, and a bias for the top-half of the viewing plane in the PPA. In their combination, these results suggest that both high and low frequency visual information is processed in specialized areas of the PPA.
Acknowledgement: NSERC, SSHRC