Recently, topographic maps in human frontal and parietal cortex were discovered using modified versions of the standard traveling wave method for mapping early visual cortex. The standard traveling wave method is effective for driving responses in occipital cortex; more cognitively demanding stimulation, such as tasks that tax attention or memory, are more effective, and perhaps necessary to measure topographic maps in higher association cortex. Much of the recent work has focused on trying to understand the functions of these topographic areas. Here, we take a step back and focus on carefully characterizing the organization and properties of these visual field maps. To do so, we estimated the population receptive field (pRF) properties in topographic areas in frontal and parietal cortex. Observers performed a difficult discrimination task that required covertly attending to stimuli within bars of different widths that randomly swept across the visual field in different directions. We estimated pRFs with a model that accounts for non-linear spatial summation (Kay et al., 2013, JNS) yielding measurements of position, size, and degree of non-linearity for each voxel. Non-linear spatial summation is more pronounced in extrastriate maps than in V1 and is likely to be even more so in association cortices. We identified at least four topographic maps along the intraparietal sulcus (IPS), two maps along the precentral sulcus (PCS), and one newly discovered map in the anterior temporal parietal junction (TPJ). Consistent with previous work, each of these maps contains a representation of the full range of polar angles in the contralateral visual field. The pRF method not only estimates polar angles, but also eccentricity and spatial extent. Extending previous work, by combining pRFs across voxels with a visual map, we demonstrate that these maps represent in an orderly manner the complete contralateral hemifield. Moreover, the pRF sizes are larger than those in early visual cortex, but like those in visual cortex they show an eccentricity dependence. Besides IPS0 and IPS1 (Swisher et al., 2007), maps of eccentricity in these areas has not been previously shown. Using the pRF method, we demonstrate clear maps of eccentricity along all IPS maps, within a portion of the TPJ, and in both PCS maps. The eccentricity and polar angle map structures are interrelated in a manner similar to early visual cortex (Wandell et al., 2007). Some of the maps form clusters of polar angle maps that share a foveal to peripheral representation. Together, these data provide critical insights into the topographic structure of these visual maps in human association cortices.
Monday, Nov 17, 2014, WCC Hall A-C, 9:00 – 10:00 AM