Visual Field Maps, Population Receptive Field Sizes, and Visual Field Coverage in the Human MT plus Complex

Amano K, Wandell BA, Dumoulin SO. Visual field maps, population receptive field sizes, and visual field coverage in the human MT+ complex. J Neurophysiol 102: 2704-2718, 2009. First published July 8, 2009; doi: 10.1152/jn.00102.2009. Human neuroimaging experiments typically localize motion-selective cortex (MT+) by contrasting responses to stationary and moving stimuli. It has long been suspected that MT+, located on the lateral surface at the temporal occipital (TO) boundary, contains several distinct visual field maps, although only one coarse map has been measured. Using a novel functional MRI model-based method we identified two maps-TO-1 and TO-2-and measured population receptive field (pRF) sizes within these maps. The angular representation of the first map, TO-1, has a lower vertical meridian on its posterior side at the boundary with the lateral - occipital cortex (i.e., the LO-2 portion). The angular representation continues through horizontal to the upper vertical meridian at the boundary with the second map, TO-2. The TO-2 angle map reverses from upper to lower visual field at increasingly anterior positions. The TO maps share a parallel eccentricity map in which center-to-periphery is represented in the ventral-to-dorsal direction; both maps have an expanded foveal representation. There is a progressive increase in the pRF size from V1/2/3 to LO-1/2 and TO-1/2, with the largest pRF sizes in TO-2. Further, within each map the pRF size increases as a function of eccentricity. The visual field coverage of both maps extends into the ipsilateral visual field, with larger sensitivity to peripheral ipsilateral stimuli in TO-2 than that in TO-1. The TO maps provide a functional segmentation of human motion-sensitive cortex that enables a more complete characterization of processing in human motion-selective cortex.