Abstract
Purpose: Human motion-selective cortex (hMT+) is typically localized based on a functional selectivity to moving stimuli. This functional definition spans several visual field maps. Conventional retinotopic mapping techniques using rings and wedges identified one visual field map thought to be the homolog of MT (Huk et al, 2002); but mapping has not provided a clear characterization of neighboring regions. We applied the population receptive field (pRF) model-based method (Dumoulin and Wandell, 2008) to reveal visual field maps and estimate pRF size within the hMT+ region. Methods: Magnetic resonance images were acquired with a 3 T General Electric Signa scanner and an eight-channel coil (Nova Medical, Wilmington, MA) centered over the subject's occipital pole (voxel size 1.5mm isotropic). In addition to novel bar stimuli, we modified the conventional wedge and ring stimuli by inserted blank periods. These stimuli are more adept to reconstruct visual field maps with larger receptive fields like hMT+. Stimulus radius was 10 deg. Results: We found at least two visual field maps in hMT+, which we refer to as temporal occipital 1 (TO-1) and 2 (TO-2). This conservative nomenclature acknowledges uncertainties in the human-monkey homologies. TO-1 borders LO-2 and TO-2 is anterior to TO-1. The TO-1 polar angle map extends from the lower to the upper vertical meridian and reverses at TO-2. The maps share a foveal representation that is distinct from that of V1/V2/V3/LO-1/LO-2. TO-1/2 represent the contralateral hemifield. The pRF size of TO-2 (σ = 5–12 deg) is significantly larger than that of TO-1 (σ = 4–8 deg) over the measured eccentricity range (1–6 deg). Discussion: The two visual field maps match the general retinotopic and functional dissociation proposed by Huk et al. (2002) and Dukelow et al. (2001). The two maps probably correspond to macaque MT and MST (Rosa and Tweedale, 2006).