Human neural responses involved in spatial pooling of locally

25 Early visual motion signals are local and one-dimensional (1D). For specification of 26 global 2D motion vectors, the visual system should appropriately integrate these signals 27 across orientation and space. Previous neurophysiological studies have suggested that 28 this integration process consists of two computational steps (estimation of local 2D 29 motion vectors followed by their spatial pooling), both being identified in the area MT. 30 Psychophysical findings, however, suggest that under certain stimulus conditions the 31 human visual system can also compute mathematically correct global motion vectors 32 from direct pooling of spatially-distributed 1D motion signals. To study the neural 33 mechanisms responsible for this novel 1D motion pooling, we conducted human MEG 34 and fMRI experiments using a global motion stimulus comprising of multiple moving 35 Gabors (global-Gabor motion). The first experiment measured MEG and BOLD 36 responses while changing motion coherence of global-Gabor motion. The second 37 experiment investigated cortical responses correlated with direction-selective 38 adaptation to the global 2D motion, not to local 1D motions. We found that hMT+ 39 responses show both coherence dependency and direction-selectivity to global motion 40 based on 1D pooling. The results provide the first evidence that hMT+ is the locus of 1D 41 motion pooling, as well as that of conventional 2D motion pooling. 42