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Kaoru Amano, Kazushi Maruya, Shin'ya Nishida; Neural responses involved in 1D motion spatial pooling. Journal of Vision 2010;10(7):841. doi: https://doi.org/10.1167/10.7.841.
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To compute two-dimensional (2D) trajectory of visual motion, the visual system has to integrate one-dimensional (1D) local motion signals not only across orientation, but also across space. While previous studies found the evidence suggesting that monkey MT/MST or human MT complex (hMT+) is involved in the integration of spatially-overlapping 1D motion signals, it remains unclear where and when in the brain 1D signals are spatially pooled. Here we non-invasively recorded human neural responses related to the pooling of 1D motion signals using a whole head MEG system (PQ2440R; Yokogawa). The first experiment recorded MEG responses evoked by the change from incoherent (0% coherence) to coherent (30, 50, 71 or 100%) Global-Gabor motion (Amano et al, 2009, Journal of Vision). Patches with 1.7 deg stationary Gaussian envelopes were presented within an annulus whose inner and outer diameters were 5 and 27 deg, respectively. The second experiment tested the direction-selectivity of the responses to Global-Gabor stimuli by using an adaptation paradigm. Motion coherence of both test and adaptation stimuli was 100%. The global motion direction of adaptation stimulus was fixed while that of test stimulus was randomly chosen from the two opposing (adapted and non-adapted) directions. We made the orientations of test Gabors orthogonal to those of adaptation Gabors to exclude local adaptation effects. In both experiments, beamformer analysis found the evoked activities in hMT+ peaking at around 150-200 ms. The responses monotonically increased with the increase in motion coherence (Exp. 1), and were significantly smaller for the adapted global direction than for the opposite direction (Exp. 2). Our finding that hMT+ responses show both coherence dependency and direction selectivity to global motion supports the idea that hMT+ is the locus of 1D motion spatial pooling.
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