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Andrew T. Smith, Matthew B. Wall, Angelika Lingnau, Hiroshi Ashida; Sensitivity to optic flow in human MT and MST measured with fMRI adaptation. Journal of Vision 2006;6(6):113. doi: https://doi.org/10.1167/6.6.113.
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© ARVO (1962-2015); The Authors (2016-present)
In primates, many neurons in MSTd are sensitive to the global flow structure of a pattern of moving dots, some cells responding preferentially to expansion and others to rotation. Such cells are rare in MT. We have explored sensitivity to optic flow in human MT and MST using an event-related fMRI adaptation paradigm, at 3 Tesla. On each trial, two brief random-dot kinematograms were presented sequentially with a gap of 2s. The first stimulus (S1, presented for 3s) is expected to reduce the response to the second (S2, presented for 1s) if they activate overlapping neural populations. In different trials, S1 and S2 contained either the same or different types of global motion. MT and MST were defined in separate experiments using the criteria of Huk et al. (J Neurosci 2002). In human MST, the compound response was smaller (indicating adaptation) when the two stimuli had the same flow structure than when they were different, suggesting specificity to global flow. The effect was large when optic flow was compared to random motion, as previously shown with more conventional paradigms (Smith et al. Eur. J. Neurosci. in press). It was smaller but robust when expansion and rotation were compared. Surprisingly, MT also showed flow specificity, even in the latter case. In V1, which is expected to respond only to local dot motions, there was no flow specificity. Our results suggest that human MT and MST both contain neurons that are selectively responsive to specific optic flow structures.
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