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Szonya Durant, Johannes. M. Zanker; Human MT+ response saturates rapidly as a function of sampling density in natural dynamic scenes. Journal of Vision 2010;10(7):842. doi: 10.1167/10.7.842.
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© ARVO (1962-2015); The Authors (2016-present)
It is known from macaque single cell electrophysiology that response to random dot optic flow movies saturates rapidly in MST as a function of dot density. In this experiment we used fMRI to investigate if human MT+ similarly saturates as a function of sampling density with more naturalistic optic flow scenes. We recorded grayscale movies using a camera moving forward. We covered the movies with a uniform grey area on which transparent hard-edged circular apertures of a fixed size (0.2 times the height of the clip in diameter) were placed in random locations. We presented movies visible through 10, 40 and 160 circular apertures. In a fourth condition we “cut out” the motion visible through the 160 apertures and randomly rearranged the apertures, so that local motion was preserved, but no global motion associated with forward movement remained. Participants viewed these movies in the scanner, whilst performing a central foveal attention task. We localised regions of interest from separate sessions for V1, V2, V3, V4 and MT+. We found that although V1 and other early striate areas increase their response with the number of apertures, area MT+, although responding significantly above baseline to all conditions does not respond differentially to the different number of apertures. This result holds if we split area MT+ into MT and MST, based on ipsilateral responses. As the amount of visible motion across these conditions does not affect the MT+ response we suggest this is due to the early saturation of response with the amount of motion present. However, we found no difference in any of the visual areas between the scrambled and normal 160 aperture conditions, suggesting these results are not necessarily dependent on the presence of coherent global motion.
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