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Amy E. Zwicker, Deborah E. Giaschi; Directional anisotropies for full-field and hemifield global motion processing. Journal of Vision 2004;4(8):848. doi: 10.1167/4.8.848.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research suggests that certain directions of motion are perceived more readily than others (e.g. Ohtani & Ejima, 1997; Raymond, 1994; Rottach et al., 1996). A consistent pattern of directional anisotropies however, has yet to emerge. Directional anisotropies for global motion perception were studied in 20 university students using random dot kinematograms (RDKs). Coherence thresholds were obtained for horizontal (left or right) and vertical (up or down) directions of motion for full-field, upper-hemifield, lower-hemifield, left-hemifield and right-hemifield RDKs. Consistent with past research, a trend toward lower thresholds for horizontal global motion relative to vertical motion was found. Separate analyses of upward, downward, leftward and rightward motion, however, revealed lower coherence thresholds for upward motion relative to all other directions of motion. This effect was occluded by higher thresholds for downward motion, relative to all other directions of motion, when downward and upward directions were paired. Finally, lower coherence thresholds were obtained for upper-hemifield RDKs, relative to the other hemifield conditions. Cortical areas MT/MST have been indicated as primary components of global motion processing, but the anisotropies reported here have not yet been described in monkey single-unit or human neuroimaging studies. The neural basis for directional and hemifield differences in motion processing is not currently known. Evolutionarily, it may be that these asymmetries in motion sensitivity developed to counteract disproportionate downward motion, as well as the more common occurrence of inferiorly presented motion cues in the surrounding environment.
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