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Andrew E. Silva, Zili Liu; Vertical opponency modulates sensitivity to horizontal motion. Journal of Vision 2014;14(10):473. doi: https://doi.org/10.1167/14.10.473.
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Introduction: Motion processing involves several antagonistic interactions. For example, different directions have been found to perceptually suppress one another when simultaneously presented (directional suppression) (Snowden, 1989). Suppression also occurs when an MT neuron encounters simultaneous motions in its preferred and anti-preferred directions in the same location, resulting in a decreased neural response (opponency) (Qian & Andersen, 1994). With MT's prominence in motion processing, its neural interactions may modulate directional suppression at the perceptual level. It is therefore reasonable to hypothesize that when affected by opponent suppression, motion signals may have a reduced ability to exert directional suppression during later processing. Thus, in a presentation consisting of opponent vertical and non-opponent horizontal motion, the directional suppression acting against the horizontal motion may be reduced, resulting in greater detectability of the horizontal direction. We tested this hypothesis in the present study. Method: A motion stimulus consisted of 49 pairs of background dots and 70 randomly distributed target dots. During each trial, half of all background dots shifted up and half shifted down. In opponent trials, dots within pairs shifted in opposite directions, while in non-opponent trials, dots within pairs shifted in the same direction. All target dots shifted either left or right, and participants indicated this direction. Results: The non-opponent condition elicited a higher d' (1.87) than the opponent condition (1.36) for horizontal motion discrimination (n = 24, p <.001). Conclusion: Opponent motion exerted stronger directional suppression than non-opponent motion, contradicting our prior hypothesis. However, a recent study suggests that some MT neurons have multiple preferred motion directions (Richert et al., 2013). Therefore, vertical opponency may suppress some horizontal-sensitive cells and result in decreased horizontal sensitivity, potentially accounting for the current results.
Meeting abstract presented at VSS 2014
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