September 2017
Volume 17, Issue 10
Open Access
Vision Sciences Society Annual Meeting Abstract  |   August 2017
Opponency in the middle temporal complex: Counter-phase dot motion is processed like non-motion
Author Affiliations
  • Andrew Silva
    University of California, Los Angeles
  • Benjamin Thompson
    University of Waterloo
  • Zili Liu
    University of California, Los Angeles
Journal of Vision August 2017, Vol.17, 931. doi:
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      Andrew Silva, Benjamin Thompson, Zili Liu; Opponency in the middle temporal complex: Counter-phase dot motion is processed like non-motion. Journal of Vision 2017;17(10):931.

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      © ARVO (1962-2015); The Authors (2016-present)

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During the opponency stage of computational motion-processing models, the responses of two directionally-selective cells with opposing preferred directions are subtracted (Adelson & Bergen, 1985). This calculation outputs the local direction of motion and reduces further processing of non-informative flicker-noise. A biological implementation of opponency involving brain area MT is speculated to exist, since MT neurons are poorly driven by counter-phase motion stimuli. Counter-phase stimuli are created by spatially pairing oppositely-moving dots such that any local area contains balanced quantities of opposing signals (Qian & Andersen, 1994). If the weak MT response to counter-phase motion is truly indicative of a noise-reducing mechanism, then this response may resemble MT's response to flickery non-motion stimuli. Furthermore, when included as background distractors in a direction discrimination task, task-irrelevant counter-phase and non-motion stimuli may similarly affect behavioral performance. In the current project, we examined these predictions using psychophysics and fMRI. We created a non-suppressed in-phase stimulus to use as a control comparison by reversing the direction of one dot in each counter-phase pair. During the psychophysical experiment, participants judged whether target dots moved coherently leftward or rightward. This task was embedded within counter-phase, in-phase, and non-motion backgrounds. During the fMRI experiment, counter-phase, in-phase, and non-motion stimuli were presented without target dots to collect clean patterns of activation. As predicted, in-phase trials elicited high BOLD responses and high behavioral thresholds, while counter-phase and non-motion trials elicited similarly low BOLD responses and behavioral thresholds. Moreover, a three-way MVPA classification of MT fMRI data found good classification of in-phase stimuli, but poor discrimination between counter-phase and non-motion stimuli. All together, these results suggest that counter-phase and non-motion stimuli are processed similarly, strengthening the idea that the weak MT response to counter-phase motion is a signature of the brain's noise-reduction mechanism.

Meeting abstract presented at VSS 2017


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