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Phase Integration Bias Predicts Performance in a Motion Binding Task

56.4009, Tuesday, 19-May, 2:45 pm - 6:45 pm, Pavilion
Session: Motion Perception: Local and higher order

Jessica Cali1, Matthew Pachai1, Patrick Bennett1, Allison Sekuler1; 1Department of Psychology, Neuroscience & Behaviour, McMaster University

Studies of motion binding often examine the integration of components such as orientation and speed. We examined motion binding using a task requiring only integration of relative phase (Cali et al., VSS, 2014). Observers discriminated clockwise and counter-clockwise motion in a stimulus comprising four sets of linearly arranged dots, two moving horizontally and two moving vertically along sinusoidal trajectories differing in phase. Across conditions, noise jitter could be added along the trajectory perpendicular to each dot’s motion. Interestingly, as originally showed by Lorenceau (Vision Res., 1996), noise improved discrimination accuracy, consistent with the notion that noise acts as a grouping cue encouraging perception of global motion. Furthermore, when noise was absent from the stimulus, accuracy was not at chance, but significantly below chance; observers consistently reported motion in the incorrect direction. Here we test the hypothesis that observers perceive reverse motion because their representation of the relative phase of the motion components is systematically biased. We asked observers to adjust the relative phase of motion components to produce the most compelling clockwise or counter-clockwise motion with stimuli that did or did not contain noise. We also measured discrimination accuracy for clockwise and counter-clockwise motion. We found that i) phase adjustment error was significantly greater with no noise; ii) discrimination accuracy was significantly below chance with no noise; and iii) the correlation between phase adjustment error and discrimination accuracy were significant in both noise conditions. Our results support the hypothesis that observers misperceive the direction of motion without noise because their representation of the relative phases of motion components is biased. This bias may occur because observers sample the motion components sequentially in the zero noise condition and simultaneously in the high noise condition. More generally, this result suggests the presence of an integration bias in other motion tasks.

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