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Local Perturbations to a Global Radial Frequency Masker Alleviate Lateral Masking Effects

26.321, Saturday, 17-May, 2:45 pm - 6:45 pm, Jacaranda Hall
Session: Perceptual organization: Segmentation, shapes and objects

Michael Slugocki1, Allison Sekuler1, Patrick Bennett1; 1Department of Psychology, Neuroscience & Behaviour, McMaster University

Radial Frequency (RF) contours, generated through the sinusoidal modulation of the radius of a circle, are a useful tool to study the processes involved in shape perception. Previous research examining RF contour detection suggests that low and high RF contours are processed by separate global and local shape detection mechanisms, respectively (Bell et al., 2007). If the processes responsible for global and local RF detection do not interact, then a lateral mask consisting of a combination of low and high RF contours should interfere with the detection of a low RF contour at least as much as a low RF contour mask alone. To test this prediction, we measured detection thresholds for a low RF contour (RF5) in the presence of a control mask (RF0), a low RF mask (RF5), a high RF mask (RF25), or a compound mask (RF5+RF25) consisting of the combination of RF5 and RF25 patterns. Consistent with previous reports, two out of the three observers show significant masking with the low RF mask relative to the control and high RF mask. Critically, these two observers showed significantly less masking for the compound mask than for the low RF mask, and did not show a significant difference in masking with the compound mask relative to the control and high RF mask. The third, anomalous, observer showed relatively high levels of masking across all conditions, including the control mask. Overall, however, our results suggest that global and local shape detection mechanisms do not operate independently of one another in masking. We currently are examining the extent to which the results reveal individual differences, and how the nature of RF interactions influences masking.

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