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Alex Baldwin, Minnie Fu, Reza Farivar, Robert Hess; Equivalent internal noise for contour integration. Journal of Vision 2017;17(10):1364. doi: 10.1167/17.10.1364.
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© ARVO (1962-2015); The Authors (2016-present)
Oriented wavelets give the percept of a contour if each wavelet has the appropriate position and orientation to belong to that contour. The rules governing this have been tested using a contour integration task: observers detect a contour of aligned wavelets buried in a background noise of randomly-oriented wavelets. Here we present a new threshold contour task that does not rely on a background noise field to limit performance. Observers discriminate which of four contours (at an eccentricity of 2.8 degrees in four quadrants) contains the appropriate conjunction of (6 c/deg log-Gabor) wavelet positions and orientations to feature "good continuation". The other three contours have orientations appropriate to the opposite direction of curvature. Thresholds are measured as a function of curvature (straighter contours are more difficult). By corrupting the orientation and position of the individual wavelets with external noise we measured noise masking functions. Both orientation and position noise elevated thresholds. Equivalent internal noise values were compared to those from tasks where observers made judgements about single elements. We found that in a contour the orientation noise was elevated (260%) but the position noise was reduced (40%). This suggests that contour processing privileges the refinement of position information at the expense of orientation. The sensitivity loss between 4 and 8 degrees of eccentricity was modest (10% threshold increase), and was abolished when the scale of the contours was doubled in the periphery. In another experiment, we introduced a "baseline" curvature to the stimuli to investigate discrimination of curvier contours. Thresholds were elevated relative to discrimination of straighter contours (190%). Contrary to results from the previous contour task, we found observers could integrate curvy contours in the periphery. The measurements from this novel paradigm could be used to investigate mid-level visual impairments, and to constrain models of the traditional contour task.
Meeting abstract presented at VSS 2017
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