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Lisa O'Kane, Ross Goutcher; Effects of orientation and noise on the detection of cyclopean form. Journal of Vision 2010;10(7):381. doi: 10.1167/10.7.381.
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© ARVO (1962-2015); The Authors (2016-present)
We present two experiments investigating effects of local orientation and different types of noise on observers' perception of cyclopean form. Observers were presented with a stimulus containing line elements distributed randomly across a surface, consistent with a disparity-defined square wave, oriented at either ±45deg. The observer's task was to determine whether the stimulus was at a clockwise or counter-clockwise orientation. Each stimulus was comprised of either horizontal or vertical line elements. Line elements had the same local orientation within each trial. Different forms of noise were added to these stimuli, in order to obtain 75% performance thresholds for correctly discriminating the orientation of the square wave. In the first experiment, noise was added via the random repositioning of lines in each eye (decorrelation noise). In the second experiment, noise was added by distorting the z positions of the lines in each eye (disparity noise). Thresholds were measured for varying line length (11 – 33 arcmin) and stimulus densities (5 – 50%). We find effects of both line element orientation and noise type. In the first experiment, decorrelation noise thresholds were lower for stimuli comprised of vertical line elements, indicating enhanced performance compared to horizontal line stimuli. In the second experiment, horizontal line stimuli showed improved performance compared to vertical line stimuli when lines were short (11 arcmin). However, performance with horizontal line stimuli reduced markedly with increasing line length to a much greater extent than vertical line stimuli. These results point to effects of noise occurring at multiple levels of processing. Results obtained using decorrelation noise are consistent with cross correlation as a method of disparity estimation, however, the effects obtained using disparity noise are consistent with disruption at the level of cyclopean form processing.
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