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Hikari Takebayashi, Jun Saiki; Orientation variance and spatial frequency modulate ensemble perception of orientation. Journal of Vision 2020;20(11):1047. doi: https://doi.org/10.1167/jov.20.11.1047.
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© ARVO (1962-2015); The Authors (2016-present)
A great deal is known about the early steps of visual processing such as the orientation and spatial frequency (SF) channels, while little is known about how signals from those channels pool one another and generate statistical representations. Here we show different pooling mechanisms of orientation information between high and low SF sinusoidal patterns. In the experiment, a set of 8-high SF gratings (3 cpd), 8-low SF gratings (0.8 cpd), or 4-high-4-low SF gratings located at the same eccentricity were randomly displayed for 250ms. Orientations of those individual gratings were jittered, and their variance was set either large or small. Observers reported the average orientation by adjusting a black bar to the point of subjective equality. We used response variability as a measure of orientation sensitivity, indexed by the concentration parameter of the von Mises distribution, with which high concentration means high sensitivity of average orientation. To get the 95% confidence interval about the concentration parameter for each condition, we generated 5000 bootstrap resamples about angular errors from the correct average. With a single object, orientation sensitivity was higher with high SF grating than with low SF grating. This high SF advantage holds in the averaging conditions with small orientation variance, but the pattern was reversed in the averaging conditions with large orientation variance, indicating that relative ensemble orientation sensitivity between high and low SF gratings is modulated by orientation variability. Moreover, the sensitivity in the 4-high-4-low SF gratings was lower than both in the 8-high and 8-low SF gratings, suggesting that the orientation signals from more than two different SF channels do not pool efficiently compared with the same or similar SF channels. The mechanisms underlying ensemble perception of orientation appear to be influenced by psychophysical characteristics in early visual processing.
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