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Huihui Zhang, David Alais; Serial dependence for discriminating grating orientation at threshold contrast is driven by perceptual decisions. Journal of Vision 2018;18(10):659. doi: https://doi.org/10.1167/18.10.659.
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Many studies have shown that recent history biases present perception, known as serial dependence, although it remains unclear whether it is driven by changes in perception or decision-making. Here we examined serial dependence for discriminating visual grating orientation (+45° or -45°) at threshold contrast. The grating was embedded in noise and its contrast was maintained at threshold level over trials (75% correct) by an Accelerated Stochastic Approximation procedure. Participants reported which orientation they perceived by clicking a mouse. To evaluate serial dependence, we conducted a linear regression of present orientation choice on present stimulus, previous stimulus, and previous choice. Unsurprisingly, the regression coefficient for present stimulus was significant. However, the regression coefficients for previous (i.e., 1-back) stimulus and previous choice were both not significant. Next, we repeated the same analysis for stimulus and choice but for larger n-back values. Positive regression coefficients for previous choices were found for trials that were 2-, 3-, 4- and 5-back from the present trial, while regression coefficients for previous stimulus were not significant over the same range. Next, we used lagged regression to evaluate the relative influence on present perceptual choice from previous series of choices. Similar to previous results, coefficients for previous choices from 2-, 3-, 4- and 5-back from the present trial were significant. Moreover, the value of coefficients decreased as the temporal distance from the present trial increased. In conclusion, our results suggest that (1) orientation discrimination at threshold contrast exhibits a positive serial dependence; (2) the serial dependence at threshold contrast originates from previous decisions rather than previous stimuli; (3) unlike traditional serial dependence which is strongest for the one back trial, serial dependence for orientation discrimination at threshold is not present at 1-back: it peaks at 2-back and declines gradually out to 5-back.
Meeting abstract presented at VSS 2018
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