Figure 2 (IMAGE)
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Experimental design, stimuli, and behavioral performance
a. Schematic of the two alternative forced choice (2-AFC) motion categorization task. The head-fixed mice were trained to group eight global motion directions into the two discrete categories by turning the wheel to the left or right. We used eight global motion directions from the predefined set of directions from 22.5° to 337.5° in steps of 45°.
b. Illustrations of how stimuli and conditions were created. First, one motion direction was sampled from eight possible motion directions and then used as a mean motion direction in each trial of two conditions. In homogeneous random dot kinematograms (RDKs), the sampled motion direction was identical to the motion direction of the rest of dots. In heterogeneous RDKs, each dot’s motion direction was randomly selected from a uniform distribution within one of the three ranges (90°, 180° and 270°) with one of eight global mean motion directions. Note that not a single dot in heterogeneous RDK was assigned to the global motion direction along the distribution’s mean.
c. The slope values of cumulative normal functions fit to each mouse’s behavioral data are shown for the homogeneous and heterogeneous conditions. Error bars indicate ±SEM. Mice performed the task reliably up to a certain difficulty level in both homogeneous and heterogeneous stimulus conditions. A difference in task performance between the two conditions was observed only for the 270 condition.
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