Figure 2. Behavioral performance of monkeys 1 (A–D) and 2 (E–H) in the DYSC task. The horizontal axis of each plot indicates the position of the sample stimulus, in degrees angle counterclockwise from the direction to the right of the fixation target (defined as 0°; sample eccentricity was fixed at 13°). The red- and blue-shaded regions indicate spans of sample angle corresponding to the spatial categories right and left (A, C, E, G), above and below (B, D, F, H), respectively. The lines and symbols indicate the probability (proportion of trials) that monkeys selected choices that were located in the right (red lines) or left (blue lines), above (blue lines) or below (red lines) spatial categories for each sample position and rule. The vertical dashed lines indicate angles corresponding to the category boundary under a given rule. A, B, Performance of monkey 1 under the LR rule, when the boundary cue was vertical. The solid lines indicated performance on trials using the boundary–sample sequence, and the dashed lines performance on trials using the sample–boundary sequence. A, Under the LR rule, monkey 1 selected left choices with high probability (blue symbols and lines) when the sample category was left (blue shading), and right choices with high probability (red symbols and lines) when the sample category was right (red shading). B, Under the LR rule, the vertical category of the choices selected by monkey 1 (above or below) did not relate systematically to the vertical category of the sample. C, D, Performance of monkey 1 under the AB rule, when the boundary cue was horizontal. C, Under the AB rule, the horizontal category of the choices selected by monkey 1 (left or right) did not relate systematically to the horizontal category of the sample. D, In contrast, under the AB rule, monkey 1 selected above choices with high probability (blue symbols and lines) when the sample category was above (blue shading), and below choices with high probability (red symbols and lines) when the sample category was below (red shading). E–H, Corresponding data for monkey 2.