Fig. 1.

Experimental design. (A) Trial sequence for the multidimensional visual categorization task. On each trial, the monkeys categorized either the motion direction or color of a random-dot stimulus. This stimulus was immediately preceded by a symbolic visual shape cue that instructed which feature (motion or color) to categorize for that trial. The monkey responded with a leftward or rightward saccade during the 3-s stimulus. (B) Either of two different cue shapes was used to instruct each task rule so as to dissociate cue- and task-rule–related activity. (C) Stimuli systematically sampled motion direction (upward to downward) and color (green to red). Each color category comprised two distinct colors, and each motion category comprised two distinct motion directions (additional ambiguous stimuli on the category boundaries were not analyzed here due to our focus on categoricality). Dashed lines indicate category boundaries. For each task rule, the two categories had a fixed mapping to a leftward (L) or rightward (R) saccadic response. (D) Illustration of sampled brain regions: lateral PFC, FEF, LIP, PIT, V4, and MT.