Figure 1.

Flexible categorization task overview. (A) A morphing system was used to generate stimulus images that varied smoothly between 4 original prototypes (located in the corners). Monkeys grouped images using 2 different categorization schemes. Stimuli lying on the category boundary were ambiguous and were assigned category labels randomly. We use the arbitrary terms Goc and Tad to describe the pairs of Cat and Dog prototypes that are on the left and right side of Scheme B, respectively. (B) The flexible categorization task followed a delayed match-to-category paradigm. The trial began with monkeys pressing a lever and fixating on a dot. The dot changed color, which served as the context cue instructing which categorization scheme to apply. After a period of fixation, monkeys were shown a stimulus image. After a delay stage, monkeys were then shown a test image and they had to assess whether it was a match or nonmatch based on the relevant categorization scheme. If the images were a match, the monkey released a lever. Otherwise, the monkeys held onto the lever through a second delay stage, at which point the correct matching image was shown. The letters above each stage indicate stage symbols used throughout the paper.