Figure 1.

A) Speed categorization task. Subjects first fixate on a target in the center of the screen, then see a cue indicating the category boundary, then a random dot motion stimulus and two response targets, and finally receive reinforcement based on their response. The stimulus and targets appeared simultaneously. B) Stimuli and boundaries. The stimulus speed varied from slow (2 deg s⁻¹) to fast (16 deg s⁻¹). The yellow cue indicated a slow reference speed (between 4 an 6 deg s⁻¹), while the blue cue indicated a faster reference (between 10 and 12 deg s⁻¹).