Figure 1: Task and behavior.

A. Schematic of the continuous curvature estimation task. Stimuli that varied in curvature and task-irrelevant features were presented in the joint receptive fields of V1 and V4 neurons as monkeys fixated a central dot. After 550–800ms, a target arc was presented in the upper hemifield, and monkeys were rewarded for making a saccade to a location on the arc that corresponded to the stimulus curvature. The reward amount was inversely related (with a threshold) to the error in curvature judgment. In a subset of experiments, the radial position, angular position, and length of the target arc were varied pseudorandomly.

B. Monkeys report medial axis curvature while ignoring other stimulus features. Example continuous estimation behavior on four sessions during which the curvature of one or many shapes was estimated on interleaved trials. Shading indicates the standard error of the mean (SEM).