Figure 1. Training and testing procedures.

(a) Sixteen images rendered familiar by repeated viewing over the course of a month in monkey 1. The exposure set for monkey 2 consisted of other background-free object images. (b) On each exposure trial during the familiarization period, the monkey maintained fixation at the center of the screen for 1600 ms. During fixation, a single image was presented for 1000 ms at the fovea. Fluid reward was delivered at the end of each trial contingent solely on the monkey’s having maintained fixation. (c) Procedure for rapid serial visual presentation during neuronal recording. On each trial, the monkey maintained central fixation while two images were presented in alternation at the fovea. The images could be both familiar (F₁ and F₂) or both novel (N₁ and N₂). (d–i) Data from a neuron giving strong periodic responses to rapidly alternating familiar images but not to rapidly alternating novel images. Successive displays in the left column show the responses of a representative neuron to familiar images presented in the sequence F₁F₂ (d) or F₂F₁ (e) and in data combined from the two sequences (f). Successive displays in the right column show responses of the same neuron to novel images presented in the sequence N₁N₂ (g) or N₂N₁ (h) and in data combined from the two sequences (i).