Fig. 2.

Stimulus context alters population activity and reliability. A: mean-normalized visual response of 131 face-responsive IT neurons to stimulus presentation, averaged across all 20 face stimuli, for the face condition (red) and the mixed condition (blue). The activity prior to stimulus-evoked response (0–70 ms; gray bar) is greater in the face condition. Average visual response (70–320 ms; black bar) is enhanced in the face condition. B: mean-normalized visual responses of 76 face-responsive IT neurons from monkey 1 (M1; top) and 55 neurons from monkey 2 (M2; bottom), averaged across all 20 face stimuli, for the face condition (red) and the mixed condition (blue). The activity prior to stimulus-evoked response (0–70 ms; gray bar) is greater in the face condition in both monkeys. Average visual response (70–320 ms; black bar) is enhanced in the face condition in both monkeys. *P < 0.05. **P < 0.01. C: baseline enhancement index is quantified as the difference between responses immediately prior to the visual response (t₂, response during 70-ms window, starting at stimulus onset) and baseline response (t₁, response during 70-ms window, starting 100 ms before stimulus) divided by their sum. D: this index was significantly greater than zero in face condition (baseline enhancement index_face = 0.065 ± 0.019, P = 0.002), which is equal to a 13.68% increase in response. But the index was not significantly different from zero in the mixed condition (baseline enhancement_mixed = −0.011 ± 0.020, P = 0.443), and was significantly different between the face and mixed conditions (baseline enhancement_face-mixed = 0.076 ± 0.017). E: the variability of neuronal responses decreases in the face block. The scatter plot shows the variability, measured as the Fano factor (variance/mean), of neural responses to all 20 face stimuli for the population of 131 face-responsive IT neurons. Variability was lower in the face condition (y-axis) than in the mixed condition (x-axis).