Shinkman P G, Bruce C J, Pfingst B E
Science. 1974 Jun 14;184(4142):1194-6. doi: 10.1126/science.184.4142.1194.
Unit responses to photic stimuli were studied in cat visual cortex. After the baseline response pattern of a cell was determined, conditioning trials were given during which reinforcement was contingent upon increased firing during a selected segment of the poststimulus interval. Density of reinforcement increased substantially in about half the cells studied; significant increases in firing occurred within, but not outside, the criterion segment.