ADAPTATION TO CONTINGENCIES IN MACAQUE PRIMARY VISUAL-CORTEX

We tested the hypothesis that neurons in the primary visual cortex (VI ) adapt selectively to contingencies in the attributes of visual stimu li. We recorded from single neurons in macaque VI and measured the eff ects of adaptation either to the sum of two gratings (compound stimulu s) or to the individual gratings. According to our hypothesis, there w ould be a component of adaptation that is specific to the compound sti mulus. In a first series of experiments, the two gratings differed in orientation. One grating had optimal orientation and the other was ort hogonal to it, and therefore did not activate the neuron under study. These experiments provided evidence in favour of our hypothesis. In mo st cells adaptation to the compound stimulus reduced responses to the compound stimulus more than it reduced responses to the optimal gratin g, and the responses to the compound stimulus were reduced more by ada ptation to the compound stimulus than by adaptation to the individual gratings. This suggests that a component of adaptation was specific to (and caused by) the simultaneous presence of the two orientations in the compound stimulus. To test whether VI neurons could adapt to other contingencies in the stimulus attributes, we performed a second serie s of experiments, in which the component gratings were parallel but di ffered in spatial frequency, and were both effective in activating the neuron under study. These experiments failed to reveal convincing con tingent effects of adaptation, suggesting that neurons cannot adapt eq ually well to all types of contingency.