Abstract
We have previously found that perturbation of activity in IT can be used to solve a visual discrimination task when the visual information alone is ambiguous. However, the degree to which independent visually and electrically evoked activities in IT contribute to this discrimination is not clear. To address this question, we designed a new discrimination paradigm based on relative stimulus timing.
A monkey was trained in a two alternative forced choice classification task. We prepared novel stimuli for every experimental session. Two of the four stimuli consisted of identical visual patterns combined with electrical biphasic pulses delivered to a visually selective IT site; the relative timing between the visual and electrical stimulation consistently differed for each. For one stimulus, the electrical stimulation was delivered just prior to the visual stimulation and for the other, during the visual stimulation.
In 9 of 13 experiments we observed clear evidence of learning, but found lower performance and slower learning in the combined, compared to visually distinct, classifications. The absolute timing of visual and electrical stimulation could not explain performance. As a probe test, we occasionally introduced a condition containing only the visual pattern that had been paired with electrical stimulation. On these trials, the monkey reliably chose the button corresponding to the pre-stimulation stimulus.
These results suggest that the visually and electrically evoked activities in IT cortex contribute to discrimination learning in an integrative manner, and that the learning we observed is not a result of simply learning to detect electrical stimulation alone.