Abstract
Activity of neurons in inferior temporal (IT) cortex is thought to be critical for the recognition of visual objects. Recently we showed that short trains of electrical microstimulation in IT can selectively bias monkeys' choice behavior in a recognition task. To examine the detailed temporal dynamics underlying these effects, we conducted combined behavioral and single unit recording during a classification task with backward masking. This paradigm allows the precise examination of the relationship between behavioral and neuronal sensitivity to visual patterns as a function of presentation time. Unlike previous studies, we compared the monkeys' behavioral and neuronal responses at the same time, replicated for new stimuli across multiple sessions. We found that for the shortest stimulus onset asynchrony (SOA) between target and mask (10ms), monkeys' performance fell to chance. At the same time we found a decrease of response amplitude for preferred target image in IT neurons, which was evident at response onset. As SOA was increased from 10ms and 60ms, neuronal and behavioral sensitivity quickly plateaued, but ROC analysis revealed that single unit sensitivity did not always match the monkeys' behavior. Guided by these findings, initial microstimulation studies using this paradigm indicate that electrical stimulation can affect choice behavior for preferred targets that are masked within 60ms. These results suggest that populations of IT cells very rapidly create a neuronal representation that can be used for recognition, and that microstimulation during this period can influence this process.
James S McDonnell Foundation, NIH/NEI R01EY014681-01A1, NSF CRCNS 0423031