Object selectivity is supposed to be inherent property of neurons in inferior temporal (IT) cortex except for plastic changes due to extensive learning. On the other hand, recent studies provide evidence for task dependent tuning shift attained by the changed object selectivity in IT neurons. Different tasks require different information to accomplish them. Thus, the tuning shift meaning the change of information represent could be a reasonable strategy for neurons to adapt to different task demands. However, the effect of task demands on the tuning property of IT neuron still remains controversial.
To explore the effect of task demands on object tuning, we measured object selectivity in IT neurons of a monkey performing three different behaving tasks, which demanded different task rules: fixation task, attention task and memory task. In fixation task, the monkey was required to simply gaze at a small fixation spot, while a random number of images were sequentially presented at the horizontally left position 4 degree apart from the point during the task. In attention task, during the sequential images presentation, one of the images suddenly changed its shape a little. The animal must detect this change to release a button, keeping fixation. To accomplish the task, the animal keeps its attention to the sequential images. In the memory task, the monkey performed a delayed match-to-sample task. When the firstly presented image appeared again during image presentation, it must release the button.
We found that almost half of the recorded object-selective IT neurons changed their stimulus tuning curves, depending on the task demands, as we regarded the tuning curves obtained during the fixation task as a basic shape of stimulus tuning in the comparison. The modulation induced by the attention task was drastic to completely alter the shape of basic tuning curves to a different one, whereas the modulation induced by the memory task was moderate not to skew the basic shape, though the change was significant.
These results suggest that neural representation of object images in the IT cortex dynamically changes with task demands. The difference of the task demands could reflect the extent of the tuning shift.