Representation of comparison signals in cortical area MT during a delayed direction discrimination task

Leo Lui, Tatiana Pasternak

Research output: Contribution to journalArticleResearchpeer-review

31 Citations (Scopus)

Abstract

Visually guided behavior often involves decisions that are based on evaluating stimuli in the context of those observed previously. Such decisions are made by monkeys comparing two consecutive stimuli, sample and test, moving in the same or opposite directions. We examined whether responses in the motion processing area MT during the comparison phase of this task (test) are modulated by the direction of the preceding stimulus (sample). This modulation, termed comparison signal, was measured by comparing responses to identical test stimuli on trials when it was preceded by sample moving in the same direction (S-trials) with trials when it was preceded by sample moving in a different direction (D-trials). The test always appeared in the neuron s receptive field (RF), whereas sample could appear in the RF or in the contralateral visual field (remote sample). With sample in-RF, we found three types of modulation carried by different sets of neurons: early suppression on S-trials and late enhancement, one on S-trials, and the other on D-trials. Under these conditions, many neurons with and without comparison effects exhibited significant, choice-related activity. Response modulation was also present following the remote sample, even though the information about its direction could only reach MT indirectly via top-down influences. However, unlike on trials with in-RF sample, these signals were dominated by response suppression, shedding light on the contribution of top-down influences to the comparison effects. These results demonstrate that during the task requiring monkeys to compare two directions of motion, MT responses during the comparison phase of this task reflect similarities and differences between the two stimuli, suggesting participation in sensory comparisons. The nature of these signals provides insights into the operation of bottom-up and top-down influences involved in this process.
Original languageEnglish
Pages (from-to)1260 - 1273
Number of pages14
JournalJournal of Neurophysiology
Volume106
Issue number3
DOIs
Publication statusPublished - 2011

Cite this