Pre-saccadic neural enhancements in marmoset area MT mimic covert attention

Abstract

Each time we make an eye movement, attention moves before the eyes, resulting in a perceptual enhancement at the target. Recent psychophysical studies suggest that this pre-saccadic attention enhances the visual features at the saccade target, whereas covert attention causes only spatially-selective enhancements. While previous non-human primate studies have found that pre-saccadic attention does enhance neural responses spatially, no studies have tested if changes in neural tuning reflects an automatic feature enhancement. Here we examined pre-saccadic attention using a saccade foraging task developed for marmoset monkeys. We recorded from neurons in the middle temporal (MT) area with peripheral receptive fields that contained a motion stimulus which would either be the target of a saccade or a distracter as a saccade was made to another location. We established that marmosets, like macaques, show enhanced pre-saccadic neural responses for saccades towards the receptive field, including increases in firing rate and motion information. We then examined if the specific changes in neural tuning might support feature enhancements for the target. Neurons exhibited diverse changes in tuning, but predominantly showed additive and multiplicative increases that were uniformly applied across motion directions. These findings confirm that marmoset monkeys, like macaques, exhibit pre-saccadic neural enhancements during saccade foraging tasks with minimal training requirements. However, at the level of individual neurons, the lack of feature-tuned enhancements is similar to neural effects reported during covert spatial attention. Significance StatementAttention leads eye movements producing perceptual enhancements at saccade targets. Recent psychophysical studies indicate that increases in pre-saccadic sensitivity are concentrated around features of the target. We tested at the neural level how pre-saccadic attention modulates the tuning curves of visual neurons in area MT of marmoset monkeys. While neurons exhibited clear pre-saccadic enhancements that were consistent with previous studies in macaques, the changes in tuning were uniform across tuning. These results show pre-saccadic enhancements are a general feature of visual processing, shared by New World monkeys, but at the level of individual neurons enhancements are uniform across features much like what has been reported previously for covert attention.