Pre-saccadic neural enhancements in marmoset area MT

Abstract

Each time we make a saccadic eye movement, attention moves before the eyes, resulting in a perceptual enhancement at the target of the movement (Kowler et al., 1995; Deubel & Schneider, 1996; Rolfs & Carrasco, 2012). Recent psychophysical studies suggest that this pre- saccadic attention may differ in important ways from covert attention when no eye movement is made (Li, Pan, & Carrasco, 2021a,b). One difference is that pre-saccadic attention involves an automatic enhancement concentrated around the features of the saccade target, such as its orientation, whereas spatial attention in covert attention enhances stimulus features uniformly (Li et al., 2016; Ohl et al., 2017). While previous neurophysiological studies have found that pre- saccadic attention enhances neural responses (Moore et al., 1998; Li & Basso, 2008; Moore & Chang, 2009; Steinmetz & Moore 2010; Merrikhi et al., 2021), no studies have tested for changes in tuning that would support a concentration of enhancement around target features. Here we examined pre-saccadic attention using a saccade foraging task developed for marmoset monkeys. We first establish that the marmoset monkey, like macaques, shows enhanced pre-saccadic neural responses in the middle temporal (MT) and middle temporal crescent (MTC) areas. To examine if changes in neural tuning might support feature enhancement, we fit an adjusted Von Mises function to the direction selective responses of neurons. Neurons exhibited diverse changes in tuning, but the predominant pattern was an additive and multiplicative increase in the tuning curve consistent with spatial gain. The changes in tuning predicted changes in neural sensitivity assessed by measures of mutual information with motion direction. Additive increases led to detriments in sensitivity while gain increases improved sensitivity. And although a subset of neurons did show a narrowing in tuning that could reflect feature-selection, there were equal number of neurons showing the opposite. Overall the modulation of neural responses during pre-saccadic attention appears highly consistent with previous studies of covert attention.