Saccadic suppression during voluntary versus reactive saccades

Abstract

Saccades are fast eye movements that reorient gaze. They can be performed voluntarily-for example, when viewing a scene-but they can also be triggered in reaction to suddenly appearing targets. The generation of these voluntary and reactive saccades have been shown to involve partially different cortical pathways. However, saccades of either type confront the visual system with a major challenge from massive image motion on the retina. Despite the fact that the whole scene is swept across the retina, a saccade usually does not elicit a percept of motion. This saccadic omission has been linked to a transient decrease of visual sensitivity during the eye movement, a phenomenon called saccadic suppression. A passive origin of saccadic suppression based on temporal masking has been proposed as well as an active central process that inhibits visual processing during the saccade. The latter one would need to include an extraretinal signal, which is generated already during saccade preparation. Since saccade generation differs for voluntary and reactive saccades, timing and nature of this extraretinal signal as well as its impact on visual sensitivity might also differ. We measured detection thresholds for luminance stimuli that were flashed during voluntary and reactive saccades and during fixation. Detection thresholds were higher during voluntary than during reactive saccades such that suppression appeared stronger during voluntary saccades. Stronger suppression in voluntary saccades could arise from a stronger extraretinal signal that activates suppression or could indicate that a suppression underlying process itself partially differs between voluntary and reactive saccades.

Foveal vision at the time of microsaccades

“…Two notable exceptions that specifically focused on foveal vision reached opposite conclusions 34,35 , with the latter reporting lack of suppression during microsaccades. The reduced sensitivity measured in our experiments may help reconcile these previous findings, particularly in the light that-at least for larger movements 54 -suppression tends to be further attenuated for involuntary saccades. Importantly, no previous study has mapped the peri-saccadic time-course of sensitivity across the fovea, primarily because of the technical challenges inherent in the required spatiotemporal precision of retinal stimulation.…”

Perceptual saccadic suppression starts in the retina

“…Despite the robustness of saccadic suppression as a perceptual phenomenon, the mechanisms behind it remain highly controversial. On the one hand, perceptual saccadic suppression may arise through internal knowledge of planned eye movements and their associated motor commands 5, 12, 16–19 . According to this popular view, internal knowledge of eye movement commands is a necessary prerequisite for saccadic suppression: a movement-related signal 17, 18 , such as corollary discharge from (pre-)motor areas, may act as a suppressive command for visual neurons to cause perceptual suppression, and maybe even in a pathway-selective manner 10 .…”

Dependence of perceptual saccadic suppression on peri-saccadic image flow properties and luminance contrast polarity

“…This phenomenon was labeled saccadic suppression (Zuber & Stark, 1966), and it has attracted investigation by vision scientists for many decades (Binda & Morrone, 2018; Castet, Jeanjean, & Masson, 2001; Castet & Masson, 2000; Matin, 1974; Schweitzer & Rolfs, 2020; Wurtz, 2008). Saccadic suppression is robust, and it occurs for both reflexive and deliberate saccades (Gremmler & Lappe, 2017). It also seems to occur for saccades of all sizes, including microsaccades (Beeler, 1967; Chen & Hafed, 2017; Hafed & Krauzlis, 2010; Zuber & Stark, 1966), and it even acts to shape the long term dynamics of visual sensitivity well after the eye movements (J.…”