Postsaccadic target blanking prevents saccadic suppression of image displacement

Abstract

Displacement of a visual target during a saccadic eye movement is normally detected only at a high threshold, implying that high-quality information about target position is not stored in the nervous system across the saccade. We show that blanking the target for 50-300 msec after a saccade restores sensitivity to the displacement. With blanking, subjects reliably detect displacements as small as 0.33 deg across 6 deg eye movements, with correspondingly steep psychophysical functions. Performance with blanking in a fixation control is inferior, evidence for a saccadic enhancement of sensitivity to image displacement. If blanking is delayed so that the target is visible immediately after the saccade in its displaced position, performance declines to non-blanking levels. Blanking the target before the saccade, and restoring it during the saccade, yields a similar but weaker effect. We interpret these results with a model in which the visual system searches for the postsaccadic goal target within a restricted spatiotemporal window. If it is not found, the assumption of stationarity of the world is broken and the system makes use of other information such as extraretinal signals for calibrating location.

Computational models of spatial updating in peri-saccadic perception

“…This phenomenon is termed 'saccadic suppression of displacement'. A poor transsaccadic transfer of location information does not explain the failure to perceive the displacement, since the displacement is easily detected in the so-called post-saccadic blanking paradigm [30]. In this version of the task, the saccade target disappears after saccade onset and reappears at its displaced position 200 ms after saccade end.…”

“…The reference object theory offers a direct explanation for the saccadic suppression of image displacement because it contains a spatio-temporal window around the saccade target in which displacements of the target are tolerated without noticing any instability [30]. The theory moreover explains the paradoxic target blanking effect in which displacements become apparent when the target is blanked after the saccade: because the target could not be found after the saccade, the assumption of stability is broken, and displacements become visible [30].…”

“…Thus, the displacement must rather be detected by comparing the pre-saccadic with the post-saccadic stimulus location. Unlike during fixation, a small displacement of a target stimulus during a saccade is often not noticed after the eye movement [29,30]. In such experiments, a target stimulus that is initially fixated jumps to a new location, and subjects have to follow the jump with a saccade.…”

“…The object reference theory [30,71] suggests an approach that avoids the need for any extraretinal signal. It rather suggests a trans-saccadic memory of reference stimuli, which will be used after saccade to align the pre-saccadic view to the post-saccadic one.…”

“…(a) Object reference theory The object reference theory [30] and the saccade target theory [31,72] rely on visual information for space constancy and ascribe a particular role to the saccade target. They suggest that most of the visual information before the saccade is discarded, and that a new representation of the visual world is generated from new incoming information after the saccade [73].…”