The Geometry of Perisaccadic Visual Perception

Abstract

Our ability to explore our surroundings requires a combination of high-resolution vision and frequent rotations of the visual axis toward objects of interest. Such gaze shifts are themselves a source of powerful retinal stimulation, and so the visual system appears to have evolved mechanisms to maintain perceptual stability during movements of the eyes in space. The mechanisms underlying this perceptual stability can be probed in the laboratory by briefly presenting a stimulus around the time of a saccadic eye movement and asking subjects to report its position. Under such conditions, there is a systematic misperception of the probes toward the saccade end point. This perisaccadic compression of visual space has been the subject of much research, but few studies have attempted to relate it to specific brain mechanisms. Here, we show that the magnitude of perceptual compression for a wide variety of probe stimuli and saccade amplitudes is quantitatively predicted by a simple heuristic model based on the geometry of retinotopic representations in the primate brain. Specifically, we propose that perisaccadic compression is determined by the distance between the probe and saccade end point on a map that has a logarithmic representation of visual space, similar to those found in numerous cortical and subcortical visual structures. Under this assumption, the psychophysical data on perisaccadic compression can be appreciated intuitively by imagining that, around the time of a saccade, the brain confounds nearby oculomotor and sensory signals while attempting to localize the position of objects in visual space.

Computational models of spatial updating in peri-saccadic perception

“…By assuming a certain qualitative ratio of magnification along the rays and circles of constant eccentricity [103 -105], the model is able to explain not only the mislocalization of spatially extended bars (figure 3b), but also the asymmetric two-dimensional spatial pattern of compression (figure 3c). The notion of cortical magnification as a crucial property to model the observed mislocalization has recently also been demonstrated by Richard et al [101], who showed that the distance between stimulus and target in cortical space, as opposed to visual space, predicts the strength of the mislocalization. Because the visual responses of neurons in the spatial re-entry model are modulated by oculomotor feedback signals, the receptive fields in the model undergo dynamic changes before and during the saccade (figure 3d ).…”

The spatial pattern of peri-saccadic compression for small saccades

“…Kaiser and Lappe (2004) showed that the magnitude of the mislocalization increased with saccade amplitude when they flashed a dot at various positions around the onset of 12-to 24-saccades. This effect was recently replicated by Richard, Churan, Guitton, and Pack (2009) with 14-to 30-saccades but modulated by the flashed stimulus position.…”

“…However, this alternative does not seem to fit with the results of Morrone et al (1997) who found a clear compression pattern for 2.5-saccades when bars were flashed at a maximal distance of 3.75-. Richard et al (2009) systematically tested the influence of both saccade amplitude and bar position for saccades of 14-, 20-, and 30-and showed that the influence of saccade amplitude on compression strength could be modulated by bar position. More precisely, for 20-and 30-saccades, they showed different patterns of compression depending on whether the bar's absolute position (i.e., relative to fixation cross) or relative position (i.e., relative to saccade target) was held constant.…”

Interaction of spatial and temporal factors in psychophysical estimates of surround suppression

“…From these considerations it follows that brief pulses of wide-field motion are processed by neurons in the visual system tens of thousands of times per day. Previous work has provided support for the existence of specialized mechanisms that suppress the perceptual effects of such motion stimuli (Murakami & Cavanagh, 1998), and we have recently begun investigating these mechanisms with stimuli similar to those used in the current experiments (Richard, Churan, Guitton, & Pack, 2007).…”