Modelling the effect of microsaccades on retinal responses to stationary contrast patterns

Abstract

We have modelled the effect of microsaccades on retinal responses to achromatic borders and lines using physiologically realistic parameters. Typical microsaccade movement sequences were applied to the retinal image of stationary spatial contrast patterns as projected on the foveal cone mosaic after being passed through the optical transfer function of the eye. The resulting temporal contrast modulation over a cone receptive field was convolved with an analytical expression for the response waveform of primate cones (photocurrent: [Schnapf, J. L., Nunn, B. J., Meister, M. & Baylor, D. A. (1990). Visual transduction in cones of the monkey Macaca fascicularis. Journal of Physiology, 427, 681-713]; photovoltage: [Schneeweis, D. M. & Schnapf, J. L. (1999). The photovoltage of macaque cone photoreceptors: Adaptation, noise, and kinetics. Journal of Neuroscience, 19, 1203-1216]). The input to the ganglion cell was derived from the cone responses by the difference-of-Gaussians receptive field model of Donner and Hemilä [Donner, K. & Hemilä, S. (1996). Modelling the spatio-temporal modulation response of ganglion cells with difference-of-Gaussians receptive fields: Relation to photoreceptor response kinetics. Visual Neuroscience, 13, 173-186]. The modelled response waveforms suggest that microsaccades may significantly enhance sensitivity to edges, "re-sharpen" the image and, most interestingly, improve resolution of two closely spaced lines. The reason is that fine spatial structure of the retinal image when moving at suitable velocities is translated into a correlated temporal structure of responses of single cones and ganglion cells. The information content of the signal is not strongly dependent on positional accuracy and the effect is thus distinct from the presumed retinal basis of vernier acuity. Other eye movements (drift) with velocity distributions similar to that of the microsaccade's slow return phase might be similarly useful, although the microsaccade has some distinguishing features that could be functionally significant, e.g., the neural motor control and the biphasic movement pattern.

Microsaccades: a neurophysiological analysis

“…Bursty firing effectively indicates the presence of previous microsaccades in the awake fixating primate, suggesting that this type of neural activity might be highly conducive to sustaining a visible image during fixation [5,17,44]. In agreement with this idea, recent research has shown that microsaccades counteract perceptual fading during fixation [6,7] and might lead to more efficient sampling of spatial detail [47]. Furthermore, the suppression of transient bursts of activity has been related to perceptual suppression during blinks [98] and to decreased target visibility in visual masking paradigms [99][100][101].…”

“…That is, microsaccades primarily generate neural responses by displacing the receptive fields (RFs) of visual neurons over otherwise stationary stimuli [5,17,44,45] or even moving stimuli [46], as discussed below and reviewed elsewhere [4,17]. Donner and Hemilä [47] modeled the effects of microsaccades on the responses of primate retinal neurons using physiologically realistic parameters. The results suggested that microsaccades might significantly enhance sensitivity to edges, re-sharpen the image and improve spatial resolution.…”

An oculomotor continuum from exploration to fixation

“…Saccadic eye movements are known to play multiple roles in vision-that is, they foveate high-interest targets, correct gaze errors, and search and integrate general information about the environment to stitch together the perception of a scene (7,35). Likewise, many microsaccade functions have been proposed (31), including the prevention of visual fading and the restoration of faded visual targets (36)(37)(38), the control of fixation position (3,39), and improved visual performance in high-acuity tasks (24,40). Our results point to a similarity in function for microsaccades and saccades, and suggest that all of the saccadic roles may be common to microsaccades, including the scanning and exploration of visual objects and scenes traditionally ascribed to (large) saccades.…”

Microsaccadic modulation of response times in spatial attention tasks

“…These occur up to several times per second and are very fast movements with saccade-like properties but with amplitudes of less than one degree. Microsaccades may result in robust changes in visual perception (e.g., Clowes, 1962;Ditchburn, 1955;Donner & Hemilä, 2007;Laubrock, Engbert, & Kliegl, 2008;Martinez-Conde, Macknik, Troncoso, & Dyar, 2006;Rattle & Foley-Fisher, 1968;Zuber & Stark, 1966), and their orientation is reliably correlated with the direction of spatial attention shifts.…”