The significance of microsaccades for vision and oculomotor control

Abstract

Over the past decade several research groups have taken a renewed interest in the special role of a type of small eye movement, called ‘microsaccades’, in various visual processes, such as the activation of neurons in the central nervous system, or the prevention of image fading. As the study of microsaccades and their relation to visual processes goes back at least half a century, it seems appropriate to review the more recent reports in light of the history of research on maintained oculomotor fixation, in general, and on microsaccades in particular. Our review shows that there is no compelling evidence to support the view that microsaccades (or, fixation saccades more generally) serve a necessary role in improving oculomotor control or in keeping the visual world visible. The role of the retinal transients produced by small saccades during fixation needs to be evaluated in the context of both the brisk image motions present during active visual tasks performed by freely moving people, as well as the role of selective attention in modulating the strength of signals throughout the visual field.

The Visual Input to the Retina during Natural Head-Free Fixation

“…to 2.7 saccades/s for subject R.S. Whereas saccades were frequent, microsaccades-defined as saccades with amplitudes of Ͻ30 arcmin-were extremely rare, a result that is in line with previous reports of both head-free (Malinov et al, 2000) and head-fixed studies (Collewijn and Kowler, 2008;Kuang et al, 2012) Even in the absence of microsaccades, the eyes moved considerably during fixation because of ocular drift, the smooth motion always present in the intervals between saccades. In all subjects, ocular drift reached velocities of several degrees per second on both the horizontal and vertical axes, with averages Ͼ1°/s (Fig.…”

“…For example, the VOR gain varies with the distance of the fixation point (Paige, 1989;Schwarz and Miles, 1991;Crane and Demer, 1997;Paige et al, 1998;Wei and Angelaki, 2004). In addition, optical adaptation experiments found that subjects converge on their own idiosyncratic degree of compensation, even though, in doing this, they progressively modify the VOR gain so that the stimulus on the retina is stationary at some point during the course of adaptation (Collewijn et al, 1981). In keeping with these previous findings, our results strongly support the proposal that the function of ocular drift is the maintenance of a specific range of retinal image motion that facilitates the acquisition and processing of visual information.…”

“…N 1 and N 2 optical nodal points, T target, P target's projection on the retina. direction of gaze (Robinson, 1963;Collewijn et al, 1975). Amplitude estimation, however, gives precise measurements of eye rotations only with the head immobilized (Robinson, 1963;Houben et al, 2006); when the head is not restrained, lack of homogeneity in the magnetic fields causes measurement artifacts (Collewijn, 1977).…”

Normal Gain of VOR with Refixation Saccades in Patients with Unilateral Vestibulopathy

“…These microsaccades, also called fixational saccades, are rapid, jerky eye movements smaller than 15 minutes of arc, that follow the main sequence and, with a velocity <50º/s [15] . In the unrestrained head condition, as in our study, they are irrelevant but still occur [16] . Because of this, we decided to include some criteria to rule them out.…”

The functional asymmetry of ON and OFF channels in the perception of contrast

“…We proposed that either presaccadic suppression (Reppas et al 2002;Royal et al 2006) during the detection task or peri-microsaccadic enhancement (Collewijn and Kowler 2008;Martinez-Conde et al 2004, 2013 during the fixation task could explain this difference in sensitivity. In the current study, however, we did not observe any significant difference in LGN P ON or P OFF neural sensitivities between the two tasks.…”