Microsaccades: Small steps on a long way

Abstract

Contrary to common wisdom, fixations are a dynamically rich behavior, composed of continual, miniature eye movements, of which microsaccades are the most salient component. Over the last few years, interest in these small movements has risen dramatically, driven by both neurophysiological and psychophysical results and by advances in techniques, analysis, and modeling of eye movements. The field has a long history but a significant portion of the earlier work has gone missing in the current literature, in part, as a result of the collapse of the field in the 1980s that followed a series of discouraging results. The present review compiles 60 years of work demonstrating the unique contribution of microsaccades to visual and oculomotor function. Specifically, the review covers the contribution of microsaccades to (1) the control of fixation position, (2) the reduction of perceptual fading and the continuity of perception, (3) the generation of synchronized visual transients, (4) visual acuity, (5) scanning of small spatial regions, (6) shifts of spatial attention, (7) resolving perceptual ambiguities in the face of multistable perception, as well as several other functions. The accumulated evidence demonstrates that microsaccades serve both perceptual and oculomotor goals and although in some cases their contribution is neither necessary nor unique, microsaccades are a malleable tool conveniently employed by the visual system.

Distinctive features of microsaccades in Alzheimer’s disease and in mild cognitive impairment

“…We found no abnormalities in microsaccade dynamics that are more directly related to the function of the brainstem saccade generator (Leigh and Zee 2006;Rolfs 2009;Otero-Millan et al 2011a), such as duration, intersaccadic intervals, peak velocity, and the peak duration-magnitude relationship (Fig. 4, Table 1).…”

“…Microsaccades can provide information on brain function and related oculomotor circuits, as well as on cognition and attention resources (Martinez-Conde et al 2009;Rolfs 2009). Here, we examined potential distinctive features of microsaccades in AD patients, aMCI patients, and healthy controls in relation with cognitive function.…”

An oculomotor continuum from exploration to fixation

“…Saccades occur at an approximate rate of three per second during exploration, whereas microsaccades occur about once a second during fixation (5,8,17). This difference, unexplained by current models of visual and oculomotor function, is in conflict with the physiological and behavioral evidence supporting a common generator for saccades and microsaccades (8-10, 12, 18), and reinforces the traditional view that exploration and fixation are two distinct oculomotor behaviors (3,7).…”

“…free-viewing | fixational eye movements | miniature eye movements | fixational saccades | natural images C lassic and current vision studies distinguish between visual exploration, characterized by the alternation of saccades and brief fixation periods, and attempted visual fixation, where subjects maintain relative gaze stability despite continuous but minute fixational eye movements (i.e., microsaccades, slow drift, and oculomotor tremor) (1)(2)(3)(4)(5)(6)(7). The theoretical separation between exploratory gaze shifts and attempted fixation dates back to the discovery of fixational eye movements in the early 1900s (2)(3)(4), and remains central to contemporary discourse in visual, cognitive, and oculomotor research (8).…”

Microsaccades Are Coupled to Heartbeat

“…Research on FEM strongly focuses on their underlying generating mechanisms and their possible function for visual processing (for reviews, see Rolfs, 2009;Hafed, 2011;Martinez-Conde et al, 2013).…”