Control and Functions of Fixational Eye Movements

Abstract

Humans and other species explore a visual scene by rapidly shifting their gaze 2-3 times every second. Although the eyes may appear immobile in the brief intervals in between saccades, microscopic (fixational) eye movements are always present, even when attending to a single point. These movements occur during the very periods in which visual information is acquired and processed and their functions have long been debated. Recent technical advances in controlling retinal stimulation during normal oculomotor activity have shed new light on the visual contributions of fixational eye movements and their degree of control. The emerging body of evidence, reviewed in this article, indicates that fixational eye movements are important components of the strategy by which the visual system processes fine spatial details, enabling both precise positioning of the stimulus on the retina and encoding of spatial information into the joint space-time domain.

Consequences of the Oculomotor Cycle for the Dynamics of Perception

“…Every few hundreds of milliseconds, saccades rapidly shift gaze toward new regions of interest [7]—sometimes even by very small amounts (microsaccades) [8,9]—enabling examination of interesting stimuli with the foveola, the retinal region with highest acuity. In the “fixation” periods in between saccades, the eyes jitter incessantly following seemingly erratic trajectories which resemble Brownian motion [10,11], a behavior often termed ocular drift [12]. Although not always considered in studies of visual functions, eye movements are always present and, thus, intertwined with the neural processing stages that encode visual information.…”

Eye movements between saccades: Measuring ocular drift and tremor

“…This approach models ocular drift as uniform linear motion and neglects its curvilinear component, resulting in a serious underestimation of its instantaneous velocity. More recent work has reported the mean instantaneous speed of ocular drift to be approximately 50′/s (Cherici et al, 2012; Rucci and Poletti, 2015). …”

Ground-based hyperspectral analysis of the urban nightscape

“…One of them is the presence in all physiologically normal eyes of several kind of optical aberrations that contribute to enlarge the eye's optical point spread function to typical sizes of order several minutes of arc (Navarro et al, 1998). The other are the fixational intesaccadic movements of the eye that continuously shift the retinal image over several adjacent photoreceptors, and whose faster component (40-100 Hz), also kown as tremor, has typical amplitudes in the range of 1 minute of arc (Rucci and Poletti, 2015). Each individual foveal photoreceptor is then illuminated during its integration time by light coming from angular regions of the space slightly wider than what would be expected from the nominal visual acuity figure.…”