Fixational Eye Movement Correction of Blink-Induced Gaze Position Errors

Abstract

Our eyes move continuously. Even when we attempt to fix our gaze, we produce “fixational” eye movements including microsaccades, drift and tremor. The potential role of microsaccades versus drifts in the control of eye position has been debated for decades and remains in question today. Here we set out to determine the corrective functions of microsaccades and drifts on gaze-position errors due to blinks in non-human primates (Macaca mulatta) and humans. Our results show that blinks contribute to the instability of gaze during fixation, and that microsaccades, but not drifts, correct fixation errors introduced by blinks. These findings provide new insights about eye position control during fixation, and indicate a more general role of microsaccades in fixation correction than thought previously.

Target Displacements during Eye Blinks Trigger Automatic Recalibration of Gaze Direction

“…This eye movement is not due to mechanical forces of the eyelid on the orbit, but due to an active neural signal [14,15]. Like every motor action, this eye movement is subject to noise [2,16]. Retinal position displacements introduced by blink-induced gaze shifts are generally not perceived as illusory object motion.…”

“…Microsaccades occurring after a blink have been shown to partially correct for blink-induced gaze instability [2], but the adaptive eye movement reported here is anticipatory and occurs during the blink. In a recent study, Khazali et al [16] showed that one function of blink-related eye movements is to reset the torsional position of the eye.…”

“…Like every motor action, these eye movements are subject to noise and introduce instabilities in gaze direction across blinks [2]. Accumulating errors across repeated blinks would be debilitating for visual performance.…”

Variability of Ocular Deviation in Strabismus

“…25,26 Over a longer time scale, slow drifts, oscillatory eye movements, vergence efforts, and blink-induced position errors come into play. 2,27 Saccades are also a major source of variability in ocular deviation because the act of making a saccade contributes to disconjugacy and position drift (Figure 5). Saccadic disconjugacy has been documented previously in humans and monkeys.…”

Micro and regular saccades across the lifespan during a visual search of “Where’s Waldo” puzzles

“…Briefly, with each microsaccade, the retinal image of a stationary object is shifted to a new location, perhaps several dozen to several hundred photoreceptor widths away (Costela, McCamy, Macknik, Otero-Millan, & Martinez-Conde, 2013; Martinez-Conde, Macknik, Troncoso, & Dyar, 2006; Martinez-Conde, Macknik, Troncoso, & Hubel, 2009; McCamy, Macknik, & Martinez-Conde, 2014; McCamy et al, 2012; Troncoso, Macknik, & Martinez-Conde, 2008), causing the retinal image to land on an unstimulated region of photoreceptors and keeping the image ‘refreshed’. Microsaccades also appear to sharpen the perception of edges (Donner & Hemila, 2007), improve spatial resolution (Ko, Poletti, & Rucci, 2010), correct fixation errors related to eye blinks (Costela et al, 2014), enhance visibility for peripheral and parafoveal visual targets (Costela et al, 2013; Martinez-Conde et al, 2006; McCamy et al, 2012), and sample informative regions of natural scenes (McCamy, Macknik, & Martinez-Conde, 2014). Microsaccade dynamics may even offer insight into such states as the viewers attentional level (Engbert & Kliegl, 2003; Yuval-Greenberg, Merriam, & Heeger, 2014) and fatigue (Di Stasi et al, 2013), as well as indicating target detection and the cognitive demands of the task (Otero-Millan, Troncoso, Macknik, Serrano-Pedraza, & Martinez-Conde, 2008; Siegenthaler et al, 2014).…”