Simultaneous recordings of ocular microtremor and microsaccades with a piezoelectric sensor and a video-oculography system

Abstract

Our eyes are in continuous motion. Even when we attempt to fix our gaze, we produce so called “fixational eye movements”, which include microsaccades, drift, and ocular microtremor (OMT). Microsaccades, the largest and fastest type of fixational eye movement, shift the retinal image from several dozen to several hundred photoreceptors and have equivalent physical characteristics to saccades, only on a smaller scale (Martinez-Conde, Otero-Millan & Macknik, 2013). OMT occurs simultaneously with drift and is the smallest of the fixational eye movements (∼1 photoreceptor width, >0.5 arcmin), with dominant frequencies ranging from 70 Hz to 103 Hz (Martinez-Conde, Macknik & Hubel, 2004). Due to OMT’s small amplitude and high frequency, the most accurate and stringent way to record it is the piezoelectric transduction method. Thus, OMT studies are far rarer than those focusing on microsaccades or drift. Here we conducted simultaneous recordings of OMT and microsaccades with a piezoelectric device and a commercial infrared video tracking system. We set out to determine whether OMT could help to restore perceptually faded targets during attempted fixation, and we also wondered whether the piezoelectric sensor could affect the characteristics of microsaccades. Our results showed that microsaccades, but not OMT, counteracted perceptual fading. We moreover found that the piezoelectric sensor affected microsaccades in a complex way, and that the oculomotor system adjusted to the stress brought on by the sensor by adjusting the magnitudes of microsaccades.

Experimental tests of hypotheses for microsaccade generation

“…The oscillations seen during eyelid closure were not ocular tremor, the smallest of fixational eye movements that occur simultaneously with drifts (∼1 photoreceptor width, >0.5 arcmin, and dominant frequencies between 70 and 103 Hz) (Martinez-Conde et al 2004). Due to their small amplitude and high frequency, piezoelectric transduction technique is the only effective way to record ocular tremor (McCamy et al 2013).…”

“…Search coil technique allowed us to measure saccadic oscillations during eyelid closure, but it was not sensitive to measure physiological ocular tremor with much high frequency (McCamy et al 2013). All subjects had saccadic oscillations under actively closed eyelids.…”

Saccadic Eye Movement Metrics Reflect Surgical Residents' Fatigue

“…48,49 Saccades were identified with a modified version of the algorithm developed by Engbert and Kliegl 47,50-53 with λ = 6 (threshold used for saccade detection) and a minimum saccadic duration of 6 ms. To reduce the amount of potential noise, we considered only binocular saccades, that is, saccades with a minimum overlap of one data sample in both eyes. [50][51][52][53][54] Additionally, we imposed a minimum intersaccadic interval of 20 ms so that potential overshoot corrections might not be categorized as new saccades. 55 .…”

Highly Informative Natural Scene Regions Increase Microsaccade Production during Visual Scanning

“…Likewise, many microsaccade functions have been proposed, such as keeping the currently fixated region centered on the optimal locus (Cornsweet, 1956;Nachmias, 1961;Boyce, 1967;St.St Cyr and Fender, 1969;Engbert and Kliegl, 2004;Putnam et al, 2005;McCamy et al, 2013b) , and blank scene (D) conditions. We averaged across images for each subject and subsequently across subjects.…”

“…First, the brain is too small to contain the anatomical machinery necessary to process information at all retinal eccentricities with as high resolution as in the fovea (McCamy et al, 2014). Instead, saccades-interleaved with fixation periodsorient the fovea to sequential visual regions for high acuity processing.…”