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

PeerJ. 2013 Feb 12:1:e14. doi: 10.7717/peerj.14. Print 2013.

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.

Keywords: Fading; Fixational eye movements; Neural adaptation; Saccadic adaptation; Tremor.

Grants and funding

This study was supported by the Barrow Neurological Foundation (awards to SLM and SM-C), the National Science Foundation (awards 0643306, 0852636 and 1153786 to SM-C, and award 0726113 to SLM), and the Department of Medical Physics and Bioengineering and the Mercer’s Institute for Research on Ageing in St. James’s Hospital Dublin (to DC) JO-M was a Fellow of the Pedro Barrié de la Maza Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.