Microsaccade generation requires a foveal anchor.

Jorge Otero-Millan,Susana Martinez-Conde,Rachel E Langston,Stephen L Macknik,Francisco Costela

doi:10.16910/jemr.12.6.14

Abstract

Visual scene characteristics can affect various aspects of saccade and microsaccade dynamics. For example, blank visual scenes are known to elicit diminished saccade and microsaccade production, compared to natural scenes. Similarly, microsaccades are less frequent in the dark. Yet, the extent to which foveal versus peripheral visual information contribute to microsaccade production remains unclear: because microsaccade directions are biased towards covert attention locations, it follows that peripheral visual stimulation could suffice to produce regular microsaccade dynamics, even without foveal stimulation being present. Here we determined the characteristics of microsaccades as a function of foveal and/or peripheral visual stimulation, while human subjects conducted four types of oculomotor tasks (fixation, free viewing, guided viewing and passive viewing). Foveal information was either available, or made unavailable, by the presentation of simulated scotomas. We found foveal stimulation to be critical for microsaccade production, and peripheral stimulation, by itself, to be insufficient to yield normal microsaccades. In each oculomotor task, microsaccade production decreased when scotomas blocked foveal stimulation. Across comparable foveal stimulation conditions, the type of peripheral stimulation (static versus dynamic) moreover affected microsaccade production, with dynamic backgrounds resulting in lower microsaccadic rates than static backgrounds. These results indicate that a foveal visual anchor is necessary for normal microsaccade generation. Whereas peripheral visual stimulation, on its own, does not suffice for normal microsaccade production, it can nevertheless modulate microsaccadic characteristics. These findings extend our current understanding of the links between visual input and ocular motor control, and may therefore help improve the diagnosis and treatment of ophthalmic conditions that degrade central vision, such as age-related macular degeneration.

Highlights

Attempts to fasten one’s gaze to a target—either during sustained fixation of a small visual feature, or while scanning large scenes—are known to result in microsaccade production
We found foveal stimulation to be critical for microsaccade production, and peripheral stimulation, by itself, to be insufficient to yield normal microsaccades
We found that microsaccade production was reduced in the absence of foveal stimulation in every type of viewing task, supporting the proposal that microsaccades require the presence of a “target to anchor to” (Jorge Otero-Millan et al, 2008)

Summary

Introduction

Attempts to fasten one’s gaze to a target—either during sustained fixation of a small visual feature, or while scanning large scenes—are known to result in microsaccade production. Microsaccades are jerk-like movements of comparable characteristics to those of larger saccades, and one of three types of fixational eye movements (FEMS), which comprise intersaccadic drift and tremor Whereas the body of research on drift and tremor has been steadily growing, most FEM investigations to date have focused on microsaccades. A main reason has been that microsaccades’ relative larger sizes and speeds allow for their easier measurement and objective characterization via commercial eye trackers and standard detection algorithms Otero-Millan et al, 2014) A main reason has been that microsaccades’ relative larger sizes and speeds allow for their easier measurement and objective characterization via commercial eye trackers and standard detection algorithms (Bellet et al, 2018; Engbert & Kliegl, 2003; Mihali et al, 2017; J. Otero-Millan et al, 2014)

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Discussion

Conclusion