Binocular Coordination: Reading Stereoscopic Sentences in Depth

Elizabeth R Schotter,Julie A Kirkby,Simon P Liversedge,Keith Rayner,Hazel I Blythe,Nicolas S Holliman

doi:10.1371/journal.pone.0035608

Elizabeth R Schotter, Julie A Kirkby + Show 4 more

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https://doi.org/10.1371/journal.pone.0035608

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Abstract

The present study employs a stereoscopic manipulation to present sentences in three dimensions to subjects as they read for comprehension. Subjects read sentences with (a) no depth cues, (b) a monocular depth cue that implied the sentence loomed out of the screen (i.e., increasing retinal size), (c) congruent monocular and binocular (retinal disparity) depth cues (i.e., both implied the sentence loomed out of the screen) and (d) incongruent monocular and binocular depth cues (i.e., the monocular cue implied the sentence loomed out of the screen and the binocular cue implied it receded behind the screen). Reading efficiency was mostly unaffected, suggesting that reading in three dimensions is similar to reading in two dimensions. Importantly, fixation disparity was driven by retinal disparity; fixations were significantly more crossed as readers progressed through the sentence in the congruent condition and significantly more uncrossed in the incongruent condition. We conclude that disparity depth cues are used on-line to drive binocular coordination during reading.

Highlights

While reading, our eyes make coordinated sideways movements to bring the part of the text into the fovea so that it may be processed with the highest resolution [1,2]
The question, is how effective is the eye movement system in coordinating the eyes to make both saccades and vergence movements concurrently to ensure that that reading can proceed normally? what information does the system utilize in order to do so?
This work is consistent with an earlier literature in which binocular coordination during fixations and saccades, and the complex interactions between the vergence and accommodation systems in response to depth cues, have been well-documented [11,12,13,14,15,16,17,18,19,20]

Summary

Introduction

Our eyes make coordinated sideways movements (saccades) to bring the part of the text into the fovea so that it may be processed with the highest resolution [1,2]. When we read such ‘‘looming’’ text, in addition to saccades, we must make vergence eye movements to accommodate changes in depth. The question, is how effective is the eye movement system in coordinating the eyes to make both saccades and vergence movements concurrently to ensure that that reading can proceed normally? It is quite clear that the eye movement system is able to deal with a certain amount of fixation disparity (offset between the locations of gaze of the two eyes) when reading, but what about disparity in more extreme circumstances?

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Conclusion