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Elizabeth Schotter, Hazel Blythe, Julie Kirkby, Keith Rayner, Simon Liversedge; Binocular coordination: Reading stereoscopic sentences in depth. Journal of Vision 2010;10(7):364. doi: 10.1167/10.7.364.
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When we fixate objects that are close to us our eyes make disconjugate convergent movements (e.g., they move nasally), and when we fixate objects that are distant, our eyes make disconjugate divergent movements (Kirkby et al. 2008). We investigated how readers controlled their eyes binocularly as they read sentences presented stereoscopically such that they appeared to loom out from the screen towards the reader. To address this question, we had subjects read sentences as we monitored the movements of each eye simultaneously. Sentences were presented in three conditions: 1) a size-constant 2D condition in which sentence depth and character size were constant throughout the sentence; 2) an increasing-size 2D condition in which sentence depth was constant, but character size increased from left to right (a monocular cue used to infer depth); 3) a 3D looming condition where character size increased from left to right AND the text was presented stereoscopically such that the perceived sentence started at the screen and loomed toward the subject at an angle of 55° from the plane of the screen. To create the looming stimuli, the stereoscopic sentences were such that a letter from the left eye stimulus was displaced to the left of the corresponding letter in the right eye stimulus.
We predicted that binocular disparity would remain constant in the 2D conditions (1&2), but the eyes would become more converged as they progressed through the sentence in the looming 3D condition (3) if readers processed the text as they would in a real depth condition. Our results showed increased divergence as readers read further in the sentence, indicating that binocular eye coordination is driven by each eye's unique retinal signal rather than by depth cues associated with sentences that appear to loom towards the reader.
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