Binocular coordination in response to two-dimensional, three-dimensional and stereoscopic visual stimuli.

PURPOSE: We were particularly interested in whether binocular coordination when viewing stereoscopic images would be more comparable to when viewing a 2D representation, or when viewing a real stimulus array in depth. METHODS: Data are reported from an experiment examining binocular coordination in response to stereoscopically presented stimuli. Movements of both eyes were recorded as participants viewed LED stimuli in a real scene with depth, a 2D image of the scene, and a stereoscopic image of the scene. RESULTS: When viewing real LEDs, vergence during saccades re-aligned the eyes in depth where necessary, with smaller adjustments during the following fixation. In contrast, when viewing the stereoscopic representation, vergence during saccades did not re-align the eyes in depth. The only effect of target depth on vergence occurred during the following fixation. CONCLUSIONS: We conclude that disparity in parafoveal objects, in isolation from other depth cues (and, minimally, conflicting with blur), was insufficient for the visual system to target saccades appropriately in depth.

Binocular coordination: reading stereoscopic sentences in depth.

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.