Figure 1.

Schematic of the display, stimulus, and conditions. (A) Experimental design: Observers viewed a visual display through 3D shutter glasses. Stimuli depicted dots moving in depth through a cylindrical volume oriented perpendicular to the display. Observers reported the perceived motion direction (toward/away). (B) Visual stimulus: On each trial, a stimulus appeared in one aperture (e.g., the one outlined in red for illustration). Observers fixated a central target (a white dot). A 1/f noise background pattern facilitated stable version and vergence. (C) Cue conditions: On each trial, one of three cue conditions was presented. Binocular cue stimuli contained opposite horizontal motions in the two eyes. Monocular cue stimuli were optic flow patterns shown to one eye. Combined cue stimuli were optic flow patterns shown to both eyes, and thus contained both cues. (D) Temporal sequence: Stimuli were presented for 250 ms. After responding, there was an inter-trial interval of 750 ms. (E) Stimulus coherence: Stimuli were presented at five motion coherences (proportion of signal dots: 0.08, 0.25, 0.50, 0.75, and 1). Signal dots (depicted here as filled black dots) moved either toward or away from the observer. Noise dots (depicted here as open circles) moved to random locations, producing motion signals of random speed and direction. The number of dots, their sizes, and the depicted optic flow patterns used in the schematics were selected to convey the MID cues, rather than portray the actual stimuli. Example stimuli are shown in the Supplementary Movies.