Figure 1.

Stimulus illustrations. A, Example random dot stereograms of the slanted discs used in the study rendered as red-cyan anaglyphs. The stimuli depict slants of −37.5° (left) and −52.5° (right) for a participant with an interpupilary spacing of 6.4 cm viewing from a distance of 65 cm. (Note, if viewing without glasses, there might be an apparent blurring of the slanted stimuli that varies with slant angle; this cue was not available when our participants viewed the stimuli in the scanner through spectral comb filters). B, Schematic of the changes that accompany a physical change of slant. C, Diagrams of the parametric slant variations in the three experimental conditions: Main: simulated rotation of a physical disc; Spatial control: projection height in the image plane was constant as slant was manipulated; Disparity control: the mean (unsigned) disparity was constant as slant was varied.