A. Example stimuli for the object condition. Object stimuli consisted of grayscale images taken from a bank of standard, non-social images (e.g. a baseball and a broccoli). Each image (average height: 2.31°, width: 2.79°) was presented on a coloured square (width: 3.5°). A black circle surrounded the tinted squares (radius: 4.95°) and a black fixation cross was set in the centre of the circle to provide vergence cues. On each trial, one eye viewed a red square, and one eye viewed a green square. B. Example stimuli for the grating condition. Grating stimuli consisted of sinusoidal luminance gratings (spatial frequency: 3 cycles/degree; Michelson contrast: 60%), displayed in a circular aperture (diameter: 3.5°). A black box surrounded the gratings (width: 4.95°) and a fixation cross was set in the centre of the box to provide vergence cues. On each trial, one eye viewed gratings tilted +45 degrees, and the other −45 degrees.