Head orientation relative to gravity modulates perceptual reversals and the first percept on the Schröder staircase: a four-orientation study with a stationary display.

Resolving an ambiguous perspective figure depends on internal references built from visual, vestibular, and proprioceptive cues and, for depicted objects, on their relation to the observer's body. Discrete head orientations between up-right and inverted have rarely been compared on the same perspective stimulus. This study tested whether the orientation of the head modulates the rate of perceptual reversals and the identity of the first percept while the stimulus on the screen remained fixed. Sixty-four adults (Mage = 21.45, SD = 2.30; 34 women) viewed the Schröder staircase on a stationary monitor for 12 s in four head orientations-up-right, 45° left, 45° right, and up-side-down-in one of two alternating orders; the figure's 180° symmetry made the up-right and inverted retinal images nominally identical. Reversal rate decreased with head tilt: up-right (M = 5.59) > 45° left (M = 4.08) > 45° right (M = 3.39) ≥ up-side-down (M = 3.05); F(3, 189) = 61.15, p < .001, η2p = .49; the 45° right and up-side-down conditions did not differ reliably. The first percept also reorganized: the normal staircase emerged first in 100% of up-right reports, the inverted staircase in 68.75% of up-side-down reports. Head orientation thus modulated both the speed of perceptual updating and the first percept. Because the visual surround and ocular torsion were not controlled, the effect is attributed to head orientation relative to gravity and the visual environment, consistent with a body-referenced account in which multisensory re-weighting and the interpretation of the depicted object may operate together.