Perceived tilt and translation during variable-radius swing motion with congruent or conflicting visual and vestibular cues

We examined the influence of dynamic visual scenes on the motion perception of subjects undergoing sinusoidal (0.45 Hz) roll swing motion at different radii. The visual scenes were presented on a flatscreen monitor with a monocular 40° field of view. There were three categories of trials: (1) trials in the dark; (2) trials where the visual scene matched the actual motion; and (3) trials where the visual scene showed swing motion at a different radius. Subjects verbally reported perceptions of head tilt and translation. When the visual and vestibular cues differed, subjects reported perceptions that were geometrically consistent with a radius between the radii of the visual scene and the actual motion. Even when sensations did not match either the visual or vestibular stimuli, reported motion perceptions were consistent with swing motions combining elements of each. Subjects were generally unable to detect cue conflicts or judge their own visual–vestibular biases, which suggests that the visual and vestibular self-motion cues are not independently accessible.