Effects of background field-of-view and depth-plane on the oculogyral illusion

This study examined the effects of background field-of-view and depth plane on the oculogyral illusion. Seven subjects viewed a stationary fixation stimulus during the postrotatory interval following a 45-sec constant-velocity chair rotation. The duration of the illusory movement of the fixation stimulus during the postrotatory interval was measured, along with the duration of the illusion of whole-body rotation (known as the somatogyral illusion) and the duration of the subject's slow-phase vestibular nystagmus. Subjects viewed the fixation stimulus by itself in a No-background condition or when surrounded by six background fields formed by the combination of two fields-of-view (35 degrees and 115 degrees) and three depth-planes (near, coplanar, and far). The different background fields inhibited the oculogyral illusion relative to the No-background condition but did not differ statistically from each other. The somatogyral durations better matched the oculogyral ones than did nystagmus decay, especially when a background field was present. These results suggest that the oculogyral illusion is more related to the experience of whole-body rotation than to oculomotor mechanisms and that the inhibitory effect of a background scene is only modestly affected by its field-of-view and depth plane.