Adaptation of the visual vertical during prolonged body tilt varies with susceptibility to motion sickness.

Judgments of the visual vertical, made without a visual reference frame-work, from a tilted-body position, result in systematic constant errors (Aubert effects). Pitblado and Mirabile (1977) showed that these errors vary with motion-sickness susceptibility, persons of intermediate susceptibility showing the greatest error. Recent exploratory work suggested patterns of progressive intra-session change in Aubert effects which might further differentiate groups of differing susceptibility. The raw data for Pitblado and Mirabile's 1977 study were reanalyzed for possible progressive change. This new analysis showed significant progressive reductions in Aubert effects for groups originally high and low, but a nearly significant increase in the intermediate group. New implications concerning group differences in vestibular function are discussed.

Cerebral asymmetries in random-dot stereopsis: reversal of direction with changes in dot size.

Visual field differences in stereoscopic form recognition using Julesz-type random dot stereograms were investigated. Dot size was varied in order to test the possibility that variations in the carrier dimension have contributed to past estimates of visual field differences. Twelve male and twelve female subjects, all right-handed, appeared for three test sessions-one with each different dot size. In each session the stimuli were flashed twenty-four times in each visual field, for 120 ms. Results showed no overall visual field effect, but a highly significant interaction between visual field and dot size. For small dots, left visual field superiority was observed, as previously reported by Durnford and Kimura. With large dots, however, the right visual field was superior. This reversal of visual field differences as a function of dot size implies that there is no consistent cerebral hemispheric specialization for stereopsis or stereoscopic form recognition per se. Instead, it appears that there is relative hemispheric specialization for responding to the carrier of stereoscopic information.