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.

Adaptation to prismatic displacement by schizophrenics and normals.

A sample of schizophrenic inpatients and a control sample of normal volunteers, matched for age and sex were tested on two tasks before and after an exposure condition in which they pointed repeatedly to a target while viewing their hands and the target through prisms. Both groups showed significant changes in both tasks--judging the straight-ahead, and pointing to a single target without sight of the hands. The groups did not differ from each other in the amount of changes in straight-ahead judgments, but normals showed greater adaptive change in the pointing task. These results contradict earlier reports that schizophrenics fail to adapt to altered visual-proprioceptive inputs; but they also help distinguish between modes of proprioceptive utilization that do and do not differentiate schizophrenics from normals.

Visual-field asymmetries in letter recognition: evidence for asymmetry in early visual registration.

Two experiments on visual-field differences in tachistoscopic letter recognition are described. In the first, a bright pre-exposure field with a black fixation point was used, and the conventionally expected dominance of the right visual field was found. However, a large number of "blank" trials were observed, in which subjects completely failed to detect the presence of the flashed target. These "blanks" were themselves significantly asymmetric between visual fields, suggesting that asymmetry in early stimulus registration may play an unsuspected role in typical measures of cerebral asymmetry in recognition accuracy. This was confirmed in a second experiment in which use of dark pre-exposure fields eliminated "blanks" and led to higher over-all accuracy, with no visual-field differences. Implications for interpretation of laterality data with normal subjects 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.

Orientation bias in the Rod-and-Frame Test.

Rod-and-frame data for a sample of 21 males and 25 females showed marked asymmetries in the magnitudes of the frame effects for left and right frame-tilt. These asymmetries are interpreted as an underlying tendency for individuals to set the rod systematically clockwise or counterclockwise of true vertical, independently of the influence of the visible frame, and the term "orientation bias" is used to describe this tendency. 14 males and 14 females demonstrated orientation biases significantly different from zero. In group comparisons males differed significantly from females, the mean bias for males as a group lying significantly left (counterclockwise) of vertical while the mean for females as a group did not differ from zero. Implications for conventional measures of field dependence are discussed. Possible diagnostic significance of orientation performance for brain injury is also considered, and an unusual individual performance is described.

Susceptibility to motion sickness and ego closeness, ego distance as measured by the autokinetic response tendency.

This paper reports results from one phase in an ongoing study of the relationship between vestibular function and various aspects of personality, cognitive style and symptom formation in mental illness. In the experiment reported here a measure of autokinesis was shown to relate to motion sickness experience as judged by actual stimulation in a rotating chair. Low and intermediate sensitive subjects showed less autokinesis than the most motion sick individuals (two-way analysis of variance F = 5.735, P = 0.006). Males in this sample showed a significantly greater autokinetic tendency than females (two-way analysis of variance F = 6.995, P = 0.011).