Abstract: The accuracy of perception of postural vertical (0°) and body tilts (15°)、30°、45°、60°、75°and 90° right or left to the body) was investigated under fourperceptual conditions by means of a tilting chair. It was found that when thesubjects set their body to tbe vertical without the aid of vision in a dark room,an average error of 1.6°to the true vertical was produced. When subjects settheir body under normal circumstances in the illuminated room and could getthe aid of visual information, tbe accuracy of judgments increased, the averageerror is 0.8° not more than one degree to the true vertical.The results show that there was a significant difference between thesevarious perceptual conditions made in the dark. The "Verbal-Body" conditionproduced larger errors than the other conditions, and the subjects in the "Vi-sion-Body" condition obtained a little error reduction. The most accurate con-dition of judgments of body positiou was found in "Body-Body" condition. How-ever, in all of these conditions, the subjects made underestimations. We sug-gested that the accuracy of perception of body position was affected remar-kably by the perceptual modality and difficuty of information transmission inperceptual processes, the ipsemodal performance (the standard and the comp-arisons were perceived by the same modality) had more advantages in the in-formation transmission and in the information processing over the cross-modalperformance.

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