EFFECT OF GRAVITATIONAL CUES ON VISUAL-SEARCH FOR ORIENTATION

To determine whether nonvisual (vestibular and somatosensory) informat ion participates in low-level orientation processing. subjects in diff erent postural conditions (upright, supine. and sitting immobilized) s earched for a target distinguishable from distractors by difference in orientation (A. Treisman's, 1985. ''pop-out'' paradigm). Searches for vertical and horizontal targets were dramatically modified as a funct ion of the postural position, indicating that the processing of orient ation in early vision is not only retinal but integrates information f rom the sensory graviceptors. This visuovestibular phenomenon is inter preted in the conceptual framework of D. H. Foster and P. A. Ward's (1 991 a) model based on local orthogonal orientation filters and T. A. S toffregen and G. E. Riccio's (1988) dynamics of balance theory.