Visual and Proprioceptive Changes during Visual Exposure to a Tilted Line

Abstract

The decrease in apparent tilt of a physically tilted line has been ascribed by Gibson a change in the visual modality ( 1 ) . Here such effects are ascribed change in a reference system for pc thus, changes will occur in both perceived orientation of the tilted visual object and of the longitudinal body axis. Accordingly, the main experimental variable here was exposure of S in a dark room a luminous line tilted 20 right. S was seated in a chair with head immobilized in the median plane. Two dependent variables were used: perceived visual object orienration, as measured by adjustment of a luminous line so that it appeared verrical; and perceived longitudinal body axis orientation, as measured by adjustment of a luminous line so that it appeared parallel S's longitudinal body axis. Both tasks were performed before and after exposure the tilted line. Three independent groups, 16 Ss in each, were used for 2-, 5-, and 10-min. exposure periods. Within each group, half the Ss were tested on body orientation first and the remainder were tested on object orienration first. Before exposure, a line and the body axis, both physically verrical, were perceived as verrical. During exposure Ss reported they saw the tilted line straighten; and eirher they felt their bodies tilted or wanted to tilt their bodies in the direction of the tilted line. Compared before, following exposure the line tilted right there were significanr changes. A physically vertical line was perceived as tilted left (mean adjusrmenr for line be seen as verrical, pooled exposure groups, was 0.83 right of physical verrical) and the physically vertical body axis was perceived as tilted righr (mean adjustment for line be seen parallel longitudinal body axis, pooled exposure groups, was 1.98 right of physical body axis). The findings show that, while S is vertical, during exposure a visual object tilted righr, there are changes toward alignment in perceived orientation of the visual object tilted right and the verrical body axis, viz., they appear rotated toward each other. The findings su-eest that the tendency toward movemenr, occurring during exposure the tilted visual object, plays a role in the observed perceptual changes.