Perception of inclination as a function of eye and head inclination

摘要

The experiment was designed to investigate the influence of the vertical orientation of the eyes and of the head on judgments of the inclination of visual stimuli about a horizontal axis. One stimulus was a 50 cm-long vertical luminous line. Detection of the inclination of such a line requires registration of binocular disparity, inclination of the eyes in the head, and inclination of the head to gravity. The second stimulus was a textured large surface. This stimulus provides extra information in the form of perspective and the overall pattern of disparity. A fixation point was placed at the centre of each stimulus at a distance of 50 cm and both stimuli were viewed in black surroundings. By turning a knob the observer rotated the initially vertical stimulus about a frontal horizontal axis passing through the fixation point until the stimulus appeared vertical with respect to gravity. Measurements were made with the line and textured surface in four conditions. (1) Head vertical, stimulus at eye level. (2) Head vertical, stimulus moved down 30?°. (3) Head tilted back 30?° around the interocular axis, stimulus at eye level. (4) Head tilted forward 30?°, stimulus moved down 30?°. When the line was at an angle to the visual axis, as in conditions 2 and 4, it was perceived as rotated towards the gaze normal by several degrees. When the line was gaze normal but viewed with inclined head, the settings indicated that head inclination and/or eye elevation was underestimated, more so by some subjects than by others. Both these effects were greatly reduced when the subjects viewed the textured stimulus. When the eyes are elevated or depressed in the head the eyes manifest incylovergence and excylovergence, respectively. If cyclovergence, and it attendant cyclodisparity, had any effect it was overridden by the factors mentioned above.