Abstract
In previous research we showed that physically shorter distances towards zenith are seen as equal to physically longer distances towards horizon. This anisotropic tendency is a consequence of an interaction of non-visual (vestibular and proprioceptive) with visual information. The aim of the present research was to investigate whether the same regularity can be found even when there is no change in non-visual information. Two experiments were done, in which 28 participants had the task to equalize perceived distances of three stimuli in three directions (separation between directions was 45 degrees). In the first experiment participants performed estimates while sitting on a chair, and in the second while lying on a rotating chair, on a left side of their body. In both experiments, experimenter moved participants towards different directions. In the first experiment, looking at different directions changes vestibular information, while in the second, vestibular information is constant. We used customized equipment to present stimuli and special glasses to prevent subjects' eye movements. On both experiments, results have shown that on 1m distance perceived distance was the same on all directions. Also, in both experiments, on 3m and 5m distance there was a significant difference between two most extreme directions (with 90 degrees separation angle), but no significant difference between nearby directions (with 45 degrees separation angle). In the first experiment, horizontal direction was perceived as shortest and vertical as longest. In the second, the last direction while subject was rotated upwards was perceived as the shortest, and the last direction while subject was rotated backwards was perceived as the longest. These results suggest that anisotropy of perceived distance exists in both cases, when there is a change in vestibular information, and when vestibular information is constant.