Equidistance Errors in a Reduced Cue Environment

Abstract

The equidistance tendency (ET) is the tendency of an observer to misperceive the depth interval between objects in a scene as being smaller than it actually is, particularly in the absence of strong depth cues and as the lateral separation between the objects decreases (Gogel, 1965). The present experiment was an attempt to create a display that would evoke a change in the influence of the ET as the lateral separation of display objects was varied. The display configuration used replicated (with updated equipment) that of a previous study (Hill and Mershon, 1985) which had reliably produced the desired effect. However, one property of the new equipment resulted in the appearance of a faintly visible background behind the main display objects that was not present in the previous experiment. In the present experiment, the display object with the poorest depth cues, which was expected to vary in perceived distance due to the ET effect, did not vary in apparent distance. Instead, one of the other objects, with stronger depth cues, varied in apparent distance. The results suggest that the presence of the faint background may have acted as an additional display object, despite its low contrast with the wider background of the visual field. This implies that even objects that are very low in salience can have a significant effect on perceived distances.