Emily Martin¹, Yunlong Zhang¹, Sahana Lawrence¹; ¹Arizona State University

Familiar size is a pictorial depth cue. One way the distance to an object could be computed is to input an object's known physical size and divide by the tangent of its visual angle. If the visual system uses this type of computation, visual angles that an observer has not viewed would be as accurate as those that had been part of the viewer's experience. A simpler computation that does not involve trigonometry is one in which connections are formed between the visual angle a novel object subtends and its distance provided by other depth cues. When all other depth cues are absent, distance is recovered using past experience and the computation of a look-up table. Fifty-two college students were asked to study the size, shape, and color of two unfamiliar objects 10 cm tall for 30 seconds. Viewed with one eye on a chin rest, they estimated the distance of objects that were identical but varied in height from 7 to 14 cm. The objects were placed 150 cm from the observer, and the apparent distance was measured by having observers position a rod to match the distance. When presented with objects that were 1.3 degrees larger in visual angle than the one they were familiarized with, they judged it to be 25 cm closer than it was positioned. When the stimulus was the same size as the training object, they located it at approximately its actual distance. In contrast, the smaller objects did not influence the apparent distance to a significant degree. The findings fit the look-up table account well but are inconsistent with the generative trigonometric model. The results are consistent with evidence that familiar size is a perceptual depth cue and not the result of a conscious thought process.

Acknowledgements: Sigma Xi chapter of Arizona State University for a travel grant and Jake Patten for statistical assistance.