How long does it take for the visual environment to influence the perceptual upright?

Abstract

The perceptual upright (PU) (the orientation in which objects appear ‘upright’) is influenced by visual and non-visual cues concerning the orientation of an observer. The orientation of the visual background accounts for about 25% of the influence. How long does it take for the perception of upright to form? We used the OCHART method (Dyde et al. 2004 Exp Brain Res. 173: 612) in which subjects identified a character (p/d) the identity of which depended on its orientation. Using a three-field tachistoscope (Ralph Gerbrands, field of view 6.3 degs) subjects viewed the character against a background. Display times were varied from 50–600ms and were immediately followed by a mask. We used the method of constant stimuli with a range of character and background orientations each presented at least six times. From this, we could identify the orientation where the character was most easily identified (PU). There was no effect of the background at the shortest exposure times, even though the subject could comfortably identify the character. There was an increase in the size of the effect with increasing exposure duration with a time constant of about 200ms. Subjects are able to identify the gist of a background with an exposure of only 26ms (Joubert et al. 2007 Vis Res. 47: 3286). However, using information from the visual background to influence character recognition seems to take substantially longer than this. It is possible that different types of orientation cues differ in the time they take to be effective.

Footnotes

 LRH and MJ acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Space Agency (CSA).