Direct manipulation of perceived angular declination affects perceived size and distance: A replication and extension of Wallach and O'Leary (1982).

Abstract

Wallach and O'Leary (1982) were the first to argue that 'slope of regard' (or gaze declination) was a distance cue. In three experiments, Wallach and O'Leary used an inverted Galilean telescope (GT) with horizontally oriented cylindrical lenses to manipulate perceived slope of regard when viewing a square, vertical object resting on the floor. Unlike prism goggles, which shift the entire scene angularly, their GT, which was mounted horizontally, maintained the visual horizon as straight ahead but compressed apparent gaze/angular declination and elevation relative to that horizon. Because of this their GT did not alter the perceived orientation of the ground plane as base-up prisms would. They used perceived object width (matched with an extendable hand-held rod) as an indirect measure of perceived distance and concluded that optically compressing slope of regard (toward horizontal) made objects on the floor appear farther away and thus wider than they were. We replicated their basic experimental manipulation and reproduced their principal finding that perceived object width was increased. However, concerned that their result could be interpreted as affecting size alone (e.g., via the horizon ratio), we sought to extend their study by collecting both explicit verbal distance estimates and implicit action measures of distance (distance thrown, when throwing to a target). Participants (N = 44) looked through an eye-level GT with a vertical compression ratio of 0.7 or through the same device without any lenses into a well-lit room. On the floor was a horizontal target 6 m away. Both explicit distance estimates and the beanbag toss distances (order counterbalanced) were affected by perceived slope of regard consistent with the predicted change in perceived distance. In summary, a direct optical distortion of angular declination without a change in the perceived horizon affects perceived distance as measured both by action (throwing) and by explicit estimation. Meeting abstract presented at VSS 2014