Perceived suprathreshold depth under conditions that elevate the stereothreshold.

PURPOSE: Previous studies considered the possibility that individuals with impaired stereoacuity can be identified by estimating the perceived depth of a target with a suprathreshold retinal image disparity. These studies showed that perceived suprathreshold depth is reduced when the image presented to one eye is blurred, but they did not address whether a similar reduction of perceived depth occurs when the stereothreshold is elevated using other manipulations.
METHODS: Stereothresholds were measured in six adult observers for a pair of bright 1-degree vertical lines during normal viewing and under five conditions that elevated the stereothreshold: monocular dioptric blur, monocular glare, binocular luminance reduction, monocular luminance reduction, and imposed disjunctive image motion. The observers subsequently matched the perceived depth of degraded targets presented with crossed or uncrossed disparities corresponding to two, four, and six times the elevated stereothreshold for each stimulus condition.
RESULTS: The image manipulations used elevated the stereothreshold by a factor of 3.7 to 5.5 times. For targets with suprathreshold disparities, monocular blur, monocular luminance reduction, and disjunctive image motion resulted in a significant decrease in perceived depth. However, the magnitude of perceived suprathreshold depth was unaffected when monocular glare was introduced or the binocular luminance of the stereotargets was reduced.
CONCLUSIONS: Not all conditions that increase the stereothreshold reduce the perceived depth of targets with suprathreshold disparities. Observers who have poor stereopsis therefore may or may not exhibit an associated reduction of perceived suprathreshold depth.