The Stereo Fly test measures gross stereo at which disparity?

The Stereo Fly test measures gross stereo at which disparity?

• A. 3000 arc seconds
• B. 1500 arc seconds
• C. 6000 arc seconds
• D. 1000 arc seconds

Answer: (A)

Gross stereopsis looks at depth perception from large binocular disparities. The Stereo Fly test is designed to probe this coarse level of depth by presenting a target with a substantial disparity so that, if stereopsis is functioning, the fly appears to pop out from the background. The disparity used in this test is 3000 arc seconds, which is about 0.83 degrees of visual angle. That large disparity makes the depth cue easy to detect for people with normal gross stereopsis, making it a good screening for the presence of binocular depth perception. Other disparities (smaller ones around 1000–1500 arc seconds or larger ones like 6000) relate to different tests or to finer versus coarser depth tasks, but 3000 arc seconds is the standard value associated with the Stereo Fly’s gross stereo measurement.

Gross stereopsis looks at depth perception from large binocular disparities. The Stereo Fly test is designed to probe this coarse level of depth by presenting a target with a substantial disparity so that, if stereopsis is functioning, the fly appears to pop out from the background. The disparity used in this test is 3000 arc seconds, which is about 0.83 degrees of visual angle. That large disparity makes the depth cue easy to detect for people with normal gross stereopsis, making it a good screening for the presence of binocular depth perception. Other disparities (smaller ones around 1000–1500 arc seconds or larger ones like 6000) relate to different tests or to finer versus coarser depth tasks, but 3000 arc seconds is the standard value associated with the Stereo Fly’s gross stereo measurement.