The imprecision of stereopsis.

Area of Science:

• Visual Perception
• Stereoscopic Vision
• Depth Perception

Background:

• Stereoscopic depth judgments are generally less precise than lateral distance judgments.
• While stereoacuity thresholds can match monocular hyperacuities, disparity increment thresholds are significantly larger than lateral separation (width) thresholds.

Purpose of the Study:

• To quantify the minimum detectable change in three-dimensional distance (disparity) between features.
• To compare disparity increment thresholds with lateral separation (width) increment thresholds.
• To investigate the effect of target presentation duration and vernier acuity on stereoscopic judgments.

Main Methods:

• Measured Weber fraction for disparity and width using briefly (150 msec) and longer (1000 msec) presented targets.
• Assessed vernier acuity by pairing offset lines presented to different eyes with varying disparities.
• Compared disparity thresholds against monocular width thresholds under comparable conditions.

Main Results:

• For brief targets, the Weber fraction for disparity (10-20%) was substantially larger than for width (2-3%).
• Longer target duration improved disparity thresholds, but they remained twice as poor as monocular width thresholds.
• Vernier acuity was significantly degraded by binocular disparity, indicating suppression of precise monocular signals.

Conclusions:

• Stereoscopic depth perception is inherently less precise than monocular lateral distance perception.
• Precise monocular visual information is actively suppressed within fused or partially-fused stereoscopic images.
• This suppression mechanism contributes to the limitations in stereoscopic depth judgment accuracy.