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This research investigates whether perceived differences in blackness can serve as cues in stereoacuity tests.

March 21, 2026

Illusory Differences Which Are Stereoacuity Test Cues

Key Points

This research investigates whether perceived differences in blackness can serve as cues in stereoacuity tests.
Examined stereoacuity tests using equally black rods.
Analyzed responses from subjects regarding perceived blackness and width differences.
Studied both binocular and monocular vision effects on perception of blackness.
Subjects perceived an illusion of unequal blackness even when rods were identical.
Stereoacuity obtained using blackness cues was generally inferior to traditional distance-based methods.
Monocular observation of the blackness illusion occurred, indicating it is not solely related to stereopsis.

Abstract

ABSTRACT Some persons perceive an illusion of unequal blackness when viewing two equally black rods in a stereoacuity test. With binocular vision, the blacker rod is usually the nearer of the two. If blackness is used as a cue to nearness, a stereoacuity test can be performed successfully without using stereopsis. Nevertheless, stereoacuity obtained by this means is usually inferior to that obtained with distance judgments. For this reason it is advisable to warn subjects against using a blackness difference as a cue to the nearer rod. Those who saw this illusion binocularly also saw it monocularly. Therefore, it is more than just an artifact of stereopsis. One person observed an illusory difference in rod width as well as blackness.

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