Depth matching with visible diplopic images: Stereopsis or vernier alignment

In order to prevent subjects from actually performing a judgment of vernier alignment between the double images rather than matching stereoscopic depth of the test objects, various precautions have previously been taken, e.g., using inexperienced subjects who were ignorant of the experimental situation and possible matching criteria. In the experiment reported here, a subject was given training in observing double images and the matching problems were also discussed. The subject was then instructed to perform stereoscopic depth judgments. The comparison between these data and data based on vernier alignment judgments under similar conditions showed that knowledge about the experimental situation and the vernier alignment criterion did not interfere with the subject’s task of matching the stereoscopic depth between visible double images.