Haploscopes

Haploscopes are optical instruments used in vision science to present different visual stimuli to each eye while maintaining binocular alignment. They enable dichoptic stimulation, which is essential for studying how the brain combines or competes between the two eyes for vision, and for assessing binocular functions such as stereopsis, suppression, and ocular dominance.

Most haploscopes employ mirrors or prisms in one or more optical paths so that two images can be directed toward the observer's left and right eyes from separate displays or from slides. The arrangement keeps the observer's eyes aligned and allows adjustment of interpupillary distance and viewing angle. Stimuli can be varied independently in each eye, including luminance, contrast, and spatial content, to create controlled binocular conditions or to induce rivalry.

Historically, haploscopes were used in psychophysical experiments to measure thresholds of depth perception and to map suppression fields in amblyopia and strabismus. They remain a fundamental tool in vision science for investigating binocular combination, binocular rivalry, and fusion.

Variants include mirror-based haploscopes and prism-based haploscopes. With advances in digital displays and virtual reality, modern dichoptic presentation often uses haploscopic principles within stereoscopic or VR setups, offering more compact and versatile implementations.

See also: binocular rivalry, stereopsis, dichoptic presentation, ocular dominance, amblyopia.