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Reference.org
Stereopsis
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<p>In the science of vision, stereopsis is the sensation that objects in space are not flat but extend into depth, and that objects are at different distances from each other. This sensation is much stronger than the suggestion of depth that is created by two-dimensional perspective. Stereopsis is an aspect of <a href="/facts/Binocular_vision/koERAQCV">binocular vision</a>. </p><p>The word stereopsis comes from the Greek stereós meaning 'solid' and ópsis meaning 'appearance, sight'. Together, these indicate seeing the outside of three-dimensional, "solid" objects. In the science of vision, the word <i>binocular depth perception</i> is used as a synonym for stereopsis. This emphasizes that stereopsis is a category of vision in which one looks with two eyes. Sometimes the term <i>relative depth</i> is also used. This term emphasizes that it is not the distance to the observer that is meant (egocentric depth). If the meaning is clear from the context, the single word <i>depth</i> is also used instead of <i>relative depth</i>. </p><p>Stereopsis comes in two qualities: coarse stereopsis and fine stereopsis. Fine stereopsis plays a role in the recognition of shapes and objects and coarse stereopsis in spatial localization. There are two neurophysiological mechanisms present in the brain for this. </p><p>Stereopsis is a specialization of the ability to direction vision that is discussed in a separate article. Stereopsis is based on small differences (disparities) in the direction in which the left and right eyes see an object, which are the result of the fact that the two eyes are about 2.5 cm apart. </p><p>Conditions for the occurrence of stereopsis are that the visual directions in the left and right eyes have a certain similarity, are stimulated more or less at the same time, and the difference between the directions in the left and right eyes (horizontal disparity) is limited. The following describes in broad terms the knowledge about normal stereopsis in humans for the aspects mentioned, and explains the basic concepts that are necessary to understand the underlying source documents. </p>