Visual space

Visual space is the perceptual space housing the visual world being experienced by an aware observer; it is the subjective counterpart of the space of physical objects before an observer's eyes.

In object space the location and shape of physical targets can be accurately described with the tools of geometry. For practical purposes it is Euclidean. It is three-dimensional and various co-ordinate systems like the Cartesian x,y,z (with a defined origin in relation to an observer's head or eyes), or bipolar with angles of elevation, azimuth and binocular parallax (based on the separation of the two eyes) are interchangeable. No elaborate mathematics are needed.

Percepts, the counterparts in the aware observer's conscious experience of objects in physical space, constitute an ordered ensemble or, as Ernst Cassirer explained, the perceptual world has a structure and is not an aggregate of scattered sensations. This visual space can be accessed by introspection, by interrogation, or by suitable experimental procedures which allow relative location as well as some structural properties to be assessed, even quantitatively.

An example illustrates the relationship between the concepts of object and visual space: Two straight lines are presented to an observer who is asked to set them so that they appear parallel. When this has been done, the lines are parallel in visual space and now a comparison is feasible with the physical lines' setting in object space. Good precision can be achieved using psychophysical procedures in human observers or behavioral ones in trained animals. The reciprocal experiment is easier to perform but does not yield a numerical read-out as readily: show objectively parallel lines and make a determination of their inclination in the observer's perception.

Considering how it arises (see below), visual space seems, as an immediate, unmediated experience, to provide a remarkably true and unproblematic representation of a real world of objects.

The distinction is mandatory between what the eye professions call visual field, the area or extent of physical space that is available to the eye or that is being imaged on the retina, and the virtual, perceptual visual space in which visual percepts are located, the subject of this entry. Confusion is caused by the use of in the German literature for both. There is no doubt that Ewald Hering and his followers meant visual space in their disquisitions.

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