Van Hare Effect

The Van Hare Effect is a 3D stereoscopic viewing technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision using psychophysical percepts. The Van Hare Effect creates the illusion of dimensionality, rather than actual dimensionality in the subject being viewed. The Van Hare Effect is achieved by employing the stereoscopic cross-eyed viewing technique on a pair of identical images placed side-by-side. In doing so, it artificially tricks the human brain and optical center into seeing depth in what is actually a two-dimensional, non-stereoscopic image. The illusion of depth is interesting in that even if the image pair is not itself originally stereoscopic, the brain perceives it as if it is.

No special viewing apparatus is required as the brain is tricked into creating a false perception of a three-dimensional still image or video simply by viewing it with the cross-eyed technique. In videos or films viewed this way, the artificial depth perception derived can to be diminished for some viewers, perhaps due to the fast changing visual picture, which appears to occupy more of the brain.

Most people can employ the Van Hare Effect but not all. The reasons for why some people cannot make the Van Hare Effect work for them are unknown and deserve further scientific study.

The Van Hare Effect was discovered in 2003 by the 3D theorist, Thomas Van Hare, who also invented three additional fields in stereoscopy -- hyperdimensionality, variable dimensionality, and computational dimensionality, aka C3D, which were all developed for military applications with the intended purpose of creating stereoscopic output from single camera drones for improved interpretation of reconnaissance imagery and capture.

Why the Van Hare Effect works remains a matter of conjecture, although it is clearly the brain itself that creates the impression of depth perception even where there is none in the image pair being viewed. The brain appears to be "trained" to view images in 3D as a general rule, even when very limited or no stereoscopic data is available. Thus, the Van Hare Effect creates the artificial impression of 3D viewing based on the brain's own past experience in interpreting objects, shapes and people, drawing on past visual experiences and knowledge of the perception of similar forms. The cross-eyed viewing technique may be the cue that allows the brain to override its assumption that the photograph or video/film being viewed is two-dimensional and instead trick it into thinking that the results are supposed to be three-dimensional. Therefore, once the brain is tricked in this manner, it may be that it works more effectively in discerning the depth and dimensional data from the existing two-dimensional images, thus giving the viewer the impression of dimensionality even where there is none.

The Pulfrich effect may likewise be partly explained in this manner, though the actual temporal changes from frame to frame in the films prepared for viewing with the Pulfrich effect do in fact provide some dimensional information to the brain. However, even where no temporal changes are evident in objects in the films being viewed with the Pulfrich effect, the brain appears to apply some depth perception to those areas of the film anyway, as if artificially compensating in a manner that inserts dimensional data where no stereoscopic-like changes are actually available. This may be related to the same processes in the brain that produce the Van Hare Effect.

The Van Hare Effect may also result partly from the brain's ability to discern dimensional information from changes in the size of objects or in the varying definition of textures within the image due to changes in resolution at a distance. It may also result from the amount of haze evident in the picture, which increases in distance and, in color images, may be perceived as a matter of color saturation or by a subtle shift toward the blue end of the spectrum. Additionally, some artificial depth perception may result from the perception of the amount of overlap seen in objects or the appearance of objects that are known to be the same size, that repeat in the image at various sizes, due to the distances involved. All of these latter reasons, however, should allow depth perception to be just as evident in a single two-dimensional image, yet typically they appear to escape notice when the viewer is examining a single image. It may be that once the Van Hare Effect is applied, these clues within the images are more easily recognized and discerned by the brain and optic center.

The Van Hare Effect may also be more readily apparent or magnified to those who have used the cross-eyed viewing technique in the past. If the viewer is accustomed to looking at stereoscopic image pairs without a viewer and by using the cross-eyed viewing technique, the viewer may have further trained their brain in a manner that enhances the Van Hare Effect. The knowledge of visual interpretation from the cross-eyed technique then is more readily applied when viewing identical image pairs instead of stereoscopic image pairs.