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trained Mongolian gerbils to jump across a gap having variable distance. For these species, motion parallax cues to depth may be more important in many natural behaviours. For many species with laterally placed eyes, such as birds and rodents, the visual fields of the two eyes have much less binocular overlap than for primates. For example, when an observer with the right eye closed translates to the right through one inter-ocular distance ( figure 1 a), the retinal displacement of an object over time matches the binocular disparity that would occur in the absence of self-motion ( figure 1 b).įor humans and non-human primates, depth perception based on binocular disparity cues generally outperforms that based on motion parallax, both in precision and accuracy. It is worth noting that motion parallax and binocular disparity cues both provide quantitative information about depth because they arise from similar geometry ( figure 1 see also ). ), we focus here on motion parallax that is generated by translation of an observer relative to the scene (i.e. Although some literature considers motion parallax induced by object motion in a scene (e.g. Motion parallax refers to the difference in image motion between objects at different depths. The binocular disparity shown here is equal to the change in position of the monocular image in a. Here, the far object projects to disparate points in the retinal image for the two eyes (bottom). Points falling along the geometric horopter, or Vieth-Muller circle (curved line), have zero binocular disparity. Hence depth from motion parallax is often expressed in units of equivalent disparity. If the eye moves through one inter-ocular distance, the position change on the retina due to motion parallax is equivalent to the object's binocular disparity (as shown in panel b). If the head translates rightward, the image of a far object (open symbol, top) moves on the retina. Similarity between motion parallax and binocular disparity as depth cues. Additionally, when an observer translates through the environment, motion parallax cues also provide a powerful source of depth information.įigure 1. Binocular disparity cues arise because the two eyes are separated horizontally, and provide information about depth. Additional powerful depth cues arise when a scene is viewed from multiple vantage points ( figure 1). Although such pictorial cues are valuable in interpreting three-dimensional scene structure, they generally do not provide precise quantitative information about depth. These include pictorial depth cues that are present in a single static image of a scene, such as occlusion, relative size, perspective, shading, texture gradients and blur. The brain makes use of a variety of cues to estimate depth.

Accurate perception of depth during self-motion is critical for success in many such tasks: for example, a lion will decide whether to chase a deer based on the distance between them, and a tennis player will stop running if the ball is not likely to be within reach.

shaking hands or playing tennis), involve interacting with objects in three-dimensional space while we are moving in the world. foraging, fighting and fleeing), as well as behaviours for social interaction and entertainment (e.g. Many behaviours that are essential for survival (e.g. Humans and animals frequently move within their environments.