As humans have two eyes and they are positioned at two different positions, the view and distances experienced from each eye is slightly different. the images views are fused together in the cerebral cortex of the brain where one 3 dimensional image is produced. The viewing of the world in 3 dimensions is said to give the viewer stereoscopic vision and enables them to distinguish the distances of various objects.
Prior experience is also an important factor when referring to depth perception, as we learn are remember the size and shape of different objects and distances and can therefore predict the size shape and distance of objects within your view. An example of this is you know roughly how tall your dad is, so if i see your dad and he appears to be substantially smaller you can determine that he is at a further distance away from you.
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Figure 8.1 Represents the same object being viewed from tow different positions causing the image produced within each eye to be different.



"In Figure 8.1, to the left, are two eyes viewing an arrow lying in the frontal plane—i.e., with no stereopsis—and to the right the arrow is inclined into the third dimension—i.e., it tends to point toward the observer. All points on the arrow are, in fact, seen single under both conditions, and yet it is clear from the right-hand figure that, if the gaze is fixed on A, the images of B′ will fall on noncorresponding points. B′ is not seen double but, instead, the noncorresponding points, bL and bR, are projected to a common point B′ and a stereoscopic percept is achieved. Thus the noncorresponding, or disparate, points on the retinas can be projected to a single point, and it is essentially this fusion of disparate images

by the brain that creates the impression of depth. If the point B′ were brought much closer to the eyes, its images would fall on such disparate points that fusion would no longer be possible, and B′ would be seen double, or one double image would be suppressed. There is thus a certain zone of disparity that, if not exceeded, allows fusion of disparate points. This is called Panum’s fusional area; it is the area on one retina such that any point in it will fuse with a single point on the other retina." {" human eye (anatomy) :: Binocular vision -- Britannica Online Encyclopedia ." Encyclopedia - Britannica Online Encyclopedia . N.p., n.d. Web. 25 June 2010. <http://www.britannica.com/EBchecked/topic/1688997/human-eye/64969/Binocular-vision?anchor=toc64969>.}




" human eye (anatomy) :: Binocular vision -- Britannica Online Encyclopedia ." Encyclopedia - Britannica Online Encyclopedia . N.p., n.d. Web. 25 June 2010. <http://www.britannica.com/EBchecked/topic/1688997/human-eye/64969/Binocular-vision?anchor=toc64969>.
Aubusson, Eileen Kennedy Peter. Biology in Context: the Spectrum of Life. Victoria : Oxford Uni. Press., 2001. Print.
"HSC Online." NSW HSC Online. N.p., n.d. Web. 22 June 2010. <http://www.hsc.csu.edu.au/biology/options/communication/2951/CommPart3.html#a1>.