Essay on Size Constancy

967 Words Nov 6th, 2012 4 Pages
Visual Perception Lab: Size Constancy

Abstract

This investigation is designed to illustrate the ability of the visual system to compensate for changes in retinal image size with viewing distance,i.e the mechanism of size constancy. The accuracy of this mechanism will be evaluated under a number of different viewing conditions and thereby investigating the various cues for judging distance.

Background
‘Size constancy’ is the perception of an object as having a fixed size, regardless of the change in size of the retinal image & the visual angle which accompanies changes in distances (i.e. as an objects moves into the distance, the retinal image decreases yet the object size remains the same). It is thus possible to accurately
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Linear perspective may additionally be known as textural gradient (i.e. pebbles on a beach seem smaller receding into the distance). It is not imperative to know the actual size of the object to get an impression of depth, so long as the elements are, on average, decreasing in size.
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Interposition refers to the occlusion or obstruction of some part of an object by another. Objects further away will be blocked by those closer to you. The Necker cube (Figure 2)is an ambiguous figure, for though it is a cube, there is no interposition present, consequently generating the visual system to spontaneously flip between the two different orientations the cube can be positioned. By erasing certain lines so as to introduce the concept of occlusion this ambiguity can be reduced.

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Shaded elements of an object appear further back/deeper down than those exposed to light, which appear closer to the surface, hence enabling shadows to assist in depth perception. Moreover, the way in which elements are shaded allows for depth perception. As the brain assumes light comes from above, elements which are lighter above & darker below appear to bulge out, whereas those that are darker above & lighter below appear to be indented. The brain additionally assumes we view things from an upright position, thus by turning upside down we can alter the perception of depth with regards to shadows. Furthermore, the position

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