With analytic perceptions, visual and auditory systems use a divide and conquer strategy. Features like color, shape, and motion are processed along distinct neural pathways, but perception requires more than simply perceiving the features of objects. When gazing at the Eiffel Tower, in Paris, we do not have the impression of blurs of color floating among a sea of various shapes. We perceive unified objects : the green grass of the champ de Mars, the iron frame of the tower and the deep-blue sky surrounding it.
This famous monument looks the same whether we view it with both eyes or with only the left or the right eye. Therefore, a change in position may reveal a different part of the champ de Mars, but still recognize that we’re looking at the tower. This also remains true if we stand on our head – the retinal image may be inverted, but we attribute this change to our inverted viewing position.
Have you ever wondered how you can recognize someone face in a blurred picture or identify an object just by seeing a small part of it ? Well, numerous researchers have asked themselves that same question.
Let’s start with object perception. This type of perception depends on the analysis of the shape of a visual stimulus, even though information like color, texture, and motion contribute to normal perception. Elmer The Elephant will, like in our childhood, illustrate this for us – despite the irregularities in how this character is depicted, we have little problem in recognizing them. We may never have seen a multicolored elephant, but our object recognition system can still discern the essential features. In this case, object recognition is derived from a perceptual ability to match an analysis of shape and form.
Now this is all good and well if the world is on a two dimensional picture, yet we are all in the face of a variable world, where we need to recognize objects countless situations. And our object constancy refers to this amazing ability.
The previous image shows three drawings of a door, each having little in common with respect to sensory information reaching the eye. And yet, we have no problem identifying the door in each drawing and discerning that all three doors are same. Therefore object constancy is essential for perception. Now, imagine how difficult life would be if we could not recognize familiar things or people unless we gazed at them from a specific point of view.
While object recognition must overcome different sources of variability – the viewing position, the retina projection of shape, the changes in lighting, and the surrounding objects. It also must accommodate the fact that changes in perceived shape can reflect changes in the object. As a result, object recognition must specific enough to support object constancy, but also specific enough to pick out slight differences between members of a category.
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