Shape and Size

William living the Life of Reilly

William resting up from a day of looking.

Baby William is doing very well. He is a lot different from when he was a week old. Back then, I couldn’t even get his attention. I suppose, since he was busy getting used to living in an air environment, that’s understandable. Plus the fact that his gaze, focused at about 8-10 inches according to the experts, would preclude any notice of grandpa standing in the background waving his hands.

Shape constancy

It is so much different now. William pays attention to all my attention-getting tricks (and I have a bunch of them). He is always looking at something; he looks at things from all angles. Literally. Today he was on his back on a pillow. He stretched his arms over his head to grasp the bottom of the shelf and was looking, upside down at the books. I wonder if, by doing this, he is developing a sense of shape constancy. Shape constancy is the phenomenon where a change in viewing the angle of an object doesn’t change a person’s perception of that object. When one looks at an object from one viewpoint, it projects a certain shape on the retina. If the viewpoint changes, the shape on the retina also changes, and yet, the object is perceived as unchanged. For example, if one looks at a square from directly above, all four sides of its outline are of equal length. However, when viewed obliquely, its outline is trapezoidal, and yet, it is still the same object.

William is probably developing a skill that he had as early as 3 months ago. According to Bower, shape constancy is exhibited in infants as young as 50-60 days. [1]

Size constancy

This is a similar phenomenon to shape constancy. Wikipedia defines it as follows:According to optical principles, for the same object, the size of the image on the retina changes as the distance from the object to the observer changes. The greater the distance, the smaller the image is sensed by the retina. When someone is observing an object, although the distance of observation is different, the perceptional size is similar to the actual size.[2]

Several studies show that this phenomenon may also be present from infancy. [3] [4]

I haven’t figured out how to empirically test this in a pre-verbal 6-month old. I’ll let you know if I come up with anything.

[1] Bower, T.G.R Slant Perception and Shape Constancy in Infants Science 18 February 1966: Vol. 151 no. 3712 pp. 832-834

[3] Slater, A. et. al Size constancy at birth: newborn infants’ responses to retinal and real size J. Exp Child Psychol. 1990 Apr. 49(2):314-22

[4] Granrud C.E. Size constancy in infants: 4-month-olds’ responses to physical versus retinal image size. J. Exp Psychol Hum Percept Perform. 2006 Dec; 32(6):1398-404

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