Constancy

Perceptual constancies
The energy patterns reaching our senses are constantly changing, even when they come from the same object. Size, shape, and brightness constancy rescue us from a confusing world in which objects would seem to shrink and grow, change shape as if they were made of rubber, and light up or fade like neon lamps. Using size to judge distance requires familiarity with the appearance of objects. What would it be like to have your vision restored after a lifetime of blindness? A newly sighted person must learn to identify objects, to read clocks, numbers, and letters, and to judge sizes and distances. Some perceptions--like seeing a line on a piece of paper--are so basic they seem to be native (inborn). But much perception is empirical, or based on prior experience. [Colin Turnbull's story of the Pygmy from the dense rain forests of Africa experiencing the vast African plains for first time and seeing a herd of buffalo grow from "insects" to buffalo in front of his eyes, like witchcraft.]

1. Size constancy. The perceived size of an object remains the same even though the size of its retinal images changes.

2. Shape constancy. Obviously the shape of the page is rectangular, but most of the time the image that reaches your eye is distorted. Even though the book's image changes, your perception of its shape remains constant.

3. Brightness constancy. The apparent brightness of an object stays the same under changing conditions of light. The white blouse continues to reflect a larger proportion of light than nearby objects when a cloud passes over head.

[Coon, Dennis. Introduction to Psychology, Exploration and Application. St. Paul: West Publishing Company, 1989.] See chapter on Perceiving.]

. . . . when any snowflake is turned 60 degrees around an axis perpendicular to its plane, its original appearance is reproduced. The reason for its constancy lies in the arrangement of the atoms in the crystals, while the variety in external shapes is caused by environmental conditions governing the growth of the crystals.... In investigating the nature and properties of the world around us, we tend to alternate between the collection of data and the organization of the results of experiments. This alternation is very important in the progress of science; the organization process would be futile without experiment. The alternation of these two methods motivates further investigations and reveals universal principles linking very distinct physical phenomena. Abilities of scientists vary: some are ingenious in the design of experiments, while others are adept at discovery of patterns and relationships. The discovery of order is thus quite subjective, and the structure of matter as it is known to us is partly of our own making; we tend to structure our perceptions and to create frames of reference suitable for relating various observations to each other.

Loeb, Arthur L. "The Architecture of Crystals." In Module, Proportion, Symmetry, Rhythm. Vision and Value series. Gyorgy Kepes, ed. New York: George Braziller, 1966. p. 38]

Physical Constants:
Speed of light
Gravitation
Electric charge

Astronomical Constants:
Acceleration
Sea level
Sun's Luminosity
Earth's orbital Velocity
Pressure at Sea level

Fundamental Physical Constants:
Permeability of vacuum
Fine structure constant

R  E  F  E  R  E  N  C  E  S 

1 Constant adj [ME, fr. MF, fr. L constant-, constans, fr. prp. of constare to stand firm, be consistent, fr. com- + stare to stand -more at Stand] [14c] 1: marked by firm steadfast resolution or faithfulness; exhibiting constancy of mind or attachment 2: Invariable, Uniform 3: continually occurring or recurring: Regular -syn. see Faithful, Continual

2 Constant n [1832] : something invariable or unchanging; as a: a number that has a fixed value in a given situation or universally or that is characteristic of some substance or instrument b: a number that is assumed not to change value in a given mathematical discussion c: a term in logic with a fixed designation.