Perceptual constancy

Subjective constancy or perceptual constancy is the perception of an object or quality as constant under changing conditions.

Vision
In vision this means perceiving a color as "constant under changing conditions of illumination" (Erickson 1975, p.11-12) and "is the achievement of a very complicated 'calculation' by an unconsciously working apparatus within our central nervous system" (Lorenz 1961, p.171).


 * "The facts behind color-constancy phenomena...are that we require fine color discriminations less frequently than gross discriminations, and when gross discriminations enable us to maintain focus on objects of prime interest, we 'systematically overlook' differences beyond the necessary degree of fineness. The mechanism which accomplishes this 'systematic overlooking' is the information-processing system of the organism, and the principle according to which it is accomplished is that this system never expands more of its capacity on a given perceptual task than is necessary according to the current needs and interests of the agent." (Sayre 1968, p.151-152)

Music
In music, subjective constancy is the identification of a musical instrument as constant under changing timbre or "conditions of changing pitch and loudness, in different environments and with different players." (Erickson ibid)