CONSTANCY HYPOTHESIS. = perceptual constancy. This hypothesis, as employed in the area of perception psychology, states that perceived objects tend to remain constant in size where their distance from the observer (and, thus, the size of their retinal images) varies (cf., theory of misapplied constancy - states that the inappropriate interpretation of cues in the perception of certain illusions is the result of the observer's having previously learned strong cues for maintaining size constancy). Also, according to the constancy hypothesis in this perceptual context, objects tend to remain constant in shape (when the angle from which they are regarded - and, thus, the shape of their retinal images - varies), in brightness (when the intensity of illumination varies), and in hue (when the color composition of illumination varies). In general, perceptual constancy is the tendency for a perceived object to appear the same when the pattern of sensory stimulation (i.e., "proximal" stimulus) alters via a change in distance, orientation, or illumination, or some other extraneous variable. Thus, there are constancies regarding color, lightness, melody, object, odor, person, position, shape, size, velocity, and words. The term Brunswik ratio [named after the Hungarian-born American psychologist Egon Brunswik (1903-1955)] refers to an index of perceptual constancy expressed as: (R-S)/(A-S), where R is the physical magnitude/intensity of the stimulus chosen as a match, S is the physical magnitude/intensity for a stimulus match with zero constancy, and A is the physical magnitude/intensity that could be chosen under 100 percent constancy; the ratio equals zero when there is no perceptual constancy, and 1.00 when there is perfect constancy; and the Thouless ratio [named after the English psychologist

Robert H. Thouless (1894-1984)] which is a modification of the Brunswik ratio, taking Fechner's law (i.e., S=k log I) into account, where the perceptual constancy ratio becomes: (log R - log S)/(log A - log S). The constancy hypothesis hold up well with changing conditions if the observer has information about the changing conditions but, when one's ability to judge the total situation is reduced (e.g., as by a "reduction screen" such as looking at the object through the small peep hole made in your hand when you make a fist), then the constancy is reduced. The constancy phenomena have been known for a long time (cf., Boring, 1957). Color constancy was known to Ewald Hering in the 1860s, and brightness constancy was known to David Katz in the early 1900s. The idea of size constancy was known to the natural philosopher P. Bouguer before 1758, to the chemist J. Priestley in 1772, to the physicist/physiologist H. Meyer in 1842, to the physiologist C. F. W. Ludwig in 1852, to P. L. Panum in 1859, to G. Fechner in 1860, to E. Hering in 1861, to E. Emmert in 1881, to G. Martius in 1889, to F. Hillebrand in 1902, to W. Poppelreuter in 1911, to W. Blumenfeld in 1913, and to W. Kohler in 1915 - all of whom described or experimented on the phenomenon. See also BRUNSWIK'S PROBABALISTIC FUNC-TIONALISM THEORY; CONDILLAC'S THEORY OF ATTENTION; CONSTANCY, PRINCIPLE OF; EMMERT'S LAW; FECHNER'S LAW; GESTALT THEORY/LAWS. REFERENCES

Brunswik, E. (1929). Zur entwicklung der albedowahrnehmung. Zeitschrift fur Psychologie, 109, 40-115. Thouless, R. H. (1931). Phenomenal regression to the real object. I., II. British Journal of Psychology, 21, 339-359; 22, 1-30. Leibowitz, H. (1956). Relation between the Brunswik and Thouless ratios and functional relations in experimental investigations of perceived shape, size, and brightness. Perceptual and Motor Skills, 6, 6568.

Boring, E. G. (1957). A history of experimental psychology. New York: Apple-ton-Century-Crofts. Myers, A. K. (1980). Quantitative indices of perceptual constancy. Psychological Bulletin, 88, 451-457.

CONSTANCY, PRINCIPLE OF. This general principle has at least two important meanings in psychological theory. In one case, for the areas of physiology, cognition, emotion, and motivation, the notion of constancy derives from the first law of thermodynamics (dealing with "conservation of energy") in physics and may be considered as a basis for the principle of homeostasis where organisms are motivated to maintain biological constancy of bodily functions and mechanisms (such as temperature regulation and hunger reduction), and psychological balance among mental/cognitive mechanisms. In another case, in the area of psychoanalysis, the principle of constancy refers to the proposition that the amount of "psychic energy" within the person's mental processes remains constant so that regulation of mental stability may be achieved either through discharge of excess energy (as via "abreaction" or release of emotional energy following the recollection of a painful memory that has been repressed), or through avoidance of an increase of excess energy (as via "ego defense mechanisms" or patterns of thought, behavior, or feeling that are reactions to a perception psychic tension or danger which enable the person to avoid conscious awareness of cognitive conflicts or anxiety-arousing wishes/ideas). In the latter usage, however, psychoanalysts have been suspect in their employment of the principle of constancy as being contradictory or ambiguous (cf., quota of affect -a quantity of instinctual energy that remains constant despite undergoing displacement and various qualitative transformations; in mental functions, a quota of affect, or "sum of excitation," possesses all the characteristics of a quantity which is capable of increase, decrease, and discharge/displacement and which, theoretically, is spread over the memory-traces of ideas, similar to an electric charge that spreads over the surface of the body). For example, Sigmund Freud (1920/1953) apparently confuses the reduction and extinction of psychic energy with its regulation; thus, in his application of the nirvana principle to psychoanalysis (that is, the tendency for the amount of energy in one's mental apparatus to reduce to zero), Freud defined this psychic-economy principle (derived from Buddhist/Hindu philosophy where "nirvana" is a psychic state achieved by the extinction of all earthly desires) in an ambiguous way as the principle of the mental apparatus for extinguishing - or at least of maintaining it at a low level - the amounts of excitation flowing into the mental apparatus. See also CONSTANCY HYPOTHESIS; FESTINGER'S COGNITIVE DISSONANCE THEORY; FREUD'S THEORY OF PERSONALITY; GENERAL SYSTEMS THEORY; HOMEO-STASIS, PRINCIPLE OF; HUNGER, THEORIES OF; HYDRAULIC THEORY; LIFE, THEORIES OF; SOLOMON'S OPPONENT-PROCESS THE-ORY OF EMOTIONS/FEELINGS/MOTIVA-TION; THERMODYNAMICS, LAWS OF. REFERENCES

Freud, S. (1894/1964). The neuropsychoses of defence. In The standard edition of the complete psychological works of Sigmund Freud. London: Hogarth Press. Freud, S. (1920/1953). Beyond the pleasure principle. In The standard edition of the complete psychological works of Sigmund Freud. London: Hogarth press.




The doctrine/theory of constructivism refers to the way in which memories, perceptions, cognitions, and other complex mental structures are assembled actively (or "built") by one's mind, rather than merely being acquired in a passive manner. Two prominent versions of constructivist theory are the radical constructivism of the Swiss psychologist Jean Piaget (1896-1980) and the social constructivism of the foreign-born American sociologists Peter L. Berger (1929- ) and Thomas Luckmann (1927- ). Piaget's theory is based on the assumption that children construct mental schema and structures by observing the effects of their own actions on the environment (e.g., in "adaptive accommodation" and "assimilation," the psychological structures/processes of the child are modified to fit the changing demands of the situation, as when an infant in a crib reaches out and attempts to get a toy from outside the crib to the inside through the crib's vertical slats by simply turning the toy slightly sideways/vertically to get it past the slats and into the crib). Social constructivist theory emphasizes the manner in which people come to share interpretations of their social milieu (cf., doctrine of liberal pluralism -asserts that the individual is at the center of efforts to improve human welfare, and states that societies are to be created where people of diverse backgrounds may pursue their personal welfare and coexist with a minimum of conflict; and doctrine of situated knowledge - an approach that arose from cultural studies and feminist criticisms of science, as a challenge to the objectivity of scientific knowledge, on one hand, but aiming to avoid complete relativism, on the other hand; this doctrine represents a perspective of "positioned rationality," whereby knowledge allegedly may emerge only from multiple- and partial-positioned viewpoints; it is opposed to the notion of "transcendence" which asserts that knowledge is "universal;" the doctrine states that knowledge must be seen from the perspective of the knower, the relationships among knowers, and the relationship between the knower and the object of knowledge). Generally, social constructivists argue for rather extreme positions, including the idea that there is no such thing as a knowable objec tive reality - but, instead, maintain that all knowledge is derived from the mental constructions of the members of a particular social system [cf., social-exchange theory -first enunciated by the American sociologist George Caspar Homans (1910- ), who presented a model of social structure based on the notion that most social behavior is founded on the individual's expectation that one's actions, with respect to others, will result in some degree of commensurate ("rewards" and "costs") return; social Darwinism theory - first described by the English philosopher Herbert Spencer (18201903), and proposes that social and cultural development may be explained by analogy with the Darwinian theory of biological evolution; thus, the theory suggests that society functions primarily through conflict and competition where the "fittest" survive and the "poorly adapted" are eliminated; social identity theory - formulated by the English-born Polish social psychologist Henri Tajfel (1919-1982), where this "social categorization" theory is based on the notion of "social identity" (i.e., the component of the "self-concept" that derives from group membership) and where social categories (including large groups such as nations, and small groups such as fraternal clubs) provide their members with a sense of one's "essential being" and even prescribes appropriate personal and social behaviors; also, members in such "social identity" groups view their groups as being superior to other groups; the minimal group paradigm/situation - studied by H. Tajfel and his colleagues in the early 1970s, refers to an experimental procedure in which the mere presence of social categorization produces intergroup discrimination; theory of situated identities - the suggestion that an individual will take on different social roles in different social settings and environments; the aristocracy theory - the notion that the social rank of some humans and animals is determined by their parents' rank; and the minimal social situation effect - studied by the American psychologist Joseph B. Sidowski (1925- ), refers to an interactive decision in which each decision-maker is unaware of the interactive nature of the decision and even of the existence of another decision-maker whose behaviors influence the outcomes]. See also CON-STRUCTIVIST THEORY OF PERCEPTION; DARWIN'S EVOLUTION THEORY; EXCHANGE/SOCIAL EXCHANGE THEORY; INGROUP BIAS THEORIES;


Spencer, H. (1891). The study of sociology.

New York: Appleton. Homans, G. C. (1950). The human group.

New York: Harcourt, Brace. Piaget, J. (1954). The construction of reality in the child. New York: Basic Books.

Sidowski, J. B. (1957). Reward and punishment in a minimal social situation. Journal of Experimental Psychology, 54, 318-326. Berger, P. L., & Luckmann, T. (1966). The social construction of reality. New York: Doubleday. Tajfel, H., Billig, M., & Bundy, R. (1971).

Social categorization and inter-group behavior. European Journal of Social Psychology, 1, 149178.

Tajfel, H. (Ed.) (1982). Social identity and intergroup relations. New York: Cambridge University Press.

CONSTRUCTIVIST THEORY OF PERCEPTION. This approach toward explaining perceptual phenomena and processes focuses on how the mind constructs perceptions. Constructivist theory takes a number of different forms, including research on the connection between perception/neural processing and re-search on how perception is determined by mental processing. The idea of approaching perception by asking what the mind does during the perceptual process is an old notion whose roots go back to the 19th century, when the German physicist/physiologist Hermann L. F. von Helmholtz (1821-1894) proposed the likelihood principle: one perceives the object that is "most likely" to occur in "that particular situation." Also, the English psychologist Sir Frederic Charles Bartlett (1886-1969) used construc-tivist concepts to explain results he observed in his studies on memory. Modern descendants of Helmholtz's likelihood principle are the English psychologist Richard Langton Gregory's (1923- ) notion that perception is governed by a mechanism he calls hypothesis testing, and by the American psychologist Ulrich Neisser's (1928- ) notion of perceptual cycle. Hypothesis testing refers to a function of sensory stimulation as providing data for hypotheses concerning the state of the external world. Hypothesis testing does not always occur at a conscious level, and per-ceivers are usually not aware of the complex mental processes that occur during a perceptual act. Perceptual cycle, also called the cyclic model of perception, refers to the set of cognitive schemata that direct perceptual processes, and the perceptual responses and feedback mechanisms through which perceptual information is sampled. The idea that mental operations occur during the perceptual process is illustrated by an early study by the German psychologist Oswald Kulpe (1862-1915): displays of various colors were presented to participants who were asked to pay attention to a particular aspect of the display (such as the positions of certain letters), but when they were asked, subsequently, to describe another aspect of the display (such as the color of a particular letter), they were not able to do it. This indicates that even though all of the information from the stimulus display reached the observer's eye, a selection process took place somewhere between the reception of this information and the person's perception so that only part of the information was actually perceived and remembered. Thus, perception seems to depend on more than simply the properties of the stimulus, and the observer/participant makes a contribution to the perceptual process. Another way that the cogni-tive/constructivist aspect of processing has been approached is by considering the eye movements that people make when observing an object. According to eye movement theory (e.g., Hochberg, 1971), as an ob server looks at a scene, information is taken in by a series of "fixations" (i.e., pauses of the eye that occur one to three times per second as the person examines part of the stimulus) and "eye movements" that propel the eye from one fixation to the next. Such eye movements are necessary in order to see all of the details of the scene, because a single fixation would reveal only the details near the fixation point. Also, eye movements have another purpose: the information they take in about different parts of the scene is used to create a "mental map" of the scene by a process of "integration" or "piecing together." Thus, Helmholtz's likelihood principle, Gregory's idea of hypothesis testing, and Hochberg's eye movement theory all treat perception as involving an active, constructing observer who processes stimulus information. The constructivist approach also assumes that perception of a whole object is constructed from information taken in from smaller parts. The essence of all constructivist theories is that perceptual experience is viewed as more than a direct response to stimulation (cf., direct perception theory); it is, instead, viewed as an elaboration or "construction" based on hypothesized cognitive and affective operations and mech-anisms. See also ATTENTION, LAWS/PRINCIPLES/THEORIES OF; DIRECT PERCEPTION THEORY; MIND/MENTAL STATES, THEORIES OF; PERCEPTION (I. GENERAL), THEORIES OF; PERCEPTION (II. COMPARATIVE APPRAISAL), THEORIES OF; UNCONSCIOUS INFERENCE, DOCTRINE OF. REFERENCES

Kulpe, O. (1904). Versuche uber abstraktion. Berlin International Congress der Experimental Psychologie, 56-68. Bartlett, F. C. (1932). Remembering: A study in experimental and social psychology. Cambridge, UK: Cambridge, University Press. Neisser, U. (1967). Cognitive psychology.

New York: Appleton-Century-Crofts.

Hochberg, J. (1971). Perception. In J. Kling & L. Riggs (Eds.), Woodworth and Schlosberg 's experimental psychology. New York: Holt, Rinehart, & Winston. Gregory, R. L. (1973). Eye and brain. New York: McGraw-Hill.

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