References

Rosenblatt, F. (1958). The perceptron: A probabilistic model for information storage and organization in the brain. Psychological Review, 65, 386-408.

Fundamentals of neural modeling: Neuropsychology and cognitive neuroscience. Cambridge, MA: M.I.T. Press. Rolls, E. T., & Treves, A. (1998). Neural networks and brain function. Oxford, UK: Oxford University Press.

NEURAL QUANTUM THEORY. In psychology, the classical theory of sensory discrimination has been contrasted historically with the neural quantum theory in a controversy sometimes called the sensory continuity-noncontinuity issue, with origins in the area of psychophysics. Some early researchers in psychophysics (e.g., R. Lotze; G. Fechner) argued for the noncontinuity (or discontinuity) position that involves the concept of threshold, whereas other researchers (e.g., G. Muller; J. Jastrow) maintained that the sensory continuum consists of a continuous series of intermediate degrees of sensation where there is no "true" threshold. The center of the controversy was whether the changes on the psychological continuum occur in a smooth or continuous manner as the value of the physical stimulus increases continuously along a specified dimension, or whether there is an abrupt, step like change from "no sensation" to "sensation" or from "sensation" to a "difference in sensation." The early theory of threshold (Fechner, 1860) holds that the brain in its waking state is physiologically active and, consequently, for an increasing stimulus to be detected, it has to generate neurological excitations that are larger than those already present as the result of the brain's spontaneous activity (cf., Herbart, 1824). The sensory con-tinuity-noncontinuity issue deals with the challenging question of how sensory mechanisms

- that are composed of discrete neural elements that obey the all-or-none law of physiology - can convert continuous energy from the environment into an apparently continuous change in sensory experience. The Hungarian-American biophysicist Georg von Bekesy (1899-1972) showed in the 1930s that discrete steps can be obtained in studies of sensory discrimination and, thereby, offers evidence for the quantal nature of sensory functions; cf., Corso (1961) who suggests that both the quantal theory and the phi-gamma hypothesis

- which represents the classical theory of sensory discrimination and predicts the general form of the psychometric function to be the integral of the normal probability distribution

- are equally acceptable in predicting the same results, and indicates that support of one theory to the exclusion of the other is not reasonable. The neural quantum theory in psychology was first introduced by S. S. Stevens, C. Morgan, and J. Volkmann in 1941 within the context of auditory discrimination; cf., J. Corso (1956) and H. Blackwell (1953) for neural quantum theory in the context of visual discrimination. Unlike the classical theory of sensory discrimination, which states that the proper form of the psychometric function for sensory discrimination is a normal ogive, the neural quantum theory asserts that the relationship between the proportion of judgments and corresponding stimulus values is represented best by a linear function, which implies that sensory discrimination is characterized by finite, discrete, or quantal steps. The neural quantum theory is intended to be consistent with the all-or-none principle because it is maintained, generally, that discriminatory judgments are mediated by the activities of underlying neural structures. In the psychological theory of neural quantum, the term quantum refers, specifically, to a "functionally distinct" unit in the neural mechanisms that are involved in sensory discrimination and, in this context, the term quantum implies a perceptual unit, not a physical unit (such as used in the science of physics to refer to distinct physical-energy units). Another version of this approach, the quantal hypothesis, asserts that continuous increments in a physical variable produce discrete (quantal) increases in sensation (cf., the law of quanta - states that with a conscious responding system, the system makes a quantity of a certain kind of energy into a thing or object unlike the thing or object "out there"). It appears, in the final analysis and on the basis of the existing data, that it is not determinable whether the theory of neural quantum provides a better explanation of sensory discrimination than the classical theory. It may be concluded, fairly, that unequivocal support of the neural quantum theory is lacking, and the tenability of the quantal hypothesis, as opposed to the phi-gamma hypothesis, is extremely difficult to evaluate due to the severe restrictions in methodology and to the statistical limitations in the treatment of data. See also ALL-OR-NONE LAW/PRINCIPLE; PSYCHOPHYSICAL LAWS/THEORY; QUANTUM THEORY; SIGNAL DETECTION, THEORY OF. REFERENCES

Herbart, J. (1824). Psychologie als wissenschaft, neu gegrundet auf erfahrung, metaphysik, und mathematik. Kon-isberg, Germany: Unzer. Lotze, R. (1852). Medicinische psychologie, oder physiologie der seele. Leipzig, Germany: Weidmann. Fechner, G. (1860). Elemente der psychophy-sik. Leipzig, Germany: Breitkopf & Hartel.

Muller, G. (1878). Zur grundlegung der psy-chophysik. Berlin, Germany: Gruben.

Jastrow, J. (1888). A critique of psycho-physic methods. American Journal of Psychology, 1, 271-309. Thurstone, L. L. (1928). The phi-gamma hypothesis. Journal of Experimental Psychology, 11, 293-305. Bekesy, G. von (1930). Uber das Fech-ner'sche gesetz und seine bedeutung fur die theorie der akustischen beobachtungsfehler und die theorie des horens. Annals der Physik, 7, 329359.

Stevens, S. S., Morgan, C., & Volkmann, J. (1941). Theory of the neural quan-

tum in the discrimination of loudness and pitch. American Journal of Psychology, 54, 315-335. Miller, G., & Garner, W. (1944). Effect of random presentation in the psychometric function: Implications for a quantal theory of discrimination. American Journal of Psychology, 57, 451-467. Blackwell, H. (1953). Evaluation of the neural quantum theory in vision. American Journal of Psychology, 66, 397-408. Corso, J. (1956). The neural quantum theory of sensory discrimination. Psychological Bulletin, 53, 371-393. Neisser, U. (1957). Response-sequences and the hypothesis of the neural quantum. American Journal of Psychology, 70, 512-527. Corso, J. (1961). The quantal hypothesis and the threshold of audibility. American Journal of Psychology, 74, 191204.

Corso, J. (1963). A theoretico-historical review of the threshold concept. Psy-chologicalBulletin, 60, 356-370. Norman, D. (1964). Sensory thresholds, response biases, and the neural quantum theory. Journal of Mathematical Psychology, 1, 88-120.

NEURAL TIMING THEORY. The American experimental/mathematical and cognitive psychologist Robert Duncan Luce (1925- ) and the sensory/auditory/experimental and physiological psychologist David M. Green (1932- ) formulated a psychophysiological theory of neural timing (and a theory of neural attention) based on the assumption that - at a hypothetical neural decision-center - signal/ sound intensity is represented by a number of independent and parallel Poisson processes whose rates are the same power function of physical intensity. Information concerning signal intensity is based on the observed times between successive neural firings/pulses. Response time is defined as the result of the decision-latency that depends, in turn, on the signal intensity, decision rule, and residual latency. The theory posits decision rules for contexts involving magnitude estimation, discrimination, recognition, and detection tasks (cf., Treisman, 1984). See also PSYCHOLOGICAL TIME, MODELS OF; PSYCHOPHYSICAL LAWS/THEORY; TIME, THEORIES OF. REFERENCES

Luce, R. D., & Green, D. M. (1972). A neural timing theory for response times and the psychophysics of intensity. Psychological Review, 79, 14-57. Luce, R. D., & Green, D. M. (1973). Neural coding and psychophysical discrimination data. Irvine, CA: University of California Press. Green, D. M., & Luce, R. D. (1974). Variability of magnitude estimates: A timing theory analysis. Perception & Psychophysics, 15, 291-300. Luce, R. D., & Green, D. M. (1978). Two tests of the neural attention hypothesis for auditory psychophysics. Perception & Psychophysics, 23, 363371.

Luce, R. D., Baird, J. C., Green, D. M., & Smith, A. F. (1980). Two classes of models for magnitude estimation. Journal of Mathematical Psychology, 22, 121-148. Treisman, M. (1984). A theory of criterion setting: An alternative to the attention band and response ratio hypotheses in magnitude estimation and cross-modality matching. Journal of Experimental Psychology: General, 113, 443-463.

NEUROBIOTAXIS, LAW OF. See NEURON/NEURAL/NERVE THEORY.

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