CAUSES OF INTRAINDIVIDUAL VARIABILITY IN REACTION-TIMES - A NEUROPHYSIOLOGICALLY ORIENTED REVIEW AND A NEW SUGGESTION

Inter-individual variation in reaction times, and its negative correla tion with intelligence, has long been established. Marked intra-indivi dual variability in reaction times, within a given RT paradigm, has al so been known for decades but, in contrast, is still unexplained and i s usually ignored. Jensen [Jensen, A. R. (1980) Bias in mental testing . New York: Free Press; Jensen, A. R. (1982) Reaction time and psychom etric g. In H. J. Eysenck (Ed.), A model for intelligence. Berlin: Spr inger; Jensen, A. R. (1992) The importance of intraindividual variatio n in reaction time, Personality and Individual Differences, 13, 869-88 1.] has proposed an ''oscillation model'' in which a reaction stimulus -induced evoked potential interacts with ''brain waves'' (EEG) to make RTs vary from trial to trial within one test session. Anderson [Ander son, B. (1994) Speed of neuron conduction is not the basis of the IQ-R T correlation: Results from a simple neural model, Intelligence, 19, 3 17-324.] and Anderson and Donaldson [Anderson, B., & Donaldson, S. (19 95) The backpropagation algorithm: Implications for the biological bas es of individual differences in intelligence, Intelligence, 21, 327-34 5.] have used simple computer models of connected neurons and neural n ets, respectively, varying the values of certain parameters such as sy naptic failure rates, to explain RT variability. I discuss these model s and argue that they do not explain the observed variability. A new p ossible explanation is proposed here: intraindividual RT variability f ollows from variable (within a S, between individual RT trials) cortic al pathway length (CPL), where CPL is the total length of the neural p athways in the cerebral cortex which an RT-induced evoked potential mu st follow in executing a correct RT response. This is an extension of the inter-individual CPL variability proposed by Reed and Jensen [Reed , T. E., & Jensen, A. R. (1993) Choice reaction time and visual pathwa y nerve conduction velocity both correlate with intelligence but appea r not to correlate with each other: Implications for information proce ssing, Intelligence, 17, 191-203.] (C) 1998 Elsevier Science Ltd. All rights reserved.