An account of human “impulsivity” on self-control tasks

Three experiments examined the effects of economic constraint (time restriction—trials restriction) on adult humans' performance on concurrent chained schedules of reinforcement in which terminal links differed both in reward size and pre-reward delay levels. In the first, terminal links offered a long delay (20, 30, 40, 50 sec) followed by 2 points, or a short delay (10 sec) followed by 1 point. Initial links consisted of the same variable interval schedules for each alternative. Subjects showed a conditional sensitivity to increases in delay. Under a time constraint, there was an increasing preference for the smaller reward as the delay to the larger reward was increased, whereas under a trials constraint subjects were totally insensitive to such changes. In the second experiment, this finding was replicated using long and short periods of video game playing as large and small rewards. In the third experiment terminal link parameters remained constant (2 points after 15 sec, or 1 point immediately), but initial link parameters were manipulated (either VI 1-sec, 8-sec, or 20-sec) so that the higher relative rate of reward shifted from being associated with the small reward to being associated with the large reward. Again subjects chose differently under the two constraints. Subjects under the time constraint exhibited a preference for the small reward at all levels of initial link, but under the trials constraint subjects preferred the large reward. Subjects in the time constraint condition thus exhibited a maladaptive insensitivity to changes in the initial link duration. These findings are interpreted as supporting a miscalculation rather than a discounting interpretation of human performance on “self-control” tasks.     

Book reviews

Lea, S. E. G., Tarpy, R. M., & Webley, P. (1987). The individual in the economy. Cambridge: Cambridge University Press. Pp. 627 + xxiv. ISBN 0-521-26872-9. £39.50 (Hardback). ISBN 0-521-317014. £13.95 (Paperback).

Davey, G. & Cullen, C. (Eds.) (1988). Human operant conditioning and behaviour modifcution. Chichester: John Wiley & Sons. Pp. x + 270. ISBN 0-471-91637-4. £29.50.

Commons, M. L., Mazur, J. E., Nevin, J. A. & Rachlin, H. (Eds.). (1987), Quantitative analyses of behavior. Vol. 5: The efect of delay and of intervening events on reinforcement value. Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Pp. 344. ISBN 0-89859-800-1. £31.00.

Pearce, J. M. (1987). An introduction to animal cognition. Hove and London: Lawrence Erlbaum Associates Ltd. Pp. 328. ISBN 0-86377-0568 (hardback) 219.95; ISBN 0-86377457-6 (paperback) £9.95.

Archer, J. (1988). The behavioural biology of aggression. Cambridge: Cambridge University Press. Pp. x + 257. ISBN 0-521-34790-4. £9.95 (paperback).

Greenberg, G. and Tobach, E. (Eds.) (1987). Cognition, language, and consciousness: Integrative tevels. The T. C. Schneirla Conference Series. Volume 2. Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Pp. ix + 301. ISBN 0-89859-7224. £27.50.

Mook, D.G. (1987). Motivation: The organisation of action. New York: Norton. Pp. xxii + 586. ISBN 0-393-95474-9. £12.95 (hardback).

Frank, H. (Ed.) (1987). Man and wolf: Advances, issues and problems in captive wow research. Dordrecht: Dr. W. Junk. Pp. xviii + 439. ISBN 90-6193-614-4. £103.25 (hardback).     

Discrimination of five-dimensional stimuli by pigeons: Limitations of feature analysis

Pigeons were trained to discriminate between stimuli constructed using five orthogonal two-valued features. The stimuli consisted of stylized monochrome drawings of seeds. Two different training procedures (conditional and simultaneous discrimination) were used. In the first two experiments, the discrimination required was between polymorphous categories, in which a positive stimulus was defined as one in which three or more of the five features took their positive values. Discrimination in both experiments was imperfect; the pigeons' behaviour only came under the control of a subset of the available features (one to three in Experiment 1, three or four in Experiment 2). In Experiment 3, single features had to be discriminated, while the remaining features varied. It was found that all five features of the “seed” stimuli could be discriminated, but one of them was exceptionally difficult. The results show that pigeons do not reliably use all the features available to them when making category discriminations. This casts doubts on feature analysis as a basis for the excellent performance pigeons show when required to discriminate between categories of natural objects.