Minicomputers

The characteristics and costs of minicomputers are discussed along with peripherals, time-sharing, and turnkey systems. The article concludes with a survey of over 100 small computer systems.     

Discriminative and associative aspects of retroactive inhibition

Original learning of paired drawings of meaningful objects or of modified Chinese characters was followed by interpolated learning in which details of drawings were changed in one of two degrees with or without rearrangement of the original pairings. Subjects were tested for accuracy of identification of the original drawings and for associative matching of the original pairs. Identification errors were attributed jointly to confusion between original and interpolated drawings, and to unlearning of those features of original drawings which were in conflict with comparable features of interpolated drawings. Rearrangement of pairs during interpolated learning produced not only associative interference on the matching test, but also additional discriminatory interference on the identification test. Effects of associative and discriminative interference upon individual drawings were uncorrelated for meaningful material and only slightly correlated for meaningless material.     

Book reviews

Encyclopaedia of Linguistics, Information and Control. Edited by A. R. Meetham with the assistance of R. A. Hudson. Oxford: Pergamon Press. 1969. Pp. xiv + 718. 300s.

The Biological Basis of Personality. By H. J. Eysenck. Springfield: Thomas. 1968. Pp. xv + 399. $18.50.

Scientific Basis of Dvug Dependence. Biological Council Symposium. Edited by H. Steinberg. London: Churchill. 1969. Pp. 429. 100s.

Minnesota Symposia on Child Psychology, Vol. 2. Edited by John P. Hill. Minneapolis: University of Minnesota Press. 1969. Pp. viii + 172.

Memory and Attention: an introduction to human information processes. By Donald A. Norman. Chichester, Sussex: John Wiley. 1969. Pp. ix + 201. 84s. (cloth); 44s. (paper). Verbal Learning and Memory: selected readings. By Leo Postman and Geoffrey Keppel. Harmondsworth: Penguin Books. 1969. Pp. 501. 12s.

Handbuch der Kinderheilkunde. Edited by H. Opitz and F. Schmidt. Rand VIII/I: Neurologie-Psychologic-Psychiatrie. Redigiert von F. Schmidt und H. Asperger. Berlin: Springer Verlag. Pp. 1060. Price DM385, S96.25.

Digital Computing. By R. S. Lehman and D. E. Bailey. London: John Wiley & Sons Ltd. 1969. Pp. xxiv + 303. 79s.

Real-Time Computers. By W. R. Uttal. New York: Harper & Row. 1968. Pp. xiv + 338. 93s.     

Effects of a conditioned reinforcer upon accuracy of match-to-sample behavior in pigeons

Three pigeons were trained to perform a two-key sequential match-to-sample task. During baseline conditions, food reinforcement was contingent upon the first match response to occur following 8-min periods, and orange illumination of both keys preceded the delivery of food by 0.5 sec. The baseline schedule of food reinforcement was in effect throughout the study. In some conditions, a 0.5-sec flash of orange keylight alone was presented contingent upon mismatch responses that followed variable time periods averaging 1 min. Rate of mismatch responses increased and accuracy of matching performances decreased as compared with baseline conditions. The ability of the 0.5-sec orange flash to reinforce mismatch responses was markedly reduced when it no longer immediately preceded the delivery of food.     

Choice for periodic schedules of reinforcement

Pigeons' responses in the presence of two concurrently available (initial-link) stimuli produced one of two different (terminal-link) stimuli according to identical but independent variable-interval schedules. Responding in the mutually exclusive terminal links was reinforced with food according to fixed-ratio schedules for six pigeons and according to fixed-interval schedules for two pigeons. None of the pigeons matched the proportion of (choice) responses in the initial links to the proportion of the rates of reinforcement obtained during the terminal links. Instead, as the values of each of the terminal-link schedules were increased by a constant amount, the choice proportions for the stimulus associated with the smaller of the two values increased, even though the relative rates of reinforcement during the terminal links decreased. These results are incompatible with those from previous studies with aperiodic (variable-interval or variable-ratio) schedules. The present results do suggest, however, that in transforming aperiodic schedules into their periodic equivalents, it may be necessary to consider the size of the smallest interreinforcement interval comprising the terminal-link schedules.