Temporal discounting and preference reversals in choice between delayed outcomes

Subjects chose between pairs of hypothetical amounts of money available after different delays. When smaller, more immediate amounts were selected over larger, more delayed amounts, the addition of a constant delay to both outcomes resulted in reversals of preference, contrary to the standard discounted utility model of economics. The delays at which preference reversed were determined for three pairs of amounts ($20 vs. $50, $100 vs. $250, and $500 vs. $1,250). The relation between the delay to the larger amount and the delay to the smaller amount at preference reversal was well fit by both linear and quadratic functions. Intercepts increased with amount, strongly suggesting that rate of discounting decreases with amount. The presence of significant negative curvature in the data from the majority of individual subjects poses problems for exponential and hyperbolic models of temporal discounting in self-control, both of which predict a linear relation between the delays to the larger and smaller amounts.     

Book reviews

Darwin's Dangerous Idea, Daniel C. Dennett, 1995. London, Penguin. 587 pp., hbk £25, ISBN: 0–713–99090–2

Verificationism: Its History and Prospects, C. J. Misak, 1995. London and New York, Routledge. xviii + 254 pp. ISBN: 0–415–12597–9(hbk); 0–415–12598–7(pbk)

Abductive Inference: Computation, Philosophy, Technology, John R. Josephson & Susan G. Josephson (Eds), 1994. Cambridge, Cambridge University Press 306 pp.

Physics and Metaphysics. Theories of Space and Time, Jennifer Trusted, 1994. London, Routledge 210 pp.     

Boundary regulation in family and personal systems: Perceptions of late adolescents

Examination of boundary regulation can provide family therapists with a framework to describe both the functioning of family systems and personal systems (i.e., the intrapsychic functioning of individual family members). In the present study, late adolescents' perceptions of boundary regulation within their family systems (i.e., ratings of family health, communication, leadership, expressiveness, cohesion, and family conflict) were related to regulation of their personal boundaries (i.e., self-reported personal competence, distress, and patterns of defense mechanism use). In addition, personal system variables reliably discriminated between adolescents who described their families as psychologically healthy versus psychologically unhealthy.     

Developmental constraints associated with children's use of the keyword method of foreign language vocabulary learning

Second- and sixth-grade (ages 7 and 11 years, respectively) subjects were instructed to learn simple Spanish vocabulary nouns using the keyword method. To remember a foreign word translation the keyword method user must: (1) associate the foreign word to an English word (the keyword) that sounds like part of the foreign word; and (2) remember an image of the keyword and translation referents interacting. Second-grade keyword users who were provided with interactive pictures remembered more vocabulary items than those who generated their own imagery links when given separate pictures of the keyword and translation referents. Second graders who generated their own linking images when given only the keywords and translation words recalled fewer items than both picture groups, and were not significantly different from control subjects. Sixth graders in the three imagery-link variations performed at comparable levels and better than control subjects. The results are in complete accord with previous speculations about the development of imagery strategies in children.     

Drug effects on responding maintained by stimulus-reinforcer and response-reinforcer contingencies.

The effects of pentobarbital and d-amphetamine were assessed on key pecking by pigeons under conventional single-key multiple schedules and under two-key multiple schedules in which discriminative stimuli appeared on one key (stimulus key) while pecks on a second key (constant key) produced food. Pecks on the stimulus key had no scheduled consequences. A 60-second variable-interval schedule operated in one component of each multiple schedule: either extinction or a 60-second variable-time schedule operated in the alternate component. When the alternate-component schedule was extinction, a high rate of responding was maintained in the variable-interval component of the single-key schedule; responding on both keys was maintained in the variable-interval component of the two-key schedule. Pentobarbital increased responding in the variable-interval component of the single-key schedule and increased stimulus-key, but not constant-key responding in that component of the two-key schedule. When the alternate-component schedule was changed to variable time, responding declined in the variable-interval component of the single-key schedule; stimulus-key responding was no longer maintained under the two-key schedule. Pentobarbital decreased responding in the variable-interval component of both schedules. With an exception, d-amphetamine only decreased responding in the variable-interval component of the single- and two-key schedules both when the alternate-component schedule was extinction and when it was variable time. The results suggest that the effects of pentobarbital, but not d-amphetamine, depend on the nature of the contingency (stimulus-reinforcer, response-reinforcer) that maintains responding.     

Cognitive arithmetic: Evidence for right hemispheric mediation in an elementary component stage

Earlier studies involving the lateralization of arithmetic abilities have provided evidence for both right and left hemisphere superiorities. It is argued here that part of this inconsistency could be due to the complexity of the arithmetic computations which have been examined. The present studies examined a subprocess shown to be involved in more complex tasks, such as subtraction. The subprocess is the identification of which of two numbers is greater, and was tested by the flashing of a pair of digits to either the left or right visual field. Errors, reaction-times to make a decision, and examination of hand × visual field interactions all indicated that this subprocess is mediated by the right hemisphere. Correlational analysis was used to identify the operations underlying the observed lateralization of this ability. This analysis indicated that an operation indexed by the spatial order in which the digits were presented was effective in the right hemisphere but not the left hemisphere. Speculations on the nature of these operations were presented.