The binocular representation of uniform motion

In the model of motion perception proposed by Swanston, Wade, and Day (1987, Perception 16 143-159) it was suggested that retinocentric motion and eye movement information are combined independently for each eye, to give left and right orbitocentric representations of movement. The weighted orbitocentric values are then added, to give a single agocentric representation. It is shown that for a physical motion observed without pursuit eye movements this formulation predicts a reduction in the perceived extent of motion with monocular as opposed to binocular viewing. This prediction was tested, and shown to be incorrect. Accordingly, a modification of the model is proposed, in which the left and right retinocentric signals are weighted according to the presence or absence of stimulation, and combined to give a binocular retinocentric representation. In a similar way left-eye and right-eye position signals are combined to give a single binocular eye movement signal for version. This is then added to the binocular retinocentric signal to give the egocentric representation. This modification provides a unified account of both static visual direction and movement perception.     

Suicidal behavior in long-term care facilities

Questionnaires were mailed to a random sample of administrators of 1,080 long-term care facilities, in order to obtain information on the extent and nature of overt suicide and intentional life-threatening behavior (ILTB). Rates were calculated for death for overt suicides and ILTB. In-depth case studies, involving observation, interviews, and examination of medical records, were conducted in four facilities. Quantitative analysis revealed that white males were most at risk. Refusing to eat or drink and refusing medications were the most common suicidal behaviors. Depression, loneliness, feelings of family rejection, and loss were significant factors.     

Perceptual learning in maze discriminations

In Experiment 1, rats were trained on a discrimination between rubber- and sandpaper-covered arms of a maze after one group had been pre-exposed to these intra-maze cues. Pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made easier by adding further discriminative stimuli, when it now significantly retarded learning. In Experiment 2, rats were trained on an extra-maze spatial discrimination, again after one group, but not another, had been pre-exposed to the extra-maze landmarks. Here too, pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made substantially easier by arranging that the two arms between which rats had to choose were always separated by 135°. The results of both experiments can be explained by supposing that perceptual learning depends on the presence of features common to S+ and S-.     

Book reviews

Buckley, Key W. (1989). Mechanical man: John Broadeus Watson and the beginnings of Behaviorism. New York: Guilford Press. Pp. 293. ISBN 0-89862-744-3. $32.45/£18.00.

Colgan, P. (1989), Animal Motivation. New York and London: Chapman and Hall. Pp. 168. ISBN 0412-31850. £25.00 (hardback). ISBN 0412-31860, £10.95 (paperback).

Antinucci, F (Ed.) (1989). Cognitive structure and development in nonhuman prinates. Hillsdale, Nj: Laweence Erlbaum Associates, Inc. Pp. 266. ISBN 0-8058-0544. £16.50 (Hardback).

Parker, S.T. & Gibson, K.R. (Eds.) (1990). “Language” and intelligence in monkeys and apes. Cambridge: Cambridge University Press. Pp. 590. ISBN 0-521-38028-6. £40.00 (hardback).

Ley, Ronald (1990). A whisper of espionnage: Wolfgang Koehler and the apes of Tenerife. Garden City Park, NY: Avery Publoshing Corporation. Pp.264. ISBN 0-89529-432-x. $19.95.     

Default Probability

A probability may be called “default” if it is neither derived from preestablished probabilities nor based on considerations of frequency or symmetry. Default probabilities presumably arise through reasoning based on causality and similarity. This article advances a model of default probability based on a featural approach to similarity. The accuracy of the model is assessed by comparing its predictions to the probabilities provided by undergraduates asked to reason about mammals.     

Media influence on attitudes toward suicide.

This experiment investigated the effects of viewing films on suicide and violence on attitudes toward suicide. Non-suicidal university students were assigned to one of three groups: One group was shown a film about suicide, a second saw a film about violence, and the third saw a neutral film. Perceptions of the appropriateness of suicide and level of emotional arousal were measured by a questionnaire administered before and after the films were shown. Both the suicide and violent film groups showed increases in arousal scores after viewing the films. The results suggest that arousal became linked to cognitions specific to film content as a result of viewing the films dealing with suicide and violence. Other findings suggest that, for the suicide and violent film groups, perceived relations with parents were important predictors of film-induced changes in attitudes toward suicide.