Hemispheric differences are found in the identification,but not the detection,of low versus high spatial frequencies

The processing of sine-wave gratings presented to the left and right visual fields was examined in four experiments. Subjects were required either to detect the presence of a grating (Experiments 1 and 2) or to identify the spatial frequency of a grating (Experiments 3 and 4). Orthogonally to this, the stimuli were presented either at threshold levels of contrast (Experiments 1 and 3) or at suprathreshold levels (Experiments 2 and 4). Visual field and spatial frequency interacted when the task required identification of spatial frequency, but not when it required only stimulus detection. Regardless of contrast level (threshold, suprathreshold), high-frequency gratings were identified more readily in the right visual field (left hemisphere), whereas low-frequency gratings showed no visual field difference (Experiment 3) or were identified more readily in the left visual field (right hemisphere) (Experiment 4). Thus, hemispheric asymmetries in the processing of spatial frequencies depend on the task. These results support Sergent’s (1982) spatial frequency hypothesis, but only when the computational demands of the task exceed those required for the simple detection of the stimuli.     

Dynamic changes in work/rest duty cycles in a study of sleep deprivation

The effects of moderate workload and 72 h of sleep deprivation were studied using a modified continuous-performance paradigm. Ten subjects were tested hourly on a number of perceptual and cognitive tasks designed to require approximately 30 min to complete, with the remainder of each hour free. As sleep deprivation continued, the average time on task increased at an accelerating rate. The rate of increase differed among tasks, with longer tasks showing greater absolute and relative increases than shorter ones. Such increases confound sleep deprivation and workload effects. In this paper, we compare the advantages and disadvantages of several experimental paradigms; describe details of the present design; and discuss methodological problems associated with separating the interactions of sleep deprivation, workload, and circadian variation with performance.     

Book reviews

Montefiore, A. & Noble, D. (Eds.). (1989). Goals, no-goals and own goals: A debate on goal-directed and intentional behaviour. London: Unwin Hyman. Pp. ix + 304. ISBN 0-04-445341-8. £30.00 (hardback).

McNaughton, N. (1989). Biology and emotion. Cambridge: Cambridge University Press. Pp. 228. ISBN 0-521-26527-4. £27.50 (hardback); ISBN 0-521-31938-2. £9.95 (paperback).

Amsel, A. (1989). Behaviorism, neobehaviorism, and cognitivism in learning theory: Historical and contemporary perspectives. Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Pp. 105. ISBN 0-8058-0332-7. £15.00 (hardback).

Bolles, R. C. & Beecher, M. D. (1988). Evolution and learning. Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Pp. 263 + xi. ISBN 89589-542-8. £23.95 (hardback).

Davey, Graham (1989). Ecological learning theory. London: Toutledge. Pp. 392 + xv. ISBN 0-415-01190-6. £14.95 (paperback).

Davison, M. & McCarthy, D. (1988). The matching law: A research review. Hillsdale, NJ: Lawrence Erlbaum Associates, Inc. Pp. 285. ISBN 0-90959-923-7. £29.95 (hardback).