Cross-cultural differences in colour vision: Acquired ‘colour-blindness’ in Africa

We report a study of the incidence of ‘colour-blindness’ in southern and central Africa, and we compare the African data with data from various European groups. There was a surprisingly high incidence of tritan errors (yellow–blue defect). The likelihood of making tritan errors increased with age, and was greater in rural areas than in towns. In Europe, no tritan errors were made by samples from the U.K., Eire or Spain, but some tritan errors were made by a sample from southern Greece. In contrast, most of a British sample of people over sixty-five years old makes tritan errors. Although tritan errors were the most frequent, they were often accompanied by protan and deutan errors. This mixed pattern of errors is consistent with the condition being acquired rather than congenital. Many languages of southern Africa categorise blues and greens with the same term. If the tritanopia we report has been endemic, it may have reduced the ‘perceptual pressure’ to split the blue-with-green categories into separate blue and green terms; a speculation consistent with Rivers, W. H. R. (1901. Introduction to A. C. Haddon (Ed.), Reports on the Cambridge Anthropological Expedition to the Torres Straits. Cambridge: Cambridge University Press) © 1998 Elsevier Science Ltd. All rights reserved..     

On the significance of “double encoding” for the superior recall of pictures to names

Ten-year-old children who were shown pictures of objects immediately preceded by the object's name recalled the material no better than those exposed to the names of the stimuli alone. Both conditions yielded significantly poorer retention than those in which pictures alone were presented or pictures followed by their names. A second study replicated this result. In addition this demonstrated, by a picture and name recognition task, that the effects could not be due to subjects in the “name prior to picture” condition ignoring the pictorial component. These results were interpreted as contradicting the “double encoding” explanation of the superiority of pictures to names in free recall. Parallel visual and verbal encoding of a pictured object does not facilitate retention unless the verbal cue is actively elicited from the subject by the stimulus. The implications of this result for other studies which have employed either simultaneous or sequential presentation of pictures and names are briefly discussed.     

The role of central processes in the perception of visual after-images

Three experiments are reported in which part of the stimulus to be after-imaged was presented to each eye, producing simultaneous, binocular, after-images. In each case the monocular stimuli were complementary to each other, so that the binocular combination constituted a meaningful whole. The subjects' reports on the appearances and fragmentations of their after-images suggest the existence of some central, integrative, mechanism.     

The effects of music and task difficulty on performance at a visual vigilance task

Forty subjects performed a visual vigilance task in music or noise and when the task was difficult or easy. Response measures taken were: correct detections, commission errors, detection latencies and d' values. For the difficult version of the task a significant increase in detection latencies was found which music prevented. Broadly similar findings were obtained for correct detections. The results are compared with other studies of detection latency and task difficulty and are discussed in terms of arousal.     

Increasing Single‐Word Requests to Multiword Requests in Children with Autism and Related Disabilities

Initial language training with children with autism often focuses on the production of single‐word requests (i.e., mands). As a child progresses in treatment, it is desirable to increase the mean length of utterance (MLU) of requests. The present study examined treatment outcomes of behavioral intervention designed to increase the MLU of requests in a larger sample of children with language delays (n = 30). Intervention consisted of prompts and differential reinforcement for lengthier requests, and trials were conducted flexibly throughout the treatment session. A non‐concurrent multiple baseline across participants design was utilized to establish experimental control, and MLU intervention consisted of a baseline and treatment phase for each participant. Nonoverlap of all pairs (NAP) was employed to estimate an effect size. Overall treatment effects were medium to large (average NAP = 0.89; average d = 2.36), and the majority of the sample (70%) demonstrated strong treatment effects. Results suggest that targeted behavioral intervention to increase the length of requests can be effective for children with autism and associated language delays. Copyright © 2015 John Wiley & Sons, Ltd.     

Identifying and individuating cognitive systems: a task-based distributed cognition alternative to agent-based extended cognition

This article argues for a task-based approach to identifying and individuating cognitive systems. The agent-based extended cognition approach faces a problem of cognitive bloat and has difficulty accommodating both sub-individual cognitive systems (“scaling down”) and some supra-individual cognitive systems (“scaling up”). The standard distributed cognition approach can accommodate a wider variety of supra-individual systems but likewise has difficulties with sub-individual systems and faces the problem of cognitive bloat. We develop a task-based variant of distributed cognition designed to scale up and down smoothly while providing a principled means of avoiding cognitive bloat. The advantages of the task-based approach are illustrated by means of two parallel case studies: re-representation in the human visual system and in a biomedical engineering laboratory.