Numerosity discrimination of tactile stimuli.

The ability of 40 college students to discriminate the number of tactile stimuli presented simultaneously was measured in two experiments. Simulation was provided by 12 solenoids fixed to points on the arms and legs. Exp. I showed a mean correct discrimination level of between 1.55 and 2.10 solenoids. Exp II compared discrimination of numerosity by a group who received immediate feedback with a no-feedback control group. Feedback produced a small increase in this ability. However, the most stimulation points correctly discriminated did not exceed three. The data are discussed in terms of the possible role of cutaneous masking.     

Numerosity discrimination in preschool children

We used a numerical bisection procedure to examine preschool children's sensitivity to the numerical attributes of stimuli. In Experiment 1 children performed two tasks. In the Cups Task they earned coins for choosing a green cup after two drumbeats and a blue cup after eight drumbeats. In the Gloves Task they earned coins for raising a red glove on their left hand after two drumbeats and a yellow glove on their right hand after eight drumbeats. Then in each task a psychometric function was obtained by presenting intermediate numerosities and recording the percentage of trials in which children chose the "many" option. In Experiment 2 children's performance in a '2 vs. 8' discrimination was compared with their performance in a "4 vs. 16" discrimination. Results showed that the individual psychometric functions were of two types, one in which the percentage of "many" choices increased gradually with stimulus numerosity and another in which it increased abruptly, in a step-like manner. Although the average point of subjective equality was close to the geometric mean of the anchor numerosities and the average functions for "2 vs. 8" and "4 vs. 16" superimposed when plotted on a common scale (the scalar property), the individual data were highly variable both across tasks (Cups and Gloves) and numerosity ranges ('2 vs. 8' and '4 vs. 16'). It is suggested that between- and within-subjects variability in the psychometric function is related to children's verbalizations about the sample stimulus.     

Differential production of positive and negative discriminative stimuli by normal and retarded children

Using an observing procedure similar to Wyckoff's (1969), two normal and two mentally retarded children were studied. The children were initially trained to earn pennies by pressing a rectangular key according to a multiple variable-interval extinction schedule of reinforcement. After discrimination training, the children were allowed to produce the discriminative stimuli by depressing a second or observing key. The retarded children were different from the normal children in that they produced more of the positive discriminative stimulus (S+) than the negative discriminative stimulus (S?). In the case of the retarded children, S+ observing started high and remained high. In the case of the normal children, S+ observing was initially substantial and then rapidly diminished.     

Executive processing differences between learning-disabled,mildly retarded,and normal achieving children

This study examined possible executive processing differences between mildly retarded, learning-disabled, and normal achieving children. To this end, the groups were compared as to their ability to recall central and secondary words from base and elaborative sentences under conditions of high and low encoding effort. Executive processing was inferred from the children's ability to maintain optimal recall performance for central and secondary words. Groups were comparable in central recall, but differences in secondary recall occurred for the high- effort encoding condition. Qualitative differences related to the prioritizing of resources (as reflected in the correlation between central and secondary recall) and monitoring the transfer of information (as reflected from central and secondary recall insertions) were found between groups. The results were discussed in terms of an executive processing frame-work that views retarded children as suffering from inefficiencies related to the sharing of resources, whereas the learning-disabled children's inefficiencies were related to the discrimination of resources.The author is indebted to Karl Schemdli, Director of Special Education and Susan Swaim, Research Director, University of Northern Colorado Laboratory School, for their administration assistance in providing children for this study. The author is indebted to Dr. Jim Nicholes for his assistance in the data collection.     

Encoding and retrieval processes in normal children and retarded adolescents

Information processing capabilities of normal and retarded individuals were studied within the context of a modified Sternberg recognition memory task. Presentation of items in the memory set was self-paced, and stimulus exposure times and response latencies were recorded.It was found that normal and retarded individuals spent the same amount of time processing subspan lists during input to the memory system; however, the normal subjects spent less time retrieving information from that system than did the retarded subjects. Part of the superiority of normal subjects was attributable to their higher scanning speeds during the stimulus comparison stage of memory retrieval. The scanning strategy of normal and retarded subjects, on the other hand, was found to be the same: serial and exhaustive. It was further demonstrated that the binary decision stage of retrieval was not related to differences in intelligence.     

Semantic processing can facilitate free recall in mildly retarded adolescents

The efficacy of semantic processing in free recall was investigated in two experiments with EMR adolescents. In Experiment 1, they were taught to use one of two semantic strategies for memorizing a 15-word list. Compared with controls, neither strategy helped recall either in original learning or transfer. In Experiment 2, one of the semantic strategies, a story mnemonic, was investigated further. Rather than being taught to construct their own stories as in Experiment 1, subjects in Experiment 2 were provided with experimenter-composed stories. They showed better immediate recall and retention after 2 months than did no-strategy controls. However, about 1 year after original learning, the retention of experimental and control subjects no longer differed. Discussion focused on the story mnemonic's potential utility and the criteria for judging such potential, e.g., amount of facilitation, ease of training and performance of the strategy, and the degree of its generalizability.     

Selected parameters of response organization in mildly mentally retarded children

The purpose of this study was to investigate the effect of response organization on reaction time (RT) and movement time (MT) of mildly mentally retarded children. Two groups of 30 subjects each were formed: a retarded group 9 yr. of age and a normal group matched for chronological age. Subjects were randomly assigned to one of three precued conditions in which they were told that the forthcoming response would be performed with the right or left hand (precue hand), be to the right or left side (precue direction), or cross or not cross the body midline (precue midline). The retarded group performed significantly more slowly than the normal group on both RT and MT. Both groups, however, were able to utilize precued hand information as opposed to other precued variables, indicating that knowing which hand to use is important when organizing responses.     

Output organization in the free recall of mildly retarded children

Output organization in multitrial free recall of ‘unrelated’ lists can be quantified using measures of intertrial consistency or subjective clustering, the latter being based on subjective ‘categories’ revealed in a post-recall sort task. It has previously been shown with picture stimuli (Todman 1982) that recall and subjective clustering, but not intertrial consistency, increase with age for nonretarded children. In the present study, mildly mentally retarded children at three age levels were given the same task. Although recall increased with age, there was no age effect on subjective clustering or intertrial consistency. Output organization of the retarded groups was compared with that of nonretarded groups at three age levels. The nonretarded groups comprised previously tested children selected to equate each group with one of the three retarded groups on mean recall. Across all age levels, intertrial consistency was significantly (p < 0.02) higher for retarded groups.