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Mentally retarded and nonretarded persons of equal mental age read lists of nine nouns presented simultaneously in a horizontal format. In the control condition all words were colored blue; in the experimental condition the fifth word was colored red (isolated). Recall of items when isolated was reliably higher than when not isolated for both groups. The proportion of fifth-position items recalled compared with total recall was almost identical for both groups whether or not the items were isolated. Results were discussed in terms of interference theory and the pedagogical implications of superior recall of words isolated by color.

Thirty-six institutionalized retarded adolescents named 48 colored pictures of objects. Winters, Winter, and Burger (1978) had previously established that for nonretarded adults the estimated age-of-acquisition of the names of these 48 objects ranged from 2 years, 6 months to 7 years of age. We found that pictures whose names had been estimated by nonretarded adults to have been acquired earlier were named more accurately and faster by retarded adolescents than were pictures whose names were estimated to have been acquired later. The implications of these results were discussed.

Mentally retarded adolescents were tested in eight experimental conditions using the Brown-Peterson paradigm of proactive inhibition. Length of retention interval, absence or presence of vocalization during the retention interval (naming colored lights), and rate of light presentation varied. The purpose was to determine the influence of amount of vocalization during the retention interval on retrieval from short-term memory. A filled retention interval had more a deleterious effect on retrieval than did an unfilled one, but significant amounts of memory loss occurred whether the interval was filled or unfilled. Amount of vocalization did not affect recall.

The recall performance of three groups of nonretarded and one group of mentally retarded persons who were tested using the Brown-Peterson paradigm was compared on two scoring methods. In one method a point was assigned to each item of a triad correctly recalled; in the other a point was added when all three words were correctly recalled in the sequence in which they were presented. The slopes of the curves were steeper over groups and trials during build-up of proactive inhibition, as well as over trials during release, when scoring for sequence of recall than when not scoring for sequence of recall. Analyses of the proportion of times complete triads were recalled by the groups in the sequence in which they were presented revealed that that sequence did not differ reliably among the groups during build-up or release. The relatively higher performance by better performing groups when scoring for sequence of recall, and the ensuing interactions, can be attributed to level of recall and chance fluctuations in the incidence of that particular sequence rather than to some cognitive factor.

One group of EMR adolescents and adults and three groups of nonretarded children and adolescents were compared during accumulation of and release from proactive inhibition. All groups demonstrated the effects of and release from proactive inhibition. Analyses of intralist intrusions indicated that these errors did not differentially affect performance by any group during the accumulation of proactive inhibition and did not occur during its release. These results were discussed in terms of the groups' discrimination abilities within and between taxonomies, short-term memory limitations, and the utilization of categorical information on this task by the mentally retarded subjects.

In Phase I of this study, mentally retarded adults judged whether exemplars were members of their respective categories. In Phase II they judged how representative the exemplars were of their categories. Comparisons were made between this group and the nonretarded groups of Bjorklund, Thompson, and Ornstein (1983) and Uyeda and Mandler (1980). There was little evidence of a developmental relationship between typicality ratings given by retarded and nonretarded persons, but there were significant relationships among the groups for specific categories. Relationships were more category-than mental age-dependent. Other analyses indicated that Rosch's (1975) finding that typical exemplars are incorporated into category structures prior to atypical exemplars was replicated with retarded persons.

Mentally retarded and nonretarded children learned pairs of pictures in a single-function order (A and B terms of each pair were in the same position throughout) or in a double-function order (all items were re-paired and served as A and B terms). Associative symmetry was demonstrated by all groups when the lists were presented single-function; forward asymmetry was demonstrated when the list was presented double-function. When categorized pairs were presented double-function, items that were correctly associated by category produced symmetry; items that were correctly associated but not by category produced forward asymmetry. The possible influence of single vs. multiple associations on associative symmetry was discussed.

Three groups of nonretarded children and adolescents and one group of mentally retarded adolescents were compared on their retrieval of words from long-term store (from 3 minutes to 3 days after list presentation). When items were uncategorized (Experiment 1), the retarded group exhibited more intertrial forgetting than did two of the nonretarded groups, but all groups were similar in reminiscence (recall of previously unrecalled words), spontaneous recovery (recall of previously recalled and subsequently forgotten words), and subjective organization of the list. When items were categorizable (Experiment 2), the results were similar except that the oldest nonretarded group organized the list better than did the retarded group. With one exception, the groups' retention rates were essentially the same after the first long-term recall trial. Results were discussed in terms of strategic/structural deficiencies.

Age-of-acquisition estimates and ratings on seven semantic dimensions by nonretarded adults were compared with the codability and retrieval speed of those items by retarded individuals. Correlational analyses indicated that age-of-acquisition estimates, codability, and retrieval speed were highly related to each other and significantly related to most of the semantic dimensions. Regression analyses revealed that codability, meaningfulness, and imagery each contributed significantly to the variance of retrieval speed. These results were compared with those of similar studies in which the lexical retrieval speed of nonretarded persons was investigated.