Language, cognition, and short-term memory in individuals with Down syndrome.

The developmentally emerging phenotype of language and cognition in individuals with Down syndrome is summarized on the basis of the project's prior work. Identified are a) the emerging divergence of expressive and receptive language, b) the emerging divergence of lexical and syntactic knowledge in each process, and c) the emerging divergence within cognitive skills of auditory short-term memory and visuospatial short-term memory from other visuospatial skills. Expressive syntax and auditory short-term memory are identified as areas of particular difficulty. Evidence for the continued acquisition of language skills in adolescence is presented. The role of the two components of working memory, auditory and visual, in language development is investigated in studies of narrative and longitudinal change in language skills. Predictors of individual differences during six years of language development are evaluated through hierarchical linear modelling. Chronological age, visuospatial short-term memory, and auditory-short term memory are identified as key predictors of performance at study entry, but not individual change over time, for expressive syntax. The same predictors account for variation in comprehension skill at study outset; and change over the six years can be predicted by chronological age and the change in visuospatial short-term memory skills.

Behavioral phenotype of individuals with Down syndrome.

Evidence is reviewed for a developmentally-emerging behavioral phenotype in individuals with Down syndrome that includes significant delay in nonverbal cognitive development accompanied by additional, specific deficits in speech, language production, and auditory short-term memory in infancy and childhood, but fewer adaptive behavior problems than individuals with other cognitive disabilities. Evidence of dementia emerges for up to half the individuals studied after age 50. Research issues affecting control group selection in establishing phenotypic characteristics are discussed, as well as the possible genetic mechanisms underlying variation in general cognitive delay, specific language impairment, and adult dementia. MRDD Research Reviews 2000;6:84-95. Wiley-Liss, Inc.

An examination of verbal working memory capacity in children with specific language impairment.

This study investigated verbal working memory capacity in children with specific language impairment (SLI). The task employed in this study was the Competing Language Processing Task (CLPT) developed by Gaulin and Campbell (1994). A total of 40 school-age children participated in this investigation, including 20 with SLI and 20 normal language (NL) age-matched controls. Results indicated that the SLI and NL groups performed similarly in terms of true/false comprehension items, but that the children with SLI evidenced significantly poorer word recall than the NL controls, even when differences in nonverbal cognitive scores were statistically controlled. Distinct patterns of word-recall errors were observed for the SLI and NL groups, as well as different patterns of associations between CLPT word recall and performance on nonverbal cognitive and language measures. The findings are interpreted within the framework of a limited-capacity model of language processing.

Verb use by individuals with Down syndrome.

Production of grammatical and lexical verbs in narratives from 29 individuals with Down syndrome and 29 typically developing control subjects matched on linguistic level (Brown's Stages 3, 4, and 5) was examined. We addressed recent theories proposing that verbs are central to syntactic development (Tomasello & Merriman, 1995). Consistent with predictions from the child talk model (Chapman et al., 1992), the individuals with Down syndrome produced fewer lexical or grammatical verbs per utterance compared to the control group but produced a greater diversity of lexical verbs. The findings suggest that the well-documented syntactic deficits evidenced by individuals with Down syndrome may reflect difficulty in accessing verbs when constructing utterances. This difficulty may stem from deficits in auditory short-term memory.

The impact of emphatic stress on novel word learning by children with specific language impairment.

This investigation examined the influence of emphatic stress on children's novel word learning. Forty school-age children participated in this study, including 20 children with specific language impairment (SLI) and 20 children with normal language (NL) development. Results indicated that there were no significant stress effects for comprehension or recognition of novel words (for which all children demonstrated relatively high levels of performance); however, children in both groups exhibited significantly better production of words that had been presented with emphatic stress than with neutral stress. These findings are discussed within a limited capacity framework of language processing.

Lexical learning by children with specific language impairment: effects of linguistic input presented at varying speaking rates.

The purpose of this study was to investigate the impact of speaking rate variations in the linguistic input provided to children during a novel word learning task. Thirty-two school-age children participated in this investigation, including 16 children with specific language impairment (SLI) and 16 normal language (NL) controls matched on mental age (MA). The younger half of the NL group also served as a vocabulary level comparison for the older half of the children with SLI. No significant rate effects were found for comprehension of novel words, with all children performing at relatively high levels of accuracy. The group with SLI demonstrated the same recognition accuracy pattern as MA matched controls for target labels versus phonetically similar/dissimilar foils only for words trained at slow rate. Rate effects were most pronounced for items with the highest difficulty level, namely production of novel words. Children with SLI produced significantly fewer words that had been presented at fast rate during training than NL children matched on mental age or vocabulary level. Individual differences and production error patterns on fast rate items were examined. The finding that variations in speaking rate had a disproportionate impact upon word learning for children with SLI was interpreted within a framework of limited processing capacity.

The influence of prosodic and gestural cues on novel word acquisition by children with specific language impairment.

The purpose of this study was to investigate the effects of prosodic and gestural cues on children's lexical learning. Acquisition of novel words was examined under linguistic input conditions that varied in terms of rate of speech, stress, and use of supplemental visual cues (i.e., gestures). Sixteen kindergarten children served as subjects in this study, including 8 children with normal language (NL) and 8 children with specific language impairment (SLI). A repeated-measures design was used such that all subjects in both groups participated in each of the three experimental conditions (the Rate, Stress, and Visual Condition). Results indicated that acquisition of novel words by the groups with NL and SLI was significantly affected by alterations in speaking rate and by the use of gestures accompanying spoken language. There were no statistically significant effects for the stress manipulations, although subjects with SLI tended to correctly produce novel words that had received emphatic stress during training more often than words presented with neutral stress. Implications of these findings are discussed with respect to the importance of considering how the manner of presentation of the linguistic signal influences the processing and acquisition of language.

Analysis of the spontaneous speech samples of children with cochlear implants or tactile aids.

Analyses were performed on the spontaneous speech samples produced by profoundly hearing-impaired children who used the 3M/House single-channel cochlear implant (n = 7), the Nucleus multichannel cochlear implant (n = 7), or the two-channel tactile aid, the Tactaid II (n = 12). Speech recordings were obtained in the predevice condition, and after 6- and 12-months use. The speech of the children in the three experimental groups was compared to that of a control group of subjects who used a tactile aid inconsistently and received minimal speech training. Several new analysis procedures were developed to describe adequately the characteristics of the children's speech. The results revealed that all three experimental groups and the control group showed an increase in their production of sounds classified as English phonemes in the postdevice conditions. It was apparent at both the 6- and 12-months postdevice intervals that the most dramatic improvements were made by the users of the Nucleus device. The changes made by the Tactaid and 3M/House users were similar. The subjects with the Nucleus device also developed more diverse phonetic repertoires over time than did the other experimental subjects. More subjects with the Nucleus device acquired fricatives, liquids, glides, voiceless consonants, and high front vowels than did the subjects in the other groups. The subjects in the control group developed the most limited phonetic repertoires.

Evaluation of a tactile aid and a cochlear implant in one child.

The speech perception and production skills have been examined in a young deaf child who used a tactile aid for 2.5 years and subsequently received a multichannel cochlear implant. Although the differences were small, there was a trend of higher performance on nearly all speech perception measures following implantation than was observed after 2.5 years of tactile-aid use. Negligible changes occurred in her speech while wearing the tactile aid but substantial improvements appeared after she had used the multichannel implant for only 6 months.