Speech production errors in adults with and without Down syndrome following verbal, written, and pictorial cues

Vowel Acoustics and Speech Intelligibility in Young Adults With Down Syndrome

Purpose Speech production deficits and reduced intelligibility are frequently noted in individuals with Down syndrome (DS) and are attributed to a combination of several factors. This study reports acoustic data on vowel production in young adults with DS and relates these findings to perceptual analysis of speech intelligibility. Method Participants were eight young adults with DS as well as eight age- and gender-matched typically developing (TD) controls. Several different acoustic measures of vowel centralization and variability were applied to tokens of corner vowels (/ɑ/, /æ/, /i/, /u/) produced in common English words. Intelligibility was assessed for single-word productions of speakers with DS, by means of transcriptions from 14 adult listeners. Results Group differentiation was found for some, but not all, of the acoustic measures. Low vowels were more acoustically centralized and variable in speakers with DS than TD controls. Acoustic findings were associated with overall intelligibility scores. Vowel formant dispersion was the most sensitive measure in distinguishing DS and TD formant data. Conclusion Corner vowels are differentially affected in speakers with DS. The acoustic characterization of vowel production and its association with speech intelligibility scores within the DS group support the conclusion of motor control deficits in the overall speech impairment. Implications are discussed for effective treatment planning.

Auditory-Perceptual Speech Features in Children With Down Syndrome

Speech disorders occur commonly in individuals with Down syndrome (DS), although data regarding the auditory-perceptual speech features are limited. This descriptive study assessed 47 perceptual speech features during connected speech samples in 26 children with DS. The most severely affected speech features were: naturalness, imprecise consonants, hyponasality, speech rate, inappropriate silences, irregular vowels, prolonged intervals, overall loudness level, pitch level, aberrant oropharyngeal resonance, hoarse voice, reduced stress, and prolonged phonemes. These findings suggest that speech disorders in DS are due to distributed impairments involving voice, speech sound production, fluency, resonance, and prosody. These data contribute to the development of a profile of impairments in speakers with DS to guide future research and inform clinical assessment and treatment.

Speech impairment in Down syndrome: a review

PURPOSE

This review summarizes research on disorders of speech production in Down syndrome (DS) for the purposes of informing clinical services and guiding future research.

METHOD

Review of the literature was based on searches using MEDLINE, Google Scholar, PsycINFO, and HighWire Press, as well as consideration of reference lists in retrieved documents (including online sources). Search terms emphasized functions related to voice, articulation, phonology, prosody, fluency, and intelligibility.

CONCLUSIONS

The following conclusions pertain to four major areas of review: voice, speech sounds, fluency and prosody, and intelligibility. The first major area is voice. Although a number of studies have reported on vocal abnormalities in DS, major questions remain about the nature and frequency of the phonatory disorder. Results of perceptual and acoustic studies have been mixed, making it difficult to draw firm conclusions or even to identify sensitive measures for future study. The second major area is speech sounds. Articulatory and phonological studies show that speech patterns in DS are a combination of delayed development and errors not seen in typical development. Delayed (i.e., developmental) and disordered (i.e., nondevelopmental) patterns are evident by the age of about 3 years, although DS-related abnormalities possibly appear earlier, even in infant babbling. The third major area is fluency and prosody. Stuttering and/or cluttering occur in DS at rates of 10%-45%, compared with about 1% in the general population. Research also points to significant disturbances in prosody. The fourth major area is intelligibility. Studies consistently show marked limitations in this area, but only recently has the research gone beyond simple rating scales.

Interhemispheric transmission time in persons with Down syndrome

BACKGROUND

The study of cerebral specialization in persons with Down syndrome (DS) has revealed an anomalous pattern of organization. Specifically, persons with DS elicit a right cerebral hemisphere lateralization for receptive language and a left cerebral hemisphere lateralization for the production of simple and complex movements: a pattern quite different from the left hemisphere lateralization typically characterizing the aforementioned processes in the non-DS population. It is thought that the putative separation between speech perception and movement planning systems as well as the cost of interhemispheric integration impedes verbal-motor behaviours in persons with DS. Moreover, morphological anomalies of callosal structure may further amplify between-hemisphere communication difficulties in the DS population. In the present investigation, we employed a behavioural technique (i.e. the Poffenberger paradigm; Poffenberger) to determine whether global anomalies of callosal structure further amplify deficits in interhemispheric communication.

METHODS

Fourteen individuals with DS and 25 chronological age-matched and gender-equated participants without intellectual disability performed a visuomotor reaction time (RT) test with their left or right hand to visual stimuli appearing left or right of visual fixation. Typically it is reported that responses to visual stimuli appearing ipsilateral to the responding hand (i.e. the uncrossed condition) are faster than responses wherein visual stimuli and responding hand are contralaterally mapped (i.e. the crossed condition). The increased RT associated with the crossed condition is reported on the order of 4 ms and has been interpreted to reflect the physiological result of interhemispheric transmission.

RESULTS

Not surprisingly persons with DS exhibited slower and more variable RTs relative to control counterparts. In addition, a reliable RT advantage favouring the uncrossed conditions was observed among control participants but not persons with DS.

CONCLUSIONS

In keeping with the extant literature, RT performance of the DS group was slower and more variable than control counterparts. This finding has been interpreted to reflect an 'adaptive reaction' wherein the perceptual-motor abilities of persons with DS are not optimized to respond to externally paced stimuli. In terms of evaluating interhemispheric transmission via the Poffenberger paradigm, our results show the finite measures of explicit brain-behaviour relations characterizing so-called healthy controls are not always tenable in the DS population. Indeed, we believe such a finding underpins the aforementioned 'adaptive reaction' exemplifying preferred movement control in persons with DS.

Speech perception and motor control in children with Down syndrome

Twelve children with and without Down syndrome (DS) performed eight subtests of an apraxia battery to determine under what conditions children with DS had difficulty performing representational and nonrepresentational gestures. Participants with DS also completed a dichotic listening test. Participants with DS performed just as well as control participants on all aspects of the apraxia battery except a subtest in which they were required to pantomime tool use from verbal instruction. This suggests that children with DS have difficulty generating an action from memory following verbal instruction. Given the sufficient context or visual demonstration, children with DS performed similar to the other participants. As well, there was a great deal of within-group variability for dichotic listening ear advantage. Participants with a greater left ear advantage on the dichotic listening test committed more errors on an imitation test that also included a verbal component than participants with a greater right ear advantage.

Speed of naming in children with Williams and Down syndromes

BACKGROUND

Williams syndrome (WS) and Down syndrome (DS) are two neurodevelopmental genetically based disorders which exhibit mental retardation with a unique cognitive profile. Naming in individuals with WS and DS has been investigated in several studies, with results indicating that the performance of children with WS and DS is at a similar level and below mental age expectations on naming tasks.

METHOD

Speed of naming pictures, colours, numbers, letters and words was assessed in 8 individuals with WS, 10 individuals with DS, and 18 mental age controls. All stimuli were presented on a computer monitor and reaction times for naming were recorded.

RESULTS

Our results indicated that speed of naming in children with DS and WS is not statistically different to that of mental age controls. However, error analysis in naming words and pictures revealed qualitative differences between the three groups.

CONCLUSION

These results challenge the tenet of increased naming speed in children with WS compared to mental age controls. The findings are discussed in the light of current evidence concerning the linguistic abilities of children with neurodevelopmental disorders and those with typical development.

Verbal intrusions precede memory decline in adults with Down syndrome

BACKGROUND

Verbal intrusion errors are irrelevant responses made in the course of verbal memory retrieval or language production that have been associated with disruption of executive functions and the prefrontal cortex. They have been observed to occur more frequently both with normal aging and with neurodegenerative diseases such as Alzheimer's disease (AD). The purpose of this study was to longitudinally examine the production of verbal intrusions among middle-aged adults with Down syndrome (DS) and unspecified intellectual disability (ID) to determine whether producing verbal intrusions at one point in time was related to subsequent verbal memory performance. Because of the combination of a relative deficit in verbal working memory (WM), premature aging, and higher risk of AD among adults with DS, it was predicted that they would make more verbal intrusions than adults with unspecified ID.

METHODS

Word List recall (WLR), the Selective Reminding Test (SRT), and the Cued Recall Test (CRT), were administered three times at 18-month intervals during a 3-year period. In Analysis 1, aetiology differences in making intrusion errors were examined. Twenty-three adults with unspecified ID in the moderate to mild range [time 1(T1) mean age = 47.2 years] and 42 adults with DS (T1 mean age = 44.3) participated. WLR is a serial WM task beginning at two word sequences and progressively increasing by one word every three trials. WLR intrusions were analysed because they were least likely to include 'educated guesses' because this test is not based on semantic categories. In Analysis 2, we only examined participants with DS. They were divided into two groups, 16 individuals who made at least one intrusion error at T1 (T1 mean age = 45.8) and 26 who did not (T1 mean age = 43.3). Longitudinal performance for these groups was analysed to determine whether the group that intruded at T1 did more poorly on subsequent memory tests.

RESULTS

A higher proportion of responses comprised intrusions for the group with DS and a higher percentage of the participants with DS made at least one intrusion error when compared with participants with unspecified ID (74% and 44% respectively). Those participants with DS who made at least one intrusion error at T1 showed a subsequent decline in performance on both WLR and the SRT.

CONCLUSIONS

The production of intrusion errors during a verbal WM task is a characteristic of middle-aged adults with DS. This suggests compromised executive function and control of inhibition within the verbal modality for this group. Further, verbal intrusions are a qualitative aspect of verbal processing that merit attention in considering the issue of deficiencies of language and verbal WM abilities among people with DS. Last, and perhaps most importantly, although not definitive diagnostically, an increase in verbal intrusions is a potentially noteworthy signal when evaluating the cognitive health of adults with DS.