The current study provides new information about phonological accuracy and intelligibility in the connected speech of boys with FXS and DS. We found that the boys with FXS (both with and without ASD) did not differ on measures of phonological accuracy or phonological process occurrence but scored lower on a measure of speech intelligibility when compared to the TD boys. Both groups of boys with FXS scored higher on phonological accuracy, scored lower on phonological process occurrence, and were not significantly different from the boys with DS in intelligibility. The boys with DS scored lower on all measures of phonological accuracy and speech intelligibility and higher in phonological process occurrence than the TD boys, indicating that they exhibit greater delays in phonological development relative to the boys with FXS and younger TD boys after controlling for nonverbal mental age.
The connected speech patterns of boys with FXS were similar to those of younger TD boys at a similar nonverbal mental age. The boys with FXS exhibited similar mastery of syllable and word shapes as measured by Proportion of Whole Proximity scores, which were almost identical to those of the TD boys, and both groups of boys with FXS used the same phonological processes as the TD boys with similar percentages of occurrence. Though the average Percent Consonants Correct, Proportion of Whole Word Proximity, and phonological process occurrence scores were similar for the boys with FXS and the TD boys, it is important to point out that there was great individual variability among the participants with FXS. For example, one 13-year-old boy with FXS-O had a Percent Consonants Correct score of 74, a Proportion of Whole-Word Proximity score of 88, and a percent occurrence of substitution processes nine, whereas another 13-year-old boy with FXS-O had Percent Consonants Correct and Proportion of Whole Word Proximity scores of 100 and a zero percent occurrence of substitution processes.
Our finding that the boys with FXS exhibited phonological accuracy in connected speech similar to that of younger TD boys is consistent with previous studies documenting the phonological accuracy in FXS at the word level. Three previous studies found that boys with FXS (ages 3 to 34 years) exhibited common sound substitutions, omissions, and distortions developmentally appropriate for younger TD children (Hanson et al. 1986
; Madison et al., 1986
; Prouty et al., 1988
). The present results are also in agreement with a study by Paul, Cohen, and colleagues (1984)
, in which three boys with FXS (ages 10 to 13) were observed to use common phonological processes such as liquid simplification and final consonant deletion, two of the most commonly occurring processes in the boys with FXS in the present study. The present data regarding phonological accuracy in connected speech are also consistent with those of single-word speech samples obtained by Roberts and colleagues (2005)
, many of which are from the same participants as those in the present study. In connected speech, like single words, the boys with FXS exhibited a delay in phoneme acquisition relative to same-age TD peers, with a Percent Consonants Correct score similar to that of the younger TD boys. We also found that the boys with FXS had a similar Proportion of Whole-Word Proximity in connected speech as in single words. Finally, the boys with FXS used many of the same phonological processes in connected speech that Roberts and colleagues (2005)
found to be productive at the single word level, such as final consonant deletion, cluster reduction, palatal fronting, later stopping, liquid simplification, and cluster simplification as well as infrequently used processes, such as final consonant deletion, early stopping, and voicing/devoicing errors.
One difference between the present results and some previous reports is in the finding of speech intelligibility in FXS (Madison et al., 1986
; Paul, Cohen, et al., 1984
; Spinelli et al., 1995
). Madison and colleagues (1986)
and Paul, Cohen, and colleagues (1984)
reported that despite the occurrence of phonological errors and phonological processes, boys with FXS were intelligible at the single word level, but the boys with FXS in the present study were found to be less intelligible in connected speech than the TD boys. Our findings regarding reduced intelligibility in FXS relative to the TD boys is consistent with another study, in which intelligibility is reported to be reduced in this population. Spinelli and colleagues (1995)
studied eight males with FXS (ages 6 to 26 years) and found that listeners had difficulty understanding all eight males as utterance length increased.
The finding of decreased intelligibility in FXS relative to TD peers despite similar scores on all measures of phonological accuracy suggests that the reduced speech intelligibility in children with FXS may not be due to differences in phonological accuracy but perhaps due to other connected factors such as prosody (e.g., rate, intonation) and fluency. These are two aspects of speech production in which boys with FXS are reported to differ from TD peers (Borghgraef, Fryns, Dielkens, Pyck, & Van den Bergh, 1987
; Hanson et al., 1986
; Palmer et al., 1988
; Reiss & Freund, 1992
; Spinelli et al., 1995
), but whether boys with FXS differ in prosody from TD peers requires further study.
The finding that the boys with FXS-ASD and the boys with FXS-O did not differ in phonological accuracy is supported by a previous study of boys with co-morbid FXS and ASD (Roberts et al., 2007
). Roberts and colleagues (2005)
compared 49 boys with FXS-ASD and 33 boys with FXS-O and found that the groups did not differ in phonological accuracy at the single word level when at similar nonverbal cognitive levels. In other studies, phonological accuracy was not found to be delayed in individualswith autism beyond mental age expectations (Bartolucci & Pierce, 1977
; Kjelgaard & Tager-Flusberg, 2001
; Rice et al., 2005
; Shriberg et al., 2001
). For example, Kjelgaard & Tager-Flusberg studied 89 children with autism (ages 4 to 14 years) and found that expressive phonology at the one word level was in the normal range for chronological age (Kjelgaard & Tager-Flusberg, 2001
). However, our findings differed with another study, which found that children with autism exhibited more motor speech and speech production difficulty than TD children (Adams, 1998
). Another finding of the present study was that boys with FXS-ASD had similar phonological accuracy when compared to younger TD boys. This finding is supported by a previous study by Shriberg and colleagues, in which they found that 30 males with autism (ages 10 to 50 years) had more residual articulation errors than their TD same-age peers, suggesting that their speech production was similar to younger TD peers (Shriberg, 2001
The connected speech measures of boys with DS revealed delays compared to the younger TD boys with a similar nonverbal mental age on all measures. The boys with DS had a lower Percent Consonants Correct score (86) than the younger TD boys (95), and had a lower average Proportion of Whole Word Proximity score of 86 as compared to that of the TD boys (95). The boys with DS used many of the same phonological processes as the TD boys, such as later stopping, liquid simplification, and cluster simplification, yet these processes occurred more often for the boys with DS than the TD boys. Thus, the boys with DS made more errors in consonant production and were more likely to change syllable shapes by omitting segments or syllables in a word than the TD boys. This change in word shapes (i.e., reduction of clusters, omission of phonemes, omission of syllables) that results in the occurrence of syllable structure processes can have a significant impact on intelligibility (Hodson & Paden, 1991
). There also was great individual variability among the participants with DS in all of these measures. For example, one 6-year-old boy with DS had a Percent Consonants Correct score of 56 and a Proportion of Whole Word Proximity score of 76; he also used syllable structure processes in 13% of opportunities. In comparison, another 6-year-old boy with DS had a Percent Consonants Correct score of 89 and a Proportion of Whole Word Proximity score of 95; he also used syllable structure processes in only 1% of opportunities.
The current findings regarding phonological accuracy in connected speech in DS are consistent with those at the single-word level as reported by Roberts and colleagues (2005)
. In single words as in connected speech, the boys with DS exhibited a delay in phonemic acquisition (as measured by Percent Consonants Correct and Proportion of Whole Word Proximity) relative to same-age TD peers. Phonological process occurrence was similar in single words and connected speech as well. Except for early stopping, all of the phonological processes Roberts and colleagues found to be productive at the single word level occurred often in connected speech, including final consonant deletion, cluster reduction, palatal fronting, later stopping, liquid simplification, and cluster simplification.
The current findings that boys with DS are delayed in their phonological development beyond mental age expectations when compared to their TD peers is supported by previous studies in which children with DS exhibited later phoneme emergence and suppressed common developmental phonological processes at a slower rate when compared to TD children but were considered delayed, not different, in their phonological development from TD peers (Bleile & Schwarz, 1984
; Kumin et al., 1994
; Smith & Stoel-Gammon, 1983
; Stoel-Gammon, 1980
). Smith and Stoel-Gammon (1983)
found that compared to four TD children (ages 1 to 3 years), five children with DS (ages 3 to 6) exhibited delayed phonemic acquisition and the occurrence of similar phonological processes in single words relative to the younger TD children.
In the present study, the boys with FXS and DS scored differently on all speech measures except that of intelligibility. The boys with FXS scored higher on measures of phonological accuracy, Percent Consonants Correct, and Proportion of Whole Word Proximity and had a lower occurrence of syllable structure and substitution processes than the boys with DS, but they did not score differently on Percent Intelligible Words. The same phonological processes occurred in the boys with DS and the boys with FXS but occurred with more frequency in the boys with DS. It is possible that the cause of reduced intelligibility in FXS may be related to factors other than phonological accuracy or process usage, which may help explain why their intelligibility scores did not differ from the boys with DS despite scoring higher on all measures of phonological accuracy. Some possible causes for this intelligibility deficit in FXS may be related to suprasegmental characteristics or fluency deficits exhibited by these boys. Rapid and fluctuating rate, intonation differences, stuttering, or cluttering which have been described as occurring in some males with FXS (Borghgraef, Fryns, Dielkens, Pyck, & Van den Bergh, 1987
; Brun-Gasca and Antigas-Dallares, 2001
; Hanson, Jackson, & Hagerman, 1986
; Reis & Freund, 1992
) may possibly contribute to intelligibility in connected speech without affecting phonological production. Other explanations may be related to acoustic characteristics of the connected speech signal produced by these children that are too subtle to be measured subjectively through phonetic transcription such as atypical pauses or stress or rate fluctuations.
The present study has several limitations that should be considered. First, percentage of intelligibility is relatively high for all four groups of participants (greater than 80%). This may be due in part to our method, in which each highly trained glosser or transcriber was allowed to listen to an utterance up to three times, and audio glosses were verified using video. Our familiarity with the play materials used and the ability to use contextual clues from the video to gloss single words, rather than utterances, also may have yielded a higher intelligibility score than a naïve listener would have given the speech sample as a whole. Given the varying amount of unintelligible utterances in the connected speech samples, it is also possible that applying a convention to “estimate” the Percent Intelligible Words inflated the outcome in the boys with FXS and DS, who had the most unintelligible utterances. This is a limitation of assessing connected speech in children who are not completely intelligible, but as the same procedure was used to calculate intelligibility for all participants, differences between groups should be preserved. A second limitation of the current study is that the standard deviations for the occurrence of phonological processes were quite large, indicating wide variability in the percentage of occurrence within each group. This may be due in part to the variable nature of spontaneous speech samples, another limitation of assessing connected speech, as children using less complex syllable shapes and fewer types of words may have fewer opportunities to use many individual phonological processes than children using more complex syllable shapes. A third limitation of the study, similar to that of the single-word study conducted by Roberts et al. (2005)
, only phonemic consonants and known target words were studied. We were therefore unable to describe the types of errors made during unintelligible speech in which target phonemes were unknown, and we did not study vowel accuracy or suprasegmental and nonsegmental aspects of speech, such as speaking rate, pauses, or fluency, and how they might impact speech production errors. A fourth limitation of the study is that comparisons of boys with FXS and DS were not sufficient for determining syndrome-specific speech characteristics; future studies should compare these children with other syndrome groups on these speech measures. A fifth and final study limitation is that our analysis represented the phonological accuracy and intelligibility characteristics of our participants at only one time point; studying the developmental trajectories of our participants may provide more information about the differences in the rate and patterns of speech development in these populations.
These limitations have implications for future research directions in connected speech phonological accuracy for these populations. First, future research should address the concurrent suprasegmental features of connected speech, such as prosody, rate, pauses, and fluency, and their possible effects on phonological accuracy and speech intelligibility. Second, future studies should address phonological development across several time points, revealing the patterns of development and developmental trajectories of each of our participant groups. Finally, our findings do not suggest why children with FXS are less intelligible than their TD counterparts despite almost identical phonological outcomes. Future research should focus on identifying possible causal factors that may contribute to limited intelligibility, such as suprasegmental characteristics, fluency, and more objective acoustic analyses of speech production.
The results of the present study have important clinical implications regarding assessment and intervention in the phonological development of boys with FXS and boys with DS. First, because there are considerable differences among individuals and both populations have speech delays relative to chronological age, a comprehensive speech assessment focusing on the child’s phonemic inventory, word shapes, phonological process occurrence, and intelligibility in connected speech should be completed. Because both groups exhibited similar phonological accuracy in words as compared to connected speech, a single word articulation test may be an efficient and effective method of assessing phonological skills in boys with FXS and DS. In boys with FXS however, a comprehensive evaluation should also include a measure of connected speech intelligibility, since intelligibility in this group is reduced compared to TD peers despite age-appropriate phonological accuracy scores. Because phonological accuracy cannot explain the reduced intelligibility in FXS, it is important to assess other factors that could affect speech intelligibility, such as oral motor speech skills, rate, fluency, and prosody in this group. Similar to assessment, intervention approaches may differ for children with FXS and DS since their speech production accuracy and phonological process occurrence differs. Because the phonological errors and phonological process usage displayed by the boys with FXS are similar to those displayed by younger TD children, intervention approaches that have proven successful in improving speech production errors in children with IQs in the normal range may be utilized. The boys with FXS showed delayed phonemic acquisition but adequate retention of word shapes as compared to the TD boys, therefore therapy should focus on correcting individual phoneme articulation and suppressing substitution processes as well as considering other speech aspects, such as prosody, that may be limiting their intelligibility in connected speech. Intervention in boys with DS should focus on improving not only intelligibility, which was also significantly lower than that of the TD boys, but also increasing phoneme acquisition, suppressing commonly used phonological processes, and retaining word shapes. The cycles approach may be particularly effective in suppressing syllable structure and substitution processes in both populations (Hodson, 2006b; Hodson & Paden,1991
). The complexity approach (Gierut, 2001, 2005), which is highly structured and targets more complex sounds than easier sounds, may also be useful in increasing the phonetic repertoire of individuals with FXS and DS. The boys with DS, in particular, may benefit from therapy tasks that address “syllableness,” in which the retention of target word shapes is addressed by marking often-deleted syllables and segments in blends and words (Hodson & Paden, 1991