Grammatical morphology and speech perception in children with specific language impairment.

Journalof Speech and Hearing Research, Volume 35, 1076-1085, October 1992

Grammatical Morphology and Speech Perception in Children With Specific Language Impairment Laurence B. Leonard Karla K. McGregor ieorge U. Allen Purdue University West Lafayette, IN Many English-speaking children with specific language impairment have been found to be especially weak intheir use of grammatical morphology. Ina separate literature, many children meeting the same subject description have shown significant limitations on tasks involving the perception of rapid acoustic changes. In this study, we attempted to determine whether there were parallels between the grammatical morphological limitations of children with specific language impairment and their performance profiles across several perceptual contrasts. Because most English grammatical morphemes have shorter durations relative to adjacent morphemes in the speech stream, we hypothesized that children with specific language impairment would be especially weak in discriminating speech stimuli whose contrastive portions had shorter durations than the noncontrastive portions. Results from a group of eight children with specific language impairment with documented morphological difficulties confirmed these predictions. Several possible accounts of the observed morphology-perception parallels are offered. KEY WORDS: specific language Impairment, language disorders, morphology, perceptlon

Children with specific language impairment show a significant deficit in language ability in the face of normal hearing and nonverbal intelligence, and the absence of frank neurological dysfunction. The cause of specific language impairment is not known, though numerous proposals have been offered. One of these proposals is that the language problems of children with specific language impairment are attributable to an auditory perceptual deficit. This point of view has been refined and advanced most effectively by Tallal and her colleagues (e.g., Tallal & Piercy, 1973a, 1973b, 1974, 1975; Tallal & Stark, 1981; Tallal, Stark, Kallman, & Mellits, 1980). Using the results of several series of studies as support, these investigators argue that children with specific language impairment (hereafter "SLI") have great difficulty in the auditory processing of stimuli that contain rapid changes. For example, the syllables [ba] and [da], which are distinguishable only by differences in their brief formant transitions, represent a perceptual contrast that has been quite problematic for these children. Although the basic findings of Tallal and her colleagues have been replicated and seem in little doubt, the interpretation of these results has been a source of controversy. A number of authors have questioned the degree to which the specific perceptual limitations observed in this work could be taken as causal factors in SLI children's problems with language in general (e.g., Leonard, 1982; Tomblin & Quinn, 1983). For example, although the [ba]-[da] distinction is difficult for children with SLI in these studies, substitutions of [b] for d] or vice versa are very rare in the speech of these children. In addition, even normally developing children under the age of 4 years, 6 months cannot perform the simplest of the tasks used in this line of 0 1992, American Speech-Language-Hearing Association

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Leonard et al.: Specific Language Impairment

research-the target identification task-yet these children produce language that seemingly requires the perception of many of the same fine distinctions. Close inspection of the tasks used in the Tallal studies suggests that more than perception is at work. Even in the simpler target identification task used in these investigations, the child must not only discriminate the target stimulus from the contrastive stimulus but also remember which one is the target stimulus and push a button only when this stimulus is heard. It is likely that these task demands lead to underestimates of children's perceptual abilities. Although we too have noted the problems of interpretation posed by these studies (e.g., Leonard, 1987), our recent work suggests that there may be at least an indirect link between the kind of perceptual difficulties observed by Tallal and certain language problems exhibited by SLI children. In particular, there seems to be a similarity between the types of stimuli that are especially problematic in perception as measured by the target identification task and the characteristics of the grammatical morphemes that are most difficult for these children to use. The purpose of the present study was to examine these similarities in a more systematic manner. We begin with a review of the relevant findings from earlier work.

Grammatical Morpheme Limitations Although children with SLI constitute a heterogeneous group, there is a common profile that emerges from studies of these children: Children with SLI often show a mild to moderate deficit in a range of language areas and a more serious deficit in the use of morphology (Leonard, 1989). The latter includes problems with inflections such as the third person singular -s as well as function words such as the articles a and the. This deficit is most readily seen when children with SLI are compared with younger normally developing children matched for mean length of utterance (MLU). In such studies, children with SLI often show significantly lower percentages of use of these grammatical morphemes in obligatory contexts (Albertini, 1980; Beastrom & Rice, 1986; Bliss, 1989; Cousins, 1979; Ingram, 1972; Johnston & Kamhi, 1984; Johnston & Schery, 1976; Khan & James, 1983; Paul & Shriberg, 1982; Steckol & Leonard, 1979; Trantham & Pedersen, 1976; Watkins & Rice, 1989). An inspection of the now-extensive literature on the use of grammatical morphemes by children with SLI acquiring English as well as the emerging literature on such use by children acquiring languages such as Italian (Leonard, Bortolini, Caselli, McGregor, & Sabbadini, 1992; Leonard, Sabbadini, Leonard, & Volterra, 1987; Leonard, Sabbadini, Volterra, & Leonard, 1988) and Hebrew (Rom & Leonard, 1990) reveals that not all grammatical morphemes are equally troublesome for children with SLI. Those that are especially problematic seem to have low phonetic substance. That is, they are nonsyllabic consonant segments and unstressed syllables characterized by shorter duration than adjacent morphemes, and, often, lower fundamental frequency and amplitude. A detailed listing of the grammatical morphemes that do and do not present great difficulty for children with SLI is provided in Appendix A. Examples of especially difficult

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morphemes include the English inflections for regular past (-ed) and third person singular (-s), the Italian articles (e.g., il, la), the English copula (e.g., is, are), and the Hebrew definite accusative marker (e0. These and others listed in Appendix A are nonsyllabic consonants or unstressed syllables that are rarely or never in sentence positions in which vowel lengthening occurs. Examples of morphemes that are not extraordinarily difficult for SLI children include Italian adjective inflections that agree with the noun in number and gender (e.g., chiave piccola "little key," pettine piccolo "little comb"), Hebrew masculine and feminine present verb inflections (e.g., holex "walks," hoixot "walk"), and Hebrew noun plural inflections (-im, -ot). These are morphemes that are syllabic and carry either primary stress or appear frequently in sentence positions (notably clause-final position) in which significant vowel lengthening occurs (Farnetani & Fori, 1982; Klatt, 1975; Morgan, 1986). The difficulty with grammatical morphemes experienced by children with SLI cannot be due to low phonetic substance alone, for these children show considerably greater use of some of the same phonetic forms in nonmorphophonemic contexts. For example, higher percentages of use are seen for [d] in braidthan in played, similarly, percentages for [s] are higher in box than in rocks. The difficulty seems to rest in the combined effects of perceiving the form and treating it as a morpheme. According to leamability theories such as that of Pinker (1984), the child must not only perceive, say, [d] in played, but also relate played to play, and place -ed in the proper place in a paradigm for play (specifically, in the cell designating past tense). Because these additional operations are not involved when [d] appears in a word such as braid, the child's acquisition and use of [d] will be more advanced in braid than in played. The specific grammatical functions of morphemes (representing the dimensions of the paradigm) exert a further influence on acquisition and use. Grammatical functions with clear semantic correlates, such as noun plural, are likely to be hypothesized sooner (Pinker, 1984). Consequently, not only will a form such as [s] appear earlier in a word such as box than ina plural noun form such as rocks, it will appear earlier in rocks than in a third person singular verb form such as knocks.

Difficult Perceptual Distinctions Examination of the perception literature reveals some striking similarities to the low phonetic substance findings for grammatical morpheme use. It appears that whenever the duration of the contrastive portion of the stimulus is shorter than that of the remaining portion of the stimulus, children with SLI have greater difficulty than normally developing children of the same age. When the duration of the contrastive feature is longer than that of the rest of the stimulus, these children perform adequately. Absolute duration does not seem to be a factor. For example, the studies of Tallal and Piercy (1975) and Tallal and Stark (1981) show that children with SLI have great difficulty with the following contrasts: 1. [ba]-[da], differing in the 40-msec formant transitions but identical in the 205-msec steady state vowel.


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2. [da]-[ta], identical in the 260-msec steady state vowel but differing in a 60-msec (for [ta]) versus 0-msec (for [da]) voice onset time. 3. [sa]-l[J'a, identical in the 250-msec vowel but differing in the frequency distribution of the 150-msec frication noise and 30-msec (for [a]) versus 0-msec for [sa]) silent interval between the offset of frication and onset of the vowel formants. 4. [cI]-[aeI], in which two steady state portions of vowels were connected without transitions, with the stimuli differing in the first, 43-msec portion but not on the second, 207-msec portion. On the other hand, children with SLI have performed as well as age-matched controls on pairs such as [dab]-[daeb], in which the contrasting vowels constituted the portions of the syllable with the longest duration, and [e]-[e] even when these vowels were shortened to 40 msec in duration. As noted earlier, one of the defining features of low phonetic substance morphemes is their shorter duration relative to adjacent portions of the utterance. Unstressed syllabic morphemes are shorter in duration than surrounding syllables, and, of course, the durations of consonant inflections and contractions are considerably shorter than those of the syllables to which they are attached. Another possible parallel exists. Just as grammatical morpheme use involves operations in addition to perception (viz., relating inflected words to their bare stem counterparts, placing the inflected form in a paradigm), performance on the target identification task involves more than simple perception. As noted above, the child must also remember which of two stimuli is the target, and to press the button only when this one is heard. The similarities between the characteristics of difficult grammatical morphemes and difficult perceptual distinctions notwithstanding, we are not yet in a position to conclude that meaningful parallels in fact exist. There remain two obstacles. First, although the subjects in the studies of Tallal and her colleagues had documented language problems, no information was reported concerning their use of grammatical morphemes. We do not know if these children in fact had especially severe problems in morphology. Second, previous studies of perceptual abilities in children with SLI have not focused on syllable-final consonant contrasts nor on weak syllable contrasts, yet these are the types of forms that are involved in the grammatical morphemes that have proven difficult for children with SLI. The purpose of the present study was to compare children with SLI and age-matched controls in the perception of contrasts that more closely mimic the characteristics of certain grammatical morphemes. To facilitate interpretation of the findings, the difficulties with grammatical morphemes of the children with SLI were carefully documented. Method Subjects Children with SLI. Eight monolingual English-speaking children ranging in age from 4:6 (years:months) to 5:7 served as the subjects with SLI. These children were part of a larger

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sample of children with SLI reported in Leonard et al. (in press). They were selected because they had reached the minimal age (4:6) for which the perception task is suitable. Four of the children were girls, four were boys. All of the children passed a hearing screening at 20 dB (HL) for each ear at 500, 1000, 2000, and 4000 Hz. In addition, all children passed an examination of oral-motor function, showed no evidence of frank neurological dysfunction such as seizure disorders or cerebral palsy, and none were under medication for the prevention of seizures. Each child's IQ on the Arthur Adaptation of the Leiter International Performance Scale (Arthur, 1952) was above 85. All of the children's composite scores (comprehension plus production) on the Test of Language Development-Primary (TOLD-P) (Newcomer & Hammill, 1982) were more than one standard deviation below the mean for their chronological age. Their mean utterance length (MLU) based on 100 spontaneous utterances placed them significantly below age level (Templin, 1957). The IQs, TOLD-P scores, and MLUs of the children with SLI at the time of the study can be seen in Appendix B. It was important to ensure that all of the children with SLI were capable of producing the consonants that were required in the use of grammatical inflections (viz., [s], [z], [t], (d]). Accordingly, the children were given a 32-item test in which these sounds were assessed in nonmorphophonemic contexts (e.g., rose, bed). Each child scored above 80% correct on this test. Finally, we examined the children's speech for evidence of production errors on the sounds used in the target identification task, [i], [u], [b], [d], [s], L], [a], and [at] (see below). Although correct production of these sounds was not a subject selection criterion, all of the children showed some correct use of each of these sounds, and none showed substitution patterns that mirrored the perceptual contrasts used in the target identification task (e.g., [b] for [d] or vice-versa). In the study by Leonard et al. (1992), grammatical morpheme use by children with SLI was found to be significantly more limited than that of younger normally developing children (ages 2:11 to 3:4) matched according to MLU. However, because only eight of these children with SLI participated in the present study, it was necessary to ensure that the findings held for this subgroup as well. Accordingly, we computed these eight children's use of grammatical morphemes in obligatory contexts and compared these percentages with those found for their normally developing MLU controls. For each child, two different percentages were computed: the percentage of use of grammatical inflections in obligatory contexts, collapsed across specific morpheme (e.g., collapsed across plural -s, past -ed, etc.), and the percentage of use of function words in obligatory contexts, collapsed across specific morpheme (e.g., collapsed across complementizer to, article the, etc.). The rationale for the distinction between inflections and function words is that perceptual stimuli mimicking each type were employed in the target identification task. The results of the comparison revealed a significant main effect indicating higher overall percentages for the MLU controls than for the children with SLI, F(1, 14) = 13.25, p < .005, and a significant main effect showing that across subject groups inflections had somewhat higher percentages than function words, F(1, 14) =



6.22, p < .05. However, no interaction was found. For the children with SLI, mean percentages for inflections and function words were 51.13 (SD = 26.61) and 38.88 (SD = 19.61), respectively. For the MLU controls, the corresponding mean percentages were 83.63 (SD = 12.48) and 67.38 (SD = 20.38). These results confirmed that the particular group of children with SLI studied here could be regarded as having especially weak grammatical morphology, at least according to MLU expectations. Normally developing children. The comparison group consisted of eight normally developing children matched to the children with SLI according to chronological age. Four of the children were girls, four were boys. The normally developing children passed all of the screening tests used with the children with SLI. All showed TOLD-P composite scores within 1 SD of the mean for their age. The IQs of the normally developing children seemed somewhat higher than those of the children with SLI. However, this difference was not statistically significant, t (14) = 1.30, p > .05. The normally developing children's IQs, TOLD-P scores, and MLUs also appear in Appendix B.

Perceptual Stimuli Five stimulus pairs were synthesized. Four of these were generated using a cascade parallel software synthesizer (Klatt, 1980). The remaining pair, [das]-[daJl, was generated using the SYN serial software synthesizer (Mattingly & Scully, 1985). A description of these stimuli appears below, followed by our rationale in selecting them. The stimulus pair [ba]-[da]. The syllables [ba] and [da] were each 250 msec in total duration, with a fundamental frequency of 120 Hz through the first 105 msec and a linear drop to 100 Hz over the remaining 145 msec. The first 5 msec contained frication noise representing the burst, followed by a 40-msec transition during which the first two formants of [da], and first three formants of [ba] changed frequency. For [ba], F1 rose from 520 to 700 Hz, F2 from 1150 to 1220 Hz, and F3 from 2450 to 2600 Hz. In the case of [da], F1 rose from 450 to 700 Hz, F2 fell from 1520 to 1220 Hz, and F3 remained at 2600 Hz. Thus, these two syllables differed in the 40-msec formant transitions and were identical in the remaining steady-state portions. The stimulus pair [dab]-[da b]. Each of these syllables was 425 msec in total duration, including the period representing consonant closure. Both syllables contained a burst in the first 5 msec followed by a 40-msec transition period. Each had a fundamental frequency of 120 Hz through the first 110 msec followed by a linear drop over the next 210 msec to 100 Hz. The final 75 msec of this period involved another 40-msec formant transition period, followed by a linear drop in amplitude to 0 over the next 35 msec. A 100-msec silent period representing consonant closure then occurred, followed by 5 msec of frication noise representing consonant release. The initial 40-msec transition period for [dab] involved a rise in F1 from 450 to 700 Hz, and a drop in F2 from 1520 to 1220 Hz. F3 remained at 2600 Hz. For [dab], F1 rose from 315 to 650 Hz, F2 dropped from 1740 to 1660 Hz, and F3 fell from 2590 to 2430 Hz. The 40-msec period immedi-

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ately preceding consonant closure for [dab] entailed a drop in F1 from 700 to 520 Hz, a drop in F2 from 1220 to 1150 Hz, and no change in F3, which remained at 2600 Hz. For [dab], this 40-msec period showed a drop in F1 from 650 to 520 Hz, a drop in F2 from 1660 to 1150 Hz, and a rise in F3 from 2430 to 2600 Hz. Thus, [dab] and [daeb] differed in the acoustic details of both 40-msec transition periods and in much of the steady state period, representing a total of 290 msec. They were identical in the 35 msec immediately preceding consonant closure (during which time the amplitude decreased) and the period of consonantal closure and burst. The stimulus pair [i]-[u]. Each of these syllables was a steady-state vowel with a total duration of 100 msec and a fundamental frequency of 100 Hz. For [i], the first three formant frequencies were 310, 2020, and 3400 Hz. For [u], these frequencies were 350, 1250, and 3300 Hz. The stimulus pair [dab-i-ba]-[dab-u-ba. Each of these stimuli was constructed by placing previously generated syllables (see above) in sequence and making a few minor modifications to facilitate the perception of these sequences as connected. The stimulus [dab-i-ba] involved the abovedescribed syllables [dab], [i], and [ba] placed in sequence separated by a 35-msec period of silence. The original syllable [dab] was altered so that the fundamental frequency remained at 120 Hz throughout the syllable, and the original [ba] was modified so that the fundamental frequency of 120 was extended an additional 15 msec before the linear drop to 100 msec. No other changes were made. The [-i-] portion of the stimulus was identical to the original [i]. The stimulus [dab-u-ba] was then constructed by simply replacing [u] for [i] in the sequence. Thus, these two stimuli were identical in the initial 425-msec syllable [dab] and the final 250-msec syllable [ba] but differed in the 100-msec steady-state vowel constituting the middle syllable. The stimulus pair [das]-[daf]. The total duration of each of these syllables was 410 msec. For both syllables, the fundamental frequency was 120 Hz for the first 70 msec, followed by a linear drop to 100 Hz over the remaining 225 msec of the vowel. A 115-msec period of frication noise followed. Each syllable began with a burst and a 40-msec transition period during which, for each syllable, F1 rose from 450 to 700 Hz, F2 fell from 1520 to 1220 Hz, and F3 remained at 2600 Hz. The vowel maintained these formant values for the next 210 msec. At this point, there was a 55-msec transition period, of which the final 10 msec co-occurred with frication. For [das], this transition period showed a drop in F1 from 700 to 390 Hz, a rise in F2 from 1220 to 1360 Hz, and a very modest rise in F3 from 2600 to 2630 Hz. For [daf], F1 dropped from 700 to 300 Hz, F2 rose from 1220 to 1650 Hz, and F3 rose slightly from 2600 to 2630 Hz. The first two pairs, [ba]-[da] and [dab]-[dwb], were selected to ensure that the results from our subjects with SLI were consistent with those of earlier studies using these same syllables (though with slightly different acoustic values, see Tallal & Stark, 1981). We expected that most of the children with SLI would have difficulty with [ba]-[da], but not with [dab]-[daeb]. The reason for this, we assume, has to do with the duration of the contrastive portion of these syllable pairs relative to the duration of the noncontrastive portions.


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TABLE 1. Predictions for each subject group for each stimulus pair. Prediction Stimulus pair

ND

SLI

F P [ba]-[da] P P [dab]-[daeb] P P [i]-[u] F P [dab-i-ba]-[dab-u-ba] F P [das]-[daf] with Note. ND = Normally developing children; SLI = children specific language impairment; P = majority of children expected to reach criterion (pass); F = majority of children not expected to reach criterion (fail). The pair [i]-[u] was not expected to be difficult for the children with SLI. However, this pair served as a useful control for the pair [dab-i-ba]-[dab-u-ba]. We expected the latter pair to be problematic for children with SLI, because the contrastive portions are of much shorter duration than the remaining portions of the stimulus. If the children with SLI had little difficulty with [i]-[u], we could be assured that any difficulties on [dab-i-ba]-[dab-u-ba] were not attributable to the absolute duration of the vowels, nor to the particular vowels selected. We viewed stimuli such as [dab-i-ba] and [dab-u-ba] as roughly analogous to short-phrase contexts containing a monosyllabic function word in medial position. The pair [das]-[daf] was also expected to be difficult for most of the SLI children, again because the contrastive portions of these syllables are shorter in duration than the noncontrastive portions. Syllables of this type were viewed as roughly analogous to word-stem-plus-inflection combinations. Our predictions of the two subject groups' ability to discriminate the stimulus pairs are listed in Table 1. To ensure that all of the perceptual contrasts were distinguishable by adults, we recruited a group of 10 young adults to serve as listeners/transcribers. Each of the listeners had completed an undergraduate course in phonetic transcription, but was unfamiliar with the nature of the study. We prepared a transcription tape that contained continuous presentations of the stimuli with an interstimulus interval (ISI) of 3 sec. The tape was arranged so that there were five presentations of the first member of a given stimulus pair (e.g., [i]), followed by five presentations of the second member of the pair (e.g., [u]). The listeners were told that they would hear a syllable presented five times, and that they were to transcribe the syllable in broad phonetic transcription after the fifth presentation. This procedure was repeated for each stimulus. The listeners were told that some of the syllables might resemble one another, or might be the same. The responses were then inspected to determine if the listeners transcribed the contrastive portions of each stimulus pair differently. The transcriptions of all 10 listeners showed clear evidence of a distinction between [ba] and [da], [dab] and [dab], [i] and [u], and [das] and [dafl. Most, but not all of the transcriptions, reflected the precise segments we had intended to generate. For example, one listener transcribed [das] as [daz], another transcribed [dab] as [dap], and so on. However, the vowel or consonant distinction intended was always noted by the listeners for these stimuli. For the

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remaining pair, [dab-i-ba]-[dab-u-ba], 9 of the 10 listeners' transcriptions showed a clear distinction between the contrastive portions of these two stimuli. Again, these 9 transcriptions did not always match our intentions. For example, one listener transcribed the two stimuli as [daiba] and [dauba]. The remaining listener did not appear to hear a difference between the two stimuli, transcribing them both as [damba]. We regarded the listeners' transcriptions as confirmation that our stimulus pairs were sufficiently clear and distinctive to proceed with the experiment proper.

Procedure The target identification procedure employed by Tallal and Stark (1981) was used here. Initially, subjects were trained to depress a 5 cm circular panel mounted on a 10 x 10 x 5 cm response box each time the stimulus designated as the "special sound" or "our sound" (the target stimulus) was heard (through headphones), and not to press the panel when a comparison sound was heard. Training began with a 250-msec tone of 100 Hz as the target stimulus. This sound was presented 10 times with an ISI of 3 sec. The child was encouraged to press the panel immediately following each presentation. The next 16 presentations involved the target stimulus alternating with a saw-tooth noise. The child was encouraged to press the panel only when the target was heard. The child then heard 16 presentations during which the target alternated with a 250-msec tone of 305 Hz. Again, the experimenter encouraged the child to press the panel only when the target was heard. At this point, the child heard up to 32 presentations of the target and the 305 Hz tone in random order, and was instructed to respond with no assistance from the experimenter. The criterion for success on this final phase of training was 12 correct out of 16 consecutive presentations (p < .05, binomial test). All children reached this criterion. At this point, the stimulus pairs of interest were presented. The testing of each pair began with the experimenter identifying one of the pair members as the target. These were: [ba, [dab], [i], [dab-i-ba], and [das]. The child was then encouraged to listen to 4 consecutive presentations of the target and to press the panel immediately after each. The child then heard 4 presentations of the target and its comparison stimulus in random order, with the experimenter correcting any error the child made. If the child did not show differential responding (defined as pressing the panel following some but not all presentations), this procedure was repeated up to 4 times until differential responding was observed. This training criterion was met by all of the subjects. Formal testing then began, during which the child heard from 16 to 48 presentations of the target and the comparison stimulus in random order. Testing ended whenever the child reached the criterion of at least 12 correct responses out of 16 consecutive presentations (p < .05), or if 48 presentations had occurred without the child reaching this criterion. At this point, the next stimulus pair was introduced, following the same procedure.



TABLE 2. Number of children In each subject group (N = 8) reaching criterion on target Identification task. Subject group

Stimulus pair [I-[u]

[dab-l-ba]-[dab-u-baj

[das]-[daj

ND 8 6 5 SLI 7 0 1 Note. ND = Normally developing children; SLI = children with specific language impairment.

The order in which the stimulus pairs were presented was randomized across children. Testing was divided into three 30-min sessions separated by two days.

Results Because the perceptual contrasts used in this study were designed to extend the list of contrasts employed by Tallal and Stark (1981), it was important to determine whether we could first replicate their results. For this reason, two of the contrasts used by Tallal and Stark, [ba]-[da] and [dab]-[daeb], were also used here. Following Tallal and Stark, we determined for each perceptual contrast whether each subject reached the statistical criterion of 12 correct out of 16 consecutive trials. The results for these two contrasts conformed to those of Tallal and Stark. Inthe earlier study, Tallal and Stark reported that the great majority of both the subjects with SLI and the normally developing subjects met criterion on [dab]-[daeb], whereas many normally developing children but few children with SLI were able to reach criterion on [ba]-[da]. Our findings were similar: All 8 normally developing subjects and 6 of our 8 subjects with SLI reached criterion on [dab]-[deb]. However, whereas 6 of our 8 normally developing subjects met criterion on [ba]-[da], only 2 of our 8 subjects with SLI reached criterion on this pair. Given the above findings, it seemed appropriate to examine the children's performance on the remaining contrasts. These were [das]-[daJ], [dab-i-ba]-[dab-u-ba], and [i]-[u]. We assumed that the first two of these resembled low phonetic substance morphemes in that the contrastive portions were briefer than the surrounding material. The remaining contrast, [i]-[u], though brief in absolute duration, lacked the longer adjacent material and was therefore expected to be much less problematic for the children with SLI. The results for these three contrasts are summarized in Table 2. The results were generally consistent with the hypotheses, in that both [das]-[daf] and [dab-i-ba]-[dab-u-ba] gave the children with SLI great difficulty, but [i]-[u] did not. In addition, the majority of the normally developing children reached criterion even on the most difficult of these contrasts. However, two aspects of these data suggested the need for closer analysis. First, it can be seen from Table 2 that one child with SLI did not reach criterion on [i]-[u]. Second, even though the majority of the normally developing children met criterion on the remaining contrasts, these contrasts were obviously more difficult for them. This raises the possibility that the results summarized in Table 2 can be explained

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entirely by assuming that children with SLI are poorer than normally developing children in general, and that for all children some contrasts are more difficult than others. Although we, too, find these assumptions to be reasonable, our hypothesis concerns an additional point, that children with SLI are disproportionately weak on certain types of contrasts. To examine this issue further, we compared the performance of children with SLI and that of normally developing children on each of these three contrasts using one-tailed t tests. For each contrast for each child, the number correct out of the first 16 test presentations was used as the score. This number was used because all children received at least 16 presentations for each contrast, but for the easier contrasts many children received no more than 16 presentations. As expected, significant differences favoring the normally developing children were seen for [das]-[dajl, t (14) = 2.18, p < .025, and [dab-i-ba]-[dab-u-ba], t (14) = 3.24, p < .005. For [das]-[daj], mean scores for the normally developing children and children with SLI were 11.75 (SD = 2.19) and 9.13 (SD = 2.30), respectively. For [dab-i-ba]-[dab-u-ba], these means were 13.00 (SD = 3.34) and 8.75 (SD = .89). The two groups did not differ significantly in their performance on [i]-[u], t (14) = 1.55, p > .05. The mean scores for normally developing children and children with SLI were 15.00 (SD = .93) and 13.50 (SD = 2.39), respectively. However, it should be noted that ceiling effects cannot be ruled out. Two children with SLI and three normally developing children made no errors on the 16 presentations for this contrast.

Discussion At a minimum, the results of the present study build on earlier work by identifying additional perceptual contrasts that are problematic for children with SLI on a target identification task. We can now say, it seems, that on this task some children with SLI have considerable difficulty with certain syllable-final consonant contrasts as well as weak syllable contrasts. However, we believe the findings also offer a means of relating two heretofore distinct literatures on children with SLI-that dealing with the morphology of these children, and that pertaining to these children's speech perception abilities. Because the perceptual stimuli used in this study roughly approximate the characteristics of low phonetic substance morphemes, and because morphemes of this type were known to be difficult for our subjects with SLI, it seems reasonable to suggest that there are real parallels between the two types of performance. Ordinarily, one step in exploring this relationship would be to compute correlation coefficients between the grammatical morpheme use of children with SLI and their performance on the perceptual task. Unfortunately, because the children performed so poorly on the perceptual contrasts suspected to be difficult-all but one child on one contrast scored at chance level-this statistic could not be computed. Yet even if a moderate to high correlation were found, we would suggest that the relationship, though meaningful, is only indirect. Both the use of low phonetic substance morphemes and the identification of the target stimulus in the perception task involve more than an ability to discriminate


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the relevant phonetic information. Forms such as -ed, -s, and the must not only be perceived, they must also be recognized as morphemes (e.g., jumped must be seen as more than jump) and they must be placed in a morphological paradigm according to their grammatical function. Support for this assumption can be seen from the fact that the phonetic forms required for the grammatical morphemes were produced with rather high accuracy levels by the children with SLI in nonmorphophonemic contexts. Similarly, the target identification task required the children not only to perceive a difference between two stimuli, but also to remember one of them as the target and to press the button only when this one was heard. Support for this assumption comes from the observation that the children with SLI in this study failed on perceptual contrasts that they could in fact make in their speech. None of the children confused [b] and [d], nor [s] and [JI in their speech, even though they had difficulty identifying the perceptual target [ba] when it alternated with [da], and [das] when it alternated with [daf]. It can also be recalled that even normally developing children seem unable to perform this type of task below the age of 4:6, an age at which most or all phonological contrasts are achieved in speech production. Instead, the results should probably be taken to mean that when a difficult but achievable discrimination is involved, any additional operations that must be performed make it vulnerable to loss. When the discrimination is less challenging, the additional operations do not place it in such jeopardy. Hence, children with SLI can use forms with greater phonetic substance to serve a morphemic function; that is, they can not only discriminate it (required even in the nonmorphophonemic case) but also relate it to the proper stem and place it in the appropriate place in the paradigm. Similarly, stimuli involving contrasts of greater phonetic substance are not only discriminated, but also stored well enough for the target (and only the target) to evoke a response on the identification task. Ifthe above interpretation is correct, there could be at least two possible sources of difficulty for the children with SU. The most obvious is that these children's perceptual abilities are extremely fragile, such that when difficult discriminations are involved, additional operations cannot be performed adequately. A second possibility is that these children have some more general resource capacity limitation, such that when additional resources are needed for one operation, such as a difficult discrimination, fewer resources remain for other operations. The distinction between these two possibilities has implications for how the difficulties of children with SLI are characterized. For example, the notion that the problems of children with SLI are attributable to a general resource capacity limitation seems consistent with Leonard's (1987) proposal that many children with SLI have intact language learning mechanisms but operate with a low level of skill in language and language-related functions. In contrast, a resource capacity limitation that surfaces only in activities requiring perception would not be in line with this proposal, even if one assumes (as we do here) that there is no damage to the perceptual system. This is because Leonard's (1987) proposal provides no basis for assuming that processing limitations should be restricted to a single area of functioning.

35

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Although we cannot yet choose between these possibilities, it should be possible to assess their relative adequacy. For example, tasks requiring difficult but nonauditory (e.g., semantic) discriminations plus additional operations might be presented to children with SLI (see Johnston, 1991). However, even if low phonetic substance material continues to be implicated as a central factor in the difficulties of children with SLI, much work remains before definitive conclusions can be drawn. First, "low phonetic substance" has been operationally defined as short in duration relative to adjacent material. Yet once a certain absolute duration is reached, relative duration might diminish in importance. Second, although the shorter duration of difficult grammatical morphemes is most frequently noted, fundamental frequency and amplitude probably interact with duration in important ways. Third, we have made only a binary distinction between grammatical morphemes with low phonetic substance and those with not-such-low phonetic substance. Yet a continuum is probably more likely. For example, the available data for English indicate that whereas main verbs are more likely to receive stress than modal verbs, the latter are more likely to receive some degree of stress than the copula and auxiliary forms of be (Altenberg, 1987). Fourth, we have placed emphasis on the perceptual aspects of low phonetic substance material, but such material also carries heavy production demands. Consonantal inflections are vulnerable to final consonant deletion and many syllabic morphemes are subject to weak syllable deletion. The chief problem could still rest in the child with SLI having to perform several different operations. However, inthis case, the difficulty could reside in the combined operations of retrieving the correct form from the correct paradigm and producing it. Comprehension data would be valuable in this regard. If differences between children with SLI and MLU controls were found to be smaller in comprehension than in production of these forms, then production factors would be implicated. Finally, it is likely that the effects of phonetic substance can be muted to some degree by the typology of the language being acquired. For example, in languages such as Italian, nouns, verbs, and adjectives must be inflected; bare stems are not permitted as in English. This property has its advantages, as it allows more flexibility in word order as well as the optional omission of grammatical subjects. But this means that inflections carry a heavier burden in the language. Consequently, it is likely that children acquiring this language pay closer attention to inflections than children who are acquiring English. This greater attention, coupled with the more frequent appearance of inflections because of their obligatory nature, could in part offset the difficult perceptual properties of particular inflections.

Acknowledgments This research was supported by NIDCD Research Grant DC00458. Some of the stimuli were prepared with assistance from NICHD Contract NO1-HD-5-2910. The authors wish to thank Rachel Stark for her advice on a number of procedural matters.



References Albertini, J. (1980). The acquisition of five grammatical morphemes: Deviance or delay? Proceedings from the Wisconsin Symposium on Research in Child Language Disorders, 1, 94-111. Altenberg, B. (1987). Prosodic patterns in spoken English: Studies in the correlation between prosody and grammar for text-tospeech conversion. Lund, Sweden: Lund University Press. Arthur, G. (1952). The Arthur Adaptation of the Leiter Intemational Performance Scale. Chicago: Stoelting. Beaatrom, S., & Rice, M. (1986, November). Comprehension and production of the articles a and the. Paper presented at the Convention of the American Speech-Language-Hearing Association, Detroit. Bllss, L. (1989). Selected syntactic usage by language-impaired children. Joumal of Communication Disorders, 22, 277-289. Cousins, A. (1979, October). Grammatical morpheme development in an aphasic child: A longitudinal study. Paper presented at the Boston University Conference on Language Development, Boston. Farnetani, E., & Forl, S. (1982). Lexical stress in spoken sentences: A study of duration and vowel formant pattem. Quaderni del Centro di Studio per le Ricerche di Fonetica, 1, 104-133. Ingram, D. (1972). The acquisition of the English verbal auxiliary and copula in normal and linguistically deviant children. Papers and Reports on Child Language Development, 4, 79-92. Johnston, J. (1991). Questions about cognition in children with specific language impairment. In J. Miller (Ed.), Research on child language disorders (pp. 299-307). Austin, TX: Pro-Ed. Johnston, J., & Kamhl, A. (1984). Syntactic and semantic aspects of the utterances of language-impaired children: The same can be less. Merrill-Palmer Quarterly, 30, 65-85. Johnston, J., & Schery, T. (1976). The use of grammatical morphemes by children with communicative disorders. In D. Morehead & A. Morehead (Eds.), Normal and deficient child language (pp. 239-258). Baltimore, MD: University Park Press. Khan, L., & James, S. (1983). Grammatical morpheme development in three language disordered children. Joumal of Childhood Communication Disorders, 6, 85-100. Klatt, D. (1975). Vowel lengthening is syntactically determined in a connected discourse. Journal of Phonetics, 3, 129-140. Klatt, D. (1980). Software for a cascade-parallel formant synthesizer. Journal of the Acoustical Society of America, 67, 971-995. Leonard, L. (1982). Phonological deficits in children with developmental language impairment. Brain and Language, 16, 73-86. Leonard, L. (1987). Is specific language impairment a useful construct? In S. Rosenberg (Ed.), Advances in applied psycholinguistics, Volume 1(pp. 1-39). New York: Cambridge University Press. Leonard, L. (1989). Language learnability and specific language impairment in children. Applied Psycholinguistics, 10, 179-202. Leonard, L., Bortollnl, U., Casell, M.C., McGregor, K., & Sabbadinl, L. (1992). Morphological deficits in children with specific language impairment: The status of features in the underlying grammar. Language Acquisition, 2, 151-179. Leonard, L., Sabbadinl, L., Leonard, J., & Volterra, V. (1987). Specific language impairment in children: A crosslinguistic study. Brain and Language, 32, 233-252. Leonard, L., Sabbadinl, L., Volterra, V., & Leonard, J. (1988). Some influences on the grammar of English- and Italian-speaking

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children with specific language impairment. Applied Psycholinguistics, 9, 39-57. Mattingly, I., & Scully, W. (1985). User's guide to SYN. Unpublished manuscript, Haskins Laboratories, New Haven, CT. Morgan, J. (1986). From simple input to complex grammar. Cambridge, MA: MIT Press. Newcomer, P., & Hammill, D. (1982). Test of Language Development-Primary. Austin, TX: Pro-Ed. Paul, R., & Shrlberg, L. (1982). Associations between phonology and syntax in speech-delayed children. Journal of Speech and Hearing Research, 25, 536-547. Pinker, S. (1984). Language learnability and language development. Cambridge, MA: Harvard University Press. Rom, A., & Leonard, L. (1990). Interpreting deficits in grammatical morphology in specifically language-impaired children: Preliminary evidence from Hebrew. Clinical Linguistics and Phonetics, 4, 93-105. Steckol, K., & Leonard, L. (1979). The use of grammatical morphemes by normal and language-impaired children. Journal of Communication Disorders, 12, 291-301. Tallal, P., & Plercy, M. (1973a). Defects of non-verbal auditory perception in children with developmental aphasia. Nature, 241, 468-469. Tallal, P., & Plercy, M. (1973b). Developmental aphasia: Impaired rate of non-verbal processing as a function of sensory modality. Neuropsychologia, 11, 389-398. Tallal, P., & Plercy, M. (1974). Developmental aphasia: Rate of auditory processing and selective impairment of consonant perception. Neuropsychologia, 12, 83-93. Tallal, P., & Plercy, M. (1975). Developmental aphasia: The perception of brief vowels and extended stop consonants. Neuropsychologia, 13, 69-74. Tallal, P., & Stark, R. (1981). Speech acoustic-cue discrimination abilities of normally developing and language-impaired children. Journal of the Acoustical Society of America, 69, 568-574. Tallal, P., Stark, R., Kallman, C., & Melllts, D. (1980). Perceptual constancy for phonemic categories: A developmental study with normal and language impaired children. Applied Psycholinguistics, 1, 49-64. Templin, M. (1957). Certain language skills in children. Minneapolis, MN: University of Minnesota Press. Tomblln, J. B., & Quinn, M. (1983). The contribution of perceptual learning to performance on the repetition task. Joumal of Speech and Hearing Research, 26, 369-372. Trantham, C., & Pedersen, J. (1976). Normal language development. Baltimore, MD: Williams & Wilkins. Watkins, R., & Rice, M. (1989, November). Verb particle acquisition in language-impaired and normally developing children. Paper presented at the Convention of the American Speech-LanguageHearing Association, St. Louis.

Received June 14, 1991 Accepted December 19, 1991 Contact author: Laurence B. Leonard, PhD, Audiology and Speech Sciences, Heavilon Hall, Purdue University, West Lafayette, IN 47907.


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Appendix A Appearing below is a summary of the use of the morphology in English, Italian, and Hebrew by children with SLI. Comparisons are based on the use of grammatical morphemes by children with SLI relative to that of a comparison group of younger normally developing children (in the same or a previously published study) with similar mean lengths of utterance (MLUs). Also considered is the MLU level at which the grammatical morpheme is ordinarily acquired. For example, if a group of children with SLI showed a low percentage of use for a particular morpheme at an MLU level below the level at which the morpheme is typically mastered, it was considered only if there was a direct comparison with a group of normally developing children at the same low MLU level. Similarly, if a group of children with SLI showed mastery of a grammatical morpheme, but were well above the MLU levels at which the morpheme is typically mastered, it was not considered. Sources for the summary are cited in the text.

English 1. The following grammatical inflections seem to be used with lower percentages by children with SLI than by normally developing children at comparable MLU levels: plural -s, possessive 's, past -ed, and third person singular -s. Progressive -ing is the inflection that appears least likely to reveal a difference, though in some studies children with SLI are relatively poor with this form as well. 2. The results for function words are similar to those for inflections, except that one can sometimes conclude only that SLI children have significant problems with a particular function word in most but not all studies that include it. The following function words were used with lower percentages by children with SLI than by MLU-matched controls in the majority of investigations: on, the articles a and the, copula, auxiliary be, and the complementizer to. Results for in are mixed, with only approximately half of the studies revealing a relative deficit on the part of children with SLI. 3. The irregular past (e.g., went, caught) has been found to be more difficult for children with SLI than for MLU controls in approximately half of the investigations that have included it.

Italian 1. Children with SLI show percentages of use for inflections that are similar to those seen for their MLU-matched compatriots. These inflections are noun plural -e, -i,adjective singular -a, -o (that must agree with the noun in number and gender), and third person singular verb -a, -e. The only inflection determined to be especially difficult to date is the third person plural verb inflection (-ano, -ono). This inflection contains two syllables, but stress appears on the stem (e.g., pdrtano "they carry," vdono "they see") and the first syllable of the inflection is unstressed. Furthermore, production with the unstressed syllable omitted would violate the phonotactic structure of Italian words (e.g., vedno). However, there are a handful of Italian verbs whose third person plural form differs from the above pattem. Such verbs consist of only two syllables when expressed in the third person plural (e.g., danno "they give," fanno "they make"). In verbs of this type, the first syllable of the inflection receives primary stress, and the final syllable can receive vowel lengthening. Italian children with SLI use this particular form with percentages as high as their MLU controls. 2. The use of function words among children with SLI does not appear to be as strong as their use of inflections. These children show lower percentages than MLU-matched control children on articles (e.g., ii, i, le) and clitics in finite verb contexts (e.g., lo "him," i "them").

Hebrew Of the three languages considered, the least information is available from Hebrew. However, the results to date appear to be consistent with those reviewed thus far. 1. Inflections do not seem to represent special problems for Hebrewspeaking children with SLI. They perform as well as MLU controls on noun plurals (im, of), adjective inflections (that must agree with the noun in number and gender), and both present and past verb inflections (e.g., holex"walks," hobdm "walk," halati "l walked," haixa "she walked"). All of these forms require, at a minimum, an addition and/or modification of a stressed syllable. 2. Hebrew makes frequent use of a free-standing accusative case marker, et, that precedes the direct object when the latter is definite. This unstressed form is used with lower percentages by children with SLI than by their younger MLU controls.



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Appendix B Chronological ages (CA) in months, Intelligence Quotients (IQ) from the Arthur Adaptation of the Leiter International Performance Scale, Spoken Language Quotients (SLQ) from the Test of Language Development-Primary (TOLD-P), standard scores from the TOLD-P subtests: Picture Vocabulary (PV), Oral Vocabulary (OV), Grammatic Understanding (GU), Sentence Imitation (SI), and Grammatic Completion (GC), and Mean Length of Utterance (MLU) in words of the children with specific language impairment and the normally developing children. Children with Specific Language Impairment TOLD-P Subtests CA 54 57 59 60 60 60 63 67 M SD Range

60 3.61 54-67

SLQ

IQ 105 120 127 86 110 92 86 99 103.1 14.3 86-127

PV

OV

GU

SI

GC

MLU

72 79 79 73 67 72 76 62

9 8 9 6 4 9 12 7

4 5 9 5 6 4 6 4

5 9 6 10 9 6 3 3

5 5 5 5 3 5 5 3

8 9 7 6 6 7 8 8

72.5 5.5 62-79

8.0 2.2 4-12

5.4 1.6 4-9

6.4 2.6 3-10

4.5 0.9 3-5

7.4 1.0 6-9

3.6 0.4 2.7-4.2

3.6 3.9 3.9 3.3 3.6 3.7 4.2 2.7

Normally Developing Children TOLD-P Subtests CA 54 54 55 60 62 62 64 67 M SD Range

59.8 4.6 54-67

la 140 98 136 97 124 106 109 100 113.8 16.2 97-140

SLO

PV

OV

GU

Si

GC

MLU

100 95 98 92 103 95 109 100

8 10 9 12 10 11 12 9

12 11 9 9 9 8 10 9

11 9 10 7 6 8 11 11

9 7 13 7 16 10 10 10

10 10 8 10 11 10 13 11

4.6 4.6 5.1 4.2 6.2 5.7 6.0 5.0

99.0 5.0 92-109

10.1 1.4 8-12

9.6 1.2 8-12

9.1 1.8 6-11

10.3 2.8 7-16

10.4 1.3 8-13

5.2 0.7 4.2-6.2


Atypical audio-visual speech perception and McGurk effects in children with specific language impairment.

Gesture-speech integration in children with specific language impairment.

Music Perception Influences Language Acquisition: Melodic and Rhythmic-Melodic Perception in Children with Specific Language Impairment.

Phonological and morphophonological effects on grammatical development in children with specific language impairment.

Grammatical Comprehension in Spanish-speaking children with Specific Language Impairment (SLI).

Perception of Filtered Speech by Children with Developmental Dyslexia and Children with Specific Language Impairments.

EEG Abnormalities in Children with Speech and Language Impairment.

Word and pseudoword reading in children with specific speech and language impairment.

Non-word repetition: the relationship between weak syllables and the omission of grammatical morphemes in children with specific language impairment.

Learning trajectories for speech motor performance in children with specific language impairment.

Speech abilities in preschool children with speech sound disorder with and without co-occurring language impairment.

Characteristics of children with specific language impairment attending language units.

Perception of Small Frequency Differences in Children with Auditory Processing Disorder or Specific Language Impairment.

Executive functions in mono- and bilingual children with language impairment - issues for speech-language pathology.

Clumsiness and perceptual problems in children with specific language impairment.

Differences in phonologic and prosodic abilities in children with phonological language impairment and phonological-grammatical language impairment assessed with non-word repetition.

[Children with specific language impairment: electrophysiological and pedaudiological findings].

Profiling relative clause constructions in children with specific language impairment.

Relative clause constructions in children with specific language impairment.

Case Marking in Hungarian Children with Specific Language Impairment.

Interactions between Bilingual Effects and Language Impairment: Exploring Grammatical Markers in Spanish-Speaking Bilingual Children.

Linguistic markers of specific language impairment in bilingual children: the case of verb morphology.

Examining the Language Phenotype in Children With Typical Development, Specific Language Impairment, and Fragile X Syndrome.

How Language Is Embodied in Bilinguals and Children with Specific Language Impairment.