Journal of Speech and Hearing Research, Volume 34, 1318-1328, December 1991
Stimulability as a Factor in the Phonological Generalization of Misarticulating Preschool Children Thomas W. Powell
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Ball State University Muncie, IN
Mary Elbert Daniel A. Dinnsen Indiana University, Bloomington
The relationship among six functionally misarticulating preschool children's phoneme-specific stimulability skills, the choice of treatment targets (i.e., stimulable or nonstimulable sounds), and generalization of correct sound production was explored in this prospective study. Each subject [age range of 4:11 (years:months) to 5:61 was taught to produce [r] and one other sound that was absent from his or her phonetic inventory using a contrasting-minimal-pairs production approach. A multiple baseline across behaviors single-subject research design provided experimental control. For 86% of the 28 monitored sounds, generalization was consistent with pretreatment stimulability skills; production of stimulable sounds tended to improve regardless of treatment target. These results suggest that nonstimulable sounds are likely to require direct treatment; thus, generalization probe responses may be maximized by treating nonstimulable sounds rather than stimulable sounds.
KEY WORDS: stimulablity, generalization, articulation/phonologIcal disorders, intervention, imitation
Stimulability has been defined, measured, and interpreted in many ways over the past 50 years (for review, see Diedrich, 1983; Madison, 1979). Moreover, stimulability data have been used for a variety of purposes including treatment target selection and prediction of self-correction or progress in treatment (Bankson & Bernthal, 1983).
The prognostic value of stimulability measures has been examined in a series of studies. Research suggests that untreated subjects with high stimulability scores show more improvement in sound production than subjects with low stimulability scores (Farquhar, 1961; Kisatsky, 1967; Snow & Milisen, 1954). With treatment, children with low stimulability scores tended to have higher gain scores than subjects with high stimulability scores (Carter & Buck, 1958; Sommers et al., 1967). In most of these studies, however, stimulability was operationally defined as the degree of correction (i.e., the difference between spontaneous and imitative error rates) averaged across phonemes (Sommers, 1983). Stimulability was thus viewed as a global ability rather than a phoneme-specific measure. More recently, subjects' pretreatment stimulability for individual sounds has been used to help explain generalization patterns (e.g., Dinnsen & Elbert, 1984; C. Dunn, 1983; Elbert & McReynolds, 1978; Powell & Elbert, 1984; Tyler, Edwards, & Saxman, 1987). There have been, however, no prospective studies examining the relationship between phoneme-specific stimulability and generalization. Shelton and McReynolds (1979) noted, for example, that "the exact role of stimulability in training is not clear" and "the relationship between this ability [stimulability] and spontaneous production in training has not been explored" (p. 88). McReynolds and Elbert (1982) also pointed out that "since the relationship between stimulability and carryover has not been explored, the effects on later stages of remediation are unknown" (p. 594). D 1991, American Speech-Language-Hearing Association
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Powell et al.: Stimulability and Generalization The purpose of this study was to investigate the relationship between stimulability and generalization among 6 preschool children receiving treatment on [r] and one other sound that was absent from their phonetic inventory. The following specific research questions are addressed in this article. 1. Are subjects' pretreatment stimulability skills positively related to their performance on posttreatment generalization measures? 2. If one controls for the effects of generalization at the distinctive feature level by teaching [r] (which appears to be relatively independent of other American English sounds), then will subjects show gains in their production of other stimulable and nonstimulable sounds? On the basis of the findings of previous studies (Elbert, Dinnsen, & Powell, 1984; Gierut, Elbert, &Dinnsen, 1987), itwas hypothesized that subjects would generalize to sounds for which they were stimulable more readily than to nonstimulable sounds.
Method Experimental Design This study used a multiple baseline across behaviors single-subject design to provide experimental control. This design involved two target behaviors that could be modified using a single treatment paradigm; however, the target behaviors had to be functionally independent such that treatment on one behavior would not directly enhance the other (McReynolds & Kearns, 1983). Previous studies of phonological intervention have shown, however, that all speech sounds are not independent. For example, Elbert, Shelton, and Amdt (1967) showed that treatment on the [s] sound resulted in gains in production of both [s] and [z], but not [r]. Thus, [r] appeared to be relatively independent of [s], whereas [s] and [z] were more closely related. The [r] sound was selected as the first treatment target for all subjects partly because of its relative independence from other sounds. During treatment on [r], changes in the production of other stimulable and nonstimulable sounds could be monitored. These changes could not easily be explained by the phonetic similarity among the sounds. Other factors in the selection of [r] included its frequency of misarticulation (Bemthal & Bankson, 1988) and the apparent clinical interest in [r] evidenced by publication of a variety of treatment approaches (e.g., Brown, 1975; Harryman & Kresheck, 1971; Shriberg, 1975, 1980; Wood, 1988). Subjects Four boys and 2 girls between the ages of 4:11 (years:months) and 5:6 served as subjects. All children were from monolingual English-speaking homes and were referred for evaluation and treatment of phonological errors. All subjects scored at or below the fifth percentile on the Soundsin-Words subtest of the Goldman-Fristoe Test of Articulation (Goldman & Fristoe, 1986). A comprehensive corpus for phonological analysis was elicited using a 306-item modification of the probe developed by Gierut (1985) to sample
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major English consonants in prevocalic, intervocalic, and postvocalic environments. The children's responses were phonetically transcribed on-line by author Powell and a graduate student in speechlanguage pathology with training in narrow phonetic transcription. Responses were also audiotaped using a Marantz PMD 360 professional stereo cassette recorder equipped with a Superscope EC-7 cardioid condenser microphone. The transcriptions were used to compile a phonetic inventory for each subject, and a conversational speech sample was used for verification. In accordance with criteria used by others (e.g., Dinnsen, Chin, Elbert, & Powell, 1990; Dyson, 1988; Stoel-Gammon, 1985), a consonant was included in the subject's phonetic inventory if it was produced in at least two items. The number of speech sounds missing from the subjects' phonetic inventories ranged from four to six. All subjects earned passing scores on the Oral Speech Mechanism Screening Examination-Revised (St. Louis & Ruscello, 1986). Two norm-referenced tests of language, the Test of Language Development-Primary (Newcomer & Hammill, 1982) and the Peabody Picture Vocabulary Test-Revised (Dunn & Dunn, 1981), were administered, and all subjects were in the average to above-average range. The general intellectual level of each subject was also in the average to above-average range as assessed by the McCarthy Scales of Children's Abilities (McCarthy, 1972) and the Kaufman Assessment Battery for Children (Kaufman & Kaufman, 1983). All subjects passed a hearing screening evaluation by responding appropriately to 500-, 1000-, 2000-, and 4000-Hz tones presented at 20 dB HL (ANSI, 1969).
Materials Analysis probe. The 306-item probe adapted from Gierut (1985) provided data for phonological analysis. Each subject's phonetic inventory was compiled prior to treatment as described above using these data. Experimental probe. Once a subject's phonetic inventory had been compiled, an experimental probe was developed to measure generalization. The experimental probe included 20 items designed to assess production of each of the two treatment sounds and 10 items assessing each additional sound that was absent from the subject's phonetic inventory. Thus, the experimental probes ranged from 60 to 80 items in length. The experimental probe items were administered in random order to the children at the conclusion of every fourth treatment session using a delayed-imitation protocol. Treatment probe. The treatment probe was the subset of 20 experimental probe items assessing production of the sound targeted for treatment (e.g., [r]). Treatment probes were administered at the conclusion of every session to provide a discrete measure of generalization-a practice supported by the work of Winner and Elbert (1988). The treatment probe for [r], which was used with all subjects, is presented in Table 1. The final consonants across these 20 monosyllabic treatment probe items were systematically varied to help control for phonetic context factors that might affect generalization. The items were randomized prior to presentation to subjects.
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TABLE 1. Treatment probe used to assess generalization of [r] production. room rope rob Ruth writhe
run rat red roof rove
ring wreck rug rice rose
ray rich ridge rush rouge
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Powell; to control for experimenter bias, treatment data were kept independently by trained observers. All subjects received treatment on [r]; however, the second target sound (phase II)varied systematically across subjects to ensure treatment of both stimulable and nonstimulable sounds (see Table 2). Reliability
Stimulability measure. Farquhar's (1961) adaptation of the Carter and Buck (1958) Nonsense Syllable Task was used to assess stimulability of singleton consonants in isolation and in nine syllables. A stimulability score was calculated for each sound missing from the phonetic inventory and was expressed as the percentage of acceptable productions across the 10 items. Unlike many previous studies, these data were used as a phoneme-specific stimulability measure and were not averaged. Subjects were credited with being stimulable for sounds produced with at least 10% accuracy during the Nonsense Syllable Task. This level was consistent with the criterion used by Elbert et al. (1984) in assessing productive phonological knowledge. Likert scale. A 16-item Likert-type scale was developed using procedures outlined by Mueller (1986) to assess social validity (Fuqua & Schwade, 1986; Kazdin, 1977; Wolf, 1978). The scale was completed by parents before treatment, immediately following treatment, and during a follow-up session to assess the degree to which their perceptions of the children's speech agreed with the reported data. Additional information regarding the development and psychometric characteristics of this scale can be found in Powell (1989). Procedures Pretesting. The battery of tests was administered to each child according to standardized procedures prior to treatment. The 306-item analysis probe and the stimulability tasks were next administered to the children while parents completed the Likert-type scale. Baseline measures. Experimental probes were developed for each subject to assess generalization and were administered three times prior to treatment. A baseline was operationally defined as stable if the variability across the three baseline measures did not exceed 10%. Treatment. For each subject, treatment commenced on [r] once a stable baseline was established. A contrastingminimal-pairs production approach was used (as in Elbert, Rockman, & Saltzman, 1980). Perceptual abilities (e.g., auditory discrimination) were not treated directly. Five minimal pairs contrasting the target (e.g., /r/) with the child's customary error (e.g., [w]) were used during the first phase of treatment. The treatment program consisted of four steps and is described in the appendix. As the child progressed through the program, reinforcement and stimulus cues were systematically decreased. Subjects were seen an average of three times per week, and each session consisted of 100 minimal pair responses (approximately 30 min). A token reinforcement system was used whereby correct responses earned chips that could be redeemed for stickers. All treatment was provided by author
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Analysis probes. All analysis probe responses were phonetically transcribed independently by two judges. Interjudge agreement ranged from 76% to 94%, with a mean of 85%. The judges then listened to the tape-recorded analysis probe responses and developed mutually acceptable transcriptions to resolve disagreements. Other measures. Transcription reliability for the treatment and experimental probes reflected the degree to which judges agreed on the production accuracy of target sounds only. The average right/wrong reliability across these measures was 96% agreement. Subjects' responses to the Carter and Buck (1958) stimulability tasks were also transcribed on-line by two judges. The percentage of agreement across all items ranged from 97% to 99%, with a mean of 98% agreement.
Results Two types of data will be reported for each subject. Treatment data (percentage of correct responses during each session) will be discussed first. Then, generalization data elicited by the experimental and treatment probes will be considered. Subject 1 The treatment and generalization data obtained from Subject 1 are presented in Figure 1. Subject 1 never produced [r], [s], [z], or [I] correctly prior to the initiation of the treatment program, as steady zero baseline measures evidenced. Once treatment was initiated, Subject 1 met the treatment criterion for [r] in 10 sessions. Next, treatment was introduced on the [s] sound, and the treatment criterion was met in only four sessions. The multiple baseline across the two target sounds provided evidence of experimental control. Generalization data for Subject 1 also are presented In Figure 1.Subject 1's generalization of correct [r] production, as measured by the experimental and treatment probes, mirrored his treatment performance. He maintained a stable zero baseTABLE 2. Summary of treatment targets and stimulabllty test results for the 6 subjects. Subject
Target 1
Target 2
1 2 3 4 5 6
[r]--stimulable [r--stimulable [r--nonstimulable [r--nonstimulable [r]--nonstimulable [r--nonstimulable
[s}-stimulable [e]--stimulable [tfl-stimulable [e--stimulable [e]-nonstimulable [g}--nonstimulable
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Subject 2 Subject 2 was stimulable for the postvocalic allophone of [r]. During treatment, he showed rapid gains in his production of word-initial r], and he met the treatment criterion in 13 treatment sessions, as Figure 2 depicts. Subject 2's production of correct [r] during generalization measures, however, peaked at 35% correct during the 10th treatment session. Thereafter, his production of [r] reverted to 0% accuracy. Subject 2 made rapid gains in his production of stimulable [e] during treatment and met the treatment criterion in four
FIGURE 1. Treatment (open circles) and generalization (filled circles) data for Subject 1 plotted as a function of treatment sessions. Phase A = Baseline, B. = [r] Treatment (shaded), B2 = [s] Treatment (shaded), C = Follow-up. 'Indlcates stimulable sounds. line for the three untreated sounds during the period he received treatment on [r]; this observation further supports the functional independence of [r] relative to other sounds. Several changes were observed, however, in Subject 1's production of sounds following the introduction of treatment on [s]. He showed rapid gains inthe production of [s] (for which he was stimulable), and he also showed gains in his production of the voiced cognate [z]. Although Subject 1's accuracy rate for stimulable [z] fluctuated, he ultimately met the generalization criterion during follow-up. The generalization criterion was not met for nonstimulable [I] during the follow-up session. Downloaded From: http://jslhr.pubs.asha.org/ by a La Trobe Univ User on 05/22/2016 Terms of Use: http://pubs.asha.org/ss/rights_and_permissions.aspx
FIGURE 2. Treatment (open circles) and generalization (filled circles) data for Subject 2 plotted as a function of treatment sessions. Phase A = Baseline, B. = [r] Treatment (shaded), B2 = [e] Treatment (shaded), C = Follow-up. 'Indicates stimulable sounds.
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sessions. Generalization of correct [e] and [] production was noted; gains in his production of correct [ were more gradual. This subject met the generalization criterion for three of the four stimulable sounds that were missing from his phonetic inventory prior to the onset of the study; stimulable [r] was not generalized. Subject 3 Unlike the first two subjects, Subject 3 was not stimulable for [r] in any position or vocalic environment prior to treatment. It was necessary to use phonetic placement cues and to reinforce successive approximations of [r] during treatment. He met the treatment criterion during the 29th treatment session (see Figure 3); however, no generalization was observed. Treatment next turned to production of [tj; six sessions were sufficient for Subject 3 to meet the treatment criterion for this stimulable sound. Subject 3 generalized correct production of [tf]; he also showed gains in his production of the nonstimulable cognate [d3]. The generalization criterion was met for only these sounds at follow-up. Subject 4 Shaping procedures also were used with Subject 4 to elicit an acceptable production of [r], and he met the treatment criterion during the 26th session (see Figure 4). Subject 4's production of [r] during generalization measures, however, remained inaccurate. Next, Subject 4 was taught to produce the stimulable [e] sound. He met the treatment criterion for this sound in four sessions. During the follow-up session, Subject 4 met the generalization criterion for both stimulable [e] and stimulable [6]. Subject 4 produced stimulable [v] inconsistently during baseline measures and evidenced gradual gains in [v] production. Once treatment was initiated on [e], however, Subject 4's production accuracy for [v] decreased, and the generalization criterion was not met. Subject 5 The extensive use of shaping procedures was also necessary with Subject 5; nevertheless, she never met the treatment criterion for [r]. She was treated for 31 sessions (see Figure 5) and advanced to the third step of the treatment program, but her [r] production remained at 0% during generalization measures. Subject 5 was next taught to produce the [e] sound. She met the treatment criterion for this nonstimulable sound in only eight sessions, but she did not generalize correct production. Subject 5's production of four additional sounds was monitored: nonstimulable [6] and stimulable [v], [z], and [I]. Her production of these untrained sounds improved, and she met the generalization criterion, although she did not generalize production of the two nonstimulable sounds that were directly treated.
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FIGURE 3. Treatment (open circles) and geonralliatlon data (filled circle) for Subject 3 plotted as a function of treatment sessions. Phase A = Baseline, B. = [r] Treatment (shaded), 82 = tn Treatment (shaded), C = Follow-up. "Indicates stimulable sounds.
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FIGURE 4. Treatment (open circles) and generalization data (filled circles) for Subject 4 plotted as a function of treatment essions. Phase A = Baseline, B. = [r] Treatment (shaded), B2 = [e] Treatment (shaded), C = Follow-up. "Indicates stimulable sounds.
Subject 6 Subject 6 met the treatment criterion for nonstimulable [r] in 12 sessions and nonstimulable [g] in 4 sessions (see Figure 6). Generalization, however, was limited. Subject 6 did not meet the generalization criterion for any of the four sounds that were monitored.
Group Trends In summary, all subjects evidenced gains in their production of [r] and one other sound during treatment. Indeed, the
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FIGURE 5. Treatment (open circles) and generalization data (filled circles) for Subject 5 plotted as a function of treatment sessions. Phase A = Baseline, B = [r] Treatment (shaded), B2 = [e] Treatment (shaded), C = Follow-up. 'Indicates stimulable sounds.
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FIGURE 6. Treatment (open circles) and generalization data (filled circles) for Subject 6 plotted as a function of treatment sessions. Phase A = Baseline, B = [r Treatment (shaded), B2 = [g9
Treatment (shaded), C = Follow-up.
treatment criterion was met for 11 of the 12 sounds that were directly treated. Although all subjects made substantial gains during treatment, the degree of generalization learning varied widely. Some subjects (e.g., Subject 1) generalized readily to treated sounds and their cognates; others (e.g., Subject 6) evidenced little generalization. Table 3 lists the 28 targets that were monitored across the 6 subjects and pretreatment stimulability scores. This table also summarizes each subject's production accuracy as assessed by the individualized experimental probes at three points: (1) following [r] treatment, (2) following treatment on the second sound, and (3) during the follow-up session.
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The first research question posed by this study involved the relationship between pretreatment stimulability and generalization scores at the conclusion of the study. This question was addressed by examining the data presented in Table 3 to identify group trends. Across the 6 subjects, production of 28 sounds was monitored. Prior to the implementation of treatment, 14 (or 50%) of these sounds were stimulable, and 14 were nonstimulable. To examine the relationship between stimulability and generalization, the data were pooled across subjects. The two variables (pretreatment stimulability and generalization assessed during the follow-up session) were scored dichotomously for each monitored sound. A sound was considered stimulable if produced with at least 10% accuracy on the Carter and Buck (1958) task. Sounds produced with 50% or greater accuracy during the follow-up session were credited as being generalized. A 2 x 2 contingency matrix was next completed (see Table 4). Of the 14 stimulable sounds, 12 met the generalization criterion at follow-up; however, only 2 of the 14 nonstimulable sounds met the generalization criterion. This pattem was not attributable to chance [X2 (1, N = 28) = 14.2857; p = .00038]. The correlation between the two binary variables was next calculated using the phi coefficient (Nunnally, 1978). For these data, phi = .71, suggesting that more than 50% of the generalization variance could be explained by the subjects' stimulability skills. Although stimulability scores could account for much of the generalization variance at follow-up, a more qualitative analysis of the data was also helpful inexplaining the relationship among stimulability, treatment targets, and generalization. Given the moderately high relationship between stimulability and generalization, one would expect subjects to meet the generalization criterion at follow-up for stimulable sounds and not to meet the criterion for nonstimulable sounds. Indeed, this prediction held true for 24 of the 28 targets (86%). The second research question asked whether subjects would evidence gains intheir production of stimulable and nonstimulable sounds following treatment on [r]. This question also was answered by analyzing the experimental probe data elicited from each subject during the final treatment session on [r]; the raw data are presented in column 1 of Table 3. Following treatment on [r], 6 of the 28 monitored sounds met the generalization criterion. Subject 1 generalized correct production of stimulable [r] with 75% accuracy. Subject 4's production accuracy for stimulable [v] also met the generalization criterion. Subject 5 met the generalization criterion for four of the six sounds that were missing from her phonetic inventory: stimulable [z], [I], [v], and nonstimulable [6]. Thus, five of the six generalized sounds were stimulable prior to the implementation of treatment. This working hypothesis was then formulated: Following treatment on [r], subjects are likely to show increases in their production of stimulable sounds, but not in their production of nonstimulable sounds. The data were again examined to test this hypothesis. For the first 2 subjects, the working hypothesis did not account well for the data. Although Subjects 1 and 2 were stimulable for seven of the eight sounds that were monitored, only Subject 1's production of [r] (which was directly treated)
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TABLE 3. Sounds missing from each subject's phonetic Inventory, pretreatment stimulabllty, and generalization scores elicited at three times. Generalization scores Phase I
Phase II
Follow-up
.90 1.00 .90 .00
.75 .00 .00 .10
.90 1.00 .30 .50
.85 1.00 .80 .30
.30 .10 .40 .20
.10 .05 .00 .10
.00 .90 .60 .20
.00 .90 .80 .50
.00 .20 .00 .00 .00 .00
.20 .00 .00 .00 .00 .00
.10 .85 .60 .00 .00 .00
.10 .95 .90 .00 .00 .00
.00 .30 .10
.00 .00 .00
.00 .25 .10
.00 .55 .50
[v]
.70
.55
.35
.20
[r]a [e]a [6]
.00 .00 .00
.00 .05 .80
.00 .15 .80
.00 .15 .70
Sound
Stimulabllty
Subject 1 [r]a [s]a [z] [I] Subject 2 [r]a [e] [6] [fl Subject 3 [r]a [t'fl [d3] [s] [z] If] Subject 4 [r]a [e]la [6] Subject 5
[z]
.30
.90
.90
1.00
[I]
.20
1.00
1.00
1.00
[v] .20 .80 Subject 6 [r]' .00 .35 [g]a .00 .00 [k] .00 .00 [Z] .00 .00 aDenotes sounds that were targeted for treatment. met the generalization criterion. Subject 1 did not generalize correct production of nonstimulable [I], which was also consistent with the working hypothesis. For these two subjects, the working hypothesis held true for only two of the eight monitored targets (25%). The working hypothesis was more successful in describing the learning patterns evidenced by the remaining 4 subjects. For these subjects, the hypothesis was consistent with 16 of the 20 targets (80%). Subjects 1 and 2 differed from other subjects in that they were stimulable for [r] prior to treatment. If only Subjects 1 and 2 were considered, then a different observation might be TABLE 4. Two-by-two contingency matrix examining the relationship between pretreatment stimulabillty and generalization at follow-up. Pretreatment stimulabillty +
Generalization
+
12
2
at follow-up
-
2
12
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.80
.90
.40 .25 .30 .30
.10 .40 .30 .30
made. That is, subjects taught to produce a stimulable sound generalized, at most, to the targeted sound (i.e., [r]). The answer to the second research question appeared to vary as a function of stimulability. Subjects who were not stimulable for [r] tended to improve production of untrained, stimulable sounds; however, subjects who were stimulable for [r] generalized, at most, to [r]. Gains in the production of untreated sounds after [r] treatment are difficult to explain. With the possible exception of /I/, no other English phoneme is closely related to /r/. Given the apparent functional independence of [r] from other speech sounds, one might hypothesize that treatment on [r] helps to focus a child's attention upon speech sounds in general, or that treatment on any sound helps a child to "learn how to learn," resulting in higher production scores for sounds that were not directly taught. Another explanation for the sound learning patterns observed following [r] training involves a further conceptualization of the child's productive phonological knowledge (in the sense of Elbert et al., 1984). Although the 28 monitored sounds were never produced spontaneously, subjects had greater productive phonological knowledge of some sounds relative to others, as the stimulability measure evidenced.
1326 Journal of Speech and Heanng Research If stimulable sounds represent greater productive phonological knowledge than nonstimulable sounds, then treatment of stimulable sounds should affect neither the production of unrelated stimulable sounds nor production of nonstimulable sounds. Following treatment on a nonstimulable sound, however, one might expect improvement in the production of stimulable sounds (which are phonologically "known" in a production sense). These predictions are consistent with the data obtained in this study and with previous research findings (Dinnsen & Elbert, 1984; Elbert et al., 1984; Fey & Stalker, 1986; Gierut et al., 1987) and deserve additional study. Social Validity Finally, the results from the Likert-type scale completed by the parents were analyzed to assess the social validity of the findings. The clinician providing the treatment in this study was not blind to the research questions or stimulability test results. Data obtained from the parents helped to control for experimenter bias and served to validate the findings. Despite the small number of subjects, the mean Likert score across the 6 subjects increased significantly from the first to the second administration [(5) = -2.835, p = .035]. This finding would be consistent with decreased parental concern following the initiation of treatment. It was also hypothesized that parents of children who evidenced much generalization would yield higher scores than those completed by parents of children who evidenced little generalization. For each subject, the mean percentage correct across the monitored sounds following treatment was calculated as an index of generalization, and the subjects were rank ordered. The posttreatment Likert scores, too, were ranked, and the two variables were correlated using Spearman's Rho. There was a moderately high relationship between generalization and Likert-type scale rankings (Rho = .76; p = .038) suggesting that the parents' perceptions were consistent with the obtained data. Discussion This paper examined the relationship among 6 misarticulating preschool children's phoneme-specific stimulability skills, choice of treatment target (i.e., stimulable or nonstimulable sounds), and generalization of sound production. Each subject was taught to produce [r] and one other sound that was absent from the phonetic inventory using a contrasting-minimal-pairs production approach. Subjects' productions of stimulable sounds tended to improve regardless of treatment target, but generalization of nonstimulable sounds was rarely observed. These results suggest that preschool children's stimulability skills are an important factor in their generalization of correct sound production during phonological intervention. Two generalization trends were identified across the 6 subjects that may predict phonological learning patterns after treatment and facilitate selection of treatment targets (as per Elbert & Gierut, 1986, pp. 105-107). These predictions follow:
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1. If a stimulable sound is taught, then the subject may learn that sound and its cognate, but generalization to other sounds will be limited. 2. If a nonstimulable sound is taught, then the subject may leam the target sound, will probably leam other stimulable sounds, but probably will not learn other nonstimulable sounds. Speech-language pathologists may use these trends to predict generalization patterns as they design programs to increase the phonetic inventories of misarticulating preschool children. If several sounds were missing from a child's phonetic inventory, then generalization hypotheses could be formulated for each available target. Treatment efficiency might be maximized by planning for generalization (Powell, 1991, Stokes & Baer, 1977) and targeting for treatment the sound whose projected generalization effect would be the greatest. Periodically, clinicians should analyze the child's phonology to assess changes in production. New hypotheses should be developed as generalization trends emerge, and new treatment targets should be selected. This approach to phonological treatment is consistent with the remediation philosophies of Elbert and Gierut (1986), Fey and Stalker (1986), Gierut (1989),
Kamhi (1984), McReynolds (1989), and others. Some have argued that it is preferable to teach stimulable sounds over nonstimulable sounds because of a presumed difference in treatment duration (e.g., Culler, 1984), but the results of this study did not clearly support this view. With the exception of [r], treatment of nonstimulable sounds generally did not require more trials than stimulable sounds. Indeed, the results from this study suggest that the number of correct responses on generalization probes can be maximized by teaching nonstimulable sounds because stimulable sounds are likely to improve without direct treatment. Although these subjects often showed gains in their production of stimulable sounds, it is true that generalization of nonstimulable sounds was limited. Other researchers have also reported limited generalization to nonstimulable sounds despite direct treatment (e.g., Fey & Stalker, 1986), and different treatment strategies may be necessary to foster generalization to nonstimulable targets. For example, additional exemplars may be taught, or increased emphasis might be placed upon the development of self-monitoring skills (Baer, 1981; Elbert, Powell, & Swartzlander, 1991; Koegel, Koegel, & Ingham, 1986; Stokes & Baer, 1977). Although the concept of stimulability as a prognostic factor in articulation treatment has been discussed in the speechlanguage pathology literature for more than 50 years, the relationship between stimulability and generalization is only now becoming apparent. For these 6 misarticulating preschoolers, stimulability was closely related to sound-learning patterns, with subjects being most likely to evidence gains in the production of stimulable sounds regardless of the specific sounds targeted for treatment.
Acknowledgments This work was supported In part by grants to Indiana University from the National Institutes of Health, No. NS20976 and DC00260. We would like to acknowledge Susan Schaler, Jennifer (Tighe)
Powell et al.: Stimulability and Generalization
Orchard, Cheryl Tarr, and Cheryl Bennett who assisted in all phases of data collection. We are also grateful to Judith A. Gierut and Rita C. Naremore for their insightful comments on a previous version of this research. Portions of this paper were presented at the Conference on Treatment Efficacy sponsored by the American Speech-Language-Hearing Foundation, San Antonio, TX, March 1989, and at the meeting of the American Speech-Language-Hearing Association, St. Louis, MO, November 1989.
References American National Standards Institute. (1969). Specifications for audiometers (ANSI S3.6-1969). New York: ANSI. Baer, D. M. (1981). How to plan for generalization. Lawrence, KS: H & H Enterprises. Bankson, N. W., & Bernthal, J. E. (1983). In defense of the traditional articulation test battery. Seminars in Speech and Language, 4, 289-296. Bernthal, J. E., & Bankson, N. W. (1988). Articulation and phonological disorders (2nd ed.). Englewood Cliffs, NJ: Prentice-Hall. Brown, J. C. (1975). Techniques for correcting /r/ misarticulations. Language, Speech, and Hearing Services in Schools, 6, 86-91. Carter, E. T., & Buck, M. W. (1958). Prognostic testing for functional articulation disorders among children in the first grade. Journal of Speech and Hearing Disorders, 23, 124-133. Culler, T. (1984). Articulation disorders: A basic guide to intervention in the schools. Austin, TX: Pro-Ed. Diedrich, W. M. (1983). Stimulability and articulation disorders. Seminars in Speech and Language, 4, 297-311. Dlnnsen, D. A., Chin, S. B., Elbert, M., & Powell, T. W. (1990). Some constraints on functionally disordered phonologies: Phonetic inventories and phonotactics. Journal of Speech and Hearing Research, 33, 28-37. Dinnsen, D.A., & Elbert, M. (1984). On the relationship between phonology and learning. In M. Elbert, D. A. Dinnsen, & G. Weismer (Eds.), Phonological theory and the misarticulating child. ASHA Monographs, 22, 59-68. Rockville, MD: ASHA. Dunn, C. (1983). A framework for generalization in disordered phonology. Journal of Childhood Communication Disorders, 7, 46-58. Dunn, L. M., & Dunn, L.M. (1981). Peabody Picture Vocabulary Test-Revised. Circle Pines, MN: American Guidance Service. Dyson, A.T. (1988). Phonetic inventories of 2- and 3-year-old children. Journal of Speech and Hearing Disorders, 53, 89-93. Elbert, M., Dinnsen, D. A., & Powell, T. W. (1984). On the predication of phonologic generalization learning patterns. Journal of Speech and Hearing Disorders, 49, 309-317. Elbert, M., & Gierut, J. A. (1986). Handbook of clinical phonology: Approaches to assessment and treatment. San Diego: CollegeHill. Elbert, M., & McReynolds, L. V. (1978). An experimental analysis of misarticulating children's generalization. Journal of Speech and Hearing Research, 21, 136-150. Elbert, M., Powell, T. W., & Swartzlander, P. (1991). Toward a technology of generalization: How many exemplars are sufficient? Journal of Speech and Hearing Research, 34, 81-87. Elbert, M., Rockman, B., & Saltzman, D. (1980). Contrasts: The use of minimal pairs in articulation training. Austin, TX: Pro-Ed. Elbert, M., Shelton, R. L., & Arndt, W. B. (1967). A task for evaluation of articulation change: I. Development of methodology. Journal of Speech and Hearing Disorders, 44, 459-471. Farquhar, M. S. (1961). Prognostic value of imitative and auditory discrimination tests. Journal of Speech and Hearing Disorders, 26, 342-347. Fey, M. E., & Stalker, C. H. (1986). A hypothesis-testing approach to treatment of a child with an idiosyncratic (morpho)phonological system. Journal of Speech and Hearing Disorders, 51, 324-336. Fuqua, R. W., & Schwade, J. (1986). Social validation of applied behavioral research: A selective review and critique. In A. Poling & R. W. Fuqua (Eds.), Research methods in applied behavior analysis: Issues and advances (pp. 265-292). New York: Plenum
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Press. Glerut, J.A. (1985). On the relationship between phonological knowledge and generalization learning in misarticulating children. Unpublished doctoral dissertation, Indiana University, Bloomington. (Also distributed by the Indiana University Linguistics Club, 1986). Glerut, J. A. (1989). Maximal opposition approach to phonological treatment. Journal of Speech and Hearing Disorders, 54, 9-19. Glerut, J.A., Elbert, M., & Dinnsen, D.A. (1987). A functional analysis of phonological knowledge and generalization learning in misarticulating children. Journal of Speech and Hearing Research, 30, 462-479. Goldman, R., & Fristoe, M. (1986). Goldman-Fristoe Test of Articulation. Circle Pines, MN: American Guidance Service. Harryman, E., & Kresheck, J. (1971). A structured program for modifying /r/ misarticulations. Language, Speech, and Hearing Services in Schools, 2(5), 52-54. Kamhi, A. G. (1984). Problem solving in child language disorders: The clinician as clinical scientist. Language, Speech, and Hearing Services in Schools, 15, 226-234. Kaufman, A. S., & Kaufman, N. L. (1983). Kaufman Assessment Battery for Children. Circle Pines, MN: American Guidance Service. KazdIn, A. E. (1977). Assessing the clinical or applied importance of behavior change through social validation. Behavior Modification, 1, 427-452. Kisatsky, T. J. (1967). The prognostic value of Carter-Buck tests in measuring articulation skills in selected kindergarten children. Exceptional Children, 34, 81-85. Koegel, L. K., Koegel, R. L., & Ingham, J. C. (1986). Programming rapid generalization of correct articulation through self-monitoring procedures. Journal of Speech and Hearing Disorders, 51, 24-32. Madison, C. (1979). Articulation stimulability reviewed. Language, Speech, and Hearing Services in Schools, 10, 185-190. McCarthy, D. (1972). McCarthy Scales of Children's Abilities. New York: The Psychological Corporation. McReynolds, L. V. (1989). Generalization issues in the treatment of communication disorders. In L. V. McReynolds & J. E. Spradlin (Eds.), Generalization strategies in the treatment of communication disorders (pp. 1-12). Toronto: B. C. Decker. McReynolds, L. V., & Elbert, M. (1982). Articulation disorders of unknown etiology and their remediation. In N.J. Lass, L. V. McReynolds, J. L. Northern, & D. E. Yoder (Eds.), Speech, language, and hearing. Vol I: Pathologies of speech and language (pp. 591-610). Philadelphia: W. B. Saunders. McReynolds, L. V., & Kearns, K. P. (1983). Single-subject experimental designs in communicative disorders. Austin, TX: Pro-Ed. Mueller, D. J. (1986). Measuring social attitudes: A handbook for researchers and practitioners. New York: Teachers College Press. Newcomer, P., & Hammill, D. (1982). Test of Language Development-Primary. Austin, TX: Pro-Ed. Nunnally, J. C. (1978). Psychometric theory (2nd ed.). New York: McGraw-Hill. Powell, T. W. (1991). Planning for phonological generalization: An approach to treatment target selection. American Journal of Speech-Language Pathology, 1, 21-27. Powell, T. W. (1989). Stimulability as a factor in the phonologic generalization of misarticulating preschool children. Unpublished doctoral dissertation, Indiana University, Bloomington. Powell, T. W., & Elbert, M. (1984). Generalization following the remediation of early- and later-developing consonant clusters. Journal of Speech and Hearing Disorders, 49, 211-218. Shelton, R. L., & McReynolds, L. V. (1979). Functional articulation disorders: Preliminaries to treatment. In N. J. Lass (Ed.), Speech and language: Advances in basic research and practice (Vol. 2, pp. 1-111). New York: Academic Press. Shrlberg, L. D. (1975). A response evocation program for /33/. Journal of Speech and Hearing Disorders, 40, 92-105. Shrlberg, L. D. (1980). An intervention procedure for children with persistent /r/ errors. Language, Speech, and Hearing Services in Schools, 11, 102-110. Snow, K., & Milisen, R. (1954). Spontaneous improvement in articulation as related to differential responses to oral and picture
1328 Journal of Speech and Hearing Research tests. Journal of Speech and Hearing Disorders, Monograph Supplement, 4, 46-49. Sommers, R. K. (1983). Articulation disorders. Englewood Cliffs, NJ: Prentice-Hall. Sommers, R. K., Lelss, R., Delp, M., Gerber, A., Fundrella, D., Smith, R., Revucky, M., Ellis, D., & Haley, V. (1967). Factors related to the effectiveness of articulation therapy for kindergarten, first, and second grade children. Journal of Speech and Hearing Research, 10, 428-437. St. Louis, K., & Ruscello, D. (1986). Oral Speech Mechanism Screening Examination-Revised. Austin, TX: Pro-Ed. Stoeol-Gammon, C. (1985). Phonetic inventories, 15-24 months: A longitudinal study. Journal of Speech and Hearing Research, 28, 505-512. Stokes, T. F., & Baeer, D. M. (1977). An implicit technology of generalization. Journal of Applied BehaviorAnalysis, 10, 349-367. Tyler, A.A., Edwards, M.L., & Saxman, J.H. (1987). Clinical application of two phonologically based treatment procedures. Journal of Speech and Hearing Disorders, 52, 393-409.
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Winner, M., & Elbert, M. (1988). Evaluating the treatment effect of repeated probes. Journal of Speech and Hearing Disorders, 53, 211-218. Wolf, M. M. (1978). Social validity: The case for subjective measurement or how applied behavior analysis is finding its heart. Journal of Applied Behavior Analysis, 11, 203-214. Wood, J. M. (1988). A clinical technique helpful in the elicitation of /3./. Language, Speech, and Hearing Services in Schools, 19, 96-99.
Received February 16, 1990 Accepted January 11, 1991 Requests for reprints should be sent to Thomas W. Powell, PhD, Department of Speech Pathology and Audiology, Ball State University, Muncie, IN 47306-0555.
Appendix Contrasting minimal pair treatment program used to teach production of two sounds that were excluded from the subjects' phonetic inventories. Phase I. [r] treatment Step A. Stimulus: Present [w] and [r] picture cards individually with an auditory model. Response mode: Imitation. Reinforcement schedule: Continuous reinforcement (CRF). Criterion level: 18/20 correct productions over three consecutive sets of 20. Step B. Stimulus: Present paired [w]-[r] picture cards simultaneously with paired auditory models. Response mode: Imitation. Reinforcement schedule: CRF. Criterion level: 18/20 over three sets of 20. Step C. Stimulus: Present paired [w]-[r] picture cards simultaneously with paired auditory models. Response mode: Imitation. Reinforcement schedule: Variable Ratio 3 (VR3). Criterion level: 18/20 over three sets of 20. Step D. Stimulus: Present paired [w]-[r] picture cards in random order. Response mode: Spontaneous. Reinforcement schedule: VR3. Criterion level: 18/20 over three sets of 20.
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Phase II. (Treatment of second target) Step A. Stimulus: Present minimal pair picture cards individually with an auditory model. Response mode: Imitation. Reinforcement schedule: CRF. Criterion level: 18/20 over three sets of 20. Step B. Stimulus: Present paired minimal pair picture cards with simultaneous auditory models. Response mode: Imitation. Reinforcement schedule: CRF. Criterion level: 18/20 over three sets of 20. Step C. Stimulus: Present paired minimal pair picture cards with simultaneous auditory models. Response mode: Imitation. Reinforcement schedule: VR3. Criterion level: 18/20 over three sets of 20. Step D. Stimulus: Present minimal pair picture cards in random order. Response mode: Spontaneous. Reinforcement schedule: VR3. Criterion level: 18/20 over three sets of 20.
Stimulability as a Factor in the Phonological Generalization of Misarticulating Preschool Children Thomas W. Powell
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Ball State University Muncie, IN
Mary Elbert Daniel A. Dinnsen Indiana University, Bloomington
The relationship among six functionally misarticulating preschool children's phoneme-specific stimulability skills, the choice of treatment targets (i.e., stimulable or nonstimulable sounds), and generalization of correct sound production was explored in this prospective study. Each subject [age range of 4:11 (years:months) to 5:61 was taught to produce [r] and one other sound that was absent from his or her phonetic inventory using a contrasting-minimal-pairs production approach. A multiple baseline across behaviors single-subject research design provided experimental control. For 86% of the 28 monitored sounds, generalization was consistent with pretreatment stimulability skills; production of stimulable sounds tended to improve regardless of treatment target. These results suggest that nonstimulable sounds are likely to require direct treatment; thus, generalization probe responses may be maximized by treating nonstimulable sounds rather than stimulable sounds.
KEY WORDS: stimulablity, generalization, articulation/phonologIcal disorders, intervention, imitation
Stimulability has been defined, measured, and interpreted in many ways over the past 50 years (for review, see Diedrich, 1983; Madison, 1979). Moreover, stimulability data have been used for a variety of purposes including treatment target selection and prediction of self-correction or progress in treatment (Bankson & Bernthal, 1983).
The prognostic value of stimulability measures has been examined in a series of studies. Research suggests that untreated subjects with high stimulability scores show more improvement in sound production than subjects with low stimulability scores (Farquhar, 1961; Kisatsky, 1967; Snow & Milisen, 1954). With treatment, children with low stimulability scores tended to have higher gain scores than subjects with high stimulability scores (Carter & Buck, 1958; Sommers et al., 1967). In most of these studies, however, stimulability was operationally defined as the degree of correction (i.e., the difference between spontaneous and imitative error rates) averaged across phonemes (Sommers, 1983). Stimulability was thus viewed as a global ability rather than a phoneme-specific measure. More recently, subjects' pretreatment stimulability for individual sounds has been used to help explain generalization patterns (e.g., Dinnsen & Elbert, 1984; C. Dunn, 1983; Elbert & McReynolds, 1978; Powell & Elbert, 1984; Tyler, Edwards, & Saxman, 1987). There have been, however, no prospective studies examining the relationship between phoneme-specific stimulability and generalization. Shelton and McReynolds (1979) noted, for example, that "the exact role of stimulability in training is not clear" and "the relationship between this ability [stimulability] and spontaneous production in training has not been explored" (p. 88). McReynolds and Elbert (1982) also pointed out that "since the relationship between stimulability and carryover has not been explored, the effects on later stages of remediation are unknown" (p. 594). D 1991, American Speech-Language-Hearing Association
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Powell et al.: Stimulability and Generalization The purpose of this study was to investigate the relationship between stimulability and generalization among 6 preschool children receiving treatment on [r] and one other sound that was absent from their phonetic inventory. The following specific research questions are addressed in this article. 1. Are subjects' pretreatment stimulability skills positively related to their performance on posttreatment generalization measures? 2. If one controls for the effects of generalization at the distinctive feature level by teaching [r] (which appears to be relatively independent of other American English sounds), then will subjects show gains in their production of other stimulable and nonstimulable sounds? On the basis of the findings of previous studies (Elbert, Dinnsen, & Powell, 1984; Gierut, Elbert, &Dinnsen, 1987), itwas hypothesized that subjects would generalize to sounds for which they were stimulable more readily than to nonstimulable sounds.
Method Experimental Design This study used a multiple baseline across behaviors single-subject design to provide experimental control. This design involved two target behaviors that could be modified using a single treatment paradigm; however, the target behaviors had to be functionally independent such that treatment on one behavior would not directly enhance the other (McReynolds & Kearns, 1983). Previous studies of phonological intervention have shown, however, that all speech sounds are not independent. For example, Elbert, Shelton, and Amdt (1967) showed that treatment on the [s] sound resulted in gains in production of both [s] and [z], but not [r]. Thus, [r] appeared to be relatively independent of [s], whereas [s] and [z] were more closely related. The [r] sound was selected as the first treatment target for all subjects partly because of its relative independence from other sounds. During treatment on [r], changes in the production of other stimulable and nonstimulable sounds could be monitored. These changes could not easily be explained by the phonetic similarity among the sounds. Other factors in the selection of [r] included its frequency of misarticulation (Bemthal & Bankson, 1988) and the apparent clinical interest in [r] evidenced by publication of a variety of treatment approaches (e.g., Brown, 1975; Harryman & Kresheck, 1971; Shriberg, 1975, 1980; Wood, 1988). Subjects Four boys and 2 girls between the ages of 4:11 (years:months) and 5:6 served as subjects. All children were from monolingual English-speaking homes and were referred for evaluation and treatment of phonological errors. All subjects scored at or below the fifth percentile on the Soundsin-Words subtest of the Goldman-Fristoe Test of Articulation (Goldman & Fristoe, 1986). A comprehensive corpus for phonological analysis was elicited using a 306-item modification of the probe developed by Gierut (1985) to sample
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major English consonants in prevocalic, intervocalic, and postvocalic environments. The children's responses were phonetically transcribed on-line by author Powell and a graduate student in speechlanguage pathology with training in narrow phonetic transcription. Responses were also audiotaped using a Marantz PMD 360 professional stereo cassette recorder equipped with a Superscope EC-7 cardioid condenser microphone. The transcriptions were used to compile a phonetic inventory for each subject, and a conversational speech sample was used for verification. In accordance with criteria used by others (e.g., Dinnsen, Chin, Elbert, & Powell, 1990; Dyson, 1988; Stoel-Gammon, 1985), a consonant was included in the subject's phonetic inventory if it was produced in at least two items. The number of speech sounds missing from the subjects' phonetic inventories ranged from four to six. All subjects earned passing scores on the Oral Speech Mechanism Screening Examination-Revised (St. Louis & Ruscello, 1986). Two norm-referenced tests of language, the Test of Language Development-Primary (Newcomer & Hammill, 1982) and the Peabody Picture Vocabulary Test-Revised (Dunn & Dunn, 1981), were administered, and all subjects were in the average to above-average range. The general intellectual level of each subject was also in the average to above-average range as assessed by the McCarthy Scales of Children's Abilities (McCarthy, 1972) and the Kaufman Assessment Battery for Children (Kaufman & Kaufman, 1983). All subjects passed a hearing screening evaluation by responding appropriately to 500-, 1000-, 2000-, and 4000-Hz tones presented at 20 dB HL (ANSI, 1969).
Materials Analysis probe. The 306-item probe adapted from Gierut (1985) provided data for phonological analysis. Each subject's phonetic inventory was compiled prior to treatment as described above using these data. Experimental probe. Once a subject's phonetic inventory had been compiled, an experimental probe was developed to measure generalization. The experimental probe included 20 items designed to assess production of each of the two treatment sounds and 10 items assessing each additional sound that was absent from the subject's phonetic inventory. Thus, the experimental probes ranged from 60 to 80 items in length. The experimental probe items were administered in random order to the children at the conclusion of every fourth treatment session using a delayed-imitation protocol. Treatment probe. The treatment probe was the subset of 20 experimental probe items assessing production of the sound targeted for treatment (e.g., [r]). Treatment probes were administered at the conclusion of every session to provide a discrete measure of generalization-a practice supported by the work of Winner and Elbert (1988). The treatment probe for [r], which was used with all subjects, is presented in Table 1. The final consonants across these 20 monosyllabic treatment probe items were systematically varied to help control for phonetic context factors that might affect generalization. The items were randomized prior to presentation to subjects.
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TABLE 1. Treatment probe used to assess generalization of [r] production. room rope rob Ruth writhe
run rat red roof rove
ring wreck rug rice rose
ray rich ridge rush rouge
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Powell; to control for experimenter bias, treatment data were kept independently by trained observers. All subjects received treatment on [r]; however, the second target sound (phase II)varied systematically across subjects to ensure treatment of both stimulable and nonstimulable sounds (see Table 2). Reliability
Stimulability measure. Farquhar's (1961) adaptation of the Carter and Buck (1958) Nonsense Syllable Task was used to assess stimulability of singleton consonants in isolation and in nine syllables. A stimulability score was calculated for each sound missing from the phonetic inventory and was expressed as the percentage of acceptable productions across the 10 items. Unlike many previous studies, these data were used as a phoneme-specific stimulability measure and were not averaged. Subjects were credited with being stimulable for sounds produced with at least 10% accuracy during the Nonsense Syllable Task. This level was consistent with the criterion used by Elbert et al. (1984) in assessing productive phonological knowledge. Likert scale. A 16-item Likert-type scale was developed using procedures outlined by Mueller (1986) to assess social validity (Fuqua & Schwade, 1986; Kazdin, 1977; Wolf, 1978). The scale was completed by parents before treatment, immediately following treatment, and during a follow-up session to assess the degree to which their perceptions of the children's speech agreed with the reported data. Additional information regarding the development and psychometric characteristics of this scale can be found in Powell (1989). Procedures Pretesting. The battery of tests was administered to each child according to standardized procedures prior to treatment. The 306-item analysis probe and the stimulability tasks were next administered to the children while parents completed the Likert-type scale. Baseline measures. Experimental probes were developed for each subject to assess generalization and were administered three times prior to treatment. A baseline was operationally defined as stable if the variability across the three baseline measures did not exceed 10%. Treatment. For each subject, treatment commenced on [r] once a stable baseline was established. A contrastingminimal-pairs production approach was used (as in Elbert, Rockman, & Saltzman, 1980). Perceptual abilities (e.g., auditory discrimination) were not treated directly. Five minimal pairs contrasting the target (e.g., /r/) with the child's customary error (e.g., [w]) were used during the first phase of treatment. The treatment program consisted of four steps and is described in the appendix. As the child progressed through the program, reinforcement and stimulus cues were systematically decreased. Subjects were seen an average of three times per week, and each session consisted of 100 minimal pair responses (approximately 30 min). A token reinforcement system was used whereby correct responses earned chips that could be redeemed for stickers. All treatment was provided by author
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Analysis probes. All analysis probe responses were phonetically transcribed independently by two judges. Interjudge agreement ranged from 76% to 94%, with a mean of 85%. The judges then listened to the tape-recorded analysis probe responses and developed mutually acceptable transcriptions to resolve disagreements. Other measures. Transcription reliability for the treatment and experimental probes reflected the degree to which judges agreed on the production accuracy of target sounds only. The average right/wrong reliability across these measures was 96% agreement. Subjects' responses to the Carter and Buck (1958) stimulability tasks were also transcribed on-line by two judges. The percentage of agreement across all items ranged from 97% to 99%, with a mean of 98% agreement.
Results Two types of data will be reported for each subject. Treatment data (percentage of correct responses during each session) will be discussed first. Then, generalization data elicited by the experimental and treatment probes will be considered. Subject 1 The treatment and generalization data obtained from Subject 1 are presented in Figure 1. Subject 1 never produced [r], [s], [z], or [I] correctly prior to the initiation of the treatment program, as steady zero baseline measures evidenced. Once treatment was initiated, Subject 1 met the treatment criterion for [r] in 10 sessions. Next, treatment was introduced on the [s] sound, and the treatment criterion was met in only four sessions. The multiple baseline across the two target sounds provided evidence of experimental control. Generalization data for Subject 1 also are presented In Figure 1.Subject 1's generalization of correct [r] production, as measured by the experimental and treatment probes, mirrored his treatment performance. He maintained a stable zero baseTABLE 2. Summary of treatment targets and stimulabllty test results for the 6 subjects. Subject
Target 1
Target 2
1 2 3 4 5 6
[r]--stimulable [r--stimulable [r--nonstimulable [r--nonstimulable [r]--nonstimulable [r--nonstimulable
[s}-stimulable [e]--stimulable [tfl-stimulable [e--stimulable [e]-nonstimulable [g}--nonstimulable
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Subject 2 Subject 2 was stimulable for the postvocalic allophone of [r]. During treatment, he showed rapid gains in his production of word-initial r], and he met the treatment criterion in 13 treatment sessions, as Figure 2 depicts. Subject 2's production of correct [r] during generalization measures, however, peaked at 35% correct during the 10th treatment session. Thereafter, his production of [r] reverted to 0% accuracy. Subject 2 made rapid gains in his production of stimulable [e] during treatment and met the treatment criterion in four
FIGURE 1. Treatment (open circles) and generalization (filled circles) data for Subject 1 plotted as a function of treatment sessions. Phase A = Baseline, B. = [r] Treatment (shaded), B2 = [s] Treatment (shaded), C = Follow-up. 'Indlcates stimulable sounds. line for the three untreated sounds during the period he received treatment on [r]; this observation further supports the functional independence of [r] relative to other sounds. Several changes were observed, however, in Subject 1's production of sounds following the introduction of treatment on [s]. He showed rapid gains inthe production of [s] (for which he was stimulable), and he also showed gains in his production of the voiced cognate [z]. Although Subject 1's accuracy rate for stimulable [z] fluctuated, he ultimately met the generalization criterion during follow-up. The generalization criterion was not met for nonstimulable [I] during the follow-up session. Downloaded From: http://jslhr.pubs.asha.org/ by a La Trobe Univ User on 05/22/2016 Terms of Use: http://pubs.asha.org/ss/rights_and_permissions.aspx
FIGURE 2. Treatment (open circles) and generalization (filled circles) data for Subject 2 plotted as a function of treatment sessions. Phase A = Baseline, B. = [r] Treatment (shaded), B2 = [e] Treatment (shaded), C = Follow-up. 'Indicates stimulable sounds.
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sessions. Generalization of correct [e] and [] production was noted; gains in his production of correct [ were more gradual. This subject met the generalization criterion for three of the four stimulable sounds that were missing from his phonetic inventory prior to the onset of the study; stimulable [r] was not generalized. Subject 3 Unlike the first two subjects, Subject 3 was not stimulable for [r] in any position or vocalic environment prior to treatment. It was necessary to use phonetic placement cues and to reinforce successive approximations of [r] during treatment. He met the treatment criterion during the 29th treatment session (see Figure 3); however, no generalization was observed. Treatment next turned to production of [tj; six sessions were sufficient for Subject 3 to meet the treatment criterion for this stimulable sound. Subject 3 generalized correct production of [tf]; he also showed gains in his production of the nonstimulable cognate [d3]. The generalization criterion was met for only these sounds at follow-up. Subject 4 Shaping procedures also were used with Subject 4 to elicit an acceptable production of [r], and he met the treatment criterion during the 26th session (see Figure 4). Subject 4's production of [r] during generalization measures, however, remained inaccurate. Next, Subject 4 was taught to produce the stimulable [e] sound. He met the treatment criterion for this sound in four sessions. During the follow-up session, Subject 4 met the generalization criterion for both stimulable [e] and stimulable [6]. Subject 4 produced stimulable [v] inconsistently during baseline measures and evidenced gradual gains in [v] production. Once treatment was initiated on [e], however, Subject 4's production accuracy for [v] decreased, and the generalization criterion was not met. Subject 5 The extensive use of shaping procedures was also necessary with Subject 5; nevertheless, she never met the treatment criterion for [r]. She was treated for 31 sessions (see Figure 5) and advanced to the third step of the treatment program, but her [r] production remained at 0% during generalization measures. Subject 5 was next taught to produce the [e] sound. She met the treatment criterion for this nonstimulable sound in only eight sessions, but she did not generalize correct production. Subject 5's production of four additional sounds was monitored: nonstimulable [6] and stimulable [v], [z], and [I]. Her production of these untrained sounds improved, and she met the generalization criterion, although she did not generalize production of the two nonstimulable sounds that were directly treated.
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FIGURE 3. Treatment (open circles) and geonralliatlon data (filled circle) for Subject 3 plotted as a function of treatment sessions. Phase A = Baseline, B. = [r] Treatment (shaded), 82 = tn Treatment (shaded), C = Follow-up. "Indicates stimulable sounds.
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FIGURE 4. Treatment (open circles) and generalization data (filled circles) for Subject 4 plotted as a function of treatment essions. Phase A = Baseline, B. = [r] Treatment (shaded), B2 = [e] Treatment (shaded), C = Follow-up. "Indicates stimulable sounds.
Subject 6 Subject 6 met the treatment criterion for nonstimulable [r] in 12 sessions and nonstimulable [g] in 4 sessions (see Figure 6). Generalization, however, was limited. Subject 6 did not meet the generalization criterion for any of the four sounds that were monitored.
Group Trends In summary, all subjects evidenced gains in their production of [r] and one other sound during treatment. Indeed, the
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FIGURE 5. Treatment (open circles) and generalization data (filled circles) for Subject 5 plotted as a function of treatment sessions. Phase A = Baseline, B = [r] Treatment (shaded), B2 = [e] Treatment (shaded), C = Follow-up. 'Indicates stimulable sounds.
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FIGURE 6. Treatment (open circles) and generalization data (filled circles) for Subject 6 plotted as a function of treatment sessions. Phase A = Baseline, B = [r Treatment (shaded), B2 = [g9
Treatment (shaded), C = Follow-up.
treatment criterion was met for 11 of the 12 sounds that were directly treated. Although all subjects made substantial gains during treatment, the degree of generalization learning varied widely. Some subjects (e.g., Subject 1) generalized readily to treated sounds and their cognates; others (e.g., Subject 6) evidenced little generalization. Table 3 lists the 28 targets that were monitored across the 6 subjects and pretreatment stimulability scores. This table also summarizes each subject's production accuracy as assessed by the individualized experimental probes at three points: (1) following [r] treatment, (2) following treatment on the second sound, and (3) during the follow-up session.
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The first research question posed by this study involved the relationship between pretreatment stimulability and generalization scores at the conclusion of the study. This question was addressed by examining the data presented in Table 3 to identify group trends. Across the 6 subjects, production of 28 sounds was monitored. Prior to the implementation of treatment, 14 (or 50%) of these sounds were stimulable, and 14 were nonstimulable. To examine the relationship between stimulability and generalization, the data were pooled across subjects. The two variables (pretreatment stimulability and generalization assessed during the follow-up session) were scored dichotomously for each monitored sound. A sound was considered stimulable if produced with at least 10% accuracy on the Carter and Buck (1958) task. Sounds produced with 50% or greater accuracy during the follow-up session were credited as being generalized. A 2 x 2 contingency matrix was next completed (see Table 4). Of the 14 stimulable sounds, 12 met the generalization criterion at follow-up; however, only 2 of the 14 nonstimulable sounds met the generalization criterion. This pattem was not attributable to chance [X2 (1, N = 28) = 14.2857; p = .00038]. The correlation between the two binary variables was next calculated using the phi coefficient (Nunnally, 1978). For these data, phi = .71, suggesting that more than 50% of the generalization variance could be explained by the subjects' stimulability skills. Although stimulability scores could account for much of the generalization variance at follow-up, a more qualitative analysis of the data was also helpful inexplaining the relationship among stimulability, treatment targets, and generalization. Given the moderately high relationship between stimulability and generalization, one would expect subjects to meet the generalization criterion at follow-up for stimulable sounds and not to meet the criterion for nonstimulable sounds. Indeed, this prediction held true for 24 of the 28 targets (86%). The second research question asked whether subjects would evidence gains intheir production of stimulable and nonstimulable sounds following treatment on [r]. This question also was answered by analyzing the experimental probe data elicited from each subject during the final treatment session on [r]; the raw data are presented in column 1 of Table 3. Following treatment on [r], 6 of the 28 monitored sounds met the generalization criterion. Subject 1 generalized correct production of stimulable [r] with 75% accuracy. Subject 4's production accuracy for stimulable [v] also met the generalization criterion. Subject 5 met the generalization criterion for four of the six sounds that were missing from her phonetic inventory: stimulable [z], [I], [v], and nonstimulable [6]. Thus, five of the six generalized sounds were stimulable prior to the implementation of treatment. This working hypothesis was then formulated: Following treatment on [r], subjects are likely to show increases in their production of stimulable sounds, but not in their production of nonstimulable sounds. The data were again examined to test this hypothesis. For the first 2 subjects, the working hypothesis did not account well for the data. Although Subjects 1 and 2 were stimulable for seven of the eight sounds that were monitored, only Subject 1's production of [r] (which was directly treated)
Powell et al.: Stimulability and Generalization
1325
TABLE 3. Sounds missing from each subject's phonetic Inventory, pretreatment stimulabllty, and generalization scores elicited at three times. Generalization scores Phase I
Phase II
Follow-up
.90 1.00 .90 .00
.75 .00 .00 .10
.90 1.00 .30 .50
.85 1.00 .80 .30
.30 .10 .40 .20
.10 .05 .00 .10
.00 .90 .60 .20
.00 .90 .80 .50
.00 .20 .00 .00 .00 .00
.20 .00 .00 .00 .00 .00
.10 .85 .60 .00 .00 .00
.10 .95 .90 .00 .00 .00
.00 .30 .10
.00 .00 .00
.00 .25 .10
.00 .55 .50
[v]
.70
.55
.35
.20
[r]a [e]a [6]
.00 .00 .00
.00 .05 .80
.00 .15 .80
.00 .15 .70
Sound
Stimulabllty
Subject 1 [r]a [s]a [z] [I] Subject 2 [r]a [e] [6] [fl Subject 3 [r]a [t'fl [d3] [s] [z] If] Subject 4 [r]a [e]la [6] Subject 5
[z]
.30
.90
.90
1.00
[I]
.20
1.00
1.00
1.00
[v] .20 .80 Subject 6 [r]' .00 .35 [g]a .00 .00 [k] .00 .00 [Z] .00 .00 aDenotes sounds that were targeted for treatment. met the generalization criterion. Subject 1 did not generalize correct production of nonstimulable [I], which was also consistent with the working hypothesis. For these two subjects, the working hypothesis held true for only two of the eight monitored targets (25%). The working hypothesis was more successful in describing the learning patterns evidenced by the remaining 4 subjects. For these subjects, the hypothesis was consistent with 16 of the 20 targets (80%). Subjects 1 and 2 differed from other subjects in that they were stimulable for [r] prior to treatment. If only Subjects 1 and 2 were considered, then a different observation might be TABLE 4. Two-by-two contingency matrix examining the relationship between pretreatment stimulabillty and generalization at follow-up. Pretreatment stimulabillty +
Generalization
+
12
2
at follow-up
-
2
12
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.80
.90
.40 .25 .30 .30
.10 .40 .30 .30
made. That is, subjects taught to produce a stimulable sound generalized, at most, to the targeted sound (i.e., [r]). The answer to the second research question appeared to vary as a function of stimulability. Subjects who were not stimulable for [r] tended to improve production of untrained, stimulable sounds; however, subjects who were stimulable for [r] generalized, at most, to [r]. Gains in the production of untreated sounds after [r] treatment are difficult to explain. With the possible exception of /I/, no other English phoneme is closely related to /r/. Given the apparent functional independence of [r] from other speech sounds, one might hypothesize that treatment on [r] helps to focus a child's attention upon speech sounds in general, or that treatment on any sound helps a child to "learn how to learn," resulting in higher production scores for sounds that were not directly taught. Another explanation for the sound learning patterns observed following [r] training involves a further conceptualization of the child's productive phonological knowledge (in the sense of Elbert et al., 1984). Although the 28 monitored sounds were never produced spontaneously, subjects had greater productive phonological knowledge of some sounds relative to others, as the stimulability measure evidenced.
1326 Journal of Speech and Heanng Research If stimulable sounds represent greater productive phonological knowledge than nonstimulable sounds, then treatment of stimulable sounds should affect neither the production of unrelated stimulable sounds nor production of nonstimulable sounds. Following treatment on a nonstimulable sound, however, one might expect improvement in the production of stimulable sounds (which are phonologically "known" in a production sense). These predictions are consistent with the data obtained in this study and with previous research findings (Dinnsen & Elbert, 1984; Elbert et al., 1984; Fey & Stalker, 1986; Gierut et al., 1987) and deserve additional study. Social Validity Finally, the results from the Likert-type scale completed by the parents were analyzed to assess the social validity of the findings. The clinician providing the treatment in this study was not blind to the research questions or stimulability test results. Data obtained from the parents helped to control for experimenter bias and served to validate the findings. Despite the small number of subjects, the mean Likert score across the 6 subjects increased significantly from the first to the second administration [(5) = -2.835, p = .035]. This finding would be consistent with decreased parental concern following the initiation of treatment. It was also hypothesized that parents of children who evidenced much generalization would yield higher scores than those completed by parents of children who evidenced little generalization. For each subject, the mean percentage correct across the monitored sounds following treatment was calculated as an index of generalization, and the subjects were rank ordered. The posttreatment Likert scores, too, were ranked, and the two variables were correlated using Spearman's Rho. There was a moderately high relationship between generalization and Likert-type scale rankings (Rho = .76; p = .038) suggesting that the parents' perceptions were consistent with the obtained data. Discussion This paper examined the relationship among 6 misarticulating preschool children's phoneme-specific stimulability skills, choice of treatment target (i.e., stimulable or nonstimulable sounds), and generalization of sound production. Each subject was taught to produce [r] and one other sound that was absent from the phonetic inventory using a contrasting-minimal-pairs production approach. Subjects' productions of stimulable sounds tended to improve regardless of treatment target, but generalization of nonstimulable sounds was rarely observed. These results suggest that preschool children's stimulability skills are an important factor in their generalization of correct sound production during phonological intervention. Two generalization trends were identified across the 6 subjects that may predict phonological learning patterns after treatment and facilitate selection of treatment targets (as per Elbert & Gierut, 1986, pp. 105-107). These predictions follow:
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1. If a stimulable sound is taught, then the subject may learn that sound and its cognate, but generalization to other sounds will be limited. 2. If a nonstimulable sound is taught, then the subject may leam the target sound, will probably leam other stimulable sounds, but probably will not learn other nonstimulable sounds. Speech-language pathologists may use these trends to predict generalization patterns as they design programs to increase the phonetic inventories of misarticulating preschool children. If several sounds were missing from a child's phonetic inventory, then generalization hypotheses could be formulated for each available target. Treatment efficiency might be maximized by planning for generalization (Powell, 1991, Stokes & Baer, 1977) and targeting for treatment the sound whose projected generalization effect would be the greatest. Periodically, clinicians should analyze the child's phonology to assess changes in production. New hypotheses should be developed as generalization trends emerge, and new treatment targets should be selected. This approach to phonological treatment is consistent with the remediation philosophies of Elbert and Gierut (1986), Fey and Stalker (1986), Gierut (1989),
Kamhi (1984), McReynolds (1989), and others. Some have argued that it is preferable to teach stimulable sounds over nonstimulable sounds because of a presumed difference in treatment duration (e.g., Culler, 1984), but the results of this study did not clearly support this view. With the exception of [r], treatment of nonstimulable sounds generally did not require more trials than stimulable sounds. Indeed, the results from this study suggest that the number of correct responses on generalization probes can be maximized by teaching nonstimulable sounds because stimulable sounds are likely to improve without direct treatment. Although these subjects often showed gains in their production of stimulable sounds, it is true that generalization of nonstimulable sounds was limited. Other researchers have also reported limited generalization to nonstimulable sounds despite direct treatment (e.g., Fey & Stalker, 1986), and different treatment strategies may be necessary to foster generalization to nonstimulable targets. For example, additional exemplars may be taught, or increased emphasis might be placed upon the development of self-monitoring skills (Baer, 1981; Elbert, Powell, & Swartzlander, 1991; Koegel, Koegel, & Ingham, 1986; Stokes & Baer, 1977). Although the concept of stimulability as a prognostic factor in articulation treatment has been discussed in the speechlanguage pathology literature for more than 50 years, the relationship between stimulability and generalization is only now becoming apparent. For these 6 misarticulating preschoolers, stimulability was closely related to sound-learning patterns, with subjects being most likely to evidence gains in the production of stimulable sounds regardless of the specific sounds targeted for treatment.
Acknowledgments This work was supported In part by grants to Indiana University from the National Institutes of Health, No. NS20976 and DC00260. We would like to acknowledge Susan Schaler, Jennifer (Tighe)
Powell et al.: Stimulability and Generalization
Orchard, Cheryl Tarr, and Cheryl Bennett who assisted in all phases of data collection. We are also grateful to Judith A. Gierut and Rita C. Naremore for their insightful comments on a previous version of this research. Portions of this paper were presented at the Conference on Treatment Efficacy sponsored by the American Speech-Language-Hearing Foundation, San Antonio, TX, March 1989, and at the meeting of the American Speech-Language-Hearing Association, St. Louis, MO, November 1989.
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Received February 16, 1990 Accepted January 11, 1991 Requests for reprints should be sent to Thomas W. Powell, PhD, Department of Speech Pathology and Audiology, Ball State University, Muncie, IN 47306-0555.
Appendix Contrasting minimal pair treatment program used to teach production of two sounds that were excluded from the subjects' phonetic inventories. Phase I. [r] treatment Step A. Stimulus: Present [w] and [r] picture cards individually with an auditory model. Response mode: Imitation. Reinforcement schedule: Continuous reinforcement (CRF). Criterion level: 18/20 correct productions over three consecutive sets of 20. Step B. Stimulus: Present paired [w]-[r] picture cards simultaneously with paired auditory models. Response mode: Imitation. Reinforcement schedule: CRF. Criterion level: 18/20 over three sets of 20. Step C. Stimulus: Present paired [w]-[r] picture cards simultaneously with paired auditory models. Response mode: Imitation. Reinforcement schedule: Variable Ratio 3 (VR3). Criterion level: 18/20 over three sets of 20. Step D. Stimulus: Present paired [w]-[r] picture cards in random order. Response mode: Spontaneous. Reinforcement schedule: VR3. Criterion level: 18/20 over three sets of 20.
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Phase II. (Treatment of second target) Step A. Stimulus: Present minimal pair picture cards individually with an auditory model. Response mode: Imitation. Reinforcement schedule: CRF. Criterion level: 18/20 over three sets of 20. Step B. Stimulus: Present paired minimal pair picture cards with simultaneous auditory models. Response mode: Imitation. Reinforcement schedule: CRF. Criterion level: 18/20 over three sets of 20. Step C. Stimulus: Present paired minimal pair picture cards with simultaneous auditory models. Response mode: Imitation. Reinforcement schedule: VR3. Criterion level: 18/20 over three sets of 20. Step D. Stimulus: Present minimal pair picture cards in random order. Response mode: Spontaneous. Reinforcement schedule: VR3. Criterion level: 18/20 over three sets of 20.
