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2/7/2005 Subsyllabic Component Durations in Three Children with Suspected Childhood Apraxia of Speech, Two Children with Typical Development, One Child with Phonologic Delay, and One Adult Beate Peter & Carol Stoel-Gammon | |
| Department of Speech and Hearing Sciences University of Washington, Seattle bvpeter@u.washington.edu csg@u.washington.edu Abstract: Previous results have indicated that suspected childhood apraxia of speech (sCAS) may be associated with a central timing deficit that surfaces in speech as well as other activities. To rule out the possibility of a linguistic deficit as the underlying feature of timing inaccuracies during speech, this study examined intrinsic and extrinsic vowel duration effects in monosyllabic words produced by three children with sCAS, one child with phonologic delay (PD), two children with typical development (TD), and one adult. Results indicated that intrinsic and extrinsic influences on vowel durations were not categorically reduced in the participants with sCAS as compared to the children with TD and the adult; the participant with PD showed reduced evidence of these influences. This finding is compatible with the idea that temporal inaccuracies in sCAS are related to deficits in central timing, not linguistic representation. Introduction: Childhood apraxia of speech is a proposed disorder label referring to children who struggle with learning to speak, presumably due to difficulties with motor programming aspects of speech production processes. An underlying cause has not been identified. Because this disorder label is not universally accepted in research and clinical communities, the term “childhood apraxia of speech” is often qualified with the adjective “suspected,” yielding the acronym “sCAS,” which will be used throughout this paper. While the disorder profiles found in the literature vary widely, a core set of characteristics is cited frequently and includes a limited phoneme inventory, frequent omission errors, vowel errors, inconsistency in error production, disordered prosody, increased errors with increased complexity of utterance, difficulty when imitating speech, predominance of simple syllable shapes, impaired oral motor skills, lower expressive vs. receptive language skills, and slower diadochokinetic rates (Davis, Jakielski and Marquardt, 1998). While subsets of these and other characteristics have been observed and described in children with sCAS, an unambiguous diagnostic marker has not yet emerged in clinical research. In recent years, one line of research focused on the disordered prosody observed in children with sCAS, exploring the possibility of identifying a diagnostic marker in that domain. For instance, Shriberg, Aram and Kwiatkowski (1997a, b, c) suggested that a perceptual measure of disordered prosody on the level of lexical stress may be characteristic of sCAS or one of its subtypes. This perceptual measure is part of the Prosody-Voice Screening Profile (PVSP; Shriberg, Kwiatkowski and Rasmussen, 1990). The label “excessive/equal/misplaced” captures the percepts of “excessively forceful, punctuated monostress, misplaced word stress and/or sound blocks or prolongations” (McSweeney and Shriberg, 2001) under a single error code. Also investigating prosody as a potential diagnostic characteristic of sCAS, but focusing on aspects of prosody related to timing, Shriberg, Green, Campbell, McSweeny and Scheer (2003) described significant differences between children with sCAS, as compared to children with typical development and children with moderate to severe speech delay of unknown origin, when the variability of pause events and speech events was measured. Specifically, the participants with sCAS showed proportionally greater variability in their pause events and/or less variability in their speech events, when compared to the other two groups, leading the authors to suggest that constraints in speech timing may characterize children with sCAS. The idea that a deficit in timing may transcend the domain of speech in individuals with a diagnosis of sCAS was investigated by Alcock, Passingham, Watkins and Vargha-Khadem (2000) in a study of family members diagnosed with “verbal dyspraxia.” These authors studied prosodic errors during speech tasks as well as music-related tasks and found that timing accuracy in these individuals was affected during both speech and music tasks while pitch accuracy was intact during both types of activities. Peter and Stoel-Gammon (in press) pursued the possibility of extralinguistic manifestions of timing deficits in individuals with sCAS by studying two children with that diagnosis and two age-matched peers with typical development, during two speech tasks and three music-related tasks. The speech tasks included imitating sentences from the Recalling Sentences in Context subtest of the Clinical Evaluation of Language Fundamentals – Preschool (CELF P; Wiig, Secord, and Semel, 1992) and imitating sequences of non-word syllables as provided by the Tennessee Test of Rhythm and Intonation Patterns (T-TRIP; Koike and Asp, 1981). For both tasks, accuracy was measured in terms of correlation coefficients of the child’s and the imitation model’s vowel durations. The music tasks included singing “Happy Birthday,” imitating sequences of hand-clapped rhythms, and entraining hand taps to a metronome at three different speeds. In all tasks, the participants with typical development showed greater timing accuracy than their peers with sCAS. An age effect was also observed, in that in nearly all measures, the older child within each diagnostic category showed higher accuracy than the younger child. These studies point to the possibility of an underlying deficit in timing associated with sCAS, and potentially present in tasks besides speech. It is not known, however, whether timing inaccuracy during speech events has a distinct linguistic component or whether it is better explained from a central timing framework. If the atypical lexical stress observed by Shriberg et al. (1997a, b, c) has a linguistic component, durational characteristics of linguistic units produced by individuals with sCAS, would be expected to differ from those observed in individuals with typical development and disorder types not based on a linguistic deficit. If the underlying deficit is primarily associated with central timing, durational characteristics of linguistic units observed in children with sCAS may not differ substantially from those produced by children with an intact linguistic system. A linguistic deficit can be ruled out in a scenario where the durational characteristics produced by children with sCAS are comparable to those found in children with typical development. One testing ground for these hypotheses is the durational profile of syllable subcomponents. In English, syllables consist of an optional onset, which can contain up to three consonants; an obligatory nucleus with an intrinsically short or long vowel (where /I/ vs. /i/ are examples of intrinsically short and intrinsically long vowels, respectively); and an optional coda composed of up to three or four consonants. The nucleus and the coda together form the syllable’s rime, which is the element interacting with the stress assigned to the syllable. Onset durations are said to be largely unaffected by the syllable’s stress assignment (Borden, Harris and Raphael, 2003; Peterson and Lehiste, 1960). In English and many other languages, vowel durations have been described, in addition to their intrinsic values, as a function of coda characteristics (“extrinsic vowel duration”), while onset characteristics are thought to be irrelevant to vowel durations. Coda voicing affects vowel duration in that voiceless codas are associated with shorter vowels than voiced codas. Coda manner affects the preceding vowel in that stops and affricates are associated with the shortest vowel durations, followed by fricatives and nasals. Combining these characteristics, Peterson and Lehiste (1960) found the following hierarchy of coda types, from greatest to least vowel shortening effect: voiceless stop, voiceless fricative, voiced stop, nasal, voiced fricative. In English, these extrinsic effects on vowel durations are thought to be essentially a linguistic, rather than an aerodynamic feature, because vowel lengthening resulting from coda voicing is four times greater in English than in other languages. English vowel durations can thus be modeled as a phonemic or a lexical property, rather than a phonetic property related to aerodynamics (Bybee, 2001; Buder and Stoel-Gammon, 2002; Keating, 1985). Two hypotheses and two possible outcomes are the focus of this paper. According to Hypothesis 1, children with sCAS have a linguistic deficit. According to Hypothesis 2, they have a central timing deficit. In Outcome A, the participants with sCAS will show evidence of intrinsic and extrinsic vowel effects to an extent comparable to that found in their peers with typical development. In Outcome B, the participants with sCAS will show systematically less evidence of intrinsic and extrinsic vowel effects than their peers with typical development. Under Hypothesis 1, only Outcome B is possible; Outcome A rules out Hypothesis 1. In other words, evidence of intrinsic and extrinsic vowel effects in the participants with sCAS comparable to those found in the participants with typical development means that the participants with sCAS do not have a linguistic deficit. Under Hypothesis 2, Outcome A and Outcome B are both possible because a central timing deficit may affect vowel durations in such a way that intrinsic and extrinsic vowel effects are obscured. Support for Hypothesis 2 can be drawn from from the previous studies mentioned in the Introduction (Alcock, Passingham, Watkins and Vargha-Khadem, 2000; Peter and Stoel-Gammon, in press). The main purpose of this study was to address these hypotheses by observing intrinsic and extrinsic vowel effects in three children with sCAS, compared to other participants, including two children with typical development. Additional purposes include (1) observing subsyllabic duration patterns in an adult and a child with a speech disorder other than sCAS, namely, phonologic delay (PD), and (2) observing the effects of two experimental variables, number of segments in the onset and number of segments in the coda, on vowel duration. Method: Participants Participants included three children with a diagnosis of sCAS, ages 4;3, 4;7, and 9;5 (years;months); two children with typical development (TD), ages 4;3 and 8;8; one child with a diagnosis of phonologic delay (PD), age 5;1, and one female adult, who was an undergraduate student in the Department of Speech and Hearing Sciences at the University of Washington. Four of these participants were included in the study by Peter and Stoel-Gammon (in press) mentioned above. In the present paper, the child participants are referred to by the acronyms of their diagnostic categories and their ages. All participants were from the Pacific Northwest region of the United States, and all child participants passed the following inclusionary criteria: (1) monolingual, English-speaking home environment, (2) hearing screening passed at 25 dB at 0.5, 1, 2, 4, and 8 kHz, (3) normal receptive language as measured by the Test of Auditory Comprehension of Language - Revised (TACL-3; Carrow-Woolfolk, 1999), (4) normal cognitive functioning as estimated by the Peabody Picture Vocabulary Test, Version B (PPVT-B; Dunn and Dunn, 1997), and (5) normal oral structures and functioning, as measured with the Motor Control Score in a subset of tasks from the Verbal Motor Production Assessment for Children (VMPAC; Hayden and Square, 1999; Items 14 through 19; Items 33 through 37). For the TD children, additional inclusionary criteria were (1) age-appropriate articulation skills, as measured by the Goldman Fristoe Test of Articulation 2 (GFTA-2; Goldman and Fristoe, 2000) and by listener judgment of normal intelligibility, and (2) age-appropriate expressive language skills, as measured by either the Recalling Sentences in Context from the Clinical Evaluation of Language Fundamentals – Preschool (CELF P; Wiig, Secord, and Semel, 1992) or the Recalling Sentences subtest from the Clinical Evaluation of Language Fundamentals 3 (CELF 3; Semel, Wiig and Secord, 1995), as appropriate for age. Regarding the participants with a diagnosis of sCAS, that diagnosis was based on the presence of at least eight of the 11 core characteristics listed by Davis, Jakielski and Marquardt (1998), mentioned above. The participant with phonologic delay was referred on the basis of a history of pervasive phonological processes (e.g., gliding, consonant sequence reduction, strident deficiency, coalescence) and low scores (standard score: 80) on standardized articulation testing; he did not meet the criteria for sCAS. Task Participants completed a word naming task, as prompted by picture stimuli. The stimuli consisted of 33 familiar monosyllabic words with systematically varied onset, vowel, and coda characteristics, e.g., {eye, eyes, pie}; {bed, red, bread}; {sick, stick, six, fixed}. Pictures were presented in random order, and participants were asked to produce the words in the carrier phrase, “I can say ___.” The original stimulus set consisted of 50 items. Seventeen of these words were excluded from analysis, in each case for one of the following reasons: not all participants were able to produce the word; acoustic analysis failed to meet reliability standards; the word was unavailable to acoustic analysis because of technical failure (e.g., the child bumped the microphone while speaking). Instrumentation and Analysis Data collection took place in a quiet clinic room in the Department of Speech and Hearing Sciences at the University of Washington. Sound was recorded with a Sony PCM M1 digital audiotape recorder. Using CoolEdit Pro 1.2 software (Syntrillium Software Corporation, 1998), the digital audio recordings were redigitized at a sampling rate of 22,050 Hz with 16 bit quantization. Acoustic analyses were performed using the Praat 4.0.45 acoustic analysis software (Boersma and Weenink, 2003). Statistical analyses and graphing were performed using Stata Intercooled 7 (Stata Corporation, 2001) and Microsoft Excel (Microsoft Corporation, 2002) software programs. To quantify associations between syllable component characteristics and vowel duration, two separate regression analyses were performed. In the first, onset complexity, vowel complexity, and coda complexity were regressed on vowel duration, where the term “complexity” refers to the number of segments or weights in that subsyllabic component, not to any articulatory characteristic. Onset complexity and coda complexity were coded with a weight of 1 for each segmental unit in the target form, such that a cluster consisting of three consonants in the onset or coda received a weight of 3. Vowel complexity was coded as a binary variable, where lax vowels received a weight of 1 and tense vowels and diphthongs received a weight of 2. Vowel complexity addresses intrinsic vowel duration, and onset and coda complexity were included as experimental variables. In the second regression model, the coda hierarchy from Peterson and Lehiste (1960), described above and referring to the target form, was modified to include liquids on the same level as nasals. This hierarchy was applied to the consonant directly adjacent to the nucleus and coded as follows: 1 = voiceless stop; 2 = voiceless fricative; 3 = voiced stop; 4 = nasals and liquids; 5 = voiced fricative. It was then regressed on vowel duration. This coda hierarchy addresses extrinsic vowel effects. Two separate regression models were necessary because of the inherent collinearities between the coda complexity variable on the one hand and the coda type hierarchy on the other. For both regression analyses, absent onsets and codas were coded as missing values rather than as zeros, so that the inferences would not be biased by the effect of absent vs. present component. Appendix A shows a matrix of the words and the coded covariates. Results: Before describing the output of the regression analyses, the following observations are offered: sCAS 4;7 reduced initial clusters, which led to short onset durations compared to those produced by other participants. He also omitted all obstruent codas. The adult produced unreleased stop codas in eight instances, in bilabial and alveolar stops but not in velars, while other participants produced only released stop codas. PD 5;1 produced the longest onset durations in this sample (mean onset duration = 0.280 s). In general, the longest vowel durations were produced by the participants with sCAS. Coda durations decreased both with typical development and age. Figure 1 shows a bar graph of all mean durations, calculated from a subset of 25 words, excluding words where the adult produced unreleased stop codas.  Figure 1. Mean syllable component durations (subset of 25 words where the adult released all coda stops). The first regression analysis, inputting onset complexity, vowel complexity, and coda complexity as covariates on vowel duration, yielded the following, statistically significant (p < 0.05) associations between syllable component characteristics and vowel duration: (1) For the adult, vowel complexity was associated with increased vowel duration; (2) for TD 8;8, onset complexity and coda complexity were associated with decreased vowel duration while vowel complexity was associated with increased vowel duration; (3) for TD 4;3, coda complexity was associated with decreased vowel duration; (4) for PD 5;1, none of the covariates were associated with vowel duration; (5) for sCAS 9;5, coda complexity was associated with decreased vowel duration; (6) for sCAS 4;7, coda complexity was associated with decreased vowel duration; and (7) for sCAS 4;3, vowel complexity was associated with increased vowel duration and coda complexity was associated with decreased vowel duration. In the second regression analysis, where the Peterson and Lehiste (1960) coda hierarchy was regressed on vowel duration, the association was found to be statistically significant (p < 0.05) for the adult, TD 4;3, sCAS 9;5, and sCAS 4;3. Figure 2 shows a summary of all observed associations. Note that the first three variables (onset complexity, vowel complexity, and coda complexity) were regressed within the same model and the coda type hierarchy was regressed separately.  Figure 2. Regression analysis results describing associations between syllable component characteristics and vowel duration. See text for definitions and coding schemes. Key: + = association with increased vowel duration, - = association with decreased vowel duration, number in parentheses = p value, shading = statistical significance at á = 0.05 Discussion: The main purpose of this study was to test two hypotheses regarding timing inaccuracies during speech in children with sCAS. According to Hypothesis 1, these timing inaccuracies are associated with an underlying linguistic deficit. According to Hypothesis 2, a central timing deficit is the underlying factor. If a linguistic deficit underlies these inaccuracies, intrinsic and extrinsic vowel duration effects should be minimal in the participants with sCAS, compared to these vowel effects observed in the participants with typical development (Outcome B). A linguistic deficit (Hypothesis 1) can be ruled out in the participants with sCAS if these vowel effects are evident to a similar extent to that observed in the participants with typical development (Outcome A). If a central timing deficit is present (Hypothesis 2), Outcome A and Outcome B are both possible, and support for this hypothesis can be drawn from other studies. The results of this study rule out a linguistic deficit as the source of timing deficits in the participants with sCAS. Regarding intrinsic vowel effects, one of the three participants with sCAS (sCAS 4;3) showed a statistically significant association between vowel complexity and vowel duration, while one of the two participants with typical development (TD 4;3) did not. Regarding extrinsic vowel effects, two of the three participants with sCAS showed a statistically significant association between the coda type hierarchy and vowel durations, while one of the two participants with typical development (TD 8;8) did not. Together, these results constitute Outcome A, and they do not permit the conclusion that a linguistic deficit, whether at the level of phonologic knowledge or lexical representation, is systematically associated with the participants with sCAS in this study. Instead, the absence of a systematic difference between these participants and the participants with typical development is consistent with the second hypothesis, which states that the timing inaccuracies observed in the participants with sCAS are associated with a central timing deficit, and which was supported by earlier findings (Alcock, Passingham, Watkins and Vargha-Khadem; 2000 Peter and Stoel-Gammon, in press). An ancillary purpose of this study was to observe durational patterns in an adult and a participant with a speech disorder other than sCAS, namely phonologic delay. The results show that the adult produced the shortest subsyllabic component durations, the only exception being the onsets produced by sCAS 4;7, who reduced onset clusters. The adult’s vowel durations were significantly associated with intrinsic vowel weights and extrinsic coda effects. The participant with PD did not adjust vowel durations to a statistically significant degree with respect to the intrinsic or the extrinsic variable. In his case, this may be evidence of an underlying linguistic weakness. A further purpose of this study was to observe how two experimental variables, onset complexity and coda complexity, interact with vowel duration. The number of segments in the onset was not expected to co-vary significantly with vowel duration, and this non-interaction was found in all participants except one. The typically developing child, age 8;8, showed a significant vowel shortening effect associated with onset complexity. It is interesting to note that in four of the remaining participants, the association between onset complexity and vowel duration was also negative, although it was far from being statistically significant at α = 0.05. Coda complexity, as quantified by number of coda segments, was associated with decreased vowel durations in all participants, and to a statistically significant degree in five of the seven participants. These results support the validity of onset and coda complexity as potentially meaningful extrinsic factors in vowel duration. Interestingly, sCAS 4;7, who omitted all obstruent codas, showed a statistically significant association between coda complexity and vowel duration, which supports the idea of an intact phonological or lexical representation of subsyllabic component quantity. One aspect not addressed in this study is the effect of speech rate on subsyllabic component durations. In general, the participants with sCAS and PD produced the longest vowels, and the participant with PD also produced the longest onsets. It is possible that a slower speech rate in these participants caused or interacted with these increased durations, but speech rate was not systematically measured. The finding that onset complexity and coda complexity interacted with vowel duration to some extent should be further investigated. Collinearities between coda complexity and coda type should be quantified, as consonant clusters are constrained with respect to the constellation of permissible consonant types in each cluster position. In order to arrive at more comprehensive conclusions regarding intrinsic and extrinsic vowel effects in the populations of interest, further studies should expand the scope of the present one. In particular, they should include greater numbers of participants and disorder types; multiple tokens per stimulus item should be elicited and measured; and stimulus types should be systematically constructed as minimal pairs. Acknowledgments: This project was supported by a traineeship grant from the National Institute of Health, NIH 05 T32 DC0003-10. The authors wish to express gratitude to the study participants and their families. We deeply appreciate their gift of time and effort on behalf of communication disorders research. We also thank Chris Moore and Richard Wright for their valued advice and help in the completion of this project. Portions of this study were presented at the Child Phonology Conference in Vancouver, B.C., July 1 - 4, 2003, and at the American Speech, Language, and Hearing Association Convention in Chicago, November 13-15, 2003. References: Alcock, K.J., Passingham, R.E., Watkins, K. and Vargha-Khadem, F. (2000). Pitch and timing abilities in inherited speech and language impairment. Brain and Language, 75, (1) Oct 15, 34-46. Boersma, P. and Weenink, D. (2003). Praat Version 4.0.45. Institute of Phonetic Sciences, Amsterdam, The Netherlands. Borden, G.J., Harris, K.S. and Raphael, L.J. (2003). Speech Science Primer: Physiologiy, Acoustics, and Perception of Speech. 4th Ed. Baltimore: Lippincott Williams & Wilkins. Buder, E.H. and Stoel-Gammon, C. (2002). American and Swedish children’s acquisition of vowel duration: Effects of vowel identity and final stop voicing. Journal of the Acoustical Society of America, 111(4), 1854-1864. Bybee, J. (2001). Phonology and Language Use. Cambridge: Cambridge University Press. Carrow-Woolfolk, E. (1999). Test for Auditory Comprehension of Language, Third Edition. Austin: pro-ed. Davis, B. L., Jakielski, K. J. and Marquardt, T. P. (1998). Developmental apraxia of speech: Determiners of differential diagnosis. Clinical Linguistics and Phonetics 12 (1), 25-45. Dunn, L. M. and Dunn, L. M. (1997). Peabody Picture Vocabulary Test-Revised. Circle Pines, MN: American Guidance Service. Goldman, R. and Fristoe, M. (2000). Goldman-Fristoe Test of Articulation 2. Circle Pines: American Guidance Service. Green, J.R., Shriberg, L.D. and Campbell, T.F. (2002). Speech timing variables in children with typical speech acquisition, speech delay, and suspected apraxia of speech. Poster presentation at the Conference on Motor Speech, March 2002, Williamsburg, VA. Hayden, D., and Square, P. (1999). Verbal Motor Production Assessment for Children. San Antonio: The Psychological Corporation. Keating, P.A. (1985). Universal phonetics and the organization of grammars. In: V.A. Fromkin (ed). Phonetic Linguistics: Essays in Honor of Peter Ladefoged. Orlando: Academic Press. Koike, K.J. and Asp, C.W. (1981). Tennessee test of rhythm and intonation patterns. Journal of Speech and Hearing Disorders, 46, 81-86. Microsoft Corporation (2002). Microsoft ® Excel 2002 (10.2614.2625). Peter, B. and Stoel-Gammon, C. (in press). Timing errors in two children with suspected childhood apraxia of speech (sCAS) during speech and music-related tasks. Clinical Linguistics and Phonetics. Peter, B. and Stoel-Gammon, C. (2003). Syllabic component durations in three children with suspected childhood apraxia of speech (sCAS) and one child with phonologic delay. Presentation at the American Speech-Language-Hearing Association Convention, Chicago, November 13-15, 2003. Peterson, G. and Lehiste, I. (1960). Duration of syllable nuclei in English. Journal of the Acoustical Society of America, 32, 693-703. Semel, E., Wiig, E.H. and Secord, W.A. (1995). Clinical Evaluation of Language Fundamentals 3 (CELF-3). San Antonio: The Psychological Corporation. Shriberg, L. D., Aram, D. M. and Kwiatkowski, J. K. (1997 a). Developmental apraxia of speech: I. Descriptive perspectives. Journal of Speech, Language, and Hearing Research, 40, 273-285. Shriberg, L. D., Aram, D. M. and Kwiatkowski, J. K. (1997 b). Developmental apraxia of speech: II. Toward a diagnostic marker. Journal of Speech, Language, and Hearing Research, 40, 286-312. Shriberg, L. D., Aram, D. M. and Kwiatkowski, J. K. (1997 c). Developmental Apraxia of Speech: III. A subtype marked by inappropriate stress. Journal of Speech, Language, and Hearing Research, 40, 313-337. Shriberg, L.D., Green, J.R., Campbell, T.F., McSweeny, J.L. and Scheer, A.R. (2003). A diagnostic marker for childhood apraxia of speech: The coefficient of variation ratio. Clinical Linguistics & Phonetics, 17(7), 575-595. Shriberg, L.D., Kwiatkowski, J. and Rasmussen, C. (1990). The Prosody-Voice Screening Profile. Tucson: Communication Skill Builders. StataCorp. (2001). Stata Statistical Software: Release 7.0. College Station, TX: Stata Corporation. Syntrillium Software Corporation (1998). CoolEdit Pro. Scottsdale, AZ. Wiig, E.H., Secord, W. and Semel, E. (1992). Clinical Evaluation of Language Fundamentals – Preschool. San Antonio: The Psychological Corporation. Appendix A: Matrix of monosyllabic words with coded covariates. Complexity variables are coded by number of segments/vowel weights. Coda type hierarchy is coded as follows: . = no coda; 1 = voiceless stop; 2 = voiceless fricative; 3 = voiced stop; 4 = nasal, liquid; 5 = voiced fricative.  For more information on earning online CEs, CLICK HERE Editor's Note: It is with great pride that we re-release this peer reviewed and CE approved version of this article. This paper was originally released on this website as a non-peer reviewed paper. The author has worked with our staff and members of the www.SpeechPathology.com Review Board (click here to visit the Review Board) to successfully complete the peer review process. We are grateful to the author and the peer reviewers for their time and commitment. | |