Effects of a Conversation-Based Intervention on the Linguistic Skills of Children With Motor Speech Disorders Who Use Augmentative and Alternative Communication Purpose This study was conducted to evaluate the effects of a conversation-based intervention on the expressive vocabulary and grammatical skills of children with severe motor speech disorders and expressive language delay who use augmentative and alternative communication. Method Eight children aged from 8 to 13 years participated in ... Research Article
Free
Research Article  |   July 12, 2017
Effects of a Conversation-Based Intervention on the Linguistic Skills of Children With Motor Speech Disorders Who Use Augmentative and Alternative Communication
 
Author Affiliations & Notes
  • Gloria Soto
    Department of Special Education and Communication Disorders, San Francisco State University, CA
  • Michael T. Clarke
    Research Department of Language and Cognition, University College London, UK
  • Disclosure: The authors have declared that no competing interests existed at the time of publication.
    Disclosure: The authors have declared that no competing interests existed at the time of publication. ×
  • Correspondence to Gloria Soto: gsoto@sfsu.edu
  • Editor: Rhea Paul
    Editor: Rhea Paul×
  • Associate Editor: Ann Tyler
    Associate Editor: Ann Tyler×
Article Information
Speech, Voice & Prosodic Disorders / Augmentative & Alternative Communication / Normal Language Processing / Language Disorders / Language / Research Articles
Research Article   |   July 12, 2017
Effects of a Conversation-Based Intervention on the Linguistic Skills of Children With Motor Speech Disorders Who Use Augmentative and Alternative Communication
Journal of Speech, Language, and Hearing Research, July 2017, Vol. 60, 1980-1998. doi:10.1044/2016_JSLHR-L-15-0246
History: Received July 15, 2015 , Revised December 1, 2015 , Accepted November 27, 2016
 
Journal of Speech, Language, and Hearing Research, July 2017, Vol. 60, 1980-1998. doi:10.1044/2016_JSLHR-L-15-0246
History: Received July 15, 2015; Revised December 1, 2015; Accepted November 27, 2016

Purpose This study was conducted to evaluate the effects of a conversation-based intervention on the expressive vocabulary and grammatical skills of children with severe motor speech disorders and expressive language delay who use augmentative and alternative communication.

Method Eight children aged from 8 to 13 years participated in the study. After a baseline period, a conversation-based intervention was provided for each participant, in which they were supported to learn and use linguistic structures essential for the formation of clauses and the grammaticalization of their utterances, such as pronouns, verbs, and bound morphemes, in the context of personally meaningful and scaffolded conversations with trained clinicians. The conversations were videotaped, transcribed, and analyzed using the Systematic Analysis of Language Transcripts (SALT; Miller & Chapman, 1991).

Results Results indicate that participants showed improvements in their use of spontaneous clauses, and a greater use of pronouns, verbs, and bound morphemes. These improvements were sustained and generalized to conversations with familiar partners.

Conclusion The results demonstrate the positive effects of the conversation-based intervention for improving the expressive vocabulary and grammatical skills of children with severe motor speech disorders and expressive language delay who use augmentative and alternative communication. Clinical and theoretical implications of conversation-based interventions are discussed and future research needs are identified.

Supplemental Materials https://doi.org/10.23641/asha.5150113

For children who have little or no intelligible speech as a consequence of severe motor speech disorders (MSDs), the use of augmentative and alternative communication (AAC) systems can prove invaluable in supporting and developing language and communication abilities (Clarke & Price, 2012; Sutton, Soto, & Blockberger, 2002). AAC refers to any form of communication that supplements or replaces natural speech. This may include unaided aspects of communication, such as the use of kinesic modalities, as well as the use of aided communication resources, such as communication books or charts, and communication technologies such as speech-generating devices (SGDs). SGDs are electronic communication aids with synthesized speech output capabilities that can permit the storage and retrieval of thousands of words and phrases.
Many children with severe MSDs are known to experience significant delays in their language development, particularly in relation to their expressive vocabulary and production of grammatically complete utterances, even when provided with AAC (Binger & Light, 2008). There are a number of intrinsic and extrinsic factors that, in combination, are proposed to be associated with their expressive language delay including children's limited exposure to language learning opportunities and the long-term restricted patterns of interpersonal interaction (Sutton et al., 2002). In brief, marked asymmetries are consistently observed in the number and type of contributions made by children and their naturally speaking partners during naturally occurring conversations. The use of question–answer exchanges is a primary way in which these children's contributions to conversation are co-constructed (Clarke & Wilkinson, 2007; Solomon-Rice & Soto, 2011), that is, where the contributions of children via aided and unaided forms, which are overwhelmingly characterized by the use of single word responses to others' initiations, are developed and expanded gradually over a sequence of turns. For instance, in the following example the child uses her SGD to provide single word responses to adult questions and comments.

Adult: I see you have a tattoo on your arm, where did you get that?

Child: Party.

Adult: You went to a party.

Child: Yes.

Adult: Oh, whose party was it?

Child: Fatima.

Adult: You went to Fatima's party. Was it Fatima's birthday party?

Child: Yes.

Adult: Did you all go somewhere special?

Child: Home.

Adult: The party was at her home?

Child: Yes.

Adult: So it was Fatima's birthday and she had a party at her home, and you got a tattoo there.

Child: Yes.

Sequences such as these are also observed in conversations between adults and young, typically developing children (Scollon, 1976). In the context of those interactions, co-construction of child contributions involving scaffolding of child language (e.g., through immediate exposure to enhanced language forms provided by adults as illustrated in the example above) is considered a major language learning facilitator for children (Scollon, 1976). As typically developing children mature, they incorporate the grammatical constructions that they have heard and learned into their own expressive language. As the length of their utterances increases, the range of grammatical structures that children use in their utterances also increases in complexity. However, for children with expressive language delay who use AAC, these early, naturally occurring patterns of everyday interaction commonly persist into adulthood, and would appear to not support language development in the same way as they do for typically developing children. In fact, these children tend to use mostly nouns in single word utterances or short, grammatically incomplete messages that lack morphological and syntactic elements, such as verbs, prepositions, pronouns, and articles, even when these are available on their communication devices (Binger & Light, 2008; Soto & Hartmann, 2006; Sutton et al., 2002).
There is now a large body of research that reports positive effects of employing verbal scaffolding procedures within conversation-based interventions on language skills development in children with communication disorders who are not users of AAC systems, including children with autism (Scherer & Olswang, 1989), specific language impairment (Camarata & Nelson, 2006; Nelson, Camarata, Welsh, Butkovsky, & Camarata, 1996; Plante et al., 2014), language learning disabilities (Stiegler & Hoffman, 2001), and language delay (see also Ruston & Schwanenflugel, 2010). In these interventions, verbal scaffolding procedures are delivered by an adult immediately after a child produces an utterance that is incomplete, immature, or ungrammatical, and that provides an opportunity for presentation of an enhanced version of the target form (Eisenberg, 2013, 2014). Scaffolding techniques afford the child opportunities to hear the target form being used in a meaningful way, and to contrast his or her own utterance with a more complex or grammatically correct one.
Although evidence exists for the facilitative effect of adult verbal scaffolding during conversations for children with a wide range of language disorders, this approach has not been systematically investigated for children with severe MSDs and expressive language delay who use AAC. The purpose of the current study was to investigate the impact of adult scaffolding within a conversation-based intervention on the expressive vocabulary and grammatical skills of children in this group. The study examined changes in the participants' use of linguistic structures that are essential to the formation of early clauses, such as verbs, pronouns, and bound morphemes, and whether gains made in intervention were generalized and sustained.
Method
Experimental Design
A multiple probe design across participants (Gast & Ledford, 2010) was used to examine the effect of a conversation-based intervention on the expressive vocabulary and grammatical skills of eight children with severe MSDs and expressive language delay who use AAC. The study design is a variation of a multiple baseline design in which baseline data are probed at different points in time rather than monitored continuously. After a period of baseline measurement, intervention was applied sequentially to four participants (Set A) who were randomly assigned to intervention order. Intervention for the second, third, and fourth participants started after the preceding individual had demonstrated sustained improvement over three consecutive intervention sessions (see description below; Gast & Ledford, 2010). Once each participant receiving intervention demonstrated an improvement in production of the experimental control variable (i.e., production of spontaneous clauses) of at least 25% over baseline levels for three consecutive intervention sessions, intervention began for the next participating child. To examine the generalizability of the findings, intervention procedures were replicated across a second set of four older participants (Set B).
Subjects
Participating Children
Eight children (three girls and five boys) were selected to participate in the study and met the criteria that they: (a) were between the ages of 8 and 14 years; (b) used a high-tech SGD with software allowing for grammaticalization of utterances; (c) demonstrated functional communicative competence at Level III on the Augmentative and Alternative Communication Profile (AACP; Kovach, 2009) 1 ; (d) used a form of direct selection techniques to formulate their messages (e.g., touching the SGD screen); (e) had English as their dominant language; (f) communicated mostly through single word utterances with little evidence of grammaticalization in unstructured interaction; (g) presented with hearing and vision within normal limits, with or without correction; (h) presented with a severe MSD (Duffy, 2013), which affected their ability to speak intelligibly; (i) had minimal functional speech with an intelligibility score of less than 50% on the Index of Augmented Speech Comprehensibility in Children to familiar partners in unknown contexts (Dowden, 1997); (j) had no diagnosis of intellectual impairment according to their educational and clinical records; and (k) attained age-equivalent scores on measures of receptive language skills of at least 6 years of age and above. Child characteristics are presented in Table 1.
Table 1. Participants' demographic characteristics.
Participants' demographic characteristics.×
Participants Age Speech disorder Mobility Speech-generating device a Speech-generating device access Languages spoken at home Receptive vocabulary age equivalent (percentile) Morphological judgment age equivalent (percentile) Expressive language (from educational records) Speech intelligibility rating (%)
Carmen 9;5 Dysarthria secondary to Pfeiffer syndrome Wheelchair user DynaVox DV4 with Gateway modified 45, 60 Finger pointing English, Spanish 8;6 b (37) 6;6 b (9) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Geli 8;10 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Vmax with EyeMax system and Gateway 45 Eye gaze English, French, Italian 6;6 b (25) 6;3 b (16) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Joe 8;8 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox with Gateway 45 Head switches, step scanning English, Spanish 6;9 b (37) 4;10 b (2) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Dante 8;8 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Head mouse English 7;0 b (37) 4;3 b (2) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Jesse 12;1 Severe verbal apraxia, etiology unspecified Ambulant Vantage Lite with Unity 84 Finger pointing English, Spanish 9;5 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 40
Mateo 13;7 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Joystick English, Spanish 8;11 c (5) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 20 (minimally verbal)
Julian 13;9 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Maestro 5 with Gateway modified 45 Finger pointing English, Spanish 9;9 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Kareem 13;3 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 60 Finger pointing English, Arabic 9;6 c (7) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Note. Ages are shown in years;months. MLU = mean length of utterance.
Note. Ages are shown in years;months. MLU = mean length of utterance.×
a Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.
Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.×
b Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).
Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).×
c Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).
Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).×
d Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).
Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).×
Table 1. Participants' demographic characteristics.
Participants' demographic characteristics.×
Participants Age Speech disorder Mobility Speech-generating device a Speech-generating device access Languages spoken at home Receptive vocabulary age equivalent (percentile) Morphological judgment age equivalent (percentile) Expressive language (from educational records) Speech intelligibility rating (%)
Carmen 9;5 Dysarthria secondary to Pfeiffer syndrome Wheelchair user DynaVox DV4 with Gateway modified 45, 60 Finger pointing English, Spanish 8;6 b (37) 6;6 b (9) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Geli 8;10 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Vmax with EyeMax system and Gateway 45 Eye gaze English, French, Italian 6;6 b (25) 6;3 b (16) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Joe 8;8 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox with Gateway 45 Head switches, step scanning English, Spanish 6;9 b (37) 4;10 b (2) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Dante 8;8 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Head mouse English 7;0 b (37) 4;3 b (2) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Jesse 12;1 Severe verbal apraxia, etiology unspecified Ambulant Vantage Lite with Unity 84 Finger pointing English, Spanish 9;5 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 40
Mateo 13;7 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Joystick English, Spanish 8;11 c (5) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 20 (minimally verbal)
Julian 13;9 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Maestro 5 with Gateway modified 45 Finger pointing English, Spanish 9;9 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Kareem 13;3 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 60 Finger pointing English, Arabic 9;6 c (7) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Note. Ages are shown in years;months. MLU = mean length of utterance.
Note. Ages are shown in years;months. MLU = mean length of utterance.×
a Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.
Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.×
b Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).
Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).×
c Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).
Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).×
d Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).
Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).×
×
Participants were administered a battery of tests to document their receptive language skills (see Table 1). All testing was conducted in English, as this was the dominant language for all children. Participants' age-equivalent scores for single word receptive vocabulary were lower than their chronological age, and their performance on the comprehension of grammatical morphemes was extremely poor across all participants. Given their age-equivalent scores for single word receptive vocabulary the children should, in theory, have been using grammatically complete sentences quite competently. However, school records reported that the participants were nonverbal or minimally verbal and communicated mostly through unaided means of communication (e.g., facial expressions, vocalizations, eye gaze, and pointing) and device-generated single word utterances consisting mostly of nouns. These observations were confirmed during baseline and preintervention generalization sessions. Formal tests of cognition were not administered. All children attended programs designed for children with AAC needs in urban public schools, and used their own SGD during the study.
Procedures
Setting
Ten graduate student clinicians participating in clinical training at a local university conducted baseline and intervention sessions. The student clinicians were enrolled in a grant-supported masters-level program in Speech-Language Pathology with an emphasis in AAC. All student clinicians had completed two seminar courses in AAC; two 180-hour practica in schools and off-campus clinics serving students with AAC needs; a 1-week hands-on summer camp for children who use AAC; and two on-campus AAC clinics. As part of their graduate training, the student clinicians had received extensive clinical training on the use of responsiveness and language-elicitation techniques such as the use of open-ended questions, conversational recasting (i.e., grammatically correct reformulation of a child's utterance), provision of vocabulary models (i.e., presentation of a target prior to the child's utterance), and use of oral cloze procedures.
The language testing and all the experimental sessions (baseline, intervention, and generalization) were completed in a quiet area at each child's school (e.g., therapy room or unoccupied library), except in the case of Julian who completed part of his sessions at home due to scheduling conflicts.
Materials
Parents and teachers of study participants provided photographs of the children at recent events, such as birthday parties, field trips, and family outings. These photographs were used during intervention to help the child choose a preferred topic of conversation. However, at different points during intervention, some participants declined to talk about the events in the photographs, and, at their own request, used other visual props such as picture books, video game catalogues, iPad apps, and video clips. Intervention procedures remained identical across different classes of visual prop (see Supplemental Material S1).
Baseline Assessment
During baseline sessions the participating children met with a student clinician and engaged in a 30–40 min conversation about a mutually agreed topic of personal relevance to the child, such as family, vacations, and favorite activities. Throughout these conversations, the clinicians used appropriate conversational responses such as open-ended questions, expectant pause, verbal redirection, and contingent queries to stimulate the conversation (e.g., King, Hengst, & DeThorne, 2013). However, during baseline condition, clinicians were not permitted to use any therapeutic technique such as gestural or verbal prompts, aided modeling (modeling of the AAC system use), explicit instruction, or any form of corrective feedback; that is, during baseline conditions, clinicians did not acknowledge correct or incorrect production, or use any correction procedures to shape the participants' productions. Baseline sessions were conducted before clinicians received intervention training and served to establish children's profiles of expressive language skills in conversational interaction. Each participant completed five baseline sessions to determine stability/variability of measured skills. Following Gast and Ledford (2010), thresholds for acceptable baseline variability were determined by dividing the mean frequency of the observed language skill (e.g., mean number of verbs used across five data points) by 2, and adding and subtracting that figure to/from the mean (mean/2 ± mean). Baselines were considered stable when the last three baseline points fell within that range (Gast & Ledford, 2010).
Generalization Probes
As recommended by Schlosser and Lee (2000), generalization probes were conducted throughout all phases of the study for each participant: (a) at least once prior to the start of intervention, (b) every six intervention sessions, and (c) when possible, at 2-, 4-, and 8-week intervals postintervention. These probes consisted of a conversation between each child and one member of the child's educational team. Mateo and Dante conversed with their respective special education teachers; Carmen and Geli with their AT/AAC specialists; Jesse, Joe, and Kareem with their instructional assistants; and Julian with his older adult sister (all child names are pseudonyms). Each child had the same conversation partner across all generalization probes. The adults were masked to the procedures of the intervention, and received no instructions on how to talk to the child, or what to talk about. The conversations were about topics both the child and the adult agreed on and typically lasted between 30–40 min. Therefore, these generalization probes occurred under conditions that were different from those of baseline and intervention sessions.
Training of Clinicians
Once the baseline sessions were completed, the clinicians received specific information about the intervention procedures. Because the training procedures were relatively straightforward and the clinicians had received extensive training in AAC discourse-based intervention during their clinical AAC program, a 40–50 min session was typically sufficient to complete the training procedures with the clinicians. Training included both verbal instructions by the first author and video models of child productions and appropriate clinical responses. The clinicians were also provided with a procedural checklist, which included intervention steps and strategies. Clinicians reviewed the checklist before each session. Clinicians worked with the participants either in baseline or treatment stages; that is, no clinician was simultaneously working in baseline with one participant while working in intervention with another.
Intervention
The targets of our intervention were key linguistic structures essential to early clause formation and grammaticalization, which includes verbs, pronouns, bound grammatical morphemes (e.g., third person -s, plural -s, past -ed, and present progressive -ing), and other frequently used words such as prepositions, articles, adjectives, and adverbs (see Supplemental Material S1). For children with severe MSDs and expressive language delay who use AAC, becoming fluent users of structural language components (i.e., pronouns, articles, verbs) and bound grammatical morphemes is an intervention priority because these not only form the basis of the English language but also have high combinatorial power and are essential to grammaticalization (Smith, 2015). On occasion, the clinician also modeled words that were child-specific and relevant to the conversation (e.g., prince, handsome). This approach is supported by reported association between individualized adult input in response to the child's initiations, and linguistic gains in children with communication disorders (see Camarata & Nelson, 2006; Hadley, Rispoli, Fitzgerald, & Bahnsen, 2011; Nelson et al., 1996; Warren, Fey, & Yoder, 2007).
During intervention, a student clinician met individually with each child twice a week, with each session lasting between 40–50 min (e.g., Ruston & Schwanenflugel, 2010). Each session consisted of a conversation between the clinician and the child. The clinician first presented the child with three photographs depicting the child at three different events, such as a birthday party, a field trip, or a vacation. The clinician then asked the child to choose a photograph he or she wanted to converse about and describe the event depicted. Upon receiving a response (e.g., “party”), the clinician elicited further information (e.g., using who, where, what questions).
The clinician then recast the child's responses into a grammatically correct sentence and followed the recast with explicit instruction and prompts (verbal and gestural) for the child to reformulate his or her original utterance. When the child produced the target response, the clinician used positive remarks to comment on the child's appropriate use of complete sentences, and continued the conversation with a contingent comment or question to encourage further communication (see sample interaction in Supplemental Material S1; Camarata & Nelson, 2006; Eisenberg, 2013; Ruston & Schwanenflugel, 2010). At each session, the participants were presented with new photographs unless the participants explicitly requested to continue a topic they had chosen in an earlier session.
During each session, the clinician delivered a minimum of 10 intervention episodes (question + recast + prompt), and targeted at least five words and two bound morphemes not observed during baseline. As many of the vocabulary targets were part of a limited set (i.e., personal pronouns, copula, prepositions, frequently used verbs), some of the same words (e.g., my, was, go, went, like, get) were practiced across multiple sessions providing for natural redundancy.
Intervention was provided at a rate of twice a week for 12 weeks for up to 24 sessions. The length, frequency, and total number of sessions was chosen to reflect the average number of sessions children with significant communication disorders are likely to receive when attending intensive discourse-based language intervention programs in the United States (cf. McGregor, 2000; Ruston & Schwanenflugel, 2010).
Data Analysis
Fidelity
Clinicians read a procedural checklist before each baseline and intervention session to remind them of study procedures, and they rated the extent to which they felt they had implemented the procedures after each session. Throughout baseline and intervention, the lead author also observed every fourth session to determine clinicians' compliance with the implementation of procedures, including comparing the clinicians' behavior against the procedural checklists. If clinicians fell below 85% compliance for any session (which happened infrequently and only at the beginning of the intervention phase), they were provided with written feedback about the step(s) that were omitted. If written feedback was not sufficient for the clinician to adhere to intervention procedures, the lead author met with the clinician and provided verbal feedback while jointly reviewing the videotape of the session when necessary. In most cases, written feedback was sufficient to return the clinician to 100% compliance with intervention procedures.
In addition, two independent observers viewed 20% of randomly selected videotaped baseline and intervention sessions per child and rated clinician performance against the procedural checklists. Clinician compliance with procedures ranged from 88%–100%. The delivery of intervention episodes occurred at an average of 15 per session (range = 8–18). Interrater reliability was estimated by calculating the Cohen's kappa, which yielded a score of .94.
Transcription and Coding
All baseline, intervention sessions, and generalization probes were videotaped and transcribed using the format and transcription conventions required for analysis via the Systematic Analysis of Language Transcripts program (SALT; Miller & Chapman, 1991). Research assistants trained in transcription of multimodal AAC and masked to the phases, procedures, and purposes of the study transcribed each session. Intelligible verbalizations, the gloss of conventional manual signs, and device-generated utterances were included in the transcription and analysis. Participants' device mishits and unintentional repetitions were not included. Adults' contributions to the conversation were also transcribed but not analyzed for the purposes of this study.
Reliability
Several steps were taken to ensure that the transcripts and results were accurate. Two separate independent observers transcribed and coded 25% of randomly selected video data across all phases of the study. They viewed the sessions in randomized order and were masked to the procedures of the different study phases. Transcription discrepancies were resolved through both independent transcribers identifying transcript differences, viewing discrepant utterances, and reaching consensus on form (Kovacs & Hill, 2015). Interjudge consensus was achieved for all discrepancies. The SALT program automatically coded and calculated the number of verbs, pronouns, and bound morphemes from the final agreed-upon transcript. Interrater reliability for the coding of spontaneous clauses was established by calculating the Cohen's kappa coefficient. Assuming .5 as the probability of chance agreement, a kappa coefficient of .96 was calculated, indicating excellent agreement.
Dependent Measures
The children's language samples were analyzed for the rate of use of verbs, pronouns, bound morphemes, and spontaneous clauses within a 60-min observation period. These represent a variety of morpho-syntactic structures that are essential to early clause formation and typically used to assess grammatical development in children (see Manhardt & Rescorla, 2002; Thordardottir, Chapman, & Wagner, 2002). As a child's language develops, the number of clauses produced during discourse increases (Scott & Stokes, 1995). Rate was used to convert the target behavior counts to a constant scale as observation times varied slightly across sessions (Gast, 2010). A spontaneous clause was defined as a basic sentence containing a subject, a verb, and a predicate that was capable of functioning alone, even if missing the article or another part of speech (e.g., I have doctor appointment; I want pet rabbit), and was produced as an initiation or in response to a preceding question or contingent comment, and not following an imitative prompt.
Visual and Statistical Analysis
The analysis of the baseline probes, intervention sessions, and generalization probes was conducted visually and statistically. The visual analysis was based on inspection of the plotted data, which has traditionally been the primary method to determine whether there is a functional relation between the independent and dependent variables, and the magnitude of any such relation (Gast, 2010; Kennedy, 2005; Kratochwill et al., 2010). As recommended by leading single subject researchers and adopted by the Department of Education's What Works Clearinghouse (Kratochwill et al., 2010), visual analysis involved the examination of within- and between-phase data patterns across six variables: (a) mean scores for data within each phase (commonly referred to as level); (b) trend of the data across baseline and intervention phases, including analysis of stability of change; (c) variability of data within each phase; (d) overlap in the data points between baseline and intervention phases; (e) immediacy of effect; and (f) consistency of data patterns across phases and participants.
Effect size estimates were calculated using nonoverlap procedures. Although a number of nonoverlap procedures are available, a recent review by Rakap, Snyder, and Pasia (2014)  recommended the combined use of Tau-U (Parker, Vannest, Davis, & Sauber, 2011), and calculation of improvement rate difference (IRD; Parker, Vannest, & Brown, 2009). Both measures are suitable for AB designs, are nonparametric so do not require data assumptions associated with parametric tests, and have proposed benchmarks for evaluating size of intervention effect. Both procedures also allow for the calculation of confidence intervals. The Tau-U is drawn from Kendall's rank correlation and the Mann–Whitney U test between groups and, essentially, considers pairwise comparisons of data points between and within phases to quantify the extent of nonoverlap between the baseline and intervention and trend within the intervention phase. It can also control for positive baseline trend. An IRD represents the difference between improvement rates (IRs) in baseline and intervention. The IR is calculated by dividing the number of “improved data points” (Parker et al., 2009) in a phase by the total number of data points in that phase. Improved data points in baseline are defined as being equal to or greater than any data point in intervention. During the intervention phase, data points are considered improved if they exceed all data points in baseline. The IRD is represented by the difference between the two IRs. The Tau-U and IRD were obtained for each child for each dependent measure. An online calculator (www.singlecaseresearch.org) was used to calculate the Tau-U and the IRD was calculated by hand. Given the applied clinical focus of the study, and following Parker et al. (2009), confidence intervals were set at 85% for both measures. Confidence intervals for the Tau-U were calculated online, and for the IRD they were calculated using the two proportions test (with bootstrapping) with NCSS software (Parker et al., 2009).
Results
Visual and statistical analyses of the data indicate that all participants demonstrated a very limited use of verbs, pronouns, bound morphemes, and almost no spontaneous clauses during baseline sessions. The use of all four linguistic measures increased for all participants during intervention sessions and was generalized and maintained above preintervention levels once the intervention had ended. The rate of production of verbs, pronouns, bound morphemes, and spontaneous clauses used by the participants in Set A (Carmen, Geli, Joe, and Dante) and Set B (Jesse, Mateo, Julian, and Kareem) during baseline, intervention, and generalization probes are shown in Figures 1, 2, 3, 4, 5, 6, 7, and 8.
Figure 1.

Set A: Rate of verb use per 60 min.

 Set A: Rate of verb use per 60 min.
Figure 1.

Set A: Rate of verb use per 60 min.

×
Figure 2.

Set A: Rate of pronoun use per 60 min.

 Set A: Rate of pronoun use per 60 min.
Figure 2.

Set A: Rate of pronoun use per 60 min.

×
Figure 3.

Set A: Rate of bound morpheme use per 60 min.

 Set A: Rate of bound morpheme use per 60 min.
Figure 3.

Set A: Rate of bound morpheme use per 60 min.

×
Figure 4.

Set A: Rate of spontaneous clause use per 60 min.

 Set A: Rate of spontaneous clause use per 60 min.
Figure 4.

Set A: Rate of spontaneous clause use per 60 min.

×
Figure 5.

Set B: Rate of verb use per 60 min.

 Set B: Rate of verb use per 60 min.
Figure 5.

Set B: Rate of verb use per 60 min.

×
Figure 6.

Set B: Rate of pronoun use per 60 min.

 Set B: Rate of pronoun use per 60 min.
Figure 6.

Set B: Rate of pronoun use per 60 min.

×
Figure 7.

Set B: Rate of bound morpheme use per 60 min.

 Set B: Rate of bound morpheme use per 60 min.
Figure 7.

Set B: Rate of bound morpheme use per 60 min.

×
Figure 8.

Set B: Rate of independent clause use per 60 min.

 Set B: Rate of independent clause use per 60 min.
Figure 8.

Set B: Rate of independent clause use per 60 min.

×
Visual inspection of the figures suggests that experimental control was maintained for all dependent variables across both sets of participants, as increases of these variables were not observed until the intervention procedures were implemented. Mean values for baseline and intervention sessions are presented in Table 2. Mean values from generalization probes prior, during, and postintervention are presented in Table 3. A summary of the results follows.
Table 2. Baseline and intervention results.
Baseline and intervention results.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Base Inter Base Inter Base Inter Base Inter Base Inter
Carmen 5 23 11.2 73.3 2.0 48.6 1.6 59.9 0 4.5
Geli 5 23 9.6 65.2 1.2 44.6 4.2 55.6 0 8.5
Joe 5 12 16.8 49.3 3.6 35.2 5.1 9.9 0 3.5
Dante 5 6 1.6 33.7 0 17.7 0 13.5 0 3.4
Jesse 5 23 10.6 53.5 2.5 57.9 0.5 24.7 0 8.2
Mateo 5 24 6.9 47.6 4.2 48.0 3.4 30.0 0 5.4
Julian 5 23 1.8 31.4 1.2 21.9 4.8 18.6 0.6 7.2
Kareem 5 12 7.1 17.3 0.6 18.9 2.4 5.0 0 3.6
Note. Base = baseline, Inter = intervention.
Note. Base = baseline, Inter = intervention.×
Table 2. Baseline and intervention results.
Baseline and intervention results.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Base Inter Base Inter Base Inter Base Inter Base Inter
Carmen 5 23 11.2 73.3 2.0 48.6 1.6 59.9 0 4.5
Geli 5 23 9.6 65.2 1.2 44.6 4.2 55.6 0 8.5
Joe 5 12 16.8 49.3 3.6 35.2 5.1 9.9 0 3.5
Dante 5 6 1.6 33.7 0 17.7 0 13.5 0 3.4
Jesse 5 23 10.6 53.5 2.5 57.9 0.5 24.7 0 8.2
Mateo 5 24 6.9 47.6 4.2 48.0 3.4 30.0 0 5.4
Julian 5 23 1.8 31.4 1.2 21.9 4.8 18.6 0.6 7.2
Kareem 5 12 7.1 17.3 0.6 18.9 2.4 5.0 0 3.6
Note. Base = baseline, Inter = intervention.
Note. Base = baseline, Inter = intervention.×
×
Table 3. Results for preintervention, during intervention, and postintervention generalization probes.
Results for preintervention, during intervention, and postintervention generalization probes.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Pre During Post Pre During Post Pre During Post Pre During Post Pre During Post
Set A
 Carmen 1 4 3 24.0 95.7 87.7 24.0 46.1 42.0 0 29.0 30.9 4 14.0 16.4
 Geli 1 4 3 15.0 52.1 35.0 6.0 37.7 25.0 9.0 45.9 35.0 0 4.9 6.0
 Joe 1 2 3 12.0 45.3 66.0 6.0 30.5 24.0 6.0 8.5 10.0 0 3.2 5.1
 Dante 1 1 2.4 21.6 0 21.6 0 4.8 0 7.2
Set B
 Jesse 1 4 1 8.0 43.9 46.3 6.0 26.4 16.0 2.0 8.5 5.0 0 10.0 8.0
 Mateo 1 4 3 18.6 63.1 57.5 21.3 48.6 48.3 9.3 30.4 20.6 0 9.7 10.4
 Julian 1 4 2 3.0 26.6 31.5 6.0 19.1 24.7 0 17.3 19.7 0 4.6 4.2
 Kareem 1 1 2 3.0 10.2 15.4 0 5.1 7.7 0 6.8 6.4 0 5.1 5.0
Table 3. Results for preintervention, during intervention, and postintervention generalization probes.
Results for preintervention, during intervention, and postintervention generalization probes.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Pre During Post Pre During Post Pre During Post Pre During Post Pre During Post
Set A
 Carmen 1 4 3 24.0 95.7 87.7 24.0 46.1 42.0 0 29.0 30.9 4 14.0 16.4
 Geli 1 4 3 15.0 52.1 35.0 6.0 37.7 25.0 9.0 45.9 35.0 0 4.9 6.0
 Joe 1 2 3 12.0 45.3 66.0 6.0 30.5 24.0 6.0 8.5 10.0 0 3.2 5.1
 Dante 1 1 2.4 21.6 0 21.6 0 4.8 0 7.2
Set B
 Jesse 1 4 1 8.0 43.9 46.3 6.0 26.4 16.0 2.0 8.5 5.0 0 10.0 8.0
 Mateo 1 4 3 18.6 63.1 57.5 21.3 48.6 48.3 9.3 30.4 20.6 0 9.7 10.4
 Julian 1 4 2 3.0 26.6 31.5 6.0 19.1 24.7 0 17.3 19.7 0 4.6 4.2
 Kareem 1 1 2 3.0 10.2 15.4 0 5.1 7.7 0 6.8 6.4 0 5.1 5.0
×
Participants Set A
Carmen
Carmen's use of all four linguistic measures increased during intervention as indicated by the change in means between baseline and intervention sessions (change in means: verbs = 62.1, pronouns = 46.6, bound morphemes = 58.3, and spontaneous clauses = 4.5). Carmen also generalized her use of all linguistic targets, as indicated by a change in means between preintervention and during intervention probes (verbs = 71.7, pronouns = 22.1, bound morphemes = 29, spontaneous clauses = 10). Her gains were sustained above preintervention levels, and in the cases of bound morphemes and spontaneous clauses continued to grow after the intervention had ended.
Geli
Geli's use of all linguistic targets also increased between baseline and intervention (change in means: verbs = 55.6, pronouns = 43.4, bound morphemes = 51.4, spontaneous clauses = 8.5). She also showed consistent generalization of skills across all dependent measures during the intervention phase (change in means: verbs = 37.1, pronouns = 31.7, bound morphemes = 36.9, and spontaneous clauses = 4.9). Although her scores decreased slightly after intervention had concluded, they all stayed above preintervention scores (see Table 3).
Joe
Joe's change in means between baseline and intervention was 32.5 for verbs, 31.6 for pronouns, 4.8 for bound morphemes, and 3.5 for spontaneous clauses. Although his gains took a little longer to generalize (see Figures 14), he demonstrated generalization of all linguistic targets as indicated by a change in means between preintervention and during intervention probes (verbs = 33.3, pronouns = 24.5, bound morphemes = 2.5, spontaneous clauses = 3.2). His use of verbs, bound morphemes, and spontaneous clauses continued to increase postintervention as shown in Table 3. The rate of use of pronouns decreased slightly but remained above preintervention levels.
Dante
Dante participated in only six intervention sessions due to an unexpected relocation. Nevertheless, he demonstrated increases in the use of all linguistic measures during intervention (change in means: verbs = 32.1, pronouns = 17.7, bound morphemes = 13.5, spontaneous clauses = 3.4). He also participated in two generalization probes, one prior to and another during intervention. He showed generalization of all dependent measures as indicated by changes in means of 19.2 for verbs, 21.6 for pronouns, 4.8 for bound morphemes, and 7.2 for spontaneous clauses.
Participants Set B
Jesse
During intervention, Jesse showed an increase in the use of all dependent measures (change in means: verbs = 42.9, pronouns = 55.4, bound morphemes = 24.2, spontaneous clauses = 8.2). As shown in Table 3, Jesse showed consistent generalization of skills across all dependent measures during the intervention phase (change in means: verbs = 35.9, pronouns = 20.4, bound morphemes = 6.5, and spontaneous clauses = 10). Her use of verbs continued to increase after intervention had ended. For the remaining dependent measures, the rate of use decreased slightly (see Figures 58) but the rate of production of these structures was higher than preintervention levels as seen in Table 3.
Mateo
Mateo showed an increase in the use of all linguistic measures once he started intervention (change in means from baseline to intervention: verbs = 40.7, pronouns = 43.8, bound morphemes = 26.6, spontaneous clauses = 5.4). These gains were generalized during the intervention phase (change in means: verbs = 44.5, pronouns = 27.3, bound morphemes = 21.1, spontaneous clauses = 9.7), and maintained above preintervention levels for all linguistic measures.
Julian
Scores on all four measures also increased for Julian once he had began intervention (change in means: verbs = 29.6, pronouns = 20.7, bound morphemes = 13.8, spontaneous clauses = 6.6). These gains also generalized (change in means: verbs = 23.6, pronouns = 13.1, bound morphemes = 17.3, spontaneous clauses = 4.6), his use of verbs, pronouns, and bound morphemes continued to increase after intervention had ended, and his use of spontaneous clauses remained above preintervention levels.
Kareem
Although Kareem's increases were more modest than other participants in the set, there were consistent increases in his use of the linguistic targets during intervention (change in means: verbs = 10.2, pronouns = 18.3, bound morphemes = 2.6, spontaneous clauses = 3.6). During generalization probes, he demonstrated an increase in the rate of use of all linguistic targets (change in means: verbs = 7.2, pronouns = 5.1, bound morphemes = 6.8, spontaneous clauses = 5.1). His use of verbs and pronouns continued to grow even after intervention had ended, and the use of bound morphemes and spontaneous clauses remained above preintervention levels.
Nonoverlap Measures: Tau-U and IRD
Tau-U and IRD data are presented in Supplemental Material S2. Tau-U scores range from 0 to 1.0 and the range of IRD scores is from −1.0 to 1.0. A score of 1.0 on Tau-U and IRD is gained when all intervention scores surpass baseline scores. Tentative benchmarks have been proposed to interpret effect sizes provided by the Tau-U (questionable < .65, effective .66–.92, very effective > .92) and IRD (questionable < 0.5, effective 0.5–0.7, very effective > 0.7). The Tau-U and IRD scores show good correspondence with each other with all scores being indicative of very effective intervention except for use of bound morphemes by Julian and verbs and bound morphemes by Kareem. Some caution is warranted, of course, with wide confidence intervals, which may be due to the number of data points used in analysis. Nevertheless, actual scores closely reflect visual analysis, and together these are indicative of a strong positive outcome of intervention.
Discussion
The purpose of our study was to examine the effects of a conversation-based intervention program targeting the grammaticalization of utterances produced by children with severe MSDs and expressive language delay who use AAC. The findings indicate that, during intervention, all participants showed improvement in their production of verbs, pronouns, and bound morphemes. The use of these linguistic structures afforded participants the ability to form spontaneous clauses where these were not being consistently used before intervention. It is important to note that these gains were generalized to conversations with familiar adults who were blind to the intervention procedures. In some cases, these skills continued to grow up to 8 weeks after the end of the intervention.
The findings support earlier research demonstrating the effectiveness of adult scaffolding during conversation to increase the production of a range of linguistic structures in children with communication disorders (Nelson et al., 1996; Plante et al., 2014; Scherer & Olswang, 1989). The current study provides strong new evidence that conversation-based intervention models can also be effective for children with severe MSDs and expressive language delay who use AAC.
The structured conversation employed as treatment in this study may have been successful in improving the children's language skills for several reasons. First, the intervention provided numerous, controlled opportunities for presenting extremely salient exemplars of the target structures within engaging conversations (Eisenberg, 2013; Scherer & Olswang, 1989). Targeting high frequency words, such as pronouns, copula, articles, and frequently used verbs, made it possible to achieve a high concentration of exposures and production attempts across different sessions and different child-directed conversation topics. This may also explain why these gains were generalized to conversations with familiar partners outside the intervention context.
This approach is broadly consistent with previous research demonstrating that the frequency of occurrence of words across several contexts predicts word learning (Adelman, Brown, & Quesada, 2006). For example, Hoff (2006)  reports that words heard by children in a variety of sentence structures are acquired more rapidly than words heard on an equally frequent basis, but in a more restricted range of sentence structures. Further, the fact that such similar results were noted in both Set A and Set B despite differences in age indicates that similar learning patterns may be expected for a range of children with severe MSDs and language delay and who use AAC.
Second, the structure of conversational discourse paired with conversational recasting used in this study served to provide meaningful contrast and highlight the saliency of the target structures, simultaneously allowing for the accomplishment of a more naturalistic and authentic interaction (Eisenberg, 2013; Scherer & Olswang, 1989). In the current study, vocabulary targets were mostly linguistic structures that denoted nonobject and function words. In contrast to object words, which can be taught by association to the referent, the meaning of function words can only be learned in relation to other words within discourse (Bloom, 2000; Levy & Nelson, 1994; Tomasello, 2003). These findings are consistent with previous research indicating that, for children with severe MSDs and expressive language delay who use AAC, contrast (provided by the adult recasts) is critical to the acquisition of grammatical morphemes (Binger, Maguire-Marshall, & Kent-Walsh, 2011).
Third, the clinicians' use of open-ended questioning, recasting, and prompting provided the necessary conversational structure to engage the children and elicit language in conversations concerning topics of their interest. This aspect of the intervention reflects evidence that children interacting in social environments with engaging and responsive communicative partners who use rich vocabulary acquire language more rapidly than children in social environments that provide fewer of these supports (Hoff, 2006).
The features of the intervention as described above mirror the ethos of dynamic systems theories that propose that learning is a consequence of complex and dynamic interactions between multiple components that must converge at specific levels of intensity for learning to be achieved (Nelson & Arkenberg, 2008; Nelson & Welsh, 1998). Evidence of rapid word learning and syntactic growth in typical and atypical populations has been found from clinical interventions grounded on such theories (see Nelson & Arkenberg, 2008  for an extensive review). Our intervention incorporated a number of these clinical properties including individualized, monitored intervention sessions, well-tailored adult input, multiple targets in each intervention session, high expectations for meaningful communication, and rich transactional learning conditions. Giving the children the option to choose the photograph was an essential component of the intervention. Research evidence suggests that when children are presented with choices over certain aspects of a language intervention activity, such as the intervention materials, they exhibit higher levels of attention and engagement that are associated with multiple and significant linguistic skill advantages (Khan, Nelson, & Whyte, 2013).
Study Limitations and Future Research Directions
The results of the present study should be interpreted with respect to the study limitations. As with all single-subject experimental designs, the size of the sample was relatively small (i.e., eight subjects). Although our analysis did not reveal differences between both sets of participants, the relationship between the intervention procedures and the grammatical skills of children with MSDs and expressive language delay who use AAC should be further explored with a larger number of participants and using experimental designs that include randomization and control groups. Also, we note that the present investigation included only familiar adults as generalization partners. Future studies would benefit from including a wider range of conversational partners, such as typical peers or unfamiliar partners.
The study included both conversational recasts and imitative prompts within a conversation-based intervention, and therefore it is not possible within the current design to assess the relative effectiveness of each. It remains unclear whether the whole intervention program or only certain aspects of it are responsible for the production of the target structures by children. A systematic comparison between conversation-based procedures with and without prompted imitation is therefore warranted. In addition, future studies employing different types of recasts and different levels of recast density are also needed. Although high levels of interrater reliability for treatment fidelity were obtained, the raters were not blinded to the phases they were observing and this could have affected their rating. Future studies should include raters that are blinded to both the purposes of the study and to the type of session they are observing.
Additional work is also required to define further the populations that can benefit from this type of intervention. This would include a more extensive description of the cognitive and linguistic skills of study participants and systematic replication of study procedures with children with different profiles, including those with more significant receptive language delay due to moderate to severe cognitive impairment. For example, in the present study we are unable to ascertain fully whether observed improvement relates to increased operational competence in SDG use or language acquisition, or both; to examine this, future studies might therefore include frequent probes of language comprehension at different study phases.
Conclusion
The findings from this study provide strong evidence of the effectiveness of short-term, one-to-one, conversation-based intervention for improving the expressive vocabulary and grammatical skills of children with severe MSDs and expressive language delay who use AAC. Although initially adult-driven, the conversations grew to be varied, complex, and directed by the children's own initiative as they became increasingly active in choosing conversational topics and the props they wanted to talk about. The repertoire of language support strategies used by clinicians in conversations of topical salience for children engendered a dynamic yet regulated interactional context for language learning in which the expectations for children's language use were high. As such, this approach challenges the proposition that intervention approaches that are naturally interactive and conversationally driven are inherently unstructured (Ruston & Schwanenflugel, 2010).
Children using AAC are frequently described as passive in their interactions with others, as being minimally responsive and reciprocal, and may present with a host of impairments that threaten participation in authentic conversations. The current study established that the use of a format for language intervention that is conversation-based, interactive, structured, and has an expectation for grammaticalization can lead to successful language outcomes.
Acknowledgments
This research was funded by National Institutes of Health Grant R15DC012418-01, awarded to Gloria Soto. Special thanks to all the children, adults, and student clinicians who participated in this study. Earlier versions of this article were presented at the Annual Convention of the American Speech-Language-Hearing Association in Chicago, November 2013, and at the Biennial Meeting of the International Society for Augmentative and Alternative Communication in Lisbon, Portugal, July 2014. We are especially grateful to Gat Harussi-Savaldi, Catherine Lipson, Celia Hughell, and Renee Starowicz for their invaluable assistance in different project activities.
References
Adelman, J., Brown, G., & Quesada, J. (2006). Contextual diversity, not word frequency, determines word-naming and lexical decision times. Psychological Science, 17, 814–823. [Article] [PubMed]
Adelman, J., Brown, G., & Quesada, J. (2006). Contextual diversity, not word frequency, determines word-naming and lexical decision times. Psychological Science, 17, 814–823. [Article] [PubMed]×
Binger, C., & Light, J. (2008). The morphology and syntax of individuals who use AAC: Research review and implications for effective practice. Augmentative and Alternative Communication, 24, 123–138. [Article] [PubMed]
Binger, C., & Light, J. (2008). The morphology and syntax of individuals who use AAC: Research review and implications for effective practice. Augmentative and Alternative Communication, 24, 123–138. [Article] [PubMed]×
Binger, C., Maguire-Marshall, M., & Kent-Walsh, J. (2011). Using aided AAC models, recasts, and contrastive targets to teach grammatical morphemes to children who use AAC. Journal of Speech, Language, and Hearing Research, 54, 160–176. [Article]
Binger, C., Maguire-Marshall, M., & Kent-Walsh, J. (2011). Using aided AAC models, recasts, and contrastive targets to teach grammatical morphemes to children who use AAC. Journal of Speech, Language, and Hearing Research, 54, 160–176. [Article] ×
Bloom, P. (2000). How children learn the meanings of words (Vol. 377) . Cambridge, MA: MIT press.
Bloom, P. (2000). How children learn the meanings of words (Vol. 377) . Cambridge, MA: MIT press.×
Boenisch, J., & Soto, G. (2015). The oral core vocabulary of typically developing English-speaking school-aged children: Implications for AAC practice. Augmentative and Alternative Communication, 31, 77–84. [Article] [PubMed]
Boenisch, J., & Soto, G. (2015). The oral core vocabulary of typically developing English-speaking school-aged children: Implications for AAC practice. Augmentative and Alternative Communication, 31, 77–84. [Article] [PubMed]×
Camarata, S., & Nelson, K. E. (2006). Conversational recast intervention with preschool and older children. In McCauley, R. & Fey, M. (Eds.), Treatment of language disorders in children (pp. 237–264). Baltimore, MD: Brookes.
Camarata, S., & Nelson, K. E. (2006). Conversational recast intervention with preschool and older children. In McCauley, R. & Fey, M. (Eds.), Treatment of language disorders in children (pp. 237–264). Baltimore, MD: Brookes.×
Carrow-Woolfolk, E. (1999). Examiner's manual: Test of Auditory Comprehension of Language–Third Edition. Austin, TX: Pro-ed.
Carrow-Woolfolk, E. (1999). Examiner's manual: Test of Auditory Comprehension of Language–Third Edition. Austin, TX: Pro-ed.×
Clarke, M. T., & Price, K. (2012). Augmentative and alternative communication for children with cerebral palsy. Paediatrics and Child Health, 22, 367–371. [Article]
Clarke, M. T., & Price, K. (2012). Augmentative and alternative communication for children with cerebral palsy. Paediatrics and Child Health, 22, 367–371. [Article] ×
Clarke, M., & Wilkinson, R. (2007). Interaction between children with cerebral palsy and their peers 1: Organizing and understanding VOCA use. Augmentative and Alternative Communication, 23, 336–348. [Article]
Clarke, M., & Wilkinson, R. (2007). Interaction between children with cerebral palsy and their peers 1: Organizing and understanding VOCA use. Augmentative and Alternative Communication, 23, 336–348. [Article] ×
Dowden, P. (1997). Augmentative and alternative communication decision making for children with severely unintelligible speech. Augmentative and Alternative Communication, 13(1), 48–59. [Article]
Dowden, P. (1997). Augmentative and alternative communication decision making for children with severely unintelligible speech. Augmentative and Alternative Communication, 13(1), 48–59. [Article] ×
Duffy, J. R. (2013). Motor speech disorders: Substrates, differential diagnosis, and management. Amsterdam, the Netherlands: Elsevier Health Sciences.
Duffy, J. R. (2013). Motor speech disorders: Substrates, differential diagnosis, and management. Amsterdam, the Netherlands: Elsevier Health Sciences.×
Dunn, L. M., & Dunn, D. M. (2007). PPVT-4: Peabody Picture Vocabulary Test–Fourth Edition. San Antonio, TX: Pearson Assessments.
Dunn, L. M., & Dunn, D. M. (2007). PPVT-4: Peabody Picture Vocabulary Test–Fourth Edition. San Antonio, TX: Pearson Assessments.×
Eisenberg, S. L. (2013). Grammar intervention: Content and procedures for facilitating children's language development. Topics in Language Disorders, 33, 165–178. [Article]
Eisenberg, S. L. (2013). Grammar intervention: Content and procedures for facilitating children's language development. Topics in Language Disorders, 33, 165–178. [Article] ×
Eisenberg, S. (2014). What works in therapy: Further thoughts on improving clinical practica for children with language disorders. Language, Speech, and Hearing Services in Schools. 45, 117–126. [Article] [PubMed]
Eisenberg, S. (2014). What works in therapy: Further thoughts on improving clinical practica for children with language disorders. Language, Speech, and Hearing Services in Schools. 45, 117–126. [Article] [PubMed]×
Gast, D. L. (2010). Single subject research methodology in behavioral sciences. New York, NY: Routledge.
Gast, D. L. (2010). Single subject research methodology in behavioral sciences. New York, NY: Routledge.×
Gast, D. L., & Ledford, J. (2010). Multiple baseline and multiple probe designs. In Gast, D. L. & Ledford, J. R. (Eds.), Single subject research methodology in behavioral sciences (pp. 129–165). New York, NY: Routledge.
Gast, D. L., & Ledford, J. (2010). Multiple baseline and multiple probe designs. In Gast, D. L. & Ledford, J. R. (Eds.), Single subject research methodology in behavioral sciences (pp. 129–165). New York, NY: Routledge.×
Gast, D. L., Lloyd, B. P., & Ledford, J. R. (2014). Multiple baseline and multiple probe designs. In Gast, D. L. (Ed.), Single case research methodology: Applications in special education and behavioral sciences (pp. 251–296). London, UK: Routledge.
Gast, D. L., Lloyd, B. P., & Ledford, J. R. (2014). Multiple baseline and multiple probe designs. In Gast, D. L. (Ed.), Single case research methodology: Applications in special education and behavioral sciences (pp. 251–296). London, UK: Routledge.×
Hadley, P. A., Rispoli, M., Fitzgerald, C., & Bahnsen, A. (2011). Predictors of morphosyntactic growth in typically developing toddlers: Contributions of parent input and child sex. Journal of Speech, Language, and Hearing Research, 54, 549–566. [Article]
Hadley, P. A., Rispoli, M., Fitzgerald, C., & Bahnsen, A. (2011). Predictors of morphosyntactic growth in typically developing toddlers: Contributions of parent input and child sex. Journal of Speech, Language, and Hearing Research, 54, 549–566. [Article] ×
Hammill, D. D., & Newcomer, P. L. (2008). Test of Language Development-Primary: Fourth Edition (TOLD-P: 4). Austin, TX: Pro-Ed.
Hammill, D. D., & Newcomer, P. L. (2008). Test of Language Development-Primary: Fourth Edition (TOLD-P: 4). Austin, TX: Pro-Ed.×
Hoff, E. (2006). How social contexts support and shape language development. Developmental Review, 26, 55–88. [Article]
Hoff, E. (2006). How social contexts support and shape language development. Developmental Review, 26, 55–88. [Article] ×
Kennedy, C. H. (2005). Single-case designs for educational research. Upper Saddle River, NJ: Prentice Hall.
Kennedy, C. H. (2005). Single-case designs for educational research. Upper Saddle River, NJ: Prentice Hall.×
Khan, K., Nelson, K., & Whyte, E. (2014). Children choose their own stories: The impact of choice on children's learning of new narrative skills. Journal of Child Language, 41(4), 949–962. [Article] [PubMed]
Khan, K., Nelson, K., & Whyte, E. (2014). Children choose their own stories: The impact of choice on children's learning of new narrative skills. Journal of Child Language, 41(4), 949–962. [Article] [PubMed]×
King, A. M., Hengst, J. A., & DeThorne, L. S. (2013). Severe speech sound disorders: An integrated multimodal intervention. Language, Speech, and Hearing Services in Schools, 44, 195–210. [Article] [PubMed]
King, A. M., Hengst, J. A., & DeThorne, L. S. (2013). Severe speech sound disorders: An integrated multimodal intervention. Language, Speech, and Hearing Services in Schools, 44, 195–210. [Article] [PubMed]×
Kovach, T. M. (2009). Augmentative & alternative communication profile: A continuum of learning. Austin, TX: LinguiSystems.
Kovach, T. M. (2009). Augmentative & alternative communication profile: A continuum of learning. Austin, TX: LinguiSystems.×
Kovacs, T., & Hill, K. (2015). A tutorial on reliability testing in AAC language sample transcription and analysis. Augmentative and Alternative Communication, 31, 148–158. [Article] [PubMed]
Kovacs, T., & Hill, K. (2015). A tutorial on reliability testing in AAC language sample transcription and analysis. Augmentative and Alternative Communication, 31, 148–158. [Article] [PubMed]×
Kratochwill, T. R., Hitchcock, J., Horner, R. H., Levin, J. R., Odom, S. L., Rindskopf, D. M., & Shadish, W. R. (2010). Single-case designs technical documentation. Retrieved from What Works Clearinghouse website. http://ies.ed.gov/ncee/wwc/Document/229
Kratochwill, T. R., Hitchcock, J., Horner, R. H., Levin, J. R., Odom, S. L., Rindskopf, D. M., & Shadish, W. R. (2010). Single-case designs technical documentation. Retrieved from What Works Clearinghouse website. http://ies.ed.gov/ncee/wwc/Document/229 ×
Levy, E., & Nelson, K. (1994). Words in discourse: A dialectical approach to the acquisition of meaning and use. Journal of Child Language, 21, 367–389. [Article] [PubMed]
Levy, E., & Nelson, K. (1994). Words in discourse: A dialectical approach to the acquisition of meaning and use. Journal of Child Language, 21, 367–389. [Article] [PubMed]×
Light, J. (1989). Toward a definition of communicative competence for individuals using augmentative and alternative communication systems. Augmentative and Alternative Communication, 5, 137–144. [Article]
Light, J. (1989). Toward a definition of communicative competence for individuals using augmentative and alternative communication systems. Augmentative and Alternative Communication, 5, 137–144. [Article] ×
Manhardt, J., & Rescorla, L. (2002). Oral narrative skills of late talkers at ages 8 and 9. Applied Psycholinguistics, 23, 1–21. [Article]
Manhardt, J., & Rescorla, L. (2002). Oral narrative skills of late talkers at ages 8 and 9. Applied Psycholinguistics, 23, 1–21. [Article] ×
McGregor, K. K. (2000). The development and enhancement of narrative skills in a preschool classroom: Towards a solution to clinician-client mismatch. American Journal of Speech-Language Pathology, 9(1), 55–71. [Article]
McGregor, K. K. (2000). The development and enhancement of narrative skills in a preschool classroom: Towards a solution to clinician-client mismatch. American Journal of Speech-Language Pathology, 9(1), 55–71. [Article] ×
Miller, J. F., & Chapman, R. S. (1991). Systematic Analysis of Language Transcripts [Computer software] . Madison, WI: University of Wisconsin–Madison, Waisman Center. Language Analysis Laboratory.
Miller, J. F., & Chapman, R. S. (1991). Systematic Analysis of Language Transcripts [Computer software] . Madison, WI: University of Wisconsin–Madison, Waisman Center. Language Analysis Laboratory.×
Nelson, K. E., & Arkenberg, M. E. (2008). Language and reading development reflect dynamic mixes of learning conditions. In Mody, M. & Silliman, E. R. (Eds.), Brain, behavior, and learning in language and reading disorders (pp. 315–348). New York, NY: Guilford.
Nelson, K. E., & Arkenberg, M. E. (2008). Language and reading development reflect dynamic mixes of learning conditions. In Mody, M. & Silliman, E. R. (Eds.), Brain, behavior, and learning in language and reading disorders (pp. 315–348). New York, NY: Guilford.×
Nelson, K. E., Camarata, S. M., Welsh, J., Butkovsky, L., & Camarata, M. (1996). Effects of imitative and conversational recasting treatment on the acquisition of grammar in children with specific language impairment and younger language-normal children. Journal of Speech, Language, and Hearing Research. 39(4), 850–859 [Article]
Nelson, K. E., Camarata, S. M., Welsh, J., Butkovsky, L., & Camarata, M. (1996). Effects of imitative and conversational recasting treatment on the acquisition of grammar in children with specific language impairment and younger language-normal children. Journal of Speech, Language, and Hearing Research. 39(4), 850–859 [Article] ×
Nelson, K. E., & Welsh, J. A. (1998). Progress in multiple language domains by deaf children and hearing children. Discussions within a rare event transactional model language delay. In Paul, R. (Ed.), Exploring the speech–language connection (pp. 179–225). Baltimore, MD: Brookes.
Nelson, K. E., & Welsh, J. A. (1998). Progress in multiple language domains by deaf children and hearing children. Discussions within a rare event transactional model language delay. In Paul, R. (Ed.), Exploring the speech–language connection (pp. 179–225). Baltimore, MD: Brookes.×
Parker, R. I., Vannest, K. J., & Brown, L. (2009). The improvement rate difference for single-case research. Exceptional Children, 75, 135–150. [Article]
Parker, R. I., Vannest, K. J., & Brown, L. (2009). The improvement rate difference for single-case research. Exceptional Children, 75, 135–150. [Article] ×
Parker, R. I., Vannest, K. J., Davis, J. L., & Sauber, S. B. (2011). Combining nonoverlap and trend for single-case research: Tau-U. Behavior Therapy, 42, 284–299. [Article] [PubMed]
Parker, R. I., Vannest, K. J., Davis, J. L., & Sauber, S. B. (2011). Combining nonoverlap and trend for single-case research: Tau-U. Behavior Therapy, 42, 284–299. [Article] [PubMed]×
Plante, E., Ogilvie, T., Vance, R., Aguilar, J. M., Dailey, N. S., Meyers, C., … Burton, R. (2014). Variability in the language input to children enhances learning in a treatment context, American Journal of Speech-Language Pathology, 23, 530–545. [Article] [PubMed]
Plante, E., Ogilvie, T., Vance, R., Aguilar, J. M., Dailey, N. S., Meyers, C., … Burton, R. (2014). Variability in the language input to children enhances learning in a treatment context, American Journal of Speech-Language Pathology, 23, 530–545. [Article] [PubMed]×
Rakap, S., Snyder, P., & Pasia, C. (2014). Comparison of nonoverlap methods for identifying treatment effect in single-subject experimental research. Behavioral Disorders, 39, 128–145.
Rakap, S., Snyder, P., & Pasia, C. (2014). Comparison of nonoverlap methods for identifying treatment effect in single-subject experimental research. Behavioral Disorders, 39, 128–145.×
Ruston, H. P., & Schwanenflugel, P. J. (2010). Effects of a conversation intervention on the expressive vocabulary development of prekindergarten children. Language, Speech, and Hearing Services in Schools, 41, 303–313. [Article] [PubMed]
Ruston, H. P., & Schwanenflugel, P. J. (2010). Effects of a conversation intervention on the expressive vocabulary development of prekindergarten children. Language, Speech, and Hearing Services in Schools, 41, 303–313. [Article] [PubMed]×
Scherer, N. J., & Olswang, L. B. (1989). Using structured discourse as a language intervention technique with autistic children. Journal of Speech and Hearing Disorders, 54, 383–394. [Article] [PubMed]
Scherer, N. J., & Olswang, L. B. (1989). Using structured discourse as a language intervention technique with autistic children. Journal of Speech and Hearing Disorders, 54, 383–394. [Article] [PubMed]×
Schlosser, R., & Lee, D. (2000). Promoting generalization and maintenance in augmentative and alternative communication: A meta-analysis of 20 years of effectiveness research. Augmentative and Alternative Communication, 16, 208–226. [Article]
Schlosser, R., & Lee, D. (2000). Promoting generalization and maintenance in augmentative and alternative communication: A meta-analysis of 20 years of effectiveness research. Augmentative and Alternative Communication, 16, 208–226. [Article] ×
Scollon, R. (1976). Conversations with a one year old: A case study of the developmental foundation of syntax. Honolulu, HI: University of Hawaii Press.
Scollon, R. (1976). Conversations with a one year old: A case study of the developmental foundation of syntax. Honolulu, HI: University of Hawaii Press.×
Scott, C. M., & Stokes, S. L. (1995). Measures of syntax in school-age children and adolescents. Language, Speech, and Hearing Services in Schools, 26, 309–319. [Article]
Scott, C. M., & Stokes, S. L. (1995). Measures of syntax in school-age children and adolescents. Language, Speech, and Hearing Services in Schools, 26, 309–319. [Article] ×
Smith, M. M. (2015). Language development of individuals who require aided communication: Reflections on state of the science and future research directions. Augmentative and Alternative Communication, 31, 215–233. [Article] [PubMed]
Smith, M. M. (2015). Language development of individuals who require aided communication: Reflections on state of the science and future research directions. Augmentative and Alternative Communication, 31, 215–233. [Article] [PubMed]×
Solomon-Rice, P., & Soto, G. (2011). Co-construction as a facilitative factor in supporting the personal narratives of children who use augmentative and alternative communication. Communication Disorders Quarterly, 32(2), 70–82. [Article]
Solomon-Rice, P., & Soto, G. (2011). Co-construction as a facilitative factor in supporting the personal narratives of children who use augmentative and alternative communication. Communication Disorders Quarterly, 32(2), 70–82. [Article] ×
Soto, G., & Hartmann, E. (2006). Analysis of narratives produced by four children who use augmentative and alternative communication. Journal of Communication Disorders, 39, 456–480. [Article] [PubMed]
Soto, G., & Hartmann, E. (2006). Analysis of narratives produced by four children who use augmentative and alternative communication. Journal of Communication Disorders, 39, 456–480. [Article] [PubMed]×
Stiegler, L. N., & Hoffman, P. R. (2001). Discourse-based intervention for word finding in children. Journal of Communication Disorders, 34, 277–303. [Article] [PubMed]
Stiegler, L. N., & Hoffman, P. R. (2001). Discourse-based intervention for word finding in children. Journal of Communication Disorders, 34, 277–303. [Article] [PubMed]×
Sutton, A., Soto, G., & Blockberger, S. (2002). Grammatical issues in graphic symbol communication. Augmentative and Alternative Communication, 18, 192–204. [Article]
Sutton, A., Soto, G., & Blockberger, S. (2002). Grammatical issues in graphic symbol communication. Augmentative and Alternative Communication, 18, 192–204. [Article] ×
Thordardottir, E. T., Chapman, R. S., & Wagner, L. (2002). Complex sentence production by adolescents with Down syndrome. Applied Psycholinguistics, 23, 163–183. [Article]
Thordardottir, E. T., Chapman, R. S., & Wagner, L. (2002). Complex sentence production by adolescents with Down syndrome. Applied Psycholinguistics, 23, 163–183. [Article] ×
Tomasello, M. (2003). Constructing a language: A usage-based theory of language acquisition. Cambridge, MA: Harvard University Press.
Tomasello, M. (2003). Constructing a language: A usage-based theory of language acquisition. Cambridge, MA: Harvard University Press.×
Warren, S. F., Fey, M. E., & Yoder, P. J. (2007). Differential treatment intensity research: A missing link to creating optimally effective communication interventions. Mental Retardation and Developmental Disabilities Research Reviews, 13, 70–77. [Article] [PubMed]
Warren, S. F., Fey, M. E., & Yoder, P. J. (2007). Differential treatment intensity research: A missing link to creating optimally effective communication interventions. Mental Retardation and Developmental Disabilities Research Reviews, 13, 70–77. [Article] [PubMed]×
Footnote
1 The AACP measures skills in four areas of AAC communicative competence: operational, linguistic, social, and strategic (Light, 1989). Skills are grouped hierarchically in five levels, from simple and early functioning to independent use and AAC system mastery. A person using AAC at Level III purposefully selects targeted symbols with few prompts (operational); is beginning to engage in dialogue and combines words to create simple phrases (linguistic); is using AAC for social interaction purposes such as making comments and greeting friends; is familiar with and can retrieve vocabulary and messages on the AAC device to communicate more effectively; and may use telegraphic messages, but understands the importance of selecting correct vocabulary to be an effective communicator and is actively learning vocabulary (strategic).
The AACP measures skills in four areas of AAC communicative competence: operational, linguistic, social, and strategic (Light, 1989). Skills are grouped hierarchically in five levels, from simple and early functioning to independent use and AAC system mastery. A person using AAC at Level III purposefully selects targeted symbols with few prompts (operational); is beginning to engage in dialogue and combines words to create simple phrases (linguistic); is using AAC for social interaction purposes such as making comments and greeting friends; is familiar with and can retrieve vocabulary and messages on the AAC device to communicate more effectively; and may use telegraphic messages, but understands the importance of selecting correct vocabulary to be an effective communicator and is actively learning vocabulary (strategic).×
Figure 1.

Set A: Rate of verb use per 60 min.

 Set A: Rate of verb use per 60 min.
Figure 1.

Set A: Rate of verb use per 60 min.

×
Figure 2.

Set A: Rate of pronoun use per 60 min.

 Set A: Rate of pronoun use per 60 min.
Figure 2.

Set A: Rate of pronoun use per 60 min.

×
Figure 3.

Set A: Rate of bound morpheme use per 60 min.

 Set A: Rate of bound morpheme use per 60 min.
Figure 3.

Set A: Rate of bound morpheme use per 60 min.

×
Figure 4.

Set A: Rate of spontaneous clause use per 60 min.

 Set A: Rate of spontaneous clause use per 60 min.
Figure 4.

Set A: Rate of spontaneous clause use per 60 min.

×
Figure 5.

Set B: Rate of verb use per 60 min.

 Set B: Rate of verb use per 60 min.
Figure 5.

Set B: Rate of verb use per 60 min.

×
Figure 6.

Set B: Rate of pronoun use per 60 min.

 Set B: Rate of pronoun use per 60 min.
Figure 6.

Set B: Rate of pronoun use per 60 min.

×
Figure 7.

Set B: Rate of bound morpheme use per 60 min.

 Set B: Rate of bound morpheme use per 60 min.
Figure 7.

Set B: Rate of bound morpheme use per 60 min.

×
Figure 8.

Set B: Rate of independent clause use per 60 min.

 Set B: Rate of independent clause use per 60 min.
Figure 8.

Set B: Rate of independent clause use per 60 min.

×
Table 1. Participants' demographic characteristics.
Participants' demographic characteristics.×
Participants Age Speech disorder Mobility Speech-generating device a Speech-generating device access Languages spoken at home Receptive vocabulary age equivalent (percentile) Morphological judgment age equivalent (percentile) Expressive language (from educational records) Speech intelligibility rating (%)
Carmen 9;5 Dysarthria secondary to Pfeiffer syndrome Wheelchair user DynaVox DV4 with Gateway modified 45, 60 Finger pointing English, Spanish 8;6 b (37) 6;6 b (9) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Geli 8;10 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Vmax with EyeMax system and Gateway 45 Eye gaze English, French, Italian 6;6 b (25) 6;3 b (16) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Joe 8;8 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox with Gateway 45 Head switches, step scanning English, Spanish 6;9 b (37) 4;10 b (2) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Dante 8;8 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Head mouse English 7;0 b (37) 4;3 b (2) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Jesse 12;1 Severe verbal apraxia, etiology unspecified Ambulant Vantage Lite with Unity 84 Finger pointing English, Spanish 9;5 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 40
Mateo 13;7 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Joystick English, Spanish 8;11 c (5) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 20 (minimally verbal)
Julian 13;9 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Maestro 5 with Gateway modified 45 Finger pointing English, Spanish 9;9 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Kareem 13;3 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 60 Finger pointing English, Arabic 9;6 c (7) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Note. Ages are shown in years;months. MLU = mean length of utterance.
Note. Ages are shown in years;months. MLU = mean length of utterance.×
a Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.
Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.×
b Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).
Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).×
c Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).
Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).×
d Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).
Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).×
Table 1. Participants' demographic characteristics.
Participants' demographic characteristics.×
Participants Age Speech disorder Mobility Speech-generating device a Speech-generating device access Languages spoken at home Receptive vocabulary age equivalent (percentile) Morphological judgment age equivalent (percentile) Expressive language (from educational records) Speech intelligibility rating (%)
Carmen 9;5 Dysarthria secondary to Pfeiffer syndrome Wheelchair user DynaVox DV4 with Gateway modified 45, 60 Finger pointing English, Spanish 8;6 b (37) 6;6 b (9) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Geli 8;10 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Vmax with EyeMax system and Gateway 45 Eye gaze English, French, Italian 6;6 b (25) 6;3 b (16) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Joe 8;8 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox with Gateway 45 Head switches, step scanning English, Spanish 6;9 b (37) 4;10 b (2) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Dante 8;8 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Head mouse English 7;0 b (37) 4;3 b (2) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Jesse 12;1 Severe verbal apraxia, etiology unspecified Ambulant Vantage Lite with Unity 84 Finger pointing English, Spanish 9;5 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 40
Mateo 13;7 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 84 Joystick English, Spanish 8;11 c (5) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 20 (minimally verbal)
Julian 13;9 Dysarthria secondary to cerebral palsy Wheelchair user DynaVox Maestro 5 with Gateway modified 45 Finger pointing English, Spanish 9;9 c (12) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 7 (minimally verbal)
Kareem 13;3 Dysarthria secondary to cerebral palsy Wheelchair user Vantage Lite with Unity 60 Finger pointing English, Arabic 9;6 c (7) <8 d (n.a.) MLU 1–2 mostly nouns and adjectives 0 (nonverbal)
Note. Ages are shown in years;months. MLU = mean length of utterance.
Note. Ages are shown in years;months. MLU = mean length of utterance.×
a Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.
Gateway and Unity are two language-based vocabulary organization systems that include: (a) core vocabulary words (i.e., most frequently used words), allowing for the creation of spontaneous and novel messages, and (b) grammatical markers, allowing for grammaticalization of the utterance.×
b Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).
Test of Auditory Comprehension of Language–Third Edition (Carrow-Woolfolk, 1999).×
c Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).
Peabody Picture Vocabulary Test–Fourth Edition (Dunn & Dunn, 2007).×
d Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).
Test of Language Development-Primary: Fourth Edition (Hammill & Newcomer, 2008).×
×
Table 2. Baseline and intervention results.
Baseline and intervention results.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Base Inter Base Inter Base Inter Base Inter Base Inter
Carmen 5 23 11.2 73.3 2.0 48.6 1.6 59.9 0 4.5
Geli 5 23 9.6 65.2 1.2 44.6 4.2 55.6 0 8.5
Joe 5 12 16.8 49.3 3.6 35.2 5.1 9.9 0 3.5
Dante 5 6 1.6 33.7 0 17.7 0 13.5 0 3.4
Jesse 5 23 10.6 53.5 2.5 57.9 0.5 24.7 0 8.2
Mateo 5 24 6.9 47.6 4.2 48.0 3.4 30.0 0 5.4
Julian 5 23 1.8 31.4 1.2 21.9 4.8 18.6 0.6 7.2
Kareem 5 12 7.1 17.3 0.6 18.9 2.4 5.0 0 3.6
Note. Base = baseline, Inter = intervention.
Note. Base = baseline, Inter = intervention.×
Table 2. Baseline and intervention results.
Baseline and intervention results.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Base Inter Base Inter Base Inter Base Inter Base Inter
Carmen 5 23 11.2 73.3 2.0 48.6 1.6 59.9 0 4.5
Geli 5 23 9.6 65.2 1.2 44.6 4.2 55.6 0 8.5
Joe 5 12 16.8 49.3 3.6 35.2 5.1 9.9 0 3.5
Dante 5 6 1.6 33.7 0 17.7 0 13.5 0 3.4
Jesse 5 23 10.6 53.5 2.5 57.9 0.5 24.7 0 8.2
Mateo 5 24 6.9 47.6 4.2 48.0 3.4 30.0 0 5.4
Julian 5 23 1.8 31.4 1.2 21.9 4.8 18.6 0.6 7.2
Kareem 5 12 7.1 17.3 0.6 18.9 2.4 5.0 0 3.6
Note. Base = baseline, Inter = intervention.
Note. Base = baseline, Inter = intervention.×
×
Table 3. Results for preintervention, during intervention, and postintervention generalization probes.
Results for preintervention, during intervention, and postintervention generalization probes.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Pre During Post Pre During Post Pre During Post Pre During Post Pre During Post
Set A
 Carmen 1 4 3 24.0 95.7 87.7 24.0 46.1 42.0 0 29.0 30.9 4 14.0 16.4
 Geli 1 4 3 15.0 52.1 35.0 6.0 37.7 25.0 9.0 45.9 35.0 0 4.9 6.0
 Joe 1 2 3 12.0 45.3 66.0 6.0 30.5 24.0 6.0 8.5 10.0 0 3.2 5.1
 Dante 1 1 2.4 21.6 0 21.6 0 4.8 0 7.2
Set B
 Jesse 1 4 1 8.0 43.9 46.3 6.0 26.4 16.0 2.0 8.5 5.0 0 10.0 8.0
 Mateo 1 4 3 18.6 63.1 57.5 21.3 48.6 48.3 9.3 30.4 20.6 0 9.7 10.4
 Julian 1 4 2 3.0 26.6 31.5 6.0 19.1 24.7 0 17.3 19.7 0 4.6 4.2
 Kareem 1 1 2 3.0 10.2 15.4 0 5.1 7.7 0 6.8 6.4 0 5.1 5.0
Table 3. Results for preintervention, during intervention, and postintervention generalization probes.
Results for preintervention, during intervention, and postintervention generalization probes.×
Participants Number of sessions
Mean number of verbs
Mean number of pronouns
Mean number of bound morphemes
Mean number of spontaneous clauses
Pre During Post Pre During Post Pre During Post Pre During Post Pre During Post
Set A
 Carmen 1 4 3 24.0 95.7 87.7 24.0 46.1 42.0 0 29.0 30.9 4 14.0 16.4
 Geli 1 4 3 15.0 52.1 35.0 6.0 37.7 25.0 9.0 45.9 35.0 0 4.9 6.0
 Joe 1 2 3 12.0 45.3 66.0 6.0 30.5 24.0 6.0 8.5 10.0 0 3.2 5.1
 Dante 1 1 2.4 21.6 0 21.6 0 4.8 0 7.2
Set B
 Jesse 1 4 1 8.0 43.9 46.3 6.0 26.4 16.0 2.0 8.5 5.0 0 10.0 8.0
 Mateo 1 4 3 18.6 63.1 57.5 21.3 48.6 48.3 9.3 30.4 20.6 0 9.7 10.4
 Julian 1 4 2 3.0 26.6 31.5 6.0 19.1 24.7 0 17.3 19.7 0 4.6 4.2
 Kareem 1 1 2 3.0 10.2 15.4 0 5.1 7.7 0 6.8 6.4 0 5.1 5.0
×