Dr. Lynn Kern Koegel is affiliated with Stanford University School of Medicine in Stanford, CA, USA, while Katherine M. Bryan and Pumpkin L. Su work at Vanderbilt School of Medicine in Nashville, TN, USA. Mohini Vaidya is associated with the Koegel Autism Center at the University of California, Santa Barbara, USA. Dr. Stephen Camarata works at Vanderbilt School of Medicine in Nashville, TN, USA.
Study Overview
This analysis explores the definitions of “nonverbal” or “minimally verbal” in interventions for children with autism spectrum disorder (ASD) with a focus on verbal communication. There is a scarcity of studies aimed at enhancing verbal communication skills in non/minimally verbal children with ASD. Inconsistencies in criteria, definitions, and age groups were identified. Recommendations are proposed for standardized assessment descriptions for young communicators.
Keywords: autism, nonverbal, minimally verbal, expressive language, communication therapy
Defining nonverbal and minimally verbal individuals is a challenge in interventions. Lack of consensus and consistency in definitions among researchers hinders progress in intervention strategies. Varied definitions can impact outcomes and choice of interventions. Clearly defined inclusion and exclusion criteria are vital for effective treatment planning and outcome comparison.
Most children under 18 months old with ASD are nonverbal or minimally verbal. Studies on older children are necessary for understanding long-term effects. The diverse nature of ASD diagnosis presents obstacles for clinical services and evidence-based practices. Research on severely affected individuals with ASD is limited.
While there are systematic reviews on Augmentative and Alternative Communication (AAC) interventions, research on verbal interventions for individuals who are nonverbal or minimally verbal is lacking. This review aims to categorize definitions of individuals with ASD in interventions focusing on expressive verbal communication.
Methodology
A systematic review was conducted on interventions for nonverbal and minimally verbal individuals with ASD. Articles were reviewed based on titles, abstracts, and full texts. Definitions of nonverbal and minimally verbal individuals, as well as measures of verbal and communication skills, were analyzed.
Findings
Recommendations
Only academic and peer-reviewed articles were considered. Excluded were dissertations, Master’s Theses, and conference presentations. Inclusion and exclusion criteria included: (a) Assessment – articles focusing solely on assessment without intervention were excluded; (b) Intervention – articles not targeting expressive verbal communication skills were excluded; (c) Diagnosis – only participants diagnosed with ASD and identified as minimally verbal were included; (d) Measurement – studies that examined verbal behavior as a dependent variable were included; (e) Design – interventions that underwent systematic investigation were included; or (f) Language – studies not in English were excluded.
Screening Measures
Title Screening.
The titles were screened by senior authors to identify studies targeting minimally verbal or nonverbal individuals. Out of 1,231 articles, 237 met the inclusion criteria. Most excluded articles did not meet the requirements.
Abstract Screening.
Abstracts from the 237 articles were reviewed, resulting in 67 articles meeting the inclusion criteria. Exclusions were primarily based on participant characteristics, intervention targets, and methods used.
Article Review and Data Evaluation
The authors reviewed 67 articles for inclusion. 31 research articles met all criteria and were thoroughly examined. Exclusions were evenly spread across different categories. The studies ranged from 1960 to 2018.
Table 1.
Definitions of nonverbal or minimally verbal children with ASD in the studies.
| Authors & Year | Number of Subjects | Number of Males | Number of Females | Average Age of Participants | Non-Verbal or Verbal Measure | Method of Evaluation (utilized for NV/MV assessment) |
|---|
Articles containing 3 or more authors will be abbreviated as et al.
Once the summary table of articles was created, each coder double-checked for accuracy. The initial Results section was written by the primary author, and twenty-two numerical outcomes were validated by the second author to match Table 1. The reliability of these results exceeded 90%. In cases where the accuracy was below 100%, the fifth author reviewed the article again and made the final decision on the results presented.
Results
The total number of unique participants with ASD in 31 studies was 650. To prevent duplicate counting, only the largest study was considered. Among the studies that reported on gender distribution, 78% consisted of males and 22% consisted of females.
Participant Ages
The age range of participants varied from 1 year and 4 months to 23 years. Eight studies focused on toddlers and preschoolers, with a combined total of 293 participants. Two studies exclusively included non-verbal children. Eleven studies centered on elementary school children, totaling 250 participants.
Ten studies encompassed preschool and elementary school children, amounting to 224 participants. Within these studies, 59 participants were non-verbal. Additionally, two studies involved a diverse group of 21 participants aged between 5 and 23, with 19 non-verbal participants.
Assessment Measures
There was a lack of consistency among studies in terms of the assessment measures used to evaluate verbal ability. Some studies utilized natural language interactions, behavioral observations, parent input, and standardized tools like VABS or CDI. Several tests were employed, including ADOS, KSPT, and vocabulary assessments. Some studies integrated IQ tests or assessments of overall functioning. Table 2 presents a comprehensive list of assessment measures found in the literature review.
Table 2.
Summary of assessment measures utilized in the reviewed studies and their respective purposes.
| Tool for Evaluation | Assesses |
|---|---|
| Standardized | |
| Autism Diagnostic Interview (ADI) | Provides insight into behavioral and background details, such as early development, language acquisition, current functioning, and social development, through reports from relatives or caregivers (Rutter, Le Couteur, & Lord, 2003). |
| Behavioral Intervention Rating Scale (BIRS) | Evaluates teachers’ views on the effectiveness of classroom intervention treatments (Strasberger et al., 2014) |
| Communication and Symbolic Behavior Scales Developmental Profile (CSBS-DP) | Assesses communicative skills (such as eye gaze, gestures, sounds, words, understanding, and play) for children with a functional communication age from 6 to 24 months; includes a Caregiver Questionnaire and Behavior Sample (Green, Charman, McConachie, et. al. 2010) |
| Early Social-Communication Scales (ESCS) | Evaluates nonverbal communication abilities in children with mental ages ranging from 8 to 30 months (Almirall et al., 2016) |
| Expressive One-Word Picture Vocabulary Test (EOWPVT) | Assesses verbal expression in individuals aged 2 years to 80+ (Schriebman & Stahmer 2014) |
| Fisher-Logemann Test of Articulation Competence | Analyzes and categorizes articulation errors (Oxman, Konstantareas, Liebovitz-Bojm, 1979) |
| Kaufman Speech Praxis Test for Children (KSPT) | Assesses a child’s imitative responses to the clinician, focusing on motor-speech proficiency (Esch, Esch, & Love, 2009) |
| Leiter International Performance Scale-Revised (Leiter-R) | Evaluates cognitive functions in children and adolescents aged 2–20 (Almirall et al., 2016) |
| MacArthur-Bates Communicative Development Inventories (MB-CDIs or CDI) | Assesses early language skills, including vocabulary comprehension, production, gestures, and grammar; based on parent reports (Green, Charman, McConachie, et. al. 2010; Koegel, Shiratova, Koegel, 2009; Rogers et al., 2006; Schriebman & Stahmer 2014) |
| Mullen Scales of Early Learning (MSEL) | Evaluates gross motor, fine motor, visual reception, receptive language, and expressive language in children from birth to 68 months (Rogers et al., 2006; Schriebman & Stahmer 2014; Wetherby, Guthrie, Woods, et. al. 2014) |
| Psychoeducational Profile-Revised (PEP-R) | Evaluates skills and behaviors (learning strengths, uneven development, emerging abilities) of children with autism and communication disabilities in the developmental age range of 6 months to 7 years Ozonoff & Cathcart 1998 |
| The Receptive-Expressive Emergent Language Scale, Third Edition (REEL-3) | Determines the developmental age equivalent for receptive and expressive language skills (Franco, Davis & Davis, 2013) |
| Vineland Adaptive Behavior Scales (VABS) | Assesses personal and social skills, receptive and expressive communication, and motor skills in individuals from birth to adulthood Green, Charman, McConachie, et. al. 2010; Rogers et al., 2006; Schriebman & Stahmer 2014; Wetherby, Guthrie, Woods, et. al. 2014 |
| Non-Standardized | |
| Naturalistic language sample | Observes naturalistic communication patterns, including spontaneous utterances, requests, imitation, behaviors, receptive & expressive communication, peer interactions, and articulation (a common feature in most reviewed studies) |
| Structured play assessment | Measures the number of unique play actions (Almirall et al., 2016) |
| Phoneme imitation task | Tests the ability to repeat phonemes (Esch, Esch, & Love, 2009) |
| Rating forms/surveys | Collects teachers’ assessments of children’s language skills (Green, Charman, McConachie, et. al. 2010), and evaluates parent satisfaction levels (Schriebman & Stahmer 2014) |
| Interview | Obtains feedback from teachers and caregivers on children’s language abilities (Green, Charman, McConachie, et. al. 2010) |
Descriptions of Participant Communication Skills
Various authors in the literature have different descriptions of Nonverbal (NV) and Minimally Verbal (MV) individuals with various criteria. Some criteria include less than 20 novel words in a 20-minute language sample, less than 20 intelligible words, 1-10 words, and 25 words or less. Some studies also mention the mean number of different words and the ability to imitate syllables.
Descriptions of NV individuals also vary. Some were described as severely language-delayed with no functional language in some studies, while others were reported to have few or no words. Some were classified as NV without clear indications of how this determination was made. Standardized measures did not always confirm the classification of NV. Table 2 provides a list of the measures used in the reviewed studies and the areas they assessed.
Discussion
Our review identified a limited number of intervention studies focusing on teaching expressive verbal communication to individuals with Autism Spectrum Disorder (ASD). Surprisingly, very few studies focused on NV individuals with ASD. Only two studies specifically focused on teaching verbal communication to NV preschool children, with unclear participant descriptions.
Research and strategic plans addressing the needs of individuals with ASD suggest evaluating pre-linguistic behaviors that may lead to verbal communication, such as joint attention, attentiveness, play, and social motivation. However, only a few studies included pre-linguistic assessments focusing on sound imitation, vocalizations, and eye gaze. While there is a vast amount of literature on teaching social and cognitive skills as precursors to verbal communication, the studies in this review aimed to enhance verbal skills in NV children, often excluding pre-linguistic behaviors.
Regarding NV children, some studies reported parents hearing their children produce words, even though the children did not have functional language. Most studies did not collect communication samples or behavioral assessments in natural settings, which is common in speech-language pathology. Studies should consistently include assessments of speech sound development, intelligence quotient scores, oral-motor skills, imitation, social withdrawal, and verbal skills.
Studies involving MV participants ranged in age from toddlers to adolescents. The number of spoken words varied greatly among NV and MV children, from less than 10 to 51-75. Teaching verbal communication to children over the age of 5 without expressive words or symbolic gestures may be more challenging, but older children can still learn to communicate verbally. Therefore, studies on NV and MV individuals should classify ages uniformly for better interpretation.
There is a consensus that teaching verbal communication to children over the age of 5 without expressive words or symbolic gestures poses challenges. Outcomes for toddlers and preschoolers with limited verbal skills differ from older children. Longitudinal studies show that both verbal and NV behaviors can predict the subsequent development of verbal communication. It is crucial for studies to consistently measure and report these areas to understand the benefits of instruction before the onset of first words.
Recommendations for communication assessment include clear identification of NV or MV participants, natural communication interactions, behavioral assessment of speech, standardized language tests, evaluation of echolalia, NV social behaviors, age considerations, estimates of cognitive ability, and more. Including these aspects in future studies would enhance our understanding of communication development in individuals with ASD.
Table 3.
An overview of the key components outlined in the definition guideline.
| Region | Recommendation | |
|---|---|---|
| Identification | It is important to clearly differentiate between nonverbal and minimally verbal participants. Accurate procedures should be used for identifying nonverbal children with ASD, while estimating word counts is crucial for minimally verbal children. | |
| Language Assessment | Context for Evaluation | When assessing language skills, include a natural interactive sample of communication, preferably with someone the child is familiar with. |
| Evaluation Methods | Language assessment should involve tasks such as identifying phonemes, forming syllables, producing words, and creating short phrases. Additionally, standardized vocabulary tests can be used for minimally verbal children with ASD. | |
| Reporting | While formal reports from parents and teachers are reliable, reports of early word use from untrained individuals may not be consistent. It is recommended to combine a variety of measures, including standardized tests and observations. | |
| Cognitive Assessment | In order to assess the impact of interventions on nonverbal and minimally verbal children with ASD, a cognitive evaluation measuring verbal and/or nonverbal reasoning abilities should be included. | |
Effective Interventions Based on Language Outcomes in ASD
It is essential to have a unified terminology to identify effective interventions tailored to the specific characteristics of individuals with ASD. Below are key classification suggestions that serve as significant milestones in the existing literature:
- Preverbal: Children under 18 months who do not demonstrate expressive verbal language. Identifying appropriate interventions early on is crucial, as some children may not initiate verbal communication by the age of 18 months, indicating potential developmental challenges.
- Nonverbal: Children over 18 months who exhibit inconsistent verbal expressions during evaluations, observations, and as reported by caregivers. This category may include characteristics such as echolalia and imitative speech.
- Minimally verbal: Individuals who use fewer words than expected for their age group, indicating lower levels of verbal output.
- Limited verbal: Refers to individuals with reduced verbal abilities beyond the minimally verbal level, typically using more than 50 consistent words.
The existing literature on interventions for nonverbal and minimally verbal individuals with ASD is diverse and limited, underscoring the necessity for a standardized approach to assessment. Developing effective interventions for individuals severely affected by ASD requires a deep understanding of their functioning, prognosis, and developmental trajectory. Challenges in categorizing participants consistently across studies impede meta-analytical efforts.
Exploring Communication Assessments in Individuals with ASD
Commonly used assessments like the ABLLS-R and VB-MAPP offer detailed insights into the communication abilities of individuals with ASD. While attempts have been made to use alternative descriptors such as “mute,” variations in defining this population may lead to missed research opportunities. Nonetheless, the comprehensive scope of the initial study decreases the likelihood of overlooking relevant literature. Some studies focusing on single-participant designs using a controlled ABAB methodology may not have been included due to our emphasis on studies with at least two participants, such as those employing multiple baseline designs.
Although some studies reviewed in this paper did not adhere to all recommended criteria for empirically-supported research, including sample descriptions, participant numbers, and replication, they were all peer-reviewed and met our inclusion criteria. Our examination did not specifically cover studies centered on Augmentative and Alternative Communication (AAC) as a treatment for nonverbal and minimally verbal individuals with ASD. Future research could explore parent-led implementation and educational initiatives utilizing various communication modalities beyond verbal interventions.
In summary, further research is warranted to establish best practices in supporting individuals with ASD as they acquire their initial vocabulary. The development of a comprehensive and standardized assessment framework is crucial to meeting the communication needs of individuals severely impacted by ASD.
Publisher’s Disclaimer
The Author Accepted Manuscript represents an unedited version approved for publication through peer review. The final published version may differ. As this analysis did not involve human subjects, IRB approval was not necessary. The authors disclose no conflicts of interest.