There is no vowel at the end of D O G: considerations for teaching speech production.
Deficits in speech and language development are one of the main features of autism (APA, 2004; Tager-Flusberg, Paul, & Lord, 2005). It has been estimated that 20 to 30 % of individuals with autism may not develop functional speech (Tager-Flusberg, Paul, & Lord, 2005). On the other hand, the development of speech and language is associated with better long term outcomes for individuals on the autism spectrum (Venter, Lord, & Schopler, 1992, Szmatari et al., 2003).
Although numerous approaches are currently being used to help children with autism speech and communication skills, many lack empirical evidence to support their efficacy. Structured behavioral teaching programs based on learning theory, however, have a strong evidence base and are widely used with much success (Goldstein, 2002). Several behavioral teaching strategies have been used to target speech and language. One such strategy is known as discrete trial instruction (DTI). In this highly structured, adult-directed approach, the therapist creates short learning opportunities (trials), often in a massed trial sequence (Lovaas, 2002). Each trial consists of an antecedent (a question or command), a target behavior (the learning goal), and a consequence (performance feedback). The antecedent may be accompanied by a prompt whic h is gradually faded. Typically, the DTI curriculum begins by targeting basic learning skills (e.g., joint attention, gross motor imitation, following single-step directions) which can then be used as the basis for targeting more complex skills (e.g., vocal imitation, speech production, requesting, labeling, etc.). For each learning goal, mastery is based on a performance criterion established in advance by the therapist.
A second set of behavioral approaches appear more natural and represent a hybrid of child-initiated and adult-directed strategies (Fey, 1986). Examples include natural learning paradigm (NLP) and incidental teaching (IT) (Koegel, Koegel, & Carter, 1999). The NLP protocol is designed to increase motivation by varying tasks, to increase responding by providing direct reinforcement, and to enhance generalization by providing loose structure and multiple exemplars (Lasky, Charlop, & Schreibman, 1988). The IT protocol is designed to increase the frequency of initiation by creating communicative temptations (e.g., providing a desired toy within sight but out of reach), waiting for a child to initiate communication, and then expanding his or her communicative attempts (e.g., Hart & Risley, 1968). For example, a therapist can place a cookie within sight but out of reach of a child who likes cookies. If the child signals his intent by pointing to the cookie and looking at the therapist, the therapist uses this initiation as a natural opportunity for language expansion (e.g., ""You want cookie? Say cookie"). NLP and IT both rely more on environmental arrangement, modeling, and shaping than on direct instruction or physical prompting (Rogers, et al., 2006). However, both approaches have been demonstrated to be effective for teaching communication skills to children with autism (Goldstein, 2002; Koegel, 2000).
Given that 20 to 30 % of children with autism do not develop functional speech, despite intensive intervention, there is a continued need to evaluate interventions in relation to the unique profiles of individual learners. In other words, when it comes to the selection of intervention strategies, one size does not fit all. Interventions must be fine tuned and matched to each learner's repertoire of abilities and limitations. For example, a child who does not spontaneously produce sounds and who demonstrates no imitation skills may require a more adult-directed program (e.g., DTI) to establish an initial vocal repertoire. However, a child who already has a vocal repertoire and who demonstrates spontaneous observational learning is far more likely to benefit from the use of more natural teaching procedures such as NLP or IT.
This article addresses the needs of those children, who, despite intensive exposure to procedures that rely primarily on modeling and shaping, fail to develop sound production or sound imitation repertoires. A review of selected literature on speech perception, articulatory phonetics, and speech production will be followed by a discussion of clinical implications in each area. Readers are cautioned that details regarding speech production training should not be the only consideration when designing programs for children who do not acquire vocal repertoires easily. Additional considerations could include, for example, the unique characteristics of motor speech disorders such as developmental apraxia of speech (DAS) and the potential value of using augmentative and alternative communication (AAC) systems. However, the scope of this paper is limited to speech production issues.
Speech Perception., Comprehension, and Production
Receptive language plays a critical role in the development of speech. Studies show that infants begin to attend selectively to speech almost from birth (Kuhl, 2000). In fact, there is evidence that infants attend to the characteristics of maternal speech in utero (DeCasper & Fifer, 1980; Jusczyk, 1997). Initially, infants only demonstrate a preference for speech over non-speech, regardless of the language spoken. By as early as nine months of age, they show a clear preference for their native language (Cutler, 1994; Kuhl, 2000). Kuhl (1994, 2000) proposed that infants develop a "language-specific filter" that is critical for speech and language development. Such a filter alters their speech perception abilities in a way that leads to greater precision through experience (Jusczyk, 1999; Paul et al., 2007).
To better understand this concept, consider a second language learner. For example, a native speaker of Japanese will have great difficulty discriminating between /r/ and /l/ because these sounds are not distinct phonemes in Japanese. This difficulty generally persists, even after training, and it is explained by the constraints of their language-specific filter. Studies have shown, however, that with the provision of multiple and exaggerated samples of speech across multiple speakers, the native Japanese speaker can be taught to make the distinction (McCleland, et al., 1999; Lively, et al, 1994). Feedback and reinforcement were not necessary to bring about this change. All that was needed was the right listening experience.
There is a direct link between speech perception and the development of phonology. Phonology is a linguistic term referring to the system of sounds in a language and the rules that determine how these sounds can be combined to form words (Owens, 2007). Speech production is dependent on the internal representation of a phonological system (Elbro, 1996). To develop this system, infants must first figure out how to extract word segments from the stream of speech to which they are exposed. Since there are no acoustic breaks between words within the speech stream, this is a considerable challenge. Current research suggests that infants learn to segment words out of the speech stream by (1) detecting sound patterns within and by (2) exploiting the statistical properties of these patterns (Kuhl, 2000). For example, it is a statistical fact that the sound sequences within words are more predictable than the sequence of sounds at word boundaries. Typical infants notice these patterns by about 8 months or even sooner, and this is believed to support the growth of word segmentation (e.g., Aslin, Saffran, & Newport, 1998; Bortfeld et al. 2005; Morgan & Denuth, 1996).
The earliest phonological representations in very young children are thought to be holistic in nature, consisting of single words and word combinations (Fowler, 1991). The "lexical restructuring hypothesis" proposed by Fowler (1991) and Walley (2008) suggests that, as a child's vocabulary develops, changes take place in the storage of phonological information. These changes involve gradual segmentation of phonological representations into smaller units and ultimately lead to the development of a conventional, language-specific phonological system. This implies that minimal or no receptive language skills will severely compromise or limit the development of phonology, and in turn, the development of speech.
Problems with receptive language have been described as a "red flag" in early development, specifically with regard to autism (Thurm, Lord, Li-Ching, & Newschaffer, 2007; Rogers, Wehner, & Hagerman, 2001). In a study comparing young children with autism spectrum disorders (ASD), children with language learning disorders (LLD) and children with typically language development (TLD), deficits in language comprehension were almost universal in the ASD group. This was in contrast to the LLD group, where problems with expressive language were noted but with intact language comprehension (Kjeelgard & Tager-Flusberg, 2001). One possible factor that may underlie these receptive language deficits in children with ASD is a general reduction in attention to spoken language. Studies have demonstrated that 2- to 3-year-old children with ASD demonstrate markedly less attention to child directed speech when compared to typical children (Paul, Chawarska, Fowler, Cicchetti & Volkmar, 2007).
Reduced attention to speech is problematic for a number of reasons. First, it has been shown that speech perception improves with experience. Less experience due to less attending can diminish the development of critical speech perception skills. Compromised speech perception abilities will not only affect the development of speech but also impact on the development of language. The delay in language development would affect the input needed for effective "lexical restructuring", and in turn, compromise phonological development.
In sum, comprehension of spoken language is critical for the development of functional speech. An individual may develop a visual language system, such as sign language or picture systems, and this may be critical for effective communication. However, for speech production to be acquired, a child must learn to comprehend spoken language.
It is important to evaluate the spoken language comprehension skills of a young non-verbal child with autism. If the evaluation reveals little or no speech comprehension, it is possible that the child is not paying sufficient attention to speech. It can not be assumed that such a child is even attending to the acoustic features of speech that are important for speech development. In fact, many children with autism demonstrate a significant preference for visual information, in some cases, to the exclusion of auditory input. Consider, for example, a young child who has learned to follow individual one-step directions when the instructions are presented in isolation (e.g., "stand up", or "clap hands") but who does not discriminate between these same directions when the instructions are presented individually in a sequence. One hypothesis that could explain this difficulty is that the child is not attending to the relevant feature of the task (i.e., the speech signal) but may instead be over-focusing on accompanying visual information (e.g., the model or gestural that is provided to facilitate performance). In fact, a child may be ignoring the speech input completely. In this case, it will be necessary to help a child shift his or her attention to the speech signal, and this will require strategies for making the speech signal more salient to the learner.
A similar problem may occur with respect to the speech signal itself. Normal listeners actually attend to two dimensions of speech simultaneously, including the segmental dimension (i.e., vowels, consonants, syllables, words) and (2) the suprasegmental dimension (i.e., pitch, volume, intonation, and prosody that extends across segmental features). It has been suggested that young children with autism may over-focus on the pitch, volume, and intonation of the speech stream (Bishop, 1997; Lepisto et al., 2008), and that this over-focus on the suprasegmental dimension may actually distract these children from attending to the speech segments. As in the case of visual over-focus, a child who ignores the segmental features of speech will need some direct support for shifting his or her attention to speech segments.
One approach for dealing with the problem of over-focus issues is by using the suprasegmental features of speech to make the segmental features of speech more salient. Specifically, a suprasegmental prompt (e.g., exaggerated intonation or melodic intonation) can be used for this purpose. A child's preference for volume and intonation may encourage increased attention to the spoken command, particularly if these suprasegmental features are exaggerated and distinct for each command. Two or three commands with distinct intonation patterns may be used until the child learns to discriminate between them. Once the child discriminates between the suprasegmental patterns unique to each command, the intonation prompts must be faded systematically until the commands consist only of the relevant segmental stimuli with normal suprasegmental features.
While this process may seem complex and in some cases, time consuming, it may be the key for helping a child pay attention to speech segments. Given the important role of language comprehension as a basis for speech development, it will probably be time well spent.
Phonetics and Sound Production
The previous section addressed the role of language comprehension in the development of speech. Now we will consider the role of sound production per se. Regardless of one's theoretical perspective on language development, it is widely agreed that infants and toddlers typically engage in a process of speech sound development that requires no direct physical prompting from adults. Rather, a young child's ability to produce all of the sounds of his or her language and then to combine these sounds into intelligible words develops gradually over the first few years of life, and it is observed in the form of successive approximations to the speech in the child's linguistic environment.
Unfortunately, for some individuals with autism, this process does not take place, regardless of the amount of input or reinforcement provided. In most cases, these are individuals who exhibit minimal spontaneous sound production and no sound imitation skills. After significant efforts to increase a child's spontaneous vocalizations have been unsuccessful, it may be necessary to take a more direct approach and actually provide physical prompts for sound production.
Children who acquire language normally do not need physical prompts to acquire a sound production repertoire. However, physical prompts can be very effective for helping some non-verbal children with autism begin the acquisition process. To design appropriate prompts, it is essential for the therapist to understand the dynamics of sound production. Incorrect use of physical prompts will typically result in incorrect sound production, and this will ultimately compromised speech intelligibility.
The International Phonetic Alphabet (IPA) is typically used to represent individual speech sounds, since there are 45 phonemes in English and only 26 letters of the alphabet. Some IPA symbols look like English orthographic symbols, and others look quite different. An excellent chart representing the complete set of American English IPA symbols (including auditory examples) is available at the following link, which was created in 2001 by members of the Language Sampling Project in the Anthropology Department of the University of Arizona: http://www.ic.arizona.edu/~lsp/IPA.html Table 1, below, present some examples of IPA symbols that will be used in the remainder of this paper. These examples are accompanied by words to illustrate the acoustic form. Notice that all IPA symbols are written between slash marks.
Generally speaking, all speech sounds are produced on exhaled air, and all can be classified as either consonants (C) or vowels (V). Specific speech sounds are produced by moving the articulators (cheeks, lips, teeth, palate, tongue, and jaw) to shape the vocal tract and the airstream in characteristic ways. During vowel production, air passes through the speech mechanism in a relatively unobstructed manner while the vocal folds vibrate. Differences between vowel sounds are due primarily to differences in the posture of the tongue, lips, and jaw. However, consonants are produced with much closer (and often complete) contact between two articulators. In fact, consonants can be classified with respect to the place of articulation (i.e., which parts of the mechanism come into close proximity), the manner of articulation (i.e., how the parts make contact) and voicing (i.e., whether articulation is accompanied by vocal fold vibration). For example, /p/ is classified as a voiceless bilabial stop because there is no vocal fold vibration, the lips come together, and the airstream is stopped completely before it is released in a puff. In contrast, /z/ is classified as a voiced ligua-alveolar fricative because it is produced with vocal fold vibration, the constriction occurs between the tongue and the alveolar ridge, and the airstream, while never completely stopped, is constrained enough to make a hissing sound. The link provided above leads to charts showing how all American English consonants are classified in relation to manner and place. For additional details about phoneme classification please see a number of other excellent sources on this topic (e.g., Menn & Stoel-Gammon 2004; Bankson & Bernthal, 2004; Pena-Brooks & Hegde, 2000).
Information about the manner, place, and voicing of speech sound production has direct application to program design. When two phonemes differ only with regard to the presence or absence of voicing, they are considered cognates. For example, /t/ and /d/ are both stops (manner) and they are both classified as lingua-alveolar (place) sounds because they are produced by contact between the tongue and the alveolar ridge. However, one is voiced (/d/) and the other is voiceless (/t/). A common error made in sound imitation programs is to teach only the voiced cognate of a pair. In some cases, the voiceless counterpart is taught but a vowel is added to the model. For example, the model /t./ is sometimes provided to prompt the production of /t/. This can lead to the addition of /./ to words ending with voiceless /t/. For example, a child may learn to say /kaet / rather than /kaet/.
Knowledge of manner, place and voicing distinctions can be very helpful in the selection of prompts. For example, it is typically quite easy to teach a child to produce /a/ and /m/. These are highly visible and early developing phonemes. It is often not too difficult then, using a chaining procedure, to teach the child to produce the CV combination /ma/. Now, perhaps the next phoneme you'd like to teach is the stop /b/. What would be a reasonable prompt to employ? This might be a difficult question until you think about the existing sounds in the child's repertoire. The child can produce /ma/ and you'd like to promote /b/. If you broke down /ma/ into its manner and place, you'd find that /m/ is a voiced bilabial nasal sound produced by closing the mouth, lowering the velum, and directing the airstream through the nose. In contrast, /b/ is a voiced, bilabial stop sound produced by raising the velum so that the air is directed through the mouth. Given the likelihood that the child will attempt to produce /ma/ when asked to imitate /b/ (since /b/ is not yet in the child's repertoire), the logical prompt would be to model /b/ and then gently hold the child's nose closed. The child's attempt to produce /m/ will result in the actual production of the desired target (/b/), because the air stream can not exit through the nose but must exit through the mouth. Systematic fading of the prompt should result in the child learning to elevate the velum to achieve the same result.
There is probably no area of sound programming where knowledge of speech production is more critical than in vowel production. Vowels serve as the nucleus of a syllable. They are typically developed early and carry a great deal of meaning in speech (Raphael, Borden, & Harris, 2006). Vowels are classified according to two key dimensions based on the position of the tongue in the oral cavity: high versus low and front versus back. For example, /o/ is a low back vowel because the tongue is low and back in the mouth. On the other hand, /i/ is a high front vowel because it is produced by raising the tongue high in the front of the mouth.
Listeners perceive a specific vowel based on a pattern of frequencies, specifically formant frequencies (Raphael, Borden, & Harris, 2006; Stevens, 1989). Formants are the meaningful frequency components of human speech. These frequencies are determined by the size and shape of the vocal tract and oral cavity (Imagine Sondra Bullock playing the wine glasses in Miss Congeniality). The vocal tract's shape is affected by the elevation of the tongue as well as whether it is in the front or back of the mouth. For example, /i/ is considered a high front vowel because the tongue is high in the mouth and forward, sitting just behind the alveolar ridge. The phoneme /?/ is a low back vowel with the tongue low and far back in the mouth. This information is essential when prompting vowel production because failure to help a child position the tongue appropriately will neutralize the vowel (i.e., make the vowel sound like /?/). That is, the jaw and lips will be prompted to be in the correct place but the tongue will simply sit in the middle neutral position for all vowels. This will result in many of the vowels sounding almost alike in running speech, greatly compromising speech intelligibility.
Based on the above information about vowel and consonant production, one last recommendation will be offered to support the selection of prompts to target sound production. Assume that you would like to introduce /d/ into the repertoire of a child who is capable of producing /a/, /i/, /./, /m/ and /b/. In this case, therapists often model /d./ to evoke /d/. However, since /d/ is not already in the child's repertoire, he or she is likely to imitate only the accompanying vowel (/./). When a physical prompt is used to assist the child in producing /d/, it typically consists of a tap behind the chin to promote jaw elevation and lingua-alveolar contact. However, a careful analysis of the sounds within the child's repertoire suggests an easier approach. Recall that the child has three vowels within repertoire: /a/. /./ and /i/. Two are low back vowels and one is a high front vowel. If the child were presented with the model /di/ instead of /d./, he or she would probably imitate /i/. The difference in this case, however, is that the tongue would be almost in the lingua-alveolar position needed for the production to /d/. This would result in far less prompting than if the child were producing /./.
The perceptual judgment or ability to identify simple single -syllable words (e.g., dog, hat) is influenced by two key variables: (1) lexical knowledge and (2) the duration of the vowel within a word (Fowler, 1991; Sutherland & Gillen, 2007). Specifically, vowel duration provides information to the listener as to the presence of a voiced versus a voiceless final consonant. Voiced stops are characterized by longer vowel duration (Hogan & Rozsypal, 1980; Blaney & Hewett, 2007).
The lexical knowledge or size of the listener's vocabulary has a direct impact on speech perception as well. Language experience results in a form of "mapping" that can actually alter perception (Kuhl, 2000). When a listener hears a word, he or she searches the lexicon for a match. Obviously, the more developed the lexicon, the better the likelihood of an accurate match. In the case of word imitation programming for children with autism, many times the words provided as models are not within the child's lexicon, thereby compromising the child's ability to perceive the word accurately.
It is normal for toddlers to make a range of phonological processing errors during early speech development. Two of the most common errors present in early speech include word-final devoicing and final consonant deletion (Dodd, 1995). Word-final devoicing results when the speaker produces the voiceless cognate rather than the voiced phoneme (e.g., saying /d? k/ instead of /d? g/). Final consonant deletion occurs when a child simply omits the final consonant in a word (e.g., saying /d? / as instead of /d? g/). These phonological processing errors are typically resolved without any intervention. It is assumed that, as receptive vocabulary grows, and as speech perception is refined, a child is more likely to perceive a word accurately and, in turn, to produce it accurately.
It is important to understand how speech perception can impact speech production when teaching a child with autism how to imitate words. It is highly probable that the child will demonstrate either final consonant deletion or final consonant devoicing within the early stages of the word imitation program. This is likely to occur for two reasons. The first is that the child's speech perception skills may be limited as a result of decreased attention to speech. The ability to detect the longer vowel duration to cue the presence of a voiced or voiceless consonant may be compromised. The second issue involves the fact that the child's lexical development will likely be delayed or idiosyncratic (Perkins, Dobbinson, Boucher, Bol, & Bloom, 2006; Gerenser, 2004). Limited lexical development would reduce the likelihood of the kind of "mapping" needed for accurate perception of the whole word.
How does this information affect the word imitation programming? Knowledge of the fact that final consonant deletion is not only probable but actually expected in early word imitation can help the clinician avoid the common mistake of overemphasizing the final consonant as a prompt. For example, if a therapist or instructor provides the model for the word /d? g/ for the child to imitate, it is quite probable that the child's production will sound like /d? /. Some therapists or instructors will then attempt to prompt the more accurate production of the word by overemphasizing the final consonant and modeling /d? g./. Unfortunately, this most often results in the child imitating the incorrect model in its entirety and producing the word /d? g /, with the vowel sound at the end. In many cases, the vowel sound then gets attached to the end of all words, ultimately making the child's word production unintelligible to the novel listener.
Two alternative prompting procedures can be considered. The first is to overemphasize the vowel as opposed to the final consonant. The vowel should be lengthened in an exaggerated way for words with a voiced final consonant. Listeners are more likely to perceive the word as having the voiced final consonant if the vowel is produced in a lengthened manner (Blaney & Hewett, 2007). The second option would be to substitute the voiceless final cognate at the end of the word in order to promote the general vocal tract qualities of the actual word. For example, to emphasize the final consonant in the word dog, the clinician could model /d? k/ as opposed to /d? g/. Placing emphasis on the final voiceless consonant /k/ would not require the addition of the vowel. Although the production of /d? k/ instead of /d? g/ is not accurate, it is more intelligible than the alternative /d? g /.
Summary and Conclusion
Despite significant advances in programming to promote speech development in individuals with autism, some children remain essentially nonverbal or minimally verbal. Factors contributing to the speech challenges of this group include severe cognitive limitations, motor speech disorders, and a combination of the two. Careful and in-depth evaluation is necessary to ascertain the factors that could be contributing to the limited progress in speech development for any particular child. Unfortunately, even the most skilled analysis may sometimes fail to identify the key factors.
Given the significant challenges of this group of children, it is essential that all of the available research and literature in speech development and speech disorders be consulted when developing programs. Applied behavior analysis has a great deal of support as a highly effective intervention model for learners with autism (Smith, Groen, & Wynn, 2000; Sallows & Graupner, 2005; Lovaas, 1987). However, behavior analysts are not always familiar with the speech perception or speech production literature. This paper reviewed key features of this literature and discussed clinical applications of these features. Collaboration between ABA and SLP professionals is recommended when supporting children with autism who have severe challenges in the development of speech production.
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Author Contact Information
Joanne Gerenser, Ph.D., CCC-SLP
Executive Director of the Eden II School for Autistic Children
150 Granite Ave. Staten Island, NY 10303
Phone: (718) 816-1422
Table 1. Examples of IPA Symbols Vowels Consonants IPA Symbol Example IPA Symbol Example /a/ Hot /m/ Mop /ae/ Cat /p/ pit /./ Hug /b/ bit /?/ Dog /t/ tab /i/ me /d/ dab /?/ about /o/ go