Objectives: The study focused on promoting expressive phonological skills in 1 Greek-speaking child with autism spectrum disorder (ASD) and comorbid speech sound disorder (SSD). Based on the phonological neighborhood density framework, it was hypothesized that the experimental manipulation through clinical implementation of phonologically overlapping stimuli would yield positive expressive phonology gains relevant to ASD. Participant and Methods: A multiple-baseline single-subject design was implemented. Three baseline sessions measured expressive phonology variables. Sixteen biweekly 30-min intervention sessions were carried out for a period of 2 months. Dependent variables included phonetic inventory size, proportion of consonants correct, occurrences of phonological processes, and percentage of whole word matches elicited via specific word probe stimuli. The Intelligibility in Context Scale was completed by the child’s teacher prior to the initiation of intervention and at a follow-up session. Experimental stimuli were grouped together in phonologically dense cohorts. Results: Comparison between pre-test and post-test measures revealed expressive phonology gains across all measured variables. Follow-up session results showed generalization of expressive phonology gains on untreated targets. Conclusions: Significant expressive phonology gains were achieved through the implementation of phonologically similar word stimuli within a systematic intervention protocol with the implementation of specific word-level variables. The findings supported this treatment approach for a child with ASD and SSD, while providing evidence for the phonological density advantage from a cross-linguistic perspective.

Children diagnosed with autism spectrum disorder (ASD) constitute a considerably heterogeneous group with linguistic development forming no exception. Heterogeneity is observed through developmental trajectories which map various aspects of communication including expressive and receptive language skills, social pragmatic profiles, and behavioral/emotional expression output across languages and across cultures [1, 2]. Despite this diversity however, research findings convincingly revealed that communication deficits and late onset of language emergence form the core characteristics of ASD [3]. Children with autism fail to achieve developmental milestones at age-expected levels, can be slow in learning to talk, or many times, do not learn to talk at all [4]. Although some children with ASD reportedly begin to produce meaningful speech during the first year of life, shortly after, this skill declines and eventually ceases around the age of 18 months [5, 6]. Plausible explanations for this developmental arrest align with neurodevelopmental underpinnings which affect brain circuitry in areas crucial to social-communicative and expressive speech development [7-9].

Over the past 15 years, phonological and articulatory skills in ASD have been studied extensively, due to the remarkable prevalence of speech sound disorders (SSD) documented in ASD speech profiles [10-12]. Specifically, reports from English corpora indicated that the prevalence of ASD comorbidity with SSD ranged between 150 and 20% [13]. Within ASD populations however, findings related to the existence, characteristics, and severity of SSD remain equivocal. Although earlier reports on phonetic, phonological, and prosodic development reported age-appropriate speech profiles [14, 15], recent reports on younger children with autism revealed atypical speech patterns. These were characterized by immature syllable structure, restricted phonetic inventories, speech sound distortions, inconsistent word productions, atypical occurrence of phonological process use, persistent use of jargon speech, late emergence of meaningful expressive vocabulary, and restricted use of phonological contrasts [10, 11, 16]. Similarly, young autistic children presented with oral motor difficulties and failed diadochokinetic tasks, had difficulties producing successive syllable repetition tokens, and lacked phonological stability across multiple productions of the same words [17-19]. Despite inconclusive evidence as to the loci of phonological difficulties in ASD, various characterizations regarding the nature of such speech challenges advocated for the presence of a multideficit motor speech disorder consistent with child apraxia of speech. Presumably, oral motor deficits hindered typical phonological planning and phonetic/articulatory programming [13, 20]. Similarly, atypical phonetic patterns in older children with ASD have been characterized as nondevelopmental sound distortions such as phoneme-specific nasal emission, lateralization of /s/ and residual erred realization of /r/ [13, 16]. It was further concluded that nondevelopmental distortions of speech sounds appeared frequently in the speech of children with ASD and persisted over time. These errors were variable, did not resolve easily and affected speech intelligibility. Regarding phonological patterns, findings suggested the occurrence of phonological processes including velar fronting and atypical initial consonant deletion [21]. Such findings bear clinical and research insights and underscore the importance of timely early intervention. Moreover, research findings are of paramount importance as they inform evidence-based practice (EBP) and contribute to data-driven analyses and theory-motivated intervention.

Yet, despite the plethora of investigations regarding description and documentation of atypical speech profiles in ASD, information on treatment to ameliorate such challenges remains sparse [10, 17]. The paucity of EBP investigations on inducing phonological gains in ASD highlights the need for advancing systematic and theory-motivated intervention protocols. Moreover, data from a cross-linguistic perspective regarding ASD/SSD interaction through EBP intervention efficacy remain understudied [22, 23]. Notably, cross-linguistic investigations related to atypical speech and language development underline the role of typological properties of a given language on speech production phenotypes. Linguistic diversity determines what is spared and what is lost in pathological communication profiles [24-26]. Furthermore, idiosyncratic properties of the ambient language (e.g., prosodic and phonotactic variables) determine the selection of intervention stimuli, guide treatment goals, and affect therapy outcomes [27-29]. To this end, early intervention with a focus on promoting speech intelligibility is of paramount importance because a robust phonological system constitutes the “backbone” for the emergence of more complex linguistic subsystems [30]. This is because, during the early stages of language development, segments and prosodic templates form the “building blocks” for later lexical, grammatical, and morphosyntactic development [31]. Furthermore, enhanced phonological representations map on to phonological awareness skills which, in turn, form the cornerstone ability for literacy development [32].

Recently, results from investigations in the area of developmental language disorders and ASD including the COST Action IS1 406 consortium titled “Enhancing Children’s Oral Language Skills across Europe and beyond” and the Child Language Committee of the International Association of Logopedics and Phoniatrics, respectively, advocated for the capitalization of research findings in supporting treatment efficacy in variable linguistic and cultural contexts [1, 27]. However, findings revealed that the majority of speech-language pathologists who serve children with communication disorders are either not familiar with EPB practices or have limited exposure to theory-motivated interventions. As a result, research information and resources related to EBP and theory-driven therapy might not reach the mainstream intervention contexts [23]. To this end, treatment efficacy, therapy decisions, therapy goals, and ultimately treatment outcomes need to be validated through processes that can be experimentally manipulated [33].

In line with the aforementioned, an emerging body of research vis-à-vis lexical organization models brings forward the role of word form variables on inducing expressive phonological gains in children with SSD [34, 35]. It has been proposed that young children capitalize on the statistical properties of the input as a way to optimize the process of language development [36, 37]. One such property is neighborhood density (number of words differing in phonological patterns by 1 phone which is deleted, added, or altered) [38]. While DENSE neighborhoods (DN) consist of many words with overlapping phonological structure (i.e., rat overlaps with mat, bat, cat, sat, rat, fat, tar, pat, etc.), SPARSE neighborhoods (SN) on the other hand contain fewer words with phonological overlaps (i.e., room, rule, root). In this context, phonological density constitutes an important aspect of word form organization because of its differential impact on phonological learning [34-38]. Empirically, typically developing toddlers are shown to imitate more accurately segments from DN as compared to sounds from SN. This is because phonologically similar words (e.g., words residing in DN) “force” children to build finer-grained phonological representations which in turn enhance the production of diverse phonological contrasts necessary for marking lexical meaning [30, 31].

Furthermore, recent investigations have focused on the impact of the DN advantage on promoting expressive phonological gains in children with SSD [34-37]. Findings from English corpora have convincingly demonstrated that the systematic implementation of stimuli from a DN yields significant phonological gains and contributes to the generalization and speech gains on untreated segments [35]. Overall, phonologically dense neighborhood effect constitutes an optimum trigger for inducing sustainable speech intelligibility gains [34]. Potentially, children with protracted phonological profiles, in this case children with ASD and comorbid SSD deficits, present a unique opportunity for advancing testable, theory-motivated hypotheses related to the selection and implementation of target stimuli during intervention [36-38]. In view of the above, a number of themes emerge: (a) the need for systematic examination of theory-driven intervention in children with ASD who present with protracted phonological development and (b) treatment efficacy of phonological intervention through the im-plementation of phonologically dense words in cross-linguistic contexts.

The present study aspired to add to this line of research through the implementation of phonologically similar targets on inducing expressive phonological gains in a bidialectal Cypriot Greek-speaking (CG) child with ASD and concomitant SSD. Given the impact of the DN advantage on expressive phonological gains in children with SSD, it was hypothesized that such effects would also induce speech gains in children with ASD and accompanied SSD. The implementation of word stimulus cohorts from phonologically dense neighborhoods would allow the examination of treatment efficacy through the implementation of specific word targets for which children might show production constraints (e.g., similarly sounding words). Potential positive gains might set the foundation for enhancing the child’s transition from unintelligible to intelligible speech.

The CG Dialect

The linguistic variety investigated in this study is CG, a variety of Standard Modern Greek (SMG) [39, 40]. Although CG is the everyday variety used by most speakers on the island of Cyprus, SMG is used in certain official settings such as school classes and the media while CG dominates in informal everyday communication. The Greek-speaking populace of Cyprus is diglossic in the sense that CG is the vernacular form (low variety) used in everyday communication whereas SMG (as the high variety) is used in educational settings, government bodies, and the media. Recent reports propose the emergence of a dialectical continuum of CG with an emerging “koine” or “urban” form of CG [41]. Its consonantal phonetic inventory contains 31 singletons, most of which have geminate counterparts. There are bilabial, labiodental, dental/alveolar, palatal, and velar phonemes. Regarding the manner of articulation there are stops, fricatives, affricates, nasals, liquids, and glides. The liquid segment /r/ is trilled. In CG voiced stops are prenasalized with voiceless cognates being either unreleased or aspirated. The /n/ and /s/ may also occur in word-final position. CG contains postalveolar fricative and affricates as well as geminates (double segments) differing from singletons mainly in duration [42]. Currently, developmental databases regarding syllable structure use in CG child speech remain sparse [43]. Thus, for the purposes of the current investigations the author analyzed the syllable structure of 600 target word items found in the CG lexical acquisition list CYLEX, a parentally reported lexical development tool [41, 43]. Percentages of syllable structure occurrences from the 600 uninflected words were as follows: CVCV (28%), CVCVCV (22%), CVCVCVCV (10%), CCVCV (8%), CVCCV (6%), and VCV (6%). The rest of the word targets (20%) consisted of variable monosyllabic, trisyllabic, and multisyllabic structures. Based on these observations, it was concluded that the predominant syllable structure one might encounter in CG was the disyllabic CVCV and trisyllabic CVCVCV. Stress pattern analysis was also performed, and results revealed 10 monosyllables, 285 disyllables (183 trochees (65%) and 102 (35%) iambs), 208 trisyllables (28 targets stressed on the ultimate, 120 targets on the penultimate, 60 on the antepenultimate), and 97 multisyllables.

Participant and Intake

The participant was a 4-year-old CG-speaking boy with a diagnosis of ASD based on the criteria from the Diagnostic Statistical Manual, 5th ed. (DSM-V) [44] and the Autism Diagnostic Observation Scale [45]. He was assessed by a certified child psychiatrist in Nicosia, Cyprus. An initial diagnosis of speech and language delay was conducted by his kindergarten speech therapist using a series of available assessment batteries adapted in CG which are used for clinical and research purposes [46, 47]. The child was referred to the Cyprus University of Technology (CUT) Rehabilitation Clinic for further phonological evaluation due to parental concerns regarding the lack of expressive language progress exhibited by the child. Phonetic and phonological skills were examined with the use of an adapted version of the Phonological Assessment Test of the Panhellenic Association of Logopedics [48]. In addition, a 15-min free language sample assessed skills in connected speech. Analyses corroborated with previous reports regarding the child’s phonological profile and confirmed significant phonological delays. The child continued to present with a restricted phonetic inventory (/p/, /t/, /n/, /k/, /m/), used immature syllable structure (vowel-consonant-vowel VCV), lacked the use of trisyllabic and multisyllabic words, and expressed significant occurrence of phonological processes (unstressed syllable deletion, word-initial onset deletion, cluster reduction and regressive assimilation). These patterns rendered his speech unintelligible. The most prevalent syllable structure used was consonant-vowel (CV), vowel consonant (VC), vowel-consonant-vowel (VCV) and consonant-vowel-consonant-vowel (CVCV) in its reduplicated form (e.g., [‘mama], [‘tata]). The child was invited to participate in an ongoing phonological intervention study on CG-speaking children with SSD which at the time was being conducted at the CUT “TheraLab” research laboratory. Parents accepted to enroll their child after signing a written consent. The participant, a monolingual CG speaker, came from a middle socioeconomic status family [49]. According to parental report he had no significant history of otitis media with effusion. Furthermore, during the intake meeting he passed a hearing screening test at 500, 1,000, 2,000, and 4,000 Hz presented at 25 dB HL [50]. At the time, the child was enrolled in a speech and language community-based language enrichment group therapy program with a focus on social pragmatic aspects across the communication spectrum. However, it should be noted that during the course of the intervention period, he had stopped attending the language enrichment program due to summer holiday recess.

Research Design

The current examination employed a single-subject multiple baseline research design [51, 52]. A 3-point baseline was followed by 16 half-hour individual treatment sessions administered twice a week over a period of 2 months (approx. 13 h of direct one-to-one sessions). A post-test session was conducted 1 week after the completion of the last intervention session succeeded by a follow-up session administered 2 months later. The author conducted all sessions.

Baseline

The purpose of the baseline was to establish stability on the repeated dependent measures in the absence of treatment. It was completed across 3 sessions over a period of 2 weeks. Phonetic and phonological skills were examined with the use of repeated administration of a 50-word probe corresponding to colored digitized pictures inserted into a PowerPoint file for presentation. These consisted of 30 bisyllabic, 10 trisyllabic, and 10 multisyllabic targets (see the Appendix). The list attempted to sample the majority of singleton consonants of CG across all possible word positions and stress patterns, excluding affricates and clusters. The particular probe list has been used for similar research investigations in CG-speaking children with SSD [53]. Each session was audiorecorded using a Marantz PMD-222 digital recorder. An Audio-Technico flat unidirectional microphone was placed on the experimental table directly in front of the child. Recorded speech samples were phonetically transcribed using the International Phonetic Alphabet [54]. Phonetic transcriptions were performed on all utterances produced by the child and were coded on the bases of independent and relational analyses [55]. These analyses yielded 6 kinds of information: (a) phonetic inventory size, (b) syllable structure use, (c) proportion of consonants correct, (d) occurrence of phonological processes, (e) percentage correct of Whole Word Matches metric (WWMs) scored as 0 for no production match and 1 as total match [56], and the Intelligibility in Context Scale adapted in Greek (ICS) completed by the child’s teacher [57]. The ICS is a 5-point scale allowing the assessment of a child’s overall speech intelligibility in connected speech (details are provided in the section below). Stimulability of all sampled segments was also performed, and information was used for the construction of experimental-stimulus cohorts described below. There were no significant changes in the child’s speech profiles between first and last baseline.

Experimental Stimuli

The experimental stimuli consisted of words from quasi-phonologically dense neighborhoods. In this context words differed from each other by 1 or 2 consonantal segments and 1 vowel. Stimuli were grouped together in blocks of disyllabic and trisyllabic cohorts containing 4 members each. The construction of each target word was based on the child’s articulatory knowledge in the sense that each word member included at least one stimulable phoneme (usually in word-initial position). This paradigm was based on research findings suggesting that when the selection of treatment stimuli considers the child’s existing articulatory knowledge (e.g., segmental stimulability), increased speech intelligibility and significant output gains on more complex segments emerge [58]. The word targets were depicted as digitized colored pictures inserted into PowerPoint files. All were selected from a variety of online resources and from the author’s private art collection of clinical tools. A total of 16 clusters of word tests were used through the intervention phase (8 disyllabic and 8 trisyllabic). The disyllabic clusters were randomly selected and were taught during treatment sessions 1–8 (first month of intervention), followed by comparable procedures with the implementation of the 3-syllable cohorts implemented across sessions 9–16 (second month of intervention). Each experimental session allowed the implementation of 2 cohorts. A schematic representation of the intervention timeline is presented in Figure 1. The complete list of experimental word stimuli cohorts is reported in the Appendix.

Fig. 1.

Investigation timeline scheme. ICS, Intelligibility in Context Scale.

Fig. 1.

Investigation timeline scheme. ICS, Intelligibility in Context Scale.

Close modal

Intervention Procedures

During the experimental session, the child interacted with the examiner and/or the caregiver while playing with various sets of toys. At the beginning of each session, the participant was familiarized through auditory bombardment with one randomly selected target cohort and its corresponding members depicted on pictures. After the examiner had presented each word target 5 times, the child was prompted to either produce spontaneously or imitatively the corresponding word given at least 5 opportunities. In case of no response, the participant was prompted to either utter the target words via phonetic/articulatory prompting (e.g., when given the word-initial onset) or produce the target through delayed imitation. All phonetically transcribed productions were coded and analyzed as correct or incorrect depending on the child’s production.

Data Reduction

Across all sessions, including baseline, post-test and follow-up, approximately 700 tokens underwent analyses. Only productions, either spontaneous or imitated, corresponding to assessment and treatment targets were analyzed. The repeated dependent measures during the baseline (pre-test), intervention phases, reassessment session (post-test) and follow-up were analyzed as per each recorded session. Phonetic inventory size included the number of singleton consonants presented in the child’s speech output as per productions of the probe targets. The same database was used for calculating syllable structure use. The proportion of consonants correct was calculated by counting the number of segments correctly produced over the total number of segments. For calculating phonological process occurrence, the study employed measures used in assessing and analyzing phonological output in young children [48]. For example, all instances of process occurrence (collapsed monosyllabic, bisyllabic, and trisyllabic productions) were counted over the total number of targets produced by the child. The percentage of correct on WWMs corresponded only to words produced accurately, including imitative realizations, with metric scoring of 0 for no production match and 1 as total match [56]. The ICS was scored numerically from a scale of 1–5 (1 = always unintelligible, 2 = usually unintelligible, 3 = sometimes unintelligible, 4 = rarely unintelligible, 5 = never unintelligible) [57].

Transcription Reliability

For purposes of test-retest reliability, a second assessor trained in phonetic transcription analyzed approximately 10% of randomly selected recorded samples coding as per the initial and final intervention sessions. Reliability on the relevant categories was based on the number of agreements divided by the sum of agreements and disagreements after the 2 transcribers had jointly listened to the targets and had compared their transcriptions for phonological inventory size (80%), proportion of consonants correct (90%), phonological processes (90 and 80% for unstressed syllable deletion and word-initial onset deletion, respectively), WWMs (100%), and syllable structure use (100%).

The dependent variable was expressive phonological gains exhibited by the child according to his performance on phonetic and phonological measurements listed in the previous section. Performance on the parameters examined was compared between pre-test (past baseline session) relative to post-test data. Follow-up measures were compared to post-test performance with the exception of the ICS which was compared to data obtained at the pre-test assessment. The results are presented in the form of descriptive statistics. In the current study, numerical score measures were variable and included percentage scores and raw numbers. Thus, a comparative magnitude of the treatment effect could not be performed directly in an isometric and isomorphic fashion [59]. For this reason, the paper discusses the direction of speech output gains on the bases of plotted trajectories relative to pre-test and post-intervention and follow-up sessions. A visual inspection of data plotting suggested an overall upward direction on all dependent variables between pre-test and post-test assessments. It was noted that the child gained 10 new consonant segments (from 5 pre-test to 15 post-test segments), with percentage of consonants correct shifting from 20 to 30%. There was an improvement in percentage correct on WWMs which increased from 12% (6/50) to 70% (30/50) between pre-test and post-test timepoints, a pattern that was also evident during the follow-up with the child maintaining 80% accuracy (16/20) as multisyllabic word accuracy increased from 20 to 60%. He also exhibited less use of phonological processes from 100 to 30% and from 100 to 65% for unstressed syllable deletion. Consequently, there was a concomitant increase in the use of more mature syllable structure. Specifically, the child exhibited less use of VCV and more use of CVCV as well as CVCVCV patterns. Taken together, all measures contributed to speech intelligibility gains as measured by the ICS scale scores showing an increase from 1 to 4. Pre-test, post-test and follow-up data are reported in Table 1.

Table 1.

Subject information and measures during pre-test; post-test, and follow-up sessions as a function of probe list production

Subject information and measures during pre-test; post-test, and follow-up sessions as a function of probe list production
Subject information and measures during pre-test; post-test, and follow-up sessions as a function of probe list production

The study set out to investigate speech intelligibility gains in 1 child diagnosed with ASD and concurrent SSD with a focus on promoting speech intelligibility through the implementation of phonologically similar words (e.g., phonologically dense targets). The use of phonologically similar targets was implemented systematically over a course of intervention sessions. This is the first study to address intervention in ASD/SSD in an understudied dialectal variation of SMG.

Comparisons between the pre-test and the post-test sessions revealed remarkable gains across measured variables. Specifically, the findings revealed improvements in phonetic and phonological domains. Speech output measures revealed segmental gains along with a reduction of structural phonological processes specific to word-initial onset and unstressed syllable deletions. The latter 2 variables contributed to the emergence of more mature syllable structure instances including CVCV and CVCVCV. Phonetic inventory size increased from 5 to 15 segments, which was established across word-initial, word-medial and word-final positions. Speech gains were also marked by the emergence of fricatives and glides which were not present at pre-test measures. Segments were also produced across more diverse places of articulation including velar and labiodental targets. Notably, gains were emerging in the use of morphophonological {-s} which in the Greek language marks noun plurality and second person singular verb form. It may be speculated that phonological gains might have contributed to the emergence of a wider-system improvement in the sense that a phonological change contributes to another linguistic subsystem such as morphophonology and inflectional morphology. Further to these findings, it was noted that when he started producing unstressed syllables (e.g., [‘nana] -> [banana] and [‘lami] -> [salami]), towards the final stages of the intervention phase, a concomitant spontaneous production of definite articles (unstressed elements in CG) and object clitics was noted in conversational speech.

An increase in the production of percentage of consonants correct and WWMs was also noted. Furthermore, improved intelligibility was noted according to the scores reported on the ICS completed by the child’s school teacher who was unfamiliar with the intervention project. Accordingly, the child’s phonological output progressed from “always unintelligible” to “rarely unintelligible.” Phonological progress was maintained and generalized to nontreated and newly presented word targets administered at the follow-up sessions. At the follow-up session, the results of the percentage of WWMs revealed a noticeable production of multisyllabic words. Note that the study employed triplets of targets such as [l e‘m o] “neck”, [l e ‘m o n i] “lemon” and [l e m o ‘n a ð a] “lemonade,” all of which were initially realized as [e ‘m o] or [‘m e m o]. By the end of the treatment phase, all 3 targets were produced with 100% accuracy. Other triplets were also successfully produced and included targets such as [ka‘la] “good”, [ka‘lami] “stick”, [kala‘maci] “straw” which initially were realized as [a‘ja] (for more examples refer to the Appendix).

The investigation attested to the usefulness of phonologically dense word stimuli relevant to theory-motivated frameworks on par with lexical organization models. Research findings have convincingly advocated for the advantage of a phonologically dense cluster of words and their positive impact on inducing phonological gains. To the first approximation, as a word form variable, word density appears to be a useful “trigger” for ameliorating speech sound disorders, mostly in English-speaking youngsters [60, 61]. Findings from the current investigation added to this line of research and supported the hypothesis advanced, that is, the prediction of speech sound gains in SSD through the implementation of carefully designed and experimentally manipulated targets and their impact on speech intelligibility. The present findings corroborated comparable data from English-speaking children and provided support for a cross-language applicability relevant to ASD speech profiles. In addition, it capitalized on the child’s existing, albeit restricted, phonological strengths (stimulability), with findings supporting comparable outcomes from English-speaking youngsters with SSD [28]. For example, word targets according to the child’s segmental stimulability skills might have enhanced the “…stabilization of the child’s knowledge of subcomponents that form the foundation of the emergence of more complex phoneme contrasts…” [28]. Along these lines, research findings suggest that treatment outcomes are usually enhanced when segmental and suprasegmental levels of therapy stimuli are constructed on the bases of “in” versus “out” phonemes and syllable structures [50]. A plausible explanation of the improved intelligibility revealed in the current findings might be related to the child’s stimulability skills. However, the robustness of this framework remains speculative and awaits further exploration.

This study adopted a novel underexplored approach to phonological treatment and expanded a theory-motivated framework to a cross-language context. Speech intelligibility was induced from carefully selected targets that were experimentally manipulated and clinically exploited to capitalize on the lexical/phonological interphase. Even though the participant was verbal at intake session, his profile was characterized by limited phonetic and lexical resources rendering his speech mostly nonintelligible. As noted earlier, the most robust gain was the appearance of accurate productions of untreated words as well as the decrease in phonological process use. These outcomes increased speech intelligibility dramatically.

However, the robustness of the current intervention regimen may be compromised by the single-subject methodology employed here. An additional limitation pertained to the quasi-density nature of the stimuli employed, in the sense that density was not calculated on the bases of currently available calculation algorithms. Nevertheless, the fact that the participant exhibited positive phonological gains within a relatively short period of time could serve as the impetus for testing efficacy and robustness through a larger data set and data points from more participants. Note that prior to the investigation, the child showed relatively slow progress over a course of previous intervention and presented with persistent speech output constraints. Furthermore, the study did not include a control group of children who were treated with a different set of experimental stimuli via a different experimental paradigm. It is possible that intelligibility gains were merely a result of the maturation process. This limits the generalizability of results and compromises the establishment of a causal link between intervention and observed gains. Nevertheless, the opposite can be inferred in the sense that speech output improvement was a result of the specific methods employed and notwithstanding the use of specific word targets.

With an increased interest in cross-linguistic language development, whether typical or atypical, scientists and clinicians need to adhere to theory-motivated and evidence-based therapies that will ensure delivery of best practice. The issue of neighborhood density in the context of multisyllabic languages and dialectal variability needs to be revisited and operationalized through large data sets from cross-language developmental phonology databases which will include Greek and CG. Clinicians working in a different language can bear in mind the theoretically motivated interventions, and EBP might inform sensitivity and specificity issues through carefully selected word stimuli. Cross-language stimuli with a focus on systematic exploration regarding phonological similarities might form the impetus for focused intervention. Regardless of the variability in theoretical and philosophical stances inherent to intervention regimens in ASD, all frameworks converge towards promoting and maintaining functional and socially appropriate communicative acts, including phonological and articulatory capacity. Research-driven findings have clinical implications as they can direct the setting of treatment goals and the selection of targeted word stimuli according to the child’s idiosyncratic speech output skills.

Overall, despite abundant research findings on treatment efficacy in English-speaking children with SSD, such investigations from a cross-language perspective warrant further systematic exploration. Given the recent keen interest in cross-language phonological treatment, the current investigation adds to this line of research in an effort to maximize phonological learning skills and promote evidence-based practice as these parameters constitute fundamental issues at the core of implementing best clinical practice processes.

The author thanks the participant, his family and his teacher for their participation and commitment to the research project. Also, thanks go to the student clinician who assisted in data collection, data reduction, and reliability measurements.

The participant’s caregiver provided informed written consent, and ethical approval was granted by the CUT Speech and Language Rehabilitation Clinic session participation protocol 2017–2018.

The author declares that she has no conflicts of interest.

Provided by an internal start-up fund awarded to the author by the Cyprus University of Technology CUT/START-UP/PETINOU/REHAB 2014–2017.

Kakia Petinou wrote this article. She is the sole author.

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