To date the consensus in the literature is that Childhood Apraxia of Speech (CAS) is a disorder of speech motor programming and planning with genetic, neurologic, or idiopathic causes [1
]. Children with the disorder have significant speech impairments due to an inability to control placement and timing of lip, tongue and vocal movements. These impairments result in inconsistent productions of the same words, difficulty sequencing speech sounds together to form fluent words and sentences and impairments of the melody (i.e. prosody) of speech. The speech of these children is often unintelligible and the disability can persist throughout the lifespan, despite normal intelligence and comprehension of language [5
]. The impaired development of speech has flow on effects, frequently disrupting development of reading, spelling and writing skills (e.g. learning letter-sound relationships for deciphering new words), social communication, and academic potential [6
]. Adults with speech disorders (including persistent CAS) are known to have a lower socio-economic status than non-speech disordered peers, an increased incidence of depression and may select occupations that require little or no personal interaction despite normal intelligence [6
]. Speech pathologists frequently report that children with CAS make slow progress in treatment and show deterioration or loss of skills once treatment stops [10
]. It is unclear if this is due to the child’s impaired motor learning or to a lack of evidence to inform effective treatment [10
]. Due to CAS’s characteristics and associated risk factors, the ultimate aim of treatment must be long term maintenance of learned skills and generalisation of treatment effects to improvement across untrained but related speech skills and speaking contexts.
There are few rigorous treatment studies published for CAS currently and no randomised control trials to date [1
]. The best evidence available consists of single case experimental designs and case series for a range of different treatments across different age ranges with samples sizes no greater than twelve (e.g. [15
]). Published speech-focussed treatments with some replicated evidence include the Rapid Syllable Transition Treatment (ReST) [12
], Dynamic Temporal and Tactile Cueing (DTTC) [17
] and the Nuffield Dyspraxia Programme - Third edition (NDP3) [19
]. Replicated evidence also exists for pre-reading and spelling interventions [15
] and alternative or augmentative communication methods [24
] that work on communication skills. These methods are the best poised to be utilised clinically at present and also to be included in any controlled trial. Other published evidence includes studies on melodic-intonation therapy (speech melody) therapy [29
] and speech rate control [30
]. Recently, intervention studies have included combined approaches such as a combined stimulability and core vocabulary approach [31
] and a combined melodic intonation therapy and touch-cue method [32
]; the PROMPT approach [33
] and technological interventions providing graphic displays of tongue movements during speech such as electropalatography [20
]. Moreover there are many published commercial programmes for CAS, which have no published evidence to date. Examples include the Kaufman Speech Praxis Treatment Kits [35
] and the Easy Does It For Apraxia series [38
]. It is relevant to note that children with CAS have different needs as their skills change with maturation and therapy and so it is plausible that multiple treatments will be effective but for different symptoms, severities and ages. In summary, while consumers and clinicians have a range of potential intervention programmes available, few have been experimentally tested and none have been experimentally compared. A Cochrane review on the topic states “there is a critical lack of well controlled treatment studies addressing treatment efficacy for CAS” [14
] pg 2.
Nuffield Dyspraxia Programme – Third edition (NDP3)
At time of writing, the Nuffield Dyspraxia Programme is in its third edition and has been utilised in clinical practices in Australia and the United Kingdom for approximately 30
]. The comprehensive treatment package includes its own assessment as well as a list of over 500 words to be targeted in therapy, and corresponding therapy stimulus pictures. The theoretical basis of the programme is that motor learning is complex and hierarchical; one needs to perform frequent and systematic practice to master foundation levels before progressing to harder, more complex speech patterns. Here mastery is defined as fluent, automatic and independent production of targeted speech behaviours. To date, a total of five empirical case studies have demonstrated positive outcomes for this treatment alone [19
], or in conjunction with electropalatography therapy [20
]. Given these results and the programme’s broad dissemination, testing the programme in a randomised control trial is appropriate.
Rapid Syllable Transition Treatment (ReST)
The ReST treatment is a more recently conceived and tested treatment approach [12
]. The programme is grounded in theory of motor control and learning and is informed by an extensive motor learning literature [42
]. The ReST treatment applies Principles of Motor Learning [43
] with an aim to maximise long-term maintenance and generalisation of treated speech skills in children with CAS. ReST involves intensive practice in producing multisyllabic pseudo-words (e.g. toobiger) to improve the accuracy of speech sounds, the ability to transition rapidly and fluently from one sound/syllable to the next, and control of the melody in the form of relative emphasis, or stress, placed on each syllable within a word. Pseudo-words are used to mimic novel word learning and this allows children to develop and practice new speech patterns without interference from existing erroneous speech patterns. There is published evidence that the effects of speech treatment using phonotactically permissible pseudo-words (non-words) generalise to improved production of real words of similar or easier composition and complexity [44
]. ReST involves two components within each treatment session. The first is a Pre-Practice (or training) Component where the stimuli are taught with cues to shape accurate production and immediate, specific feedback is given after each production. This is followed by a longer Practice Component incorporating those Principles of Motor Learning that have been shown to facilitate long-term learning and generalisation of skill. For example, “right/wrong” (i.e. Knowledge of Results or KR) feedback is provided by the clinician, fading from high frequency to low frequency over the session (i.e. provided on a total 50% of responses) and this KR feedback is delayed with a silent interval between response and feedback to encourage self-evaluation. Two published case series involving a total of ten children [12
] indicate strong clinical effects for ReST treatment, motivating further study in a phase three trial.
Based on these foundational studies, we are well poised to conduct a larger scale clinical trial of ReST treatment against NDP3. Our hypotheses for this planned randomised control trial are: 1) treatment gains from pre-treatment to 1
week post-treatment will be similar for both treatments, 2) ReST treatment will result in greater maintenance of treatment effects at 1 and 4
months post-treatment than NDP3 treatment, and 3) ReST treatment will result in greater generalisation of treatment effects to untrained but related speech behaviours at 1
month and 4
months post-treatment than NDP3 treatment.