Word-final complexity in speech sound intervention: two case studies

In speech sound intervention, consonant clusters promote generalisation (i.e. improvement in untreated sounds and words), ostensibly due to their relative complexity compared to other phonological targets. However, our understanding of clusters as intervention targets is largely restricted to those in word-initial position (e.g. [fl-], flip). The present study extends available work to consider the effects of word-final consonant cluster targets (e.g. [-ks]). Phonologically complex word-final clusters may be morphologically simple (e.g. mix) or morphologically complex (e.g. packs, inflected with third-person singular) - yet this cross-domain complexity remains an understudied phenomenon. Presently, two case studies provide an initial investigation of word-final cluster intervention targets for children with phonologically based speech sound disorders. Intervention targets for both Anna (3;7 [years;months]) and David (4;1) featured the phonologically complex word-final cluster [-ks], with Anna's target being morphologically simple and David's being morphologically complex. Intervention was provided in 45-minute, individual sessions three times per week for a maximum of 18 sessions. Both children demonstrated high target accuracy by intervention's end. Following intervention, both children demonstrated progress in intelligibility and ability to produce word-final consonant clusters; David further demonstrated generalisation across multiple measures. Results are interpreted with consideration of individual differences and existing research on complexity in phonological intervention. Overall, present findings motivate continued research, as manipulation of word-final complexity allows for emphasis on a context that is relevant for children with speech sound disorders, for peers with difficulties in morphology (including word-final grammatical morphemes) and for the substantial proportion of children demonstrating weaknesses in both domains.