Abstract
Speech–language pathologists (SLPs) devote 21% of their time to treating speech sound disorders. There is a developing literature describing promising interventions that promote phonological generalization. There is a smaller evidence base on how to treat co-occurring language impairment. The purpose of this article was to discuss the best practice options for managing co-occurring phonological disorder and expressive language impairment (PD + LI).
Between the ages of 3 and 11 years, 50% to 75% of children who have a phonological disorder of unknown origin are also reported to show weakness in some other area of language ability. There is limited knowledge about how to plan intervention for children with co-occurring PD + LI. The presence of phonological disorder is strongly associated with poorer literacy outcomes but only when accompanied by co-occurring language impairment. The presence of co-occurring language impairment may also be related to severity and persistence of the phonological disorder. Children with PD + LI may show different phonological error types than children with PD alone. The former group shows more frequent omission errors than distortions, with similar patterns of substitution, when severity level is controlled. Children with LI who have co-occurring phonological impairment show even weaker finite verb morphology (FVM) skills than children with LI alone, even after controlling for final consonant deletion in the former group. The long-term academic outcomes of adolescents with a history of early PD + LI are poorer than those without the co-occurrence. In an effort to minimize the long-term negative impact associated with having a severe, persistent phonological disorder and co-occurring expressive language difficulties, clinicians will need to carefully weigh the evidence to ensure that intervention is planned in the ways known to best facilitate growth in both areas. Planning intervention for children with PD + LI is complex given the need to address multiple goal areas. Evidence is limited for treatment strategies for children with PD + LI. To the author’s knowledge, no studies have considered how factors affecting treatment target selection pertain to children with PD + LI.
Phonology/Morphology Interactions
Assessment and treatment of children with PD + LI should consider the interaction between phonological structure and productivity of inflectional grammatical morphemes in typical development and children with language impairments.
As early as the toddler years, there is evidence of this interaction, with the presence of fricatives in the phonological inventory at 18 months predicting the emergence of grammatical morphemes at 24 and 30 months (Sotto et al., 2014).
Prior to mastery of grammatical morphology, it is common for young children to make omission errors (e.g., Abby eat _ her food fast). Regardless of language development status (typical or delayed), a common explanation is that omission errors represent children’s incomplete, or emerging, grammatical morphology (Rice et al., 1998).
For children with LI, persistent omission errors in FVM (i.e., morphemes that mark verb tense and agreement with the subject) as a by-product of weak grammatical knowledge are key clinical markers for LI during the preschool years.
Research has asked whether, in addition to incomplete grammatical knowledge, omission errors might also be attributed to phonological factors or complexity associated with the uninflected bare stem of the verb (e.g., see vs. pick vs. ask) or the complexity of the phonological form that results from inflection (e.g., sees vs. picks vs. asks).
Typically developing children are more likely to correctly produce regular past tense verb morphology (e.g., Abby kicked the ball) when the final consonant of a verb stem is a non-alveolar sound. Although children with LI are less accurate, they also demonstrate this pattern (Marchman, 1997; Marchman et al., 1994; Oetting & Horohov, 1997).
Typically developing children and children with LI are also more accurate in production of finite verb morphemes when the stem final phonology of a verb is simple (e.g., ending in a vowel, as in “sees”) rather than complex (e.g., ending in a cluster, as in “kicks”) and yields a voiceless (e.g., “hopped”) rather than voiced (e.g., “hugged”) cluster (Tomas et al., 2015).
Similarly, children are more accurate in producing grammatical morphemes when the verb to be inflected occurs at the end rather than middle of the utterance, and when the inflection is a single sound (e.g., regular past tense of “skip” produced as “skipped”) rather than a syllable (e.g., regular past tense of “paint” produced as “painted”) (Tomas et al., 2015).
Typically developing children are more accurate in production of the third-person singular present tense (e.g., Abby eats her food fast) when the uninflected verb stem is similar to many other words in the language (kick vs. move). In contrast, children with LI are more accurate with verbs that are more phonologically distinct (Hoover et al., 2012).
Children’s ability to produce consonant clusters in single syllable words (e.g., waste), even if misarticulated, is a predictor of grammatical morpheme accuracy beyond age, receptive vocabulary, and percentage of phonemes correct (Howland et al., 2019).
These data suggest that having a reduced phonological inventory or reduce syllable structures would present a particular challenge to inflecting words that require phonological complexity.
Treatment Approach
The authors describe a morphophonological treatment approach for children with PD + LI, which allows the clinician to directly target FVM in concert with weaknesses in phonological inventory. The goal is parallel growth in phonology and FVM, and subsequent increases in phonology should support the phonological complexity required to produce finite verb morphemes in English. Tyler and colleagues developed a morphophonological intervention focusing on parallel growth of phonology and morphology, while also considering the optimal schedule of presenting FVM and phonology goals (Tyler et al., 2002). The morphophonological approach involves selecting multiple goals in phonology and multiple goals in FVM—typically four goals per domain. Goals for a single child might include third-person singular present tense (e.g., she sits), regular past tense (e.g., she kicked), copula be (she is happy) and auxiliary be (she is kicking), as well as four phonemes (singleton or consonant clusters). The intention is that each goal within each domain will be presented in a “cyclical” format, whereby a specific goal is emphasized each week until all goals within a domain have been presented to the child. Once all goals have been targeted, they are “recycled.” Domains can either be targeted sequentially in blocks (i.e., a block of FVM treatment followed by a block of phonology treatment) or they could alternate weekly.
Tyler and colleagues tested the efficacy of the approach with a group of preschool children with PD + LI to determine whether
the approach resulted in gains in phonology and FVM that were significantly greater than a no-treatment control group;
gains in one area (phonology or FVM) would occur naturally, following treatment delivered in the other area; and
the amount of gain in phonology and FVM depended on which domain was targeted first (i.e., phonology or FVM).
Half of the children received a 12-week block of phonology treatment (Phon1), followed by a 12-week block of FVM treatment and the other half received the opposite (FVM1). Outcome measures included (a) a phonology composite composed of the accuracy of treatment targets and untreated generalization sounds, (b) a FVM composite composed of the accuracy of finite verb morphemes, and (c) mean length of utterance.
Study Results
Children in the Phon1 group demonstrated significantly greater gains in phonology than children in the no-treatment control group.
Children in the FVM1 group demonstrated significantly greater gains in FVM compared with the no-treatment control group.
Cross-domain effects were observed after treatment for children in the FVM1 group. The FVM treatment group made significantly greater gains in children’s phonological skills compared with the no-treatment control group; similar cross-domain growth in untreated FVM skills was not observed after the phonology treatment.
Regardless of which treatment was targeted first, after completing both blocks of treatment, the two groups made equivalent gains in phonology and FVM.
Regardless of which domain was targeted first, the treatment resulted in greater gains in phonology than FVM skills.
Both the phonology and FVM treatment were effective on its own.
In a follow-up study, Tyler and colleagues (2003) sought to identify an optimal goal attack strategy for the approach. Four goal attack strategies were compared: (a) a vertical block of FVM first, followed by a phonology block; (b) a vertical block of phonology first, followed by a FVM block; (c) weekly alternations of phonology and FVM goals; and (d) simultaneous treatment of phonology and FVM within a treatment session. After 12 weeks of treatment, significant gains in FVM were observed for the children who received FVM treatment first as well as for children whose goals were alternated weekly. In addition, after 12 weeks of treatment, children in the FVM first group and the alternating goal and simultaneous goal subgroups demonstrated significant gains in phonology compared with the control group.
Implications
FVM treatment results in some degree of cross-domain generalization in phonology, but phonology treatment does not affect FVM development. If delivering separate blocks of treatment targeting FVM and phonology, the key recommendations are either (a) to begin treatment with FVM when using a blocked, vertical strategy or (b) to alternate phonology and FVM goals on a weekly basis if a blocked, vertical strategy is not desired.
The data appear to indicate that it would be best to keep phonology and morphology goals separate in therapeutic lessons, that is, not working on both goals at the same time. The authors do not offer explanations for why this would be the case. In a recent issue of Word of Mouth, I summarized an article on cognitive load and learning. Expecting a child to simultaneously attend to both phonological and morphological goals would result in a high cognitive load, so that performance on both goals would be reduced. If SLPs see children with PD + LI twice a week, they can devote one session to phonology and one to morphology. Many children with PD + LI received therapy only once a week. In these instances, SLPs should consider clearly differentiating the time and activities between the two goals. For some children, SLPs may elect to spend several weeks on one goal and then several on another goal. In this instance, beginning first with morphology would be recommended. An exception to beginning with treating morphology first might be children who exhibit productive language but have a PD that significantly affects their intelligibility. But for all children, the SLP will want to keep the goals separated so as to avoid cognitive overload for students.