Occasionally we get member questions that are so good we want to share them. We bring in expert guest posters for these, as well, so you hear from somebody other than us. Enjoy!
Both working memory and processing speed have long been players in the language impairment literature. Historically, they have each been suggested to be the cause of language impairment, which has been a point of disagreement among researchers and clinicians alike (Bishop, 1992; Gathercole & Baddeley, 1990a). What we can agree on is that some, but not all, children with language impairments also show phonological working memory and processing speed weaknesses (Leonard et al., 2007; Miller, Kail, Leonard, & Tomblin, 2001; Montgomery, Magimairaj, & Finney, 2010). So they are abilities that need to be considered when determining the strengths and weaknesses of each child.
While working memory and processing speed have been related to vocabulary, language comprehension and academic achievement more broadly (Boudreau & Costanza-Smith, 2011), the greatest attention has been paid to the relationship between working memory and processing speed and vocabulary/word learning (e.g., Gathercole & Baddeley, 1989, 1990b; Gray, 2006; Weismer & Hesketh, 1996). Indeed, most studies have shown that children with better working memory and processing speed are better word learners than children with poorer working memory and processing speed (for counter-proposals, see Abel & Schuele, 2013; Ramachandra, Hewitt, & Brackenbury, 2011). The premise here is that processing speed and working memory relate to the ability to store a novel phonological form in memory while attaching a meaning and establishing a long-term representation of the phonological form.
To my knowledge, there is nothing in the literature that specifically suggests that working memory or processing speed better influence receptive or expressive vocabulary. Instead, it seems that a receptive–expressive vocabulary discrepancy may be due to differences in task demands rather than underlying abilities. Most receptive vocabulary assessments (i.e., PPVT) ask a child to identify which picture goes with a given word. Task demand-wise this is pretty light; children hear the word in isolation and just have to identify from a limited array which picture best matches it. Conversely, expressive vocabulary assessments ask children to generate a name for a picture (i.e., EOWPVT) or provide synonyms for commonly known words (i.e., EVT). This is much more taxing. Children have to retrieve a word and produce it to get the item correct. Ellis Weismer & Hesketh (1996) showed this pattern in a word learning study. They found that 7-year old children with specific language impairment (SLI) were better with recognition than production of recently learned words and accelerated rate of speech negatively impacted the children with SLI more than their typically developing peers. The authors suggest that the increased difficulty with faster rate is because the children with SLI have more difficulty using the faster input to learn new vocabulary due to their processing speed limitations. Importantly, the negative effect of faster rate was greater for the production of novel words versus comprehension/recognition of novel words, which they authors tie back to increased demands for their production task compared to the comprehension and recognition tasks. So the takeaway from this is that it seems likely that processing speed and working memory don’t differentially influence receptive and expressive vocabulary knowledge, but instead may impact performance on receptive versus expressive vocabulary tasks.
Now to the last part of the question—what does this mean for treatment? The current evidence suggests that targeting working memory and processing results in improved working memory and processing but there is no evidence that the training generalizes to language (Kamhi, 2014), and isn’t that what we want it to do? There are suggestions from the ADHD and attention literature that suggest that these types of generalizations may happen but the evidence isn’t there as of yet. Instead, for now, clinicians should focus on how to support working memory and processing speed, rather than how to treat it. Some suggestions put forth by Boudreau & Costanza-Smith (2011) include:
By doing this, we are giving children strategies on how to manage their working memory and processing speed difficulties within the scope of the classroom and academic performance and we can still spend our valuable intervention time focusing on their language needs.
This blog post by:
Alyson Abel, PhD
San Diego State University
members of The Informed SLP
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