Encoding Deficits Impede Word Learning and Memory in Adults With Developmental Language Disorders

Abstract

Purpose: The aim of this study was to determine whether the word-learning challenges associated with developmental language disorder (DLD) result from encoding or retention deficits.

Method: In Study 1, 59 postsecondary students with DLD and 60 with normal development (ND) took the California Verbal Learning Test-Second Edition, Adult Version (Delis, Kramer, Kaplan, & Ober, 2000). In Study 2, 23 postsecondary students with DLD and 24 with ND attempted to learn 9 novel words in each of 3 training conditions: uncued test, cued test, and no test (passive study). Retention was measured 1 day and 1 week later.

Results: By the end of training, students with DLD had encoded fewer familiar words (Study 1) and fewer novel words (Study 2) than their ND peers as evinced by word recall. They also demonstrated poorer encoding as evinced by slower growth in recall from Trials 1 to 2 (Studies 1 and 2), less semantic clustering of recalled words, and poorer recognition (Study 1). The DLD and ND groups were similar in the relative amount of information they could recall after retention periods of 5 and 20 min (Study 1). After a 1-day retention period, the DLD group recalled less information that had been encoded via passive study, but they performed as well as their ND peers when recalling information that had been encoded via tests (Study 2). Compared to passive study, encoding via tests also resulted in more robust lexical engagement after a 1-week retention for DLD and ND groups.

Conclusions: Encoding, not retention, is the problematic stage of word learning for adults with DLD. Self-testing with feedback lessens the deficit.

Supplemental materials: https://doi.org/10.23641/asha.5435200.

Figures

Figure 1.

The word recall of the developmental language disorder (DLD) and normal development (ND) groups after each encoding trial and at short and long delays. Cued recall at short and long delays is also depicted. Standard error bars are included.

Figure 2.

Mean proportion of features correctly recalled by the developmental language disorder (DLD) and normal development (ND) groups plotted by time and encoding condition. Error bars depict standard error.

Figure 3.

Naming accuracy by diagnostic group and training condition. Accuracy is expressed as the mean proportion of features correctly recalled after a 24-hr retention interval (Day 2). Error bars depict standard error. DLD = developmental language disorder; ND = normal development.