A real-time mechanism underlying lexical deficits in developmental language disorder: Between-word inhibition

Abstract

Eight to 11% of children have a clinical disorder in oral language (Developmental Language Disorder, DLD). Language deficits in DLD can affect all levels of language and persist through adulthood. Word-level processing may be critical as words link phonology, orthography, syntax and semantics. Thus, a lexical deficit could cascade throughout language. Cognitively, word recognition is a competition process: as the input (e.g., lizard) unfolds, multiple candidates (liver, wizard) compete for recognition. Children with DLD do not fully resolve this competition, but it is unclear what cognitive mechanisms underlie this. We examined lexical inhibition-the ability of more active words to suppress competitors-in 79 adolescents with and without DLD. Participants heard words (e.g. net) in which the onset was manipulated to briefly favor a competitor (neck). This was predicted to inhibit the target, slowing recognition. Word recognition was measured using a task in which participants heard the stimulus, and clicked on a picture of the item from an array of competitors, while eye-movements were monitored as a measure of how strongly the participant was committed to that interpretation over time. TD listeners showed evidence of inhibition with greater interference for stimuli that briefly activated a competitor word. DLD listeners did not. This suggests deficits in DLD may stem from a failure to engage lexical inhibition. This in turn could have ripple effects throughout the language system. This supports theoretical approaches to DLD that emphasize lexical-level deficits, and deficits in real-time processing.

Keywords: Developmental Language Disorder; Inhibition; Specific language impairment; Word recognition.

Figure 1:

A) Composite language and nonverbal cognitive scores for each participant. B) Distribution of composite language and nonverbal IQ scores.

Figure 2:

Sample display of a single trial. Here, the target was the experimental item mug (which could be cross-spliced with the non-displayed competitor, mud); the cohort competitor was mitt, and the unrelated items were spark and truck.

Figure 3.

A) Looks to target for MatchSplice trials for TD and DLD participants. Average fixations are smoothed with a 12 msec triangular windows, and error bars computed with BDOTs. Trial onset is at 0 msec (100 msec before stimulus onset). Target fixations were significantly lower in DLD than TD children from 592 – 2000 msec (Table 1). B) Looks to the target as a function of time during MatchSplice (M), WordSplice (W) and NWsplice (N) trials for TD participants. Target fixations in the WordSplice (W) condition were significantly lower than the NWSplice (N) condition from 528 -1276 msec (indicating the effect of lexical inhibition during this window; see Table 1 for other contrasts). C) Looks to the target as a function of time and stimulus condition for DLD participants. At no point was the WordSplice condition lower than the NWSplice (though there was an effect of coarticulation).

Figure 4.

Difference curves for fixations to target as a function of stimulus condition. A) Effect of coarticulatory mismatch: NWsplice (N) trials subtracted from looks to target for MatchSplice (M) trials for TD and DLD participants. These did not differ between groups except for a short period at 496-552 msec. B) Effect of lexical inhibition, over and above coarticulatory mismatch: WordSplice trials subtracted from N trials. This showed a significant group difference between 512 and 1780 msec with greater inhibition in the TD group. C) Effect of lexical inhibition, including coarticulatory mismatch: W trials subtracted from M trials. These differed from 696-1048 msec with greater inhibition in TD adolescents.

Figure 5:

Looks to the target as a function of time and condition in the TD/M group who was matched to the DLD group on non-verbal cognitive abilities.