Context effects on phoneme categorization in children with dyslexia

Abstract

Research shows that, on average, children with dyslexia behave less categorically in phoneme categorization tasks. This study investigates three subtle ways that struggling readers may perform differently than their typically developing peers in this experimental context: sensitivity to the frequency distribution from which speech tokens are drawn, bias induced by previous stimulus presentations, and fatigue during the course of the task. We replicate findings that reading skill is related to categorical labeling, but we do not find evidence that sensitivity to the stimulus frequency distribution, the influence of previous stimulus presentations, and a measure of task engagement differs in children with dyslexia. It is, therefore, unlikely that the reliable relationship between reading skill and categorical labeling is attributable to artifacts of the task design, abnormal neural encoding, or executive function. Rather, categorical labeling may index a general feature of linguistic development whose causal relationship to literacy remains to be ascertained.

FIG. 1.

(Color online) Plots of model psychometric function parameter estimates versus reading score. Each point corresponds to parameter estimates for one subject in one condition (bimodal or uniform distribution). Lines indicate the best fit regression line with 95% confidence intervals in shaded regions.

FIG. 2.

(Color online) Estimates of coefficients from a mixed effects generalized linear model (GLM) fit to group behavioral data. Bars indicate the 95% confidence interval surrounding a given estimate.

FIG. 3.

(Color online) Each point represents the average accuracy within a group in a certain interval of the task. Error bars mark the 95% confidence interval of the mean. The x axis marks progress through the task: 10% marks the first 21 of 210 trials, 20% marks trials 22–42, and so on. Dark lines indicate the best fit regression line.