Investigating speech perception in children with dyslexia: is there evidence of a consistent deficit in individuals?

Abstract

Purpose: The claim that speech perception abilities are impaired in dyslexia was investigated in a group of 62 children with dyslexia and 51 average readers matched in age.

Method: To test whether there was robust evidence of speech perception deficits in children with dyslexia, speech perception in noise and quiet was measured using 8 different tasks involving the identification and discrimination of a complex and highly natural synthetic "bee"-"pea" contrast (copy synthesized from natural models) and the perception of naturally produced words.

Results: Children with dyslexia, on average, performed more poorly than did average readers in the synthetic syllables identification task in quiet and in across-category discrimination (but not when tested using an adaptive procedure). They did not differ from average readers on 2 tasks of word recognition in noise or identification of synthetic syllables in noise. For all tasks, a majority of individual children with dyslexia performed within norms. Finally, speech perception generally did not correlate with pseudoword reading or phonological processing--the core skills related to dyslexia.

Conclusions: On the tasks and speech stimuli that the authors used, most children with dyslexia did not appear to show a consistent deficit in speech perception.

Figure 1

Individual scores and regression line of the slope of the identification function for ID-Q (left panel) and ID-N (right panel) for the AR (full triangles and line) and the DYS (open circles, dotted line) groups as a function of age (in months). A larger value corresponds to a steeper slope. ID-Q = identification task presented in quiet; ID-N = identification task presented in noise; AR = average readers group; DYS = group with dyslexia.

Figure 2

Proportion of times the endpoint stimuli were correctly labeled as a function of trial number shown separately for the AR and DYS children. The smooth dashed lines result from a logistic regression using trial number as a continuous predictor but not accounting for the effects of the child’s age.

Figure 3

Identification functions for the “bee”–“pea” continuum for the AR group (at left) and the DYS group (at right) in quiet (top) and in noise (bottom). The circles indicate the proportion of “bee” responses along the voice onset time (VOT) continuum in ms for the data aggregated across all participants within the group. The size of each circle is proportional to the number of presentations at a given VOT. The solid lines result from a logistic regression on each set of aggregated data. Note that all endpoint stimuli were labeled correctly at least 89% of the time, even in noise.

Figure 4

Box plot of the proportion of correct discrimination scores for each pair of stimuli presented using the fixed procedure (FixedAC-Q and FixedWC-Q). The DYS children are represented in white boxes, and the AR children are represented in gray boxes. The horizontal line represents chance level of performance, which is set at .33 proportion correct in this task. FixedAC-Q = fixed presentation discrimination task: across-category stimulus pairs; Fixed WC-Q = fixed presentation discrimination task: within-category stimulus pairs.

Figure 5

Just noticeable difference in ms VOT (jndVOT) relative to a fixed reference stimulus of 60-ms VOT for Adapt WC-Q (left panel) and Adapt WC-N (right panel) for the AR group (full triangles and line) and DYS group (open circles, dotted line) as a function of age (in months). A discrimination threshold of < 37 ms VOT (marked on the y axis by a notch) is within category.

Figure 6

Scatterplot showing the relationship between standardized scores in pseudoword reading and standardized scores in FixedAC-Q.