Subcortical differentiation of stop consonants relates to reading and speech-in-noise perception

Abstract

Children with reading impairments have deficits in phonological awareness, phonemic categorization, speech-in-noise perception, and psychophysical tasks such as frequency and temporal discrimination. Many of these children also exhibit abnormal encoding of speech stimuli in the auditory brainstem, even though responses to click stimuli are normal. In typically developing children the auditory brainstem response reflects acoustic differences between contrastive stop consonants. The current study investigated whether this subcortical differentiation of stop consonants was related to reading ability and speech-in-noise performance. Across a group of children with a wide range of reading ability, the subcortical differentiation of 3 speech stimuli ([ba], [da], [ga]) was found to be correlated with phonological awareness, reading, and speech-in-noise perception, with better performers exhibiting greater differences among responses to the 3 syllables. When subjects were categorized into terciles based on phonological awareness and speech-in-noise performance, the top-performing third in each grouping had greater subcortical differentiation than the bottom third. These results are consistent with the view that the neural processes underlying phonological awareness and speech-in-noise perception depend on reciprocal interactions between cognitive and perceptual processes.

Fig. 1.

Timing differences present in the responses (Bottom Panels) are absent in the stimuli (Top Panels). For the stimuli and responses, [ba] is plotted in blue, [da] in red, and [ga] in green. (Left) The time domain grand averages of high-pass filtered responses from typically developing children (n = 20) are plotted below the [ba], [da], and [ga] stimuli. The peaks analyzed in the present study are marked on the responses (onset: 1, 2; major: 3, 4, 6, 7, 9, 10, 12, 13; minor: 5, 8, 11, 14; endpoint: 15, 16). For visual coherence, the stimuli have been shifted in time by 8 ms to account for the neural conduction lag. (Right) The 52- to 57-ms region of the responses and time-adjusted stimuli have been magnified to highlight latency differences found among the responses (Bottom) that are not present in the stimuli (Top). These latency differences are thought to reflect the differing second formants of the stimuli schematically plotted in the inset (Top Left).

Fig. 2.

Subcortical differentiation is related to phonological awareness and speech-in-noise performance. The relationships between the stop consonant differentiation score (minor peaks) and phonological awareness (Left) and speech-in-noise performance (Right) are plotted. Performers in the top and bottom terciles for each measure are marked in black and red, respectively. The stop consonant differentiation scores of performers in the top (black) and bottom (red) terciles on each measure are plotted in the insets (means ± 1 standard error). *, P < 0.05.

Fig.3.

Children who are poor performers on measures of phonological awareness (PA) and speech-in-noise perception (HINT) have reduced subcortical differentiation of 3 stop consonant stimuli relative to good performers. Normalized latency differences are plotted over time for the good performers (Left) and poor performers (Right) for phonological awareness (Top) and speech-in-noise perception (Bottom). There is better separation among [ga] (green), [ba] (blue), and [da] (red) responses for the good performers. Response latencies were normalized by subtracting individual peak latencies from the grand average of responses to all 3 stimuli (see Methods and ref. 2). Minor peaks are marked with arrows.