Abnormal neural encoding of repeated speech stimuli in noise in children with learning problems

Objectives: This study investigated whether neurophysiologic responses to repeated speech stimuli, presented in quiet and noise, differed between normal children (NL) and children with learning problems (LP). Methods: Subjects were normal-hearing, school-age children. NL subjects scored significantly better than LP subjects on measures of reading, spelling and speech sound discrimination. Stimuli (40ms /da/) were presented to the right ear at 80dB SPL. Stimuli were presented in trains of four, separated within trains by 360ms. The interval between trains was 1060ms. Stimuli were presented in quiet and in white noise (S/N+15). Cortical responses were recorded from an electrode placed along the midline at Cz. Results: Correlations between the first and 4th responses were lower in noise than in quiet for LP subjects only. Response correlations in quiet were no different between groups. There were no root-mean-square (RMS) amplitude differences between groups. Conclusions: Response correlation in noise suggested that the LP population consisted of two subgroups, one whose responses appeared relatively normal, and another whose responses were severely degraded by repetition in noise. Response correlations in noise were related to behavioral measures of auditory processing and spelling. These findings suggest that abnormal, asynchronous, auditory cortical encoding may underlie some language-based learning problems.