Precortical and cortical contributions to backward masking in children with language-learning impairment

It has been shown that children with language-learning impairment (LLI) demonstrate higher (poorer) signal thresholds in backward masking, but not in simultaneous masking, when compared with their age-matched peers. The purpose of the present study was to examine the possible connection between precortical and cortical contributions to a specific auditory processing deficit in children with LLI. Ten children with LLI and ten children with normally developing language (NDL) participated in a series of simultaneous (ipsilateral) and backward (ipsilateral and contralateral) masking tasks. The same backward masking stimulus was then used to elicit the auditory brainstem response (ABR), the long-latency response (LLR), and the mismatch-negativity response (MMN).; In the ipsilateral psychophysical conditions, compared to children with NDL, children with LLI had significantly higher signal thresholds in backward masking, while their thresholds in simultaneous masking were no different. In the contralateral backward masking condition, signal thresholds remained significantly higher (poorer) in children with LLI. Continued difficulty with backward masking in the contralateral condition suggests a precortical contribution to backward masking behaviors in children with LLI.; An ABR, elicited with a 1-kHz tone signal in a signal-alone condition (without masker), failed to differentiate children with LLI from those with NDL. However, wave V of the ABR was delayed and physiological threshold was elevated when signals were presented in the context of backward masking. These neurophysiological data further support a hypothesis of precortical involvement, indicating an upper brainstem contribution to backward masking behavior in children with LLI.; The group difference found in the ABR was not preserved in the N1 and P2 components of the LLR. The MMN, an auditory cortical potential passively elicited by small changes in simple and complex stimuli, revealed a group difference in the form of prolonged latency and hemispheric asymmetry. This asymmetry was characterized by diminished amplitude over the right hemisphere. These psychoacoustic and electrophysiological data suggest the possibility of a dual auditory processing deficit in children with LLI: (1) a precortical component independent of cognitive factors (e.g., attention, memory, nonverbal skills), and (2) a cortical component resulting in impaired auditory memory, characterized by poor integration of complex auditory information.