Effects of stimulus level on cortical auditory event-related potentials evoked by speech.

The effect of stimulus level on cortical auditory event-related potentials (ERPs) evoked by consonant-vowel (CV) contrasts, /ta/, /da/, and /sa/, was investigated. The lowest level at which CVs were discriminated with >95% accuracy was determined for 15 normally hearing adults. ERPs were obtained at 0, 20, and 40 dB SL above this level during active listening. ERP latencies decreased as level increased. P300 amplitude did not vary with CV level or type; however, obligatory ERPs decreased in amplitude as level increased. The effect of level on P300 latency is likely related to the cognitive processing speed needed to perform speech discrimination. Obligatory ERP amplitude results suggest that attention demands vary with level during discrimination of speech features.