Effects of stimulus frequency and complexity on the mismatch negativity and other components of the cortical...

This study investigated, first, the effect of stimulus frequency on mismatch negativity (MMN), N1, and P2 components of the cortical auditory event-related potential (ERP) evoked during passive listening to an oddball sequence. The hypothesis was that these components would show frequency-related changes, reflected in their latency and magnitude. Second, the effect of stimulus complexity on those same ERPs was investigated using words and consonant-vowel tokens (CVs) discriminated on the basis of formant change. Twelve normally hearing listeners were tested with tone bursts in the speech frequency range (400/440, 1,500/1,650, and 3,000/3,300 Hz), words (/baed/ vs /daed/) and CVs (/bae/ vs /dae/). N1 amplitude and latency decreased as frequency increased. P2 amplitude, but not latency, decreased as frequency increased. Frequency-related changes in MMN were similar to those for N1, resulting in a larger MMN area to low frequency contrasts. N1 amplitude and latency for speech sounds were similar to those found for low tones but MMN had a smaller area. Overall, MMN was present in 46%-71% of tests for tone contrasts but for only 25%-32% of speech contrasts. The magnitude of N1 and MMN for tones appear to be closely related, and both reflect the tonotopicity of the auditory cortex.