Effects of stimulus frequency and complexity on the mismatch negativity and other components of the cortical auditory-evoked potential

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, 1500/1650, and 3000/3300 Hz), words (/bæd/ vs /dæd/) and CVs (/bæ/ vs /dæ/). 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.