Twelve subjects were run in a paradigm designed to compare event-related brain potentials (ERPs) elicited by infrequent pitch-deviant and time-deviant tones under different attentional conditions. Tones with a pitch of 500 Hz or 1000 Hz were presented at regular interstimulus intervals of 800 ms. Changes in pitch or a shortening of interstimulus interval to 400 ms each occurred with 10% probability. Three different tasks (reading or reaction time to pitch or to timing deviances) were assigned on separate runs.
N150 to deviant tones was not influenced by task. Its amplitude, peak latency, and frontally maximum distribution did not differ between pitch and timing deviance, but to pitch deviance it had an earlier onset. P350 amplitude to both types of deviant tones was larger than to standard tones when subjects pressed to time-deviant tones; only P350 to pitch-deviant tones was larger than to standards when subjects pressed to pitch-deviant tones. P350 latency was longer to timing deviance regardless of task.
Our results support the view that negativities generated by mismatches in expected timing and pitch are qualitatively the same. ERP differences between these two types of deviance were probably due to differences in stimulus salience or discriminability.