Effects of complex tonal stimuli on latency and amplitude of a late auditory evoked potential

An optimum stimulus for evoking late auditory potentials is not well established. A typical stimulus for clinical purposes is either a brief speech signal or a brief single-frequency tone. Based on previous research, it is reasonable to assume that a complex stimulus may enhance waveform morphology relative to a single-frequency stimulus. The current project investigated the effects on P1 latency and P1/N1 amplitude of a two-frequency complex stimulus with the second frequency having either a dissonant or harmonic relationship to a single-frequency reference stimulus. An 80 ms 1000 Hz tone with 10 ms rise/fall times served as the reference stimulus. The two-frequency complex stimuli consisted of the reference (1000 Hz) frequency mixed with a second frequency of equal duration and amplitude at 1100, 1250, 1500, 2000, or 4000 Hz, resulting in three dissonant and two harmonic stimuli. One dissonant stimulus (1000 + 1100 Hz) was designed to fall within the critical band of the reference stimulus. Stimuli were presented in a counterbalanced order to 20 normal hearing adult subjects. Two replicate runs were obtained for each stimulus condition. Results showed that the complex stimuli had no significant effect on P1 latency relative to the reference stimulus, but produced a significant increase in P1/N1 amplitude for the harmonic stimuli.