Auditory evoked responses in human auditory cortex to the variation of sound intensity in an ongoing tone

Abstract

In daily life, variations of sound intensity, frequency, and other auditory parameters, can be perceived as transitions from one sound to another. The neural mechanisms underlying the processing of intensity change are currently unclear. The present study sought to clarify the effects of frequency and initial sound pressure level (SPL) on the auditory evoked response elicited by sounds of different SPL. We examined responses approximately 100 ms after an SPL change (the N1m'). Experiment 1 examined the effects of frequency on the N1m'. Experiment 2 examined the effects of initial SPL on the N1m'. The results revealed that N1m' amplitude increased with greater SPL changes. The increase in N1m' amplitude with increasing SPL was almost constant for low frequency sounds (250 and 1000 Hz); however, this increase was reduced for high frequency sounds (4000 Hz). The increase in N1m' amplitude was reduced with high initial SPL. The pattern of amplitude change may reflect a difference in activation in the auditory nerve and/or primary auditory cortex.