Latency of brain stem responses to chirps (linear Frequency-Ramp bursts): Relationship between Certain Physical Parameters of the Stimulus and Nervous Activity

Abstract

The latency of Jewett wave V to 4-kHz tone (T) bursts was first studied on 55 normally hearing ears. In another group of 31 subjects, shift in latency was investigated as a function of certain physical parameters of the stimulus. Using T bursts and chirps - frequency-ramp (FR) bursts of 6 ms duration with an interstimulus interval of 33 ms and a constant attenuation, we noticed that (1) in all subjects, wave V latency was greater with ascending FR bursts than with descending ones; (2) in all subjects with even slight sensorineural hearing losses, the difference in latency between 1-kHz T bursts and 1- to 2-kHz FR bursts was less than that between 2-kHz T bursts and 2- to 4-kHz FR bursts, and (3) in subjects with normal internal ears on standard audiometry, the converse occurred, except in 4 subjects in a group of 6 who had been exposed to loud impact noises. Possible underlying mechanisms are discussed.

Key Words:

• Electric-response audiometry (ERA)
• Brain-stem electric responses (BER)
• Wave V latency
• Frequency-ramp bursts
• Chirps