Modifying the stimulus parameters
Conducting noise exposure experiments
ABR Overview
An ABR is a synchronous neural response to an auditory stimulus. ABR testing can be used to
estimate hearing sensitivity. The ABR is an early potential, occurring shortly after stimulus
onset, and is typically in the 1 - 2.5 microVolt range, so small that it can be masked by the
background activity of the brain. Because ABRs are repeatable in response to stimuli, signal
averaging can be used to clearly identify the response in recorded data.
A short click or tone stimulus is presented rapidly and response data is collected and averaged
to reduce background noise and isolate the signal. Typically, four times as many sweeps
averaged together will reduce the background noise by half.
When viewing ABR responses, you can expect to see an averaged waveform trace, consisting
of multiple features with at least two distinct peaks. The response shape should be consistent
but can change in response to changes in the auditory stimulus, such as intensity or polarity.
After averaging, the response should clearly stand out above the noise
fl
oor of the system.
Identifying the Threshold
As the level of the stimulus is decreased, the amplitude of the response gets smaller and the
latency gets longer, this makes the biologic features less distinct. The lowest intensity at which
the response is present is generally considered the hearing threshold for the given set of
variables. The determination of response or no response is left up to the researcher. Because
noise and artifacts can mask the very small threshold response, quiet recordings are critical to
accurate threshold testing.
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ABR Testing with the RZ6 and Medusa4Z | 6
