auditory evoked potentials (AEPs) definition
- electrophysiologic responses that arise from one or more places within the peripheral and/or central auditory system.
- a response to acoustic stimuli
AEPs are recorded from specific places such as?
scalp, on the ears, within the ears
AEPs appear as what onscreen?
waveforms, with positive and negative waves (components) at certain times after presentation of stimuli
What provides amplitude information on a waveform?
height/depth of a peak
What provides latency information on a waveform?
a peak’s time of appearance
If an AEP can follow/phase-lock to a repetitive pattern in a stimulus, how is it usually analyzed?
in the frequency domain
What are the 3 main ways AEPs are classified?
- latency
- anatomical site of generation
- relationship to the stimulus
Latency descriptors for AEPs
- short (<15 msec)
- middle (15-80 msec)
- long (>80 msec)
Exogenous potential definition
- A sensory evoked potential typically elicited and subsequently affected by physical parameters of the stimulus (intensity, frequency, duration).
- ex: ABR
Endogenous potential definition
- a potential less influenced by stimulus’ physical parameters, and rather the contextual factors of the stimulus.
- exhibit very long latencies
- arise from demands on psychological processes (attention, memory) to a particular event, like listening to a rare stimulus in sequence of a repetitive stimulus
- ex: P300
What items are included in typical instrumentation for electrophysiology?
- computer
- amplifier box
- electrode box
- electrodes
- transducers
Sampling of a digital signal involves what?
Breaking up a continuous signal into a limited number of manageable units (ex: recording ABR for 10 msec with 256 sampling points)
Time domain analysis definition
- evaluates the amplitude of signal over time
- signal appears as a waveform with alternating positive and negative values
Frequency domain analysis (spectrum) definition
- removes time to reveal the spectral energies of the signal as the waveform is translated to its respective amplitude values across frequencies
- ASSR is usually analyzed this way
What are the typical stimuli generated for electrophysiologic testing?
- clicks
- tone bursts
- speech
What are some acquisition parameters used in electrophysiology?
- differential amplification
- filtering
- signal averaging
Acquisition parameters are used for what?
- to extract the smaller AEP signal and to attenuate noise
What is the purpose of amplification?
- to reduce background noise through differential recording
- to bring the signal of interest to the forefront
How many electrodes are required for a basic differential recording?
a minimum of 3 electrodes (non-inverting, inverting, and ground)
What is common-mode rejection?
the cancelling of signals common to both inputs
Filtering is used for what?
- to improve the SNR by suppressing noise not in the frequency bands associated with the AEP
- essentially, to pass signals of interest while rejecting noise
What is the Fast Fournier Transform?
an algorithm that breaks down the AEP into its component frequencies
What are the types of filters?
- high pass
- low pass
- bandpass
- notch (band-reject)
Signal averaging definition
- noise is NOT time-locked to the stimulus, so it cancels itself out
- time-locked signals sum together, further pushing them to the forefront
