The Auditory Steady-State Response (ASSR) was recorded in 20 awake adults with normal
hearing on ten EEG channels simultaneously to find derivations with the best signal-to-noise
ratios (SNRs). Stimuli were 20% frequency modulated tones of 0.5 and 2 kHz at 20 dB
SL, 100% amplitude modulated at 90 or 94 Hz, and presented one at a time to one ear.
ASSR recordings using a set of at least three channels improved SNRs significantly
by an average of between 6% (500 Hz right ear) to 118% (2 kHz right ear) above the
SNRs from the conventional channels. Assuming that the recording time was proportional
to 1/(SNR)2, this translates into a recording time of 89% (500 Hz right ear) to 21% (2 kHz right
ear) of that for conventional single-channel recording.
The three channels comprised the electrode positions inion, right mastoid, and left
mastoid. All three electrode positions were referenced to Cz. Adding a fourth channel
(Pz-Cz) increases the number of participants with significant responses from the 500
Hz right ear stimulus from 13 to 17. Electrode position F4 and other commonly used
positions such as the forehead and right earlobe made significantly less contribution
to test efficiency.
Key Words
Amplitude modulation - amplitude modulation following response - auditory steady-state
response - EEG - EEG derivation - electrode position - objective audiometry - signal-to-noise
ratio - steady-state evoked potential
