Event Related Average module

[mbinder]

I have a short question about the Event Average module in ActiView.
What is the meaning of the grey 'noise' line?

Thank you,
Marek

[Coen]

The gray trace displays the average results with alternating polarity of successive sweeps (odd numbered sweeps are not inverted, even numbered sweeps are inverted). This alternating polarity of the averaged sweeps cancels out the evoked response (locked to the trigger moments), and just leaves the noise content in the signal (random with respect to the trigger moments). The difference in amplitude between the resulting signal and noise traces indicates the signal-to-noise ratio. It is instructive to see that in some situations a result which looks like a valid ERP is nothing more than noise (gray trace has same amplitude as red/blue trace).

Best regards, Coen (BioSemi)

[ctownsend]

I hope you don't mind me resurrecting an almost 15 year old thread. So you're saying that the "Noise" trace is created by subtracting, instead of summing, alternate stimulus sweeps. Does this mean that if I use an alternating polarity stimulus as is commonly done then the "Noise" trace is effectively the signal trace and the "Average" trace effectively becomes the noise trace? Is that correct? Or is there some other way to handle alternating stimuli?

[Coen]

That depends on whether the evoked responses also alternate in polarity. With ABR for example, that's not the case (so the noise trace still shows the noise).

Best regards, Coen (BioSemi)

[ctownsend]

Ok. But if I want to see the cochlear microphonic then that would show up in the "noise" trace?