Re: Questions (what else!)

May 2, 2005

nne,

> 1) A client has very small earlobes, and when doing the assessment I

> noticed a regular blip on the EEG record, esp on the right, which I assume

> was heartbeat picked up from the earlobe references, which were touching her

> neck. What effect will this have on the recorded data? Would it be in the

> higher frequencies (like muscle artefact) or the lower frequencies (like eye

> blink)? I assume that I should have stopped and moved the reference

> electrodes up her ear off her neck. A learning for next time.

When you get the ActivEEG electrodes tihs problem should go away, since you can

easily use the mastoid bone for a reference. Usually the only way to get the

ECG artifact is to be over a blood vessel directly, and a small move usually

fixes it (unless you have a very overweight client). The pulse rate for most

people will be around 50-80/minute--around 1-1.5 Hz, so it would appear as very

slow activity, probably out of the range we are measuring. If it's strong

enough, it could result in some harmonics, spikes at multiples of the pulse

rate, but these would get smaller the higher the multiple.

> 2) I’ve just done a couple of assessments with the new spreadsheet (5

> April 05) and with both of them the variances were much greater between EC

> EO and Task than on the previous ones with the previous spreadsheet. The

> scale has also changed ( I assume this is just the addition of a decimal

> point). For one person there was great variance esp at P3/P4. For the

> other person it was much larger that her other variances generally in Beta

> and HiBeta at task.

Don't believe there has been a change in the variances lately, depending on how

early the sheet was that you were using before. At one point I was using

Coefficient of Variance (standard deviation divided by mean) and now I am using

Variance divided by mean (variance is standard deviation squared, so the number

will be larger). The spreadsheet sets the scale by itself depending on the

values shown by that client. Try rerunning old data in the new spreadsheet, and

the graphs should look about the same. The whole point of the display is to

identify those signals where there are more or larger outliers (i.e. a more

variable signal), so we would hope it would change from client to client.

Pete

Van Deusen

16246 SW 92nd Ave, Miami, FL 33157

305/251-0337 or (cellular) 305/321-1595

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