Success! 8 of 10 dissertation experiments
Well today was the day that would never end. I only had one experiment today, but it took the whole day. To be fair, we didn’t start until the afternoon, but it was well into the evening when we wrapped up and that was exhausting. Since it’s been such a long day, I’ll recap how things went. For everyone who’s interested, but also for myself since I hope this will help with my dissertation writing sooner or later.
It seems like only yesterday I hit the halfway point, but we’re already 80% done with the data collection for aim 1. Which means that we can finally answer the big question, does my “super secret technique” (SST), the thing I did for my qualifying exam, actually work? Or was it just a big fluke? I’ve looked over that qualifying exam data several times since first collecting it and defending my QE. If it’s an error in the way I processed it, I can’t find it. That doesn’t mean it’s meaningful though and to answer that question we need more than one person!
Next week I plan to start the data analysis. It needs to go quickly, because things need to hurry along at this point. However, until I get my last two datasets, which happens tomorrow FYI, there’s not a lot of free time. Ugh it’s so stressful not knowing if I have something or not I haven;’t even started recapping the events of the day and we’re already three paragraphs deep! Okay, back to the topic at hand.
The data collection went smoothly once we started. I had some seriously obnoxious impedance issues for whatever reason today. I’m not sure if it was an equipment issue, or if it was person specific, but man did I spend twice as long on setup as I would normally only to have the equipment not care. I mean eventually we got it marginally good, as in within an acceptable range, but not great, so there’s that. But man was it a battle start to finish. I feel like it’s a lot like working on a car. No matter which bolts you start loosening, the last one always, always, gives you trouble.
Once we got started though everything went super smooth and I got the data I needed. Checking impedances post experiment, which we do always, showed they at least remained stable(ish). Normally they improve as the gel warms up, but they were still in the acceptable, but not great range.
So impedance is a measure of how hard it is for electricity to travel across something. Think of it like a material is impeding the flow. Since EEG records electrical activity from the brain, high impedance means less signal reaching the sensor because it has a harder time traveling across the scalp to the sensor (through everything in between, which means hair). This lowers the signal to noise ratio, meaning more noise, less signal (the thing we’re interested in recording). An infinitely high impedance for example would mean you just have line noise and whatever else electrical interference you can pick up.
More often than not, we can get the impedances pretty low (for EEG that is), anything under 20 kOhm is, for out application considered great, anything between roughly 20-60 kOhm is considered okay, and anything higher and you might as well just put it away because you’re not going to have much to show for your efforts. Which is why we measure impedances before and after our experiments, to verify we have good data and sometimes we include this information in papers so others know that our data are good.
So yeah, it was one of those days where impedances were 150+ kOhm and nothing I did could fix it. I’m assuming it’s equipment related, but who even knows? The moon might not have been in the right spot in the sky, a bird in Germany flew left instead of right, it’s just one of those unknowable things. It could be a skin thing too, who knows? The equipment has been cleaned and I’m hoping it won’t be a problem for the next person, sometimes oxidation builds up on the electrode, so scraping it gently to remove that oxidation can help drive impedances lower. Basically anything I could think to do to fix the problem has been done and with any luck tomorrow will go off without too much problems.
Tomorrow will be another long day, so tomorrow’s post will probably come late too. For now I’m going to try to unwind a bit and brace myself for tomorrow coming far sooner than I want.
One more day…