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Not too surprising, considering brainwave frequencies aren't so far from the tempo bpm or the speed of vibrato and etc commonly used in music. When you think about the degree of focus it takes to play, and that the focus when playing a duet will have the beat as a commonality, one would pretty much expect the brainwaves to be affected similarly.
Now what would have been interesting would have been if they had also been monitoring some listeners, to see what % of listeners ended up In sync with the performer's brainwaves.
But music does that. "Sonic driving" of brainwaves via sound is a pretty well known effect. It is part of what makes music sometimes actually kind of mind-altering or mood altering in a very real nuts and bolts sort of way. Slower beats/tempos in music can correspond to brain frequencies that are active when people are asleep or relaxed. Faster beats can relate to brainwave frequencies dealing with more alert frames of mind.
A couple quick examples..
Bach's Jesu would be in the brain's delta wave (deep sleep) or, if one considered the pacing of the notes with their durations, more like theta (dreaming) range.
This piece, on the other hand is largely in the beta range, which is what is what the brain frequencies are doing when you are alert, and doing analytical or logical thinking..
For some people the effect will be more noticeable than others folks. But the rather direct effect that is possible on the brain's electrical activity, especially when the sound is at concert volumes and the attentions focussed on it is part of what is cool about music and some of the mechanics of how it can change a person's mood or frame of mind while listening.
"This young wine may have a lot of tannins now, but in 5 or 10 years it is going to be spectacular, despite the fact that right now it tastes like crude oil. You know this is how it is supposed to taste at this stage of development." ~ Itzhak Perlman
When you do anything accompanied, even if it's jogging, there's unconscious mutual motivation involved, that's true. But I once duetted a Dvorak Slavonic dance with a friend at a concert and one of us finished a bar before the other, lol.
And I've seen Perlman finish pieces half a bar before his accompanist.
@Gordon Shumway Curious, was this a piece that you both knew by heart or where you focused in on the sheet music?
I ask because I focus in on the music, I live inside the beat of the music, if the people I play with get off time or hit a few bad notes while I'm paying attention to them my train jumps track and apparently collides with every tree in the forest. Hard to recover.
If I continue to play it means I was either focused in on the sheet music or just not paying attention to what anyone else was doing.
Shane "Chicken" Wang said
was this a piece that you both knew by heart or where you focused in on the sheet music?
Bit of both, I think. We'd rehearsed it well, but we were both reading from music. It's just that a dozen bars from the end there was an accelerando, and we both accelerated at different rates. With hindsight, that was an obvious stumbling block we could have rehearsed more, or maybe it was just a case of forgetting to listen to each other.
Understand that. Had a night at a county fair opening for Doug Stone in a fantastic country band that died from outside interference from the "manager", who coincidentally owned the bus, go figure.
We could swap instruments back and forth and one of the gags was that no one would take my sax. I was playing bass and trying to sing a Keith Whitley song called Back to You,(High road low road, some old side road, really don't matter to me, If it gets me, back to you). Somewhat fast paced. The drummer kept changing the tempo until I broke. Which turned into watermelon cantaloupe. ( you can sing any church song with the words watermelon cantaloupe as long as you keep the tempo, no one really notices.)
I never thought of my brain sinking up with other people, that could have lasting side effects on some, but I have had many experiences where it felt like everyone was in the same track and several where I just wanted to jump from the burning building.