Thanks for your replies @wjcroft!
I was not aware of the Vernon paper. I did a very cursory literature search before we started experimenting, but mostly found papers on various psychological and cognitive effects of binaural beats, not on measured entrainment.
It’s interesting that the frequencies that we tried (8 and 17 Hz) are in or close to the range where Vernon et al. and Goodin et al. both looked for and failed to find any entrainment effect.
It looks, from reading both these papers (Goodin’s 2012 PLoS One paper is here: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0034789), like the alpha and beta bands have proved resistant to binaural beat entrainment in several (though not all) other studies as well.
Interestingly, Vernon suggests that future studies should try binaural beat “bursts”, shorter even than their one minute trial segments. This is somewhat contradictory to the feedback we got from many people suggesting that our segments were too short, and we needed to try a longer time in order for entrainment to occur.
I think the next step in our binaural investigation is a more thorough look at the existing literature. I will probably compile a short-form summary of the design and results of previous experiments. Once I’ve got a better understanding of what has been tried so far, and what has worked and what hasn’t, we’ll see if we can come up with a good experiment design that will give the best shot at successful entrainment and hopefully shed some additional light on what makes binaural beats seemingly ineffective in some circumstances and seemingly effective in others.
I think a possibility would be to do an experiment that had ~20 minute segments and included both time periods where attention was focused on the beat audio and where it was focused elsewhere (as in Vernon and Goodin’s tests).
Attentional focus is a variable that does not seem to have been well explored in the binaural beat entrainment literature I’ve seen so far.
Regarding detection and electrode placement: it seems to me that the beat frequency would necessarily be detectable somewhere in the auditory processing areas of the brain. But, this probably would not qualify as supporting the hypothesis of entrainment, since the hypothesis is that there is a FFR that leads to larger-scale changes in frequency and thereby to changes to cognition or consciousness. In principle, I suppose this means that binaural beat research has to make some principled distinction as to what “counts” as entrainment. Probably this distinction could be informed by neurofeedback studies. In practice, though, given that even a “high density” recording like that taken by Goodin et al. did not detect a frequency effect from the binaural beats, it seems likely that surface electrodes are not sensitive and precise enough to detect non-entrainment (if that’s a meaningful term) binaural beat neural activity.
Thanks for your comments, and for bringing your knowledge and experience to the discussion.
