Nice to see that we finally have another BM question here..it has been a while..
I hope I got your question correctly...Let me try to give you an answer and a couple of comments:
On your question "Do the BM's in a dichotic experiment using two harmonically related
tones (e.g. 200/300 hz) have the same vibration profile or are they
- I guess you mean by "dichotic" in this context that you present one tone (i.e., 200Hz) to one ear and the other one to the other ear (if you mean just the same signal to both ears, which would be called diotic, due to symmetry reasons they can not be different). Following current theories (out there in the literature), the BM vibrations have different vibration profiles for different frequencies in the sense that if you would "plot" them overlapping, they would not match exactly. There is (afaik) no experiment that directly looked at that, but since the two frequencies do project on different places on the BM, there is hardly any reason to think that the sum of these two would not (although there is some interaction, see e.g. two-tone suppression).
On your question "but then it opens up the question of how one perceives the fundamental."
- This is an old question, related to theories about pitch (place vs. time coding). Have a look at these theories (and there are other members on the list that are much more experts on pitch). Even though I heard people (and it is a good working hypothesis) say "The brain exists to keep the cochlea warm", there is some computation going on in the brain. So no need (and no good reason) to try and explain everything by BM coding.
On your idea "If the same, it opens up possibilities of a feedback process involving higher levels of the auditory system."
- We know that there are efferents in the system, even though the exact role is still unclear and disputed. From all we know (von Békésy's work, physiology, oae, models...), it is hard to not conclude that the two vibrations are different. Everything else is not supported by data and/or models - and innovative ideas are essential, but still need support, especially if about a topic we do have access to experimentally.
There are alternative approaches to the traveling wave, but I guess (and maybe Andrew Bell can comment on that) they would agree as well.
There is an extensive literature out there, and if pitch is what you are interested in, this seems to be a good starting point to check out old and current theories of pitch. For that purpose, it is sufficient to assume that the BM does the job of a very good frequency analyzer and that cochlear processing is a pure bottom-up process.
Hope that helps...
All the best
On 07/08/12 16:36, Ranjit Randhawa wrote:
Dear List, I have always wondered about what drives BM vibrations and decided it depends on how one answers the following question. Do the BM's in a dichotic experiment using two harmonically related tones (e.g. 200/300 hz) have the same vibration profile or are they different? If different, then one can assume that the stimulus drives such vibration, but then it opens up the question of how one perceives the fundamental. If the same, it opens up possibilities of a feedback process involving higher levels of the auditory system. I don't know if this is beyond the scope of this forum in which case I apologize. However, if this topic is not too crazy, I would welcome any answers, guesses or speculations. Thanking in advance, Randy Randhawa