Subject: Re: Is there considerable phase locking up to 6 kHz? From: "Richard F. Lyon" <DickLyon(at)ACM.ORG> Date: Wed, 17 Mar 2004 07:59:04 -0800At 3:08 PM +0100 03/17/2004, Christian Kaernbach wrote: >Dear Chen-Gia Tsai, > >>I use three stimuli: >>A={400*9, 400*11, 400*13} Hz >>B={400*11, 400*13, 400*15} Hz >>C={400*13, 400*15, 400*17} Hz >> >>If we listen to [ABC], we can hear an ascending melody, > >I seem not to get your point. If ABC of the above three stimuli is >perceived as an ascending melody, this is surely due to their spectral >content being at increasingly high frequency values. The mid-frequncy of >A is 4400 Hz, of B 5200 Hz, of C it is 6000 Hz. Why should any simple >"place" model of pitch perception not predict that one perceives a >rising melody in ABC? > >Temporal pitch extraction would extract 400 Hz in all three cases (if >operating flawlessly, and all effects of compression etc. put aside) . >Thus, if listening to your temporal pitch extractor (if you were >selectively able to do so) you would hear 400, 400, 400 Hz, i.e. no rise >in pitch (but change in timbre). > >Best, >Christian Kaernbach Christian, Your question is a good one, and points out how much we assume and gloss over in these discussions. First of all, there are at least two relevant pitches. The ascending melody is almost certainly just the "place" pitch as you note. The "ambiguous musical pitch" is lower, and is the one determined (presumably) be temporal autocorrelation-like mechanisms. As you note, the period would correspond to 400 Hz. But the envelope period is 800 Hz. Complexes of odd-numbered unresolved or partially-resolved partials tend to have a somewhat ambiguous pitch, fighting between the low "fundamental" and a couple of values close to the "difference frequency" or "envelope frequency". For very high frequencies like these, the envelope is most salient, since there is not enough fine structure to notice that after one envelope period the fine structure is in reverse phase. Hence the question. If there is no phase locking or fine structure synchrony at all, you expect a pitch corresponding to the envelope frequency 800 Hz. With some synchrony, you expect a pitch corresponding to an autocorrelation peak that's shifted from the envelope period by about a half-cycle of the center frequency (many many experiments have shown such effects, and subtle variations on them, but mostly at lower frequencies). In the present question, it was noted, if I understood correctly, that the "musical pitch" was not 800, but near there and somewhat ambiguous. This is exactly what you would expect if autocorrelation mechanisms are at work on a small amount of information synchronized to the fine structure near the envelope peaks. But it you rule out synchrony, you have to invent other mechanisms. That's the step I object to. Some of the other responses to this discussion are real red herrings, I think. The ideal of "learning" at such a low level of the system is too far fetched to take seriously. And the idea that "FCT is the only realistic cochlear transform" is just a mathematician trying to force a biological system to be something he can analyze. Dick