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Hi Bob,
There are studies which suggest that place and pitch are far from synonymous. Consider Zheng's research and the references therein clearly demonstrate pitch reorganisation in rodents : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3438459/ Also Cariani's research into temporal properties of hearing, in papers from '96 to 2001 and more... suggest that in certain frequency ranges time codes dominate! Further, the alive and dead Cochlea exhibits large frequency shifts at the same place w.r.t. each other ... consequently it could be assumed that the neural control (efferent control) is very important for tuning our peripheral hearing circuit ... in my opinion, temporal control is working in conjunction with place effects... hard to think of them operating in isolation. In the hypothesised mixed mode cochlear amplifier, the degree of feedback is critical to the tuning properties of each Cochlear segment. http://adsabs.harvard.edu/abs/2011AIPC.1403..611F In a dead mouse ear, with no feedback, there is roughly a .25 octave shift (from memory) w.r.t. a healthy ear. Matt On 12/02/2012 07:47 AM, Bob Masta wrote: Can someone explain the supposed mechanism behind neural timing and pitch shift? I don't understand what is being proposed. As I undestand it, since pitch is encoded as *place* along the BM, the neurons respond with a firing rate that encodes *loudness* for their particular frequency place. The firing rate does not encode the frequency of the sound itself. What am I missing here? Best regards, Bob Masta ============= On 1 Dec 2012 at 9:50, Pierre Divenyi wrote:Hi Oded, Your three-step reasoning makes sense but, indeed, it should be experimentally verified. As to the age-related change of neural oscillations, Art Wingfield believes that the brain "slows down" as we get older. Such a slowing-down could also explain the upward AP shift because our reference would shift downward. How this central effect squares with the peripheral, BM-stiffening effect is unknown but, again, could be studied in the lab. -Pierre On 12/1/12 5:17 AM, "Oded Ghitza" <oghitza@xxxxxx> wrote: Hi Pierre, If (1) you accept Julius's model of pitch perception, (2) interpret -- as he did -- the central component of the model as a mechanism that adjusts f0 of an internal harmonic sieve to the point where the MMSE between the sieve and the input pattern is minimum, and (3) assume that such mechanism is realized by a neuronal circuitry with oscillations ("rhythms") at the core (maybe related to Langer, in the late 80's and in the context of pitch perception, who measured "temporal rings" in chicks); then, a possible way to examine the phenomenon (whether perceived pitch should go up or down, in particular), is to look at how the frequency range of neuronal oscillations change with age. -- Oded. |