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Re: Sound localization standard model question and confusion

I have a confusion about the evidence for elevation sound localization.

The current theory for sound localization in mammals (which I will refer to as the standard model) posits that azimuth localization is done by binaural cues (interaural time and level differences) and the elevation localization is performed by the monaural spectral cue. Further, the standard model has the elevation localization via that spectral analysis occurring in the dorsal cochlear nucleus (DCN). While I have some problems overall with the standard model, I want to address a confusion I have about the elevation localization part of the model and its supporting data.

The data that supports the DCN as the site of elevation localization is in two parts. The first, which is clear, is that the DCN is sensitive to spectral notches. The spectral notches are what carries the information imparted by the HRTF for elevations and azimuths. Then, because the DCN can perform that spectral notch analysis, and because the DCN only gets an auditory signal from the ipsilateral ear (thus monaural), the conclusion is the DCN could perform the elevation localization using the monaural signal. So far this is good. Further, since the DCN only has output to the inferior colliculus (IC), it is assumed the IC takes that DCN signal and uses it to determine the elevation of the sound.

This DCN to IC connection lead to the experiments that lesioned the connection from the DCN to the IC (the DAS); the expectation was, if the DCN is the processing unit for elevation localization, then elevation localization should be severely impaired. The experiment and data for this is from: May, B. (2000) "Role of the dorsal cochlear nucleus in the sound localization behavior of cats." The conclusion -- as used in all current textbooks -- based on this experiment (and one earlier one) is that the DCN does do the elevation localization.

See my data comparison at:
(sorry for the very long URL, blame Google Docs)

And this finally leads to my confusion: I do not see that conclusion in the data. I am baffled as to how that conclusion is reached. I have reproduced the data in a way to easily compare the before and after effects of the DAS severing. In that comparison; I have put the data only from the -30, 0, and +30 degree elevations (omitting the +60 degree line and two other points). If someone showed you that data and claimed it showed a treatment that destroyed elevation localization, what would you say? While clearly there is an effect on elevation localization (certainly for elevations above 30 deg), the hypothesis is that elevation localization is exclusively done in the DCN. To me, the a-priori expectation for the results seems not met.

Am I the only one with this confusion? This result is 11 years old; can anyone explain what is going on?

Thank you for your patience.
Mark Riggle