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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
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
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.