Auditory midbrain laminar structure appears adapted
to f0 extraction: further evidence and implications of the double critical
bandwidth
Martin Braun
Hear Res 1999, Mar, 129:1-2, 71-82
Abstract
The psychoacoustic 'critical bandwidth' (CB), e.g. approximately 2.6 semitones
(= 0.22 octave) at 1.5-3 kHz, is known from many spectral integration
phenomena. Cat data suggest that it is represented in the inferior colliculus
(IC) (Ehret and Merzenich, 1985, Science 227, 1245-1247), where it is
consistently related to the fibrodendritic laminae (Schreiner and Langner,
1997, Nature 388, 383-386). The recent discovery of the CB and the double
CB (2CB) in the statistics of frequency spacing of spontaneous otoacoustic
emissions (Braun, 1997. Hear. Res. 114, 197-203) has initiated further
investigations of the novel phenomenon of 2CB. Meta-analysis of psychoacoustic
valuation studies of pure-tone intervals again revealed the effects of
CB and 2CB. Valuations showed a significant stepwise change with interval
size: <CB unpleasant, CB-2CB pleasant, >2CB indifferent. Scrutiny
of cat and human data indicated that for both species, at least in the
midspectrum (1-3 kHz in humans), the tonotopic ranges within single IC
laminae and the tonotopic distances between neighboring laminae may equal
1 CB (distances to second next laminae being 2CB). This unique architecture
would provide the most economical neural convergence of period information
from pairs of adjacent harmonic partials 3-6 of complex sound. The resulting
summed postsynaptic potentials would thus contain a beat frequency equaling
f0 of sound input and being detectable by the known neural behavior of
characteristic periodicity response.
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