Responses of Neurons in the Auditory Pathway of the Barn Owl to Partially
Correlated Binaural Signals.
Albeck, Yehuda and Masakazu Konishi.
From.
APStracts 2:0179N, 1995.
SUMMARY AND CONCLUSIONS
1. Extracellular single-unit recording in anesthetized barn owls was used to
study neuronal response to dichotic stimuli of variable binaural correlation
(BC). Recordings were made in the output fibers of nucleus laminaris (NL), the
anterior division of the ventral lateral lemniscal nucleus (VLVa), the core of
the central nucleus of the inferior colliculus (ICcC), the lateral shell of
the central nucleus of the inferior colliculus (ICcLS) and the external
nucleus of the inferior colliculus (ICx). 2. The response of all neurons
sensitive to interaural time difference (ITD) varied with BC. The relationship
between BC and impulse number fits a linear, a parabolic, or a ramp model. A
linear or parabolic model fits most neurons in low-level nuclei. Higher-order
neurons in ICx, did not respond to noise bursts with strong negative binaural
correlation, creating a ramp-like response to BC. 3. A neuron's ability to
detect ITD varied as a function of BC. Conversely, a neuron's response to BC
changed with ITD. Neurons in NL, VLVa and ICcC show almost periodic ITD
response curves. In these neurons peaks and troughs of ITD response curves
diminished as BC decreased, creating a flat ITD response when BC = 0. When BC
was set to -1, the most favorable ITD became the least favorable one and vice
versa. The ITD response curve of ICx neurons usually has a single dominant
peak. The response of those neurons to a negatively correlated noise pair (BC
= -1) showed two ITD peaks, flanking the position of the primary peak. 4. The
parabolic BC response of NL neurons fits the prediction of the cross-
correlation model, assuming half-wave rectification of the sound by the
cochlea. Linear response is not predicted by the model. However, the parabolic
and the linear neurons probably do not belong to two distinct groups as the
difference between them is not statistically significant. Thus, the cross-
correlation model provides a good description of the binaural response not
only in NL but also in VLVa and ICcC. 5. Almost all ramp neurons occured in
either ICx or ICcLS where neurons are more broadly tuned to frequency than
those in the lower nuclei. The synthesis of this response type requires,
however, not only the convergence of different frequency channels but also
inhibition between different ITD channels. We modeled the ramp response as a
three-step process. First, different spectral channels converge to create
broad frequency tuning. The response to variation in BC will be linear (or
parabolic) because it is a sum of linear (parabolic) responses. Second, the
activity in some adjacent ITD channels is subtracted by lateral inhibition.
Finally, the result is rectified using a high threshold to avoid negative
activity.
Received 4 August 1994; accepted in final form 4 June 1995.
APS Manuscript Number J485-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.