Relationship between binaural characteristic delay and phase is consistent with cochlear disparities ARO 2012

1. Relationship between binaural characteristic delay
and phase is consistent with cochlear disparities
Shotaro Karino & Philip X. Joris
Lab. of Auditory Neurophysiology
Univ. of Leuven, Belgium
2. AN: single pair
3. AN: Four pair example
Methods
Introduction
The sensitivity of low-frequency binaural cells
in the inferior colliculus (IC) to interaural time
differences (ITDs) was discovered using pure
tones (Rose et al., 1966). That study
introduced the concept of characteristic delay
(CD) as the ITD of constant relative response
amplitude at different stimulus frequencies.
This concept was refined and put on a
quantitative basis by Yin and Kuwada (1983),
who also defined characteristic phase (CP)
as the frequency-independent component in
the relationship between best interaural
phase and frequency. McAlpine et al. (1996)
reported a surprising inverse relationship
between CD and CP, where large CDs are
associated with small, negative CPs and
large CPs with small, negative CDs. This
observation has not been followed up and its
basis is unclear.
• 4 cats, barbiturate anesthesia
• auditory nerve (AN) fiber recordings with
high impedance micropipettes (sequential)
• closed, calibrated acoustic system
• spike timing at 1 μs
• stimuli: long duration (1000/1500 ms) pure
tones straddling the response area
• analysis: count coincidences across spike
trains of pairs of nerve fibers, for different
delays (cross correlograms)
5. AN: CD-CP relationship
Phase-frequency
relationships for
different ranges of
CFs, pooled across
animals and SPLs.
Syncrate
superimposed in
color, normalized to
maximum.
Scale of ordinate
and abscissa is
identical for all plots.
Conclusions
6. Comparison AN-IC
CD-CP relationship for all pairs from 1 animal, with
maximal difference in CF of 0.1 octave.
Each datapoint is the CD-CP value for one AN pair,
measured with linear regression (weighted for syncrate).
CD-CP relationship in 4 animals, unsigned.
Maximal difference in CF was 0.3 octave.
Comparison of CD-CP relationship in IC (+)
with that expected from random cochlear
disparities (o).
• IC neurons show an inverse CD-CP relationship
(~ Mc Alpine et al., 1996)
• cochlear disparities can create a variety of phase-frequency
relationships
• linear fits to these phase-frequency functions also show an
inverse CD-CP relationship
• the inverse relationship is
qualitatively consistent with
spatial derivative of traveling
wave
Supported by the Fund for Scientific Research
– Flanders (G.0714.09 and G.0961.11),
and Research Fund K.U.Leuven
(OT/05/57 and OT/09/50).
CF reference: 1622 Hz
4. AN: population overview
1. IC: CD-CP relationship
A Tuning curves B coincidence counts
at different delays C Composite curve
D Phase-frequency plot based on
period histograms of B
E Time-frequency plot obtained by
multiplying phase (in D) by stimulus
period
CFs: 1509 Hz, 1622 Hz, DCF = 0.1 oct, 70 dB, BF pair = 1000 Hz
CD-CP relationship in the IC (N = 228).
Color code indicates best ITD (peak composite curve).
A phase-frequency curves of panel 3, restricted to syncrate > 0.7 of maximum.
B CD-CP relationship in the AN. Only pairs with CFs within 1/3 oct. are included.
C Model pairs to illustrate CD-CP relationship. Pairs within a row have the same
BF and best ITD (squares).
CD-CP analysis for one
IC neuron (CF 1.9 kHz).