ORCID Profile
0000-0001-5893-4525
Current Organisation
University of Nottingham
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Publisher: Springer Science and Business Media LLC
Date: 04-2001
DOI: 10.1038/86049
Publisher: Elsevier BV
Date: 11-2000
DOI: 10.1016/S0378-5955(00)00187-8
Abstract: Convergent input from cells in the medial superior olive (MSO) and lateral superior olive (LSO) onto a single inferior colliculus (IC) cell explains many findings that are not compatible with a simple coincidence detector mechanism. Here this explanation is tested using a physiologically accurate computer model of the binaural pathway in which the input to the IC cell is either from two MSO cells or a MSO and a LSO cell. Auditory nerve (AN) spike trains are formed by a stochastic hair cell model following a basilar membrane simulation using a gammatone filter. In subsequent cells input spikes cause post-synaptic potentials (PSPs) which are summed causing the cell to fire when the sum crosses a threshold. The in idual cells are matched to the physiology by varying the number of inputs, the magnitude and duration of the PSPs and the firing threshold. Non-linear best-phase-versus-frequency functions arise if the two IC inputs have different best frequencies and different characteristic delays. One input can be selectively suppressed by turning on an additional tone at the worst phase of that input. Non-zero characteristic phases arise if the characteristic frequencies of the AN fibres feeding into a single superior olive cell are mismatched.
Publisher: Acoustical Society of America (ASA)
Date: 07-1996
DOI: 10.1121/1.415862
Abstract: The binaural masking level difference (BMLD) is a striking and well-documented psychophysical effect which relates to the ability to use the phase of low-frequency sounds to dissociate them from masking noise. When identical tones and noise are presented to both ears, detectability is improved by up to 15 dB simply by inverting the phase of either the tone or noise in one ear. Measurements of BMLDs were made in single delay-sensitive neurones in the inferior colliculus of the guinea pig. These have confirmed and extended an earlier report [D. M. Caird, A. R. Palmer, and A. Rees, Hear. Res. 57, 91–106 (1991)] by demonstrating that when signals are optimized for the frequency, level, and interaural delay sensitivities of each neurone, BMLDs can be measured which are in a direction, and of a magnitude, consistent with appropriate psychophysical observations in human subjects. In addition, BMLDs were found to be consistent with the delay sensitivities of the neurones to the signal and masker, the major determinant of the masked threshold for optimized signals being the activity evoked in the neurone by the masking noise. Within-channel signal-to-noise (S/N) ratios at masked threshold for single neurones varied from +20 to −7 dB, depending on the binaural configuration and the units’ delay sensitivities. In single neurones, the size of the BMLD for optimized signals increased with the level of the noise. The BMLD increased by 5 dB over a 40-dB range of noise, consistent with psychophysical observations. This came about because as noise level increased, masked threshold for optimized tones increased more slowly in Nπ noise than in N0 noise. For all binaural comparisons, both positive (π signals more detectable, as in the psychophysics) and negative BMLDs were observed, often in the same neurone, a result entirely consistent with the sensitivity to the interaural delay of the noise and tone signals. For 500-Hz signals in zero and π phase masked by identical noise the majority of BMLDs determined with the PEST procedure was negative, a result which is taken to indicate that increases in spike rate may not be an appropriate cue for masked threshold under these conditions.
Publisher: Acoustical Society of Japan
Date: 2002
DOI: 10.1250/AST.23.61
Publisher: Oxford University PressNew York
Date: 05-01-2009
DOI: 10.1093/ACPROF:OSO/9780195148220.003.0014
Abstract: This chapter shows that careful attention to the frequency range over which interaural time difference (ITD) -processing is carried out has important consequences both for the form of the sensory representation of ITDs and the means by which this sensory representation is translated in the central nervous system. Cross-species comparisons have proved to be a powerful tool in furthering the understanding of the brain. However, in some instances, even when basic neural mechanisms appear completely analogous, care needs to be exercised before accepting that this implies a complete commonality.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Alan Palmer.