The neural coding of auditory space

1989 ◽  
Vol 146 (1) ◽  
pp. 307-322 ◽  
Author(s):  
T. T. Takahashi
Keyword(s):  
Inferior Colliculus ◽  
Auditory System ◽  
Phase Difference ◽  
Neural Coding ◽  
Interaural Time Difference ◽  
Limited Range ◽  
Directional Sensitivity ◽  
Amplitude Difference ◽  
Interaural Phase ◽  
Interaural Phase Difference

The barn owl's auditory system computes interaural differences in time and amplitude and derives from them the horizontal and vertical coordinates of the sound source, respectively. Within the external nucleus of its inferior colliculus are auditory neurones, called ‘space-specific neurones’, that have spatial receptive fields. To activate a space-specific neurone, a sound must originate from a circumscribed region of space, or, if the sounds are delivered to each ear separately, using earphones, the stimuli must have the combination of interaural time and amplitude difference that simulates a sound broadcast from their receptive field. The sound-localization cues are processed in parallel, non-overlapping pathways extending from the cochlear nuclei to the subdivision of the inferior colliculus that innervates the space-specific neurones. Processing in the time pathway involves the coding of monaural phase angle, the derivation of sensitivity for interaural phase difference, and the calculation of interaural time difference (ITD) from interaural phase difference. The last process involves groups of neurones in the inferior colliculus whose collective firing signals a unique ITD, even though the activity of each constituent neurone signals multiple ITDs. The projections of these ensembles to the space-specific neurone endow the latter with a selectivity for ITD. Processing in the amplitude channel, about which less is known, initially involves an inhibitory process that sharpens the directional sensitivity of neurones in a lateral lemniscal nucleus. The inhibition is mediated by a commissural projection from the same lemniscal nucleus of the opposite side. At higher levels of the auditory system, neurones that are tuned to a limited range of interaural amplitude differences are found. It is proposed that at these higher stages, interaural amplitude difference, like ITD, is coded amidst an ensemble of neurones.

scholarly journals First Spike Latency Code for Interaural Phase Difference Discrimination in the Guinea Pig Inferior Colliculus

2011 ◽  
Vol 31 (25) ◽  
pp. 9192-9204 ◽  
Author(s):  
O. Zohar ◽  
T. M. Shackleton ◽  
I. Nelken ◽  
A. R. Palmer ◽  
M. Shamir
Keyword(s):  
Guinea Pig ◽  
Inferior Colliculus ◽  
Phase Difference ◽  
Interaural Phase ◽  
Interaural Phase Difference ◽  
Spike Latency

scholarly journals Temporal characteristics of neural sensitivities to the interaural phase difference in the inferior colliculus

2002 ◽  
Vol 23 (5) ◽  
pp. 286-286
Author(s):  
Shigeto Furukawa ◽  
Katuhiro Maki ◽  
Makio Kashino ◽  
Hiroshi Riquimaroux ◽  
Tatsuya Hirahara
Keyword(s):  
Inferior Colliculus ◽  
Phase Difference ◽  
Temporal Characteristics ◽  
Interaural Phase ◽  
Interaural Phase Difference

Interaural Phase Disparity of Stutterers and Nonstutterers

1972 ◽  
Vol 15 (4) ◽  
pp. 771-780 ◽  
Author(s):  
Courtney Stromsta
Keyword(s):  
Control System ◽  
Phase Shift ◽  
Phase Difference ◽  
Auditory Feedback ◽  
Laryngeal Function ◽  
Interaural Phase ◽  
Frequency Criterion ◽  
Interaural Phase Difference ◽  
The Mean ◽  
Phase Differences

Stutterers and nonstutterers cancelled the auditory sensation evoked by bone-conducted sinusoidal signals. They accomplished this by appropriate phase and amplitude adjustments of simultaneously presented bilateral air-conducted signals of the same frequency. Criterion measures of interaural phase difference at the point of cancellation were obtained for seven frequencies. The mean interaural phase differences obtained by stutterers were consistently greater than those of the nonstutterers. Based on time-equivalent values of the mean interaural phase differences, the values for stutterers were approximately twice as great as for nonstutterers at 150, 300, and 1200 Hz. The mean interaural phase difference found to exist for stutterers at 150 Hz approximates the magnitude of phase shift of normally delayed air-conducted auditory feedback of speech sounds that serves to induce experimental blockage of phonation. This relationship, in view of other findings, offers credence to the idea that disturbance of laryngeal function effected by an anomalous audition-phonation control system could be a causative agent in stuttering.

scholarly journals Representation of Dynamic Interaural Phase Difference in Auditory Cortex of Awake Rhesus Macaques

2009 ◽  
Vol 101 (4) ◽  
pp. 1781-1799 ◽  
Author(s):  
Brian H. Scott ◽  
Brian J. Malone ◽  
Malcolm N. Semple
Keyword(s):  
Auditory Cortex ◽  
Phase Difference ◽  
Rhesus Macaques ◽  
Discharge Rate ◽  
Auditory Pathway ◽  
Neural Representation ◽  
Characteristic Analysis ◽  
Binaural Cues ◽  
Interaural Phase ◽  
Interaural Phase Difference

Neurons in auditory cortex of awake primates are selective for the spatial location of a sound source, yet the neural representation of the binaural cues that underlie this tuning remains undefined. We examined this representation in 283 single neurons across the low-frequency auditory core in alert macaques, trained to discriminate binaural cues for sound azimuth. In response to binaural beat stimuli, which mimic acoustic motion by modulating the relative phase of a tone at the two ears, these neurons robustly modulate their discharge rate in response to this directional cue. In accordance with prior studies, the preferred interaural phase difference (IPD) of these neurons typically corresponds to azimuthal locations contralateral to the recorded hemisphere. Whereas binaural beats evoke only transient discharges in anesthetized cortex, neurons in awake cortex respond throughout the IPD cycle. In this regard, responses are consistent with observations at earlier stations of the auditory pathway. Discharge rate is a band-pass function of the frequency of IPD modulation in most neurons (73%), but both discharge rate and temporal synchrony are independent of the direction of phase modulation. When subjected to a receiver operator characteristic analysis, the responses of individual neurons are insufficient to account for the perceptual acuity of these macaques in an IPD discrimination task, suggesting the need for neural pooling at the cortical level.

scholarly journals Azimuth and envelope coding in the inferior colliculus of the unanesthetized rabbit: effect of reverberation and distance

2014 ◽  
Vol 112 (6) ◽  
pp. 1340-1355 ◽  
Author(s):  
Shigeyuki Kuwada ◽  
Brian Bishop ◽  
Duck O. Kim
Keyword(s):  
Inferior Colliculus ◽  
Auditory System ◽  
Neural Coding ◽  
Neural Responses ◽  
Auditory Space ◽  
Unanesthetized Rabbit ◽  
Reverberant Environments ◽  
Monaural Stimulation ◽  
Neural Gain

Recognition and localization of a sound are the major functions of the auditory system. In real situations, the listener and different degrees of reverberation transform the signal between the source and the ears. The present study was designed to provide these transformations and examine their influence on neural responses. Using the virtual auditory space (VAS) method to create anechoic and moderately and highly reverberant environments, we found the following: 1) In reverberation, azimuth tuning was somewhat degraded with distance whereas the direction of azimuth tuning remained unchanged. These features remained unchanged in the anechoic condition. 2) In reverberation, azimuth tuning and envelope synchrony were degraded most for neurons with low best frequencies and least for neurons with high best frequencies. 3) More neurons showed envelope synchrony to binaural than to monaural stimulation in both anechoic and reverberant environments. 4) The percentage of envelope-coding neurons and their synchrony decreased in reverberation with distance, whereas it remained constant in the anechoic condition. 5) At far distances, for both binaural and monaural stimulation, the neural gain in reverberation could be as high as 30 dB and as much as 10 dB higher than those in the anechoic condition. 6) The majority of neurons were able to code both envelope and azimuth in all of the environments. This study provides a foundation for understanding the neural coding of azimuth and envelope synchrony at different distances in reverberant and anechoic environments. This is necessary to understand how the auditory system processes “where” and “what” information in real environments.

scholarly journals Dependency of the Interaural Phase Difference Sensitivities of Inferior Collicular Neurons on a Preceding Tone and Its Implications in Neural Population Coding

2005 ◽  
Vol 93 (6) ◽  
pp. 3313-3326 ◽  
Author(s):  
Shigeto Furukawa ◽  
Katuhiro Maki ◽  
Makio Kashino ◽  
Hiroshi Riquimaroux
Keyword(s):  
Phase Difference ◽  
Channel Model ◽  
Population Coding ◽  
Vector Model ◽  
Neural Population ◽  
Population Vector ◽  
Interaural Phase ◽  
Interaural Phase Difference ◽  
Inferior Collicular ◽  
The Difference

This study examined the sensitivities of the neuronal responses in the inferior colliculus (IC) to the interaural phase difference (IPD) of a preceding tone, and explored its implications in the neural-population representation of the IPD. Single-unit responses were recorded from the IC of anesthetized gerbils. The stimulus was a dichotic tone sequence with a common frequency (typically the unit’s best frequency) and level (10–20 dB relative to the threshold), consisting of a conditioner (200 ms) followed by a probe (50 ms) with a silent gap (5–100 ms) between them. The IPDs of the 2 tones were varied independently. The presence of a conditioner generally suppressed the probe-driven responses; the effect size increased as the conditioner IPD approached the unit’s most responsive IPD. The units’ preferred IPDs were relatively invariant with the conditioner IPD. Two types of models were used to evaluate the effects of a conditioner on the IPD representation at the level of IC neural population. One was a version of the population-vector model. The other was the hemispheric-channel model, which assumed that the stimulus IPD is represented by the activities of 2 broadly tuned hemispheric channels. Both models predicted that, in the presence of a conditioner, the IPD representation would shift in a direction away from the conditioner IPD. This appears to emphasize the difference between the conditioner and the probe IPDs. The results indicate that in the IC, neural processes for IPD adapt to the stimulus history to enhance the representational contrast between successive sounds.

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