scholarly journals Responses of Neurons in the Inferior Colliculus to Binaural Masking Level Difference Stimuli Measured by Rate-Versus-Level Functions

1997 ◽  
Vol 77 (6) ◽  
pp. 3085-3106 ◽  
Author(s):  
Dan Jiang ◽  
David McAlpine ◽  
Alan R. Palmer
Keyword(s):  
Inferior Colliculus ◽  
Discharge Rate ◽  
Detection Threshold ◽  
Low Frequency ◽  
Broadband Noise ◽  
Coincidence Detection ◽  
Level Difference ◽  
Rate Versus ◽  
Versus Level ◽  
Masking Level Difference

Jiang, Dan, David McAlpine, and Alan R. Palmer. Responses of neurons in the inferior colliculus to binaural masking level difference stimuli measured by rate-versus-level functions. J. Neurophysiol. 77: 3085–3106, 1997. The psychophysical detection threshold of a low-frequency tone masked by broadband noise is reduced by ≤15 dB by inversion of the tone in one ear (called the binaural masking level difference: BMLD). The contribution of 120 low-frequency neurons (best frequencies 168–2,090 Hz) in the inferior colliculus (ICC) of the guinea pig to binaural unmasking of 500-Hz tones masked by broadband noise was examined. We measured rate-level functions of the responses to identical signals (So) and noise (No) at the two ears (NoSo) and to identical noise but with the signal inverted at one ear (NoSπ): the noise was 7–15 dB suprathreshold. The masked threshold was estimated by the standard separation, “D”. The neural BMLD was estimated as the difference between the masked thresholds for NoSo and NoSπ. The presence of So and Sπ tones was indicated by discharge rate increases in 55.3% of neurons. In 36.4% of neurons, the presence of So tones was indicated by an increase in discharge rate and Sπ tones by a decrease. In 6.8% of neurons, both So and Sπ tones caused a decrease in discharge rate. In only 1.5% of neurons was So indicated by a decrease and Sπ by an increase in discharge rate. Responses to the binaural configurations were consistent with the neuron's interaural delay sensitivities; 34.4% of neurons showing increases in discharge rate to both So and Sπ tones gave positive BMLDs ≥3 dB (Sπ tones were detected at lower levels than So), whereas 37.3% gave negative BMLDs ≥3 dB. For neurons in which So signals caused an increase in the discharge rate and Sπ a decrease, 72.7% gave positive BMLDs ≥3 dB and only 4.5% gave negative BMLDs ≥3 dB. The results suggest that the responses of single ICC neurons are consistent with the psychophysical BMLDs for NoSo versus NoSπ at 500 Hz, and with current binaural interaction models based on coincidence detection. The neurons likely to contribute to the psychophysical BMLD are those with BFs near 500 Hz, but detection of So and Sπ tones may depend on different populations of neurons.

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. II. Responses to band-pass filtered noises

1987 ◽  
Vol 58 (3) ◽  
pp. 543-561 ◽  
Author(s):  
J. C. Chan ◽  
T. C. Yin ◽  
A. D. Musicant
Keyword(s):  
Inferior Colliculus ◽  
Time Delays ◽  
Discharge Rate ◽  
Low Frequency ◽  
Central Peak ◽  
Broadband Noise ◽  
Central Nucleus ◽  
Rate Curve ◽  
Median Frequency ◽  
Band Pass

1. We studied cells in the central nucleus of the inferior colliculus of the cat that were sensitive to interaural time delays (ITDs) in order to evaluate the influence of the stimulus spectrum of noise signals. Stimuli were sharply filtered low-, high-, and band-pass noise signals whose cutoff frequencies and bandwidths were systematically varied. The responses to ITDs of these noise signals were compared with responses obtained to ITDs of broadband noise and pure tones. 2. The discharge rate in response to band-pass noise as a function of ITD was usually a cyclic function with decreasing peak amplitudes at longer ITDs. The reciprocal of the mean interval between adjacent peaks indicated how rapidly the response rate varied with ITD and was termed the response frequency (RF). This RF was approximately equal to the median frequency of the stimulus spectrum filtered by the cell's sync-rate curve, which was the product of the synchronization to interaural phase and the discharge rate plotted against frequency. This suggests that the RF was determined by all the spectral components in the stimulus that fell within the frequency range in which the cell's response was synchronized. The contribution of each component was proportional to the sync-rate for that frequency. 3. The central peak of the ITD function usually fell within the physiological range of ITDs (+/- 400 microseconds). The location of this peak did not vary significantly with changes in stimulus spectrum by comparison with responses to tones of different frequency. Its shape also remained constant, except for a decrease in width when high-frequency components within the range of the sync-rate curve were added to the stimulus. A few cells responded with a minimal discharge instead of a maximal near-zero ITD, and this central minimum had similar properties as the central peak. The amplitude of the secondary peaks of the ITD function decreased as the stimulus bandwidth that overlapped the sync-rate curve broadened. 4. The sum of the ITD functions to two band-pass signals was similar to that of a broadband signal whose spectrum was composed of the sum of the band-pass spectra. 5. From these binaural responses we could make inferences about the response characteristics of the monaural inputs to binaural neurons. We then verified these predictions by studying responses of low-frequency trapezoid body fibers to band-pass noises.

Neural Responses in the Inferior Colliculus to Binaural Masking Level Differences Created by Inverting the Noise in One Ear

2000 ◽  
Vol 84 (2) ◽  
pp. 844-852 ◽  
Author(s):  
Alan R. Palmer ◽  
Dan Jiang ◽  
David McAlpine
Keyword(s):  
Inferior Colliculus ◽  
Discharge Rate ◽  
Low Frequency ◽  
Signal Frequency ◽  
Binaural Processing ◽  
Average Value ◽  
Masking Level Difference ◽  
Masking Noise ◽  
Interaural Time Delay ◽  
Lower Magnitude

We have measured the responses of inferior colliculus neurons in the anesthetized guinea pig to signals which in human psychophysical experiments reveal a release of masking as a result of binaural processing (the binaural masking level difference: BMLD). More specifically we have used diotic tones at 500 Hz (So) masked by noise that is either identical at the two ears (No) or inverted in one ear (Nπ). This combination of signals and noise maskers produces a prominent masking release in humans such that the So signal is about 6–12 dB more detectable in the presence of the Nπ noise than the No noise. Low-frequency inferior colliculus neurons are sensitive to the interaural delay of the masking noise and generally respond most to the components nearest their best frequency. Since most inferior colliculus neurons have peaks in their delay functions close to zero interaural time delay this means that while No noise is effective in driving the unit, Nπ noise is much less effective. As the level of an So tone was progressively increased in the presence of No and Nπ noises, the first response could be either an increase or a decrease in the activity due to the noise. However, because Nπ generated little or no activity itself, the predominant response to the So tone was an increase in discharge in this condition. Masked thresholds were defined as the point at which the standard separation D (related to the d′ of signal detection theory) = 1 in either direction. BMLDs were measured in single neurons and in the majority of units were in a direction consistent with the psychophysical observations irrespective of the direction of the discharge rate change that occurred at threshold. The lowest masked thresholds always occurred at or near the signal frequency of 500 Hz. An average value of the single unit BMLD around 500 Hz was 3.6 dB (NoSo vs. NπSo) compared with 6.6 dB for the NoSo versus NoSπ BMLD we had previously reported. This lower magnitude is consistent with the hierarchy of human psychophysical BMLDs.

Temporal Damping in Response to Broadband Noise. II. Auditory Nerve

2008 ◽  
Vol 99 (4) ◽  
pp. 1942-1952 ◽  
Author(s):  
Philip X. Joris ◽  
Dries H. Louage ◽  
Marcel van der Heijden
Keyword(s):  
Inferior Colliculus ◽  
Auditory Nerve ◽  
Low Frequency ◽  
Auditory Pathway ◽  
Broadband Noise ◽  
Linear Summation ◽  
Interaural Time Differences ◽  
Oscillatory Response ◽  
Original Report ◽  
Composite Curve

II. Auditory nerve. Low-frequency neurons in the inferior colliculus (IC) show a damped oscillatory response as a function of interaural time differences (ITDs) of broadband noise. It was previously shown that several features of such noise-delay functions are well predicted by the composite curve, generated by the linear summation of responses to tones with varying ITD. This indicates a surprising degree of linearity at the midbrain level of the auditory pathway. A similar comparison between responses to tones and to noise has not been made at a more peripheral, monaural level and it is therefore unclear to what extent this linearity reflects peripheral physiology. Here, we compare cat auditory nerve responses to broadband noise and to isolevel tones. We constructed shuffled autocorrelograms for responses to tones and summed across frequencies to obtain a monaural composite curve. We then compare this composite curve to the shuffled autocorrelogram of responses to broadband noise and find that the match between tonal and noise responses is poorer at the level of the auditory nerve than at the level of the IC. The apparent linearity of responses in the IC is thus even more surprising than was apparent from its original report because it results from mechanisms interposed between the auditory nerve and the IC.

Comparison of Bandwidths in the Inferior Colliculus and the Auditory Nerve. II: Measurement Using a Temporally Manipulated Stimulus

2008 ◽  
Vol 100 (4) ◽  
pp. 2312-2327 ◽  
Author(s):  
Myles Mc Laughlin ◽  
Joelle Nsimire Chabwine ◽  
Marcel van der Heijden ◽  
Philip X. Joris
Keyword(s):  
Correlation Function ◽  
Inferior Colliculus ◽  
Auditory Nerve ◽  
Low Frequency ◽  
Population Level ◽  
Broadband Noise ◽  
Center Frequency ◽  
Future Studies ◽  
Two Populations

To localize low-frequency sounds, humans rely on an interaural comparison of the temporally encoded sound waveform after peripheral filtering. This process can be compared with cross-correlation. For a broadband stimulus, after filtering, the correlation function has a damped oscillatory shape where the periodicity reflects the filter's center frequency and the damping reflects the bandwidth (BW). The physiological equivalent of the correlation function is the noise delay (ND) function, which is obtained from binaural cells by measuring response rate to broadband noise with varying interaural time delays (ITDs). For monaural neurons, delay functions are obtained by counting coincidences for varying delays across spike trains obtained to the same stimulus. Previously, we showed that BWs in monaural and binaural neurons were similar. However, earlier work showed that the damping of delay functions differs significantly between these two populations. Here, we address this paradox by looking at the role of sensitivity to changes in interaural correlation. We measured delay and correlation functions in the cat inferior colliculus (IC) and auditory nerve (AN). We find that, at a population level, AN and IC neurons with similar characteristic frequencies (CF) and BWs can have different responses to changes in correlation. Notably, binaural neurons often show compression, which is not found in the AN and which makes the shape of delay functions more invariant with CF at the level of the IC than at the AN. We conclude that binaural sensitivity is more dependent on correlation sensitivity than has hitherto been appreciated and that the mechanisms underlying correlation sensitivity should be addressed in future studies.

scholarly journals Neural Correlates and Mechanisms of Spatial Release From Masking: Single-Unit and Population Responses in the Inferior Colliculus

2005 ◽  
Vol 94 (2) ◽  
pp. 1180-1198 ◽  
Author(s):  
Courtney C. Lane ◽  
Bertrand Delgutte
Keyword(s):  
Inferior Colliculus ◽  
Single Unit ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Broadband Noise ◽  
Auditory Signal ◽  
Spatial Release ◽  
Additional Processing ◽  
Release From Masking ◽  
Correlator Model

Spatial release from masking (SRM), a factor in listening in noisy environments, is the improvement in auditory signal detection obtained when a signal is separated in space from a masker. To study the neural mechanisms of SRM, we recorded from single units in the inferior colliculus (IC) of barbiturate-anesthetized cats, focusing on low-frequency neurons sensitive to interaural time differences. The stimulus was a broadband chirp train with a 40-Hz repetition rate in continuous broadband noise, and the unit responses were measured for several signal and masker (virtual) locations. Masked thresholds (the lowest signal-to-noise ratio, SNR, for which the signal could be detected for 75% of the stimulus presentations) changed systematically with signal and masker location. Single-unit thresholds did not necessarily improve with signal and masker separation; instead, they tended to reflect the units' azimuth preference. Both how the signal was detected (through a rate increase or decrease) and how the noise masked the signal response (suppressive or excitatory masking) changed with signal and masker azimuth, consistent with a cross-correlator model of binaural processing. However, additional processing, perhaps related to the signal's amplitude modulation rate, appeared to influence the units' responses. The population masked thresholds (the most sensitive unit's threshold at each signal and masker location) did improve with signal and masker separation as a result of the variety of azimuth preferences in our unit sample. The population thresholds were similar to human behavioral thresholds in both SNR value and shape, indicating that these units may provide a neural substrate for low-frequency SRM.

Human Frequency-Following Responses to Binaural Masking Level Difference Stimuli

2005 ◽  
Vol 16 (03) ◽  
pp. 184-195 ◽  
Author(s):  
James R. Wilson ◽  
Ananthanarayan Krishnan
Keyword(s):  
Evoked Potential ◽  
Phase Locking ◽  
Low Frequency ◽  
Event Related Potential ◽  
Medial Superior Olive ◽  
Behavioral Threshold ◽  
Level Difference ◽  
Interaural Phase ◽  
Masking Level Difference ◽  
Low Pass

Binaural masking level difference is the behavioral threshold difference between a diotic condition (SoNo) and a dichotic condition with a 180° interaural phase delay of either the signal (SπNo) or the masker (SoNπ). Threshold disparity is partially related to coincidence-detecting units in the medial superior olive that are sensitive to low-frequency binaural stimuli with interaural phase differences. Previous surface evoked potential studies report significant latency and amplitude differences to SπNo stimuli with respect to SoNo stimuli in the P1-N1 auditory event related potential, but no study has reported physiologic masking level differences in a brain stem evoked potential. The human frequency-following response (FFR) represents activity from low-frequency, phase locking neural units in the upper brainstem. Unmasked FFRs to 500 Hz tone bursts and masked FFRs using a 1.5 kHz low-pass masker were recorded from nine normal-hearing adult subjects. Significant reduction in FFR amplitude occurred in the SoNo condition, re the So condition, with masker intensities near the psychoacoustic SoNo masking level. Significant FFR amplitude recovery was observed for both the SoNπ and SπNo conditions. These results support the role of phase-locked neural activity in brainstem mechanisms involved in perceptual masking release.

Masking release for gap detection

1992 ◽  
Vol 336 (1278) ◽  
pp. 331-337 ◽  
Keyword(s):  
Random Noise ◽  
Detection Threshold ◽  
Signal Frequency ◽  
Frequency Noise ◽  
Gap Detection ◽  
Noise Masking ◽  
Level Difference ◽  
Masking Release ◽  
Masking Level Difference ◽  
Release From Masking

In random noise, masking is influenced almost entirely by noise components in a narrow band around the signal frequency. However, when the noise is not random, but has a modulation pattern which is coherent across frequency, noise components relatively remote from the signal frequency can actually produce a release from masking. This masking release has been called comodulation masking release (CMR). The present research investigated whether a similar release from masking occurs in the analysis of a suprathreshold signal. Specifically, the ability to detect the presence of a temporal gap was investigated in conditions which do and do not result in CMR for detection threshold. Similar conditions were investigated for the masking level difference (a binaural masking release phenomenon). The results indicated that suprathreshold masking release for gap detection occurred for both the masking-level difference (MLD) and for CMR. However, masking release for gap detection was generally smaller than that obtained for detection threshold. The largest gap detection masking release effects obtained corresponded to relatively low levels of stimulation, where gap detection was relatively poor.

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. III. Evidence for cross-correlation

1987 ◽  
Vol 58 (3) ◽  
pp. 562-583 ◽  
Author(s):  
T. C. Yin ◽  
J. C. Chan ◽  
L. H. Carney
Keyword(s):  
Inferior Colliculus ◽  
Acoustic Signal ◽  
Cross Correlation ◽  
Low Frequency ◽  
Nerve Fibers ◽  
Broadband Noise ◽  
The Other ◽  
Central Nucleus ◽  
Interaural Phase ◽  
Phase Relationships

1. We tested the coincidence, or cross-correlation, model of Jeffress, which proposes a neuronal mechanism for sensitivity to interaural time differences (ITDs) in low-frequency cells in the central nucleus of the inferior colliculus (ICC) of the cat. Different tokens of Gaussian noise stimuli were delivered to the two ears. We studied the neural responses to changes in ITDs of these stimuli and examined the manner in which the binaural cells responded to them. All of our results support the idea that the central binaural neurons perform an operation very similar to cross-correlation on the inputs arriving from each side. These inputs are transformed from the actual acoustic signal by the peripheral auditory system, and these transformations are reflected in the properties of the cross-correlations. 2. The responses to ITDs of identical broadband noise stimuli to the two ears varies cyclically as a function of ITD at a frequency close to the best frequency of the neuron. This cyclic response is a consequence of the narrowband filtering of the wideband acoustic signal by the auditory nerve fibers. To examine the effects of using stimuli to the two ears that were correlated to each other to different degrees, we generated pairs of noises. Each pair consisted of one standard noise, which was delivered to one ear, and a linear sum of two standard uncorrelated noises, which was delivered to the other ear. The responses of 34 neurons in the ICC to ITDs of noises with variable interaural coherence were examined. When partially correlated noises were delivered, there was a positive and approximately linear relationship between the degree of modulation of the response as a function of ITD and interaural coherence. The degree of modulation was measured by the synchronization coefficient, or vector strength, over one period of the ITD curve. 3. We examined the effects of altering the interaural phase relationships of the input noise stimuli. The phase of the noise stimuli was changed by digitally filtering the standard noise so that only a phase delay was imposed. The responses to ITDs with differing interaural phase relationships were then studied by delivering a phase-shifted noise to one ear and the standard noise to the other. The ITD curves in response to phase-shifted noise were shifted by about the same amount as the shift of the stimulus; the shift of the response was measured with respect to the case with identical noises to the two ears.(ABSTRACT TRUNCATED AT 400 WORDS)

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