Effects of Amplitude Modulation on the Coding of Interaural Time Differences of Low-Frequency Sounds in the Inferior Colliculus. II. Neural Mechanisms

2003 ◽  
Vol 90 (5) ◽  
pp. 2827-2836 ◽  
Author(s):  
W. R. D'Angelo ◽  
S. J. Sterbing ◽  
E.-M. Ostapoff ◽  
S. Kuwada
Keyword(s):  
Inferior Colliculus ◽  
Background Noise ◽  
Modulation Depth ◽  
Interaural Time Difference ◽  
Low Frequency ◽  
Companion Paper ◽  
Neural Mechanisms ◽  
Physical Factors ◽  
Correlation Spectrum ◽  
The Difference

In our companion paper, we reported on interaural time difference (ITD)-sensitive neurons that enhanced, suppressed, or did not change their response when identical AM was added to both ears. Here, we first examined physical factors such as the difference in the interaural correlation, spectrum, or energy between the modulated and unmodulated signals. These were insufficient to explain the observed enhancement and suppression. We then examined neural mechanisms by selectively modulating the signal to each ear, varying modulation depth, and adding background noise to the unmodulated signal. These experiments implicated excitatory and inhibitory monaural inputs to the inferior colliculus (IC). These monaural inputs are postulated to adapt to an unmodulated signal and adapt less to a modulated signal. Thus enhancement or suppression is created by the convergence of these excitatory or inhibitory inputs with the inputs from the binaural comparators. Under modulation, the role of the monaural input is to shift the threshold of the IC neuron. Consistent with this role, background noise mimicked the effect of modulation. Functionally, enhancement and suppression may serve in detecting the degree of modulation in a sound source while preserving ITD information.

scholarly journals Effect of inter-aural modulation depth difference on interaural time difference thresholds for speech: An observational study

F1000Research ◽  
2020 ◽  
Vol 9 ◽  
pp. 115
Author(s):  
Arivudainambi Pitchaimuthu ◽  
Vibha Kanagokar ◽  
Srividya Grama Bhagavan ◽  
Jayashree S. Bhat
Keyword(s):  
Repeated Measures ◽  
Background Noise ◽  
Modulation Depth ◽  
Interaural Time Difference ◽  
Vital Role ◽  
Time Difference ◽  
Depth Difference ◽  
Main Effect ◽  
The Difference ◽  
Age Range

Background: The temporal envelope (ENV) plays a vital role in conveying inter-aural time difference (ITD) in many clinical populations. However, the presence of background noise and electronic features, such as compression, reduces the modulation depth of ENV to a different degree in both ears. The effect of ENV modulation depth differences between the ears on ITD thresholds is unknown; therefore, this was the aim of the current study’s investigation. Methods: Six normally hearing young adults (age range 20-30 years) participated in the current study. Six vowel-consonant-vowel (VCV) (/aka/, /aga/, /apa/, /aba/, /ata/, /ada/) tokens were used as the probe stimuli. ENV depth of VCV tokens was smeared by 0%, 29%, and 50%, which results in 100%, 71%, and 50% of the original modulation depth. ITD thresholds were estimated as a function of the difference in temporal ENV depth between the ears, wherein in one ear the modulation depth was retained at 100% and in the other ear, the modulation depth was changed to 100%, 71%, and 50%. Results: Repeated measures of ANOVA revealed a significant main effect of interaural modulation depth differences on the ITD threshold (F(2,10)= 9.04, p= 0.006). ITD thresholds increased with an increase in the inter-aural modulation depth difference. Conclusion: Inter-aural ENV depth is critical for ITD perception.

scholarly journals Disparity in interaural time difference improves the accuracy of neural representations of individual concurrent narrowband sounds in rat inferior colliculus and auditory cortex

2020 ◽  
Vol 123 (2) ◽  
pp. 695-706
Author(s):  
Lu Luo ◽  
Na Xu ◽  
Qian Wang ◽  
Liang Li
Keyword(s):  
Auditory Cortex ◽  
Inferior Colliculus ◽  
Interaural Time Difference ◽  
Critical Role ◽  
Low Frequency ◽  
Time Difference ◽  
Neural Representation ◽  
Frequency Bands ◽  
Neural Segregation ◽  
Peripheral Auditory System

The central mechanisms underlying binaural unmasking for spectrally overlapping concurrent sounds, which are unresolved in the peripheral auditory system, remain largely unknown. In this study, frequency-following responses (FFRs) to two binaurally presented independent narrowband noises (NBNs) with overlapping spectra were recorded simultaneously in the inferior colliculus (IC) and auditory cortex (AC) in anesthetized rats. The results showed that for both IC FFRs and AC FFRs, introducing an interaural time difference (ITD) disparity between the two concurrent NBNs enhanced the representation fidelity, reflected by the increased coherence between the responses evoked by double-NBN stimulation and the responses evoked by single NBNs. The ITD disparity effect varied across frequency bands, being more marked for higher frequency bands in the IC and lower frequency bands in the AC. Moreover, the coherence between IC responses and AC responses was also enhanced by the ITD disparity, and the enhancement was most prominent for low-frequency bands and the IC and the AC on the same side. These results suggest a critical role of the ITD cue in the neural segregation of spectrotemporally overlapping sounds. NEW & NOTEWORTHY When two spectrally overlapped narrowband noises are presented at the same time with the same sound-pressure level, they mask each other. Introducing a disparity in interaural time difference between these two narrowband noises improves the accuracy of the neural representation of individual sounds in both the inferior colliculus and the auditory cortex. The lower frequency signal transformation from the inferior colliculus to the auditory cortex on the same side is also enhanced, showing the effect of binaural unmasking.

Temporal coding of envelopes and their interaural delays in the inferior colliculus of the unanesthetized rabbit

1989 ◽  
Vol 61 (2) ◽  
pp. 257-268 ◽  
Author(s):  
R. Batra ◽  
S. Kuwada ◽  
T. R. Stanford
Keyword(s):  
Inferior Colliculus ◽  
Phase Locking ◽  
Acoustic Stimulus ◽  
Low Frequency ◽  
Auditory Pathway ◽  
Temporal Coding ◽  
Time Of Arrival ◽  
Unanesthetized Rabbit ◽  
The Difference ◽  
Ipsilateral Stimulation

1. The difference in the time of arrival of a sound at the two ears can be used to locate its source along the azimuth. Traditionally, it has been thought that only the on-going interaural temporal disparities (ITDs) produced by sounds of lower frequency (approximately less than 2 kHz) could be used for this purpose. However, ongoing ITDs of low frequency are also produced by envelopes of amplitude-modulated (AM) tones. These ITDs can be detected and used to lateralize complex high-frequency sounds (1, 8, 12, 15, 22, 24, 26). Auditory neurons synchronize to the modulation envelope, but do so at progressively lower modulation frequencies at higher levels of the auditory pathway. Some neurons of the cochlear nucleus synchronize best to frequencies as high as 700 Hz, but those of the inferior colliculus (IC) exhibit their best synchrony below 200 Hz. Even though synchrony to higher modulation frequencies is reduced at higher levels of the auditory pathway, is information about ITDs retained? 2. We answered this question by extracellularly recording the responses of neurons in the IC of the unanesthetized rabbit. We used an unanesthetized preparation because anesthesia alters the responses of neurons in the IC to both monaurally presented tones and ITDs. The unanesthetized rabbit is ideal for auditory research. Recordings can be maintained for long periods, and the acoustic stimulus to each ear can be independently controlled. 3. We studied the responses of 89 units to sinusoidally AM tones presented to the contralateral ear. For each unit, we recorded the response at several modulation frequencies. The degree of phase locking to the envelope at each frequency was measured using the synchronization coefficient. Two measures were used to assess the range of modulation frequencies over which phase locking occurred. The "best AM frequency" was the frequency at which we observed the greatest phase locking. The "highest AM frequency" was the highest frequency at which significant phase locking (0.001 level) was observed. We could not assess synchrony to ipsilateral AM tones directly, because most units did not respond to ipsilateral stimulation. 4. We studied the sensitivity of 63 units to ITDs produced by the envelopes of AM tones. Sensitivity to ITDs was tested by presenting AM tones to the two ears that had the same carrier frequency, but modulation frequencies that differed by 1 Hz. Units that were sensitive to ITDs responded to this stimulus by varying their response rate cyclically at the difference frequency, i.e., 1 Hz.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of GABAergic Inhibition in the Coding of Interaural Time Differences of Low-Frequency Sounds in the Inferior Colliculus

2005 ◽  
Vol 93 (6) ◽  
pp. 3390-3400 ◽  
Author(s):  
W. R. D’Angelo ◽  
S. J. Sterbing ◽  
E.-M. Ostapoff ◽  
S. Kuwada
Keyword(s):  
Inferior Colliculus ◽  
Signal To Noise Ratio ◽  
Interaural Time Difference ◽  
Low Frequency ◽  
Gabaergic Inhibition ◽  
Interaural Time Differences ◽  
Gaba Antagonists ◽  
Inhibitory Transmitter ◽  
Almost All

A major cue for the localization of sound in space is the interaural time difference (ITD). We examined the role of inhibition in the shaping of ITD responses in the inferior colliculus (IC) by iontophoretically ejecting γ-aminobutyric acid (GABA) antagonists and GABA itself using a multibarrel pipette. The GABA antagonists block inhibition, whereas the applied GABA provides a constant level of inhibition. The effects on ITD responses were evaluated before, during and after the application of the drugs. If GABA-mediated inhibition is involved in shaping ITD tuning in IC neurons, then applying additional amounts of this inhibitory transmitter should alter ITD tuning. Indeed, for almost all neurons tested, applying GABA reduced the firing rate and consequently sharpened ITD tuning. Conversely, blocking GABA-mediated inhibition increased the activity of IC neurons, often reduced the signal-to-noise ratio and often broadened ITD tuning. Blocking GABA could also alter the shape of the ITD function and shift its peak suggesting that the role of inhibition is multifaceted. These effects indicate that GABAergic inhibition at the level of the IC is important for ITD coding.

Central and peripheral contributions to coding of acoustic space by neurons in inferior colliculus of cat

1986 ◽  
Vol 55 (3) ◽  
pp. 587-603 ◽  
Author(s):  
M. B. Calford ◽  
D. R. Moore ◽  
M. E. Hutchings
Keyword(s):  
Inferior Colliculus ◽  
Single Unit ◽  
Arrival Time ◽  
Interaural Time Difference ◽  
Free Field ◽  
Low Frequency ◽  
Intensity Function ◽  
Central Nucleus ◽  
Stimulus Position ◽  
Acoustic Space

Recordings of response to free-field stimuli at best frequency were made from single units in the central nucleus of the inferior colliculus of anesthetized cats. Stimulus position was varied in azimuth, and the responses of units were compared with variation in the intensity and arrival time of the sound at each ear, derived from cochlear microphonic (CM) recordings. CM recordings were made at each frequency and at every point in space for which single-unit data were collected. Interaural time difference (delay) increased monotonically, but not linearly, as the stimulus was moved away from the midline. However, a given delay did not represent a single azimuth across frequency. Low-frequency interaural intensity differences (IIDs) were monotonic across azimuth and peaked at, or near, the poles. Higher-frequency IIDs were nonmonotonic and peaked relatively close to the midline, decreasing toward the poles. Units that showed little variation in discharge across azimuth formed 28% of the sample and were classified as omnidirectional. For other units, the spike-count intensity function and the variation of the CM with azimuth were combined to form a derived monaural azimuth function. For 29% of those units showing azimuthal sensitivity, the derived monaural azimuth function matched the actual azimuth function. This suggested that these units received input from only one ear. The largest group of azimuthally sensitive units (47%) was formed from those units inferred to be IID sensitive. At higher frequencies these units displayed a peaked azimuth function paralleling the nonmonotonic relation of IID to azimuth. The proportion of inferred IID-sensitive units was close to that found in dichotic studies.

Tuning to Interaural Time Difference and Frequency Differs Between the Auditory Arcopallium and the External Nucleus of the Inferior Colliculus

2009 ◽  
Vol 101 (5) ◽  
pp. 2348-2361 ◽  
Author(s):  
Katrin Vonderschen ◽  
Hermann Wagner
Keyword(s):  
Inferior Colliculus ◽  
Tuning Curve ◽  
Interaural Time Difference ◽  
Low Frequency ◽  
Steep Slope ◽  
Time Difference ◽  
Interaural Time Differences ◽  
Tuning Curves ◽  
Barn Owls ◽  
Zero Time

Barn owls process sound-localization information in two parallel pathways, the midbrain and the forebrain pathway. Exctracellular recordings of neural responses to auditory stimuli from far advanced stations of these pathways, the auditory arcopallium in the forebrain and the external nucleus of the inferior colliculus in the midbrain, demonstrated that the representations of interaural time difference and frequency in the forebrain pathway differ from those in the midbrain pathway. Specifically, low-frequency representation was conserved in the forebrain pathway, while it was lost in the midbrain pathway. Variation of interaural time difference yielded symmetrical tuning curves in the midbrain pathway. By contrast, the typical forebrain-tuning curve was asymmetric with a steep slope crossing zero time difference and a less-steep slope toward larger contralateral time disparities. Low sound frequencies contributed sensitivity to contralateral leading sounds underlying these asymmetries, whereas high frequencies enhanced the steepness of slopes at small interaural time differences. Furthermore, the peaks of time-disparity tuning curves were wider in the forebrain than in the midbrain. The distribution of the steepest slopes of best interaural time differences in the auditory arcopallium, but not in the external nucleus of the inferior colliculus, was centered at zero time difference. The distribution observed in the auditory arocpallium is reminiscent of the situation observed in small mammals. We speculate that the forebrain representation may serve as a population code supporting fine discrimination of central interaural time differences and coarse indication of laterality of a stimulus for large interaural time differences.

scholarly journals Roles of Inhibition in Complex Auditory Responses in the Inferior Colliculus: Inhibited Combination-Sensitive Neurons

2006 ◽  
Vol 95 (4) ◽  
pp. 2179-2192 ◽  
Author(s):  
Kiran Nataraj ◽  
Jeffrey J. Wenstrup
Keyword(s):  
Inferior Colliculus ◽  
Low Frequency ◽  
Neural Mechanisms ◽  
The Other ◽  
Inhibitory Neurons ◽  
Type I ◽  
Excitatory Response ◽  
Frequency Responses ◽  
Auditory Responses ◽  
Vocal Signals

We studied the functional properties and underlying neural mechanisms associated with inhibitory combination-sensitive neurons in the mustached bat's inferior colliculus (IC). In these neurons, the excitatory response to best frequency tones was suppressed by lower frequency signals (usually in the range of 12–30 kHz) in a time-dependant manner. Of 143 inhibitory units, the majority (71%) were type I, in which low-frequency sounds evoked inhibition only. In the remainder, however, the low-frequency inhibitory signal also evoked excitation. Of these, excitation preceded the inhibition in type E/I units (16%), whereas in type I/E units (13%), excitation followed the inhibition. Type E/I and I/E units were distinct in the tuning and threshold sensitivity of low-frequency responses, whereas type I units overlapped the other types in these features. In 71 neurons, antagonists to receptors for glycine [strychnine (STRY)] or GABA [bicuculline (BIC)] were applied microiontophoretically. These antagonists failed to eliminate combination-sensitive inhibition in 92% (STRY), 93% (BIC), and 87% (BIC + STRY) of the type I units tested. However, inhibition was reduced in many neurons. Results were similar for type E/I and I/E inhibitory neurons. The results indicate that there are distinct populations of combination-sensitive inhibited neurons in the IC and that these populations are at least partly independent of glycine or GABAA receptors in the IC. We propose that these populations originate in different brain stem auditory nuclei, that they may be modified by interactions within the IC, and that they may perform different spectrotemporal analyses of vocal signals.

scholarly journals Responses of Inferior Colliculus Neurons to Double Harmonic Tones

2007 ◽  
Vol 98 (6) ◽  
pp. 3171-3184 ◽  
Author(s):  
Donal G. Sinex ◽  
Hongzhe Li
Keyword(s):  
Inferior Colliculus ◽  
Auditory System ◽  
Temporal Pattern ◽  
Second Harmonic ◽  
Neural Mechanisms ◽  
Acoustic Properties ◽  
Discharge Pattern ◽  
The Difference ◽  
Discharge Patterns ◽  
Simultaneous Sounds

The auditory system can segregate sounds that overlap in time and frequency, if the sounds differ in acoustic properties such as fundamental frequency (f0). However, the neural mechanisms that underlie this ability are poorly understood. Responses of neurons in the inferior colliculus (IC) of the anesthetized chinchilla were measured. The stimuli were harmonic tones, presented alone (single harmonic tones) and in the presence of a second harmonic tone with a different f0 (double harmonic tones). Responses to single harmonic tones exhibited no stimulus-related temporal pattern, or in some cases, a simple envelope modulated at f0. Responses to double harmonic tones exhibited complex slowly modulated discharge patterns. The discharge pattern varied with the difference in f0 and with characteristic frequency. The discharge pattern also varied with the relative levels of the two tones; complex temporal patterns were observed when levels were equal, but as the level difference increased, the discharge pattern reverted to that associated with single harmonic tones. The results indicated that IC neurons convey information about simultaneous sounds in their temporal discharge patterns and that the patterns are produced by interactions between adjacent components in the spectrum. The representation is “low-resolution,” in that it does not convey information about single resolved components from either individual sound.

Comparisons of downhole geophones and hydrophones

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 841-847 ◽  
Author(s):  
Christine E. Krohn ◽  
S. T. Chen
Keyword(s):  
High Frequency ◽  
Background Noise ◽  
Low Frequency ◽  
Measured Signal ◽  
Coherent Noise ◽  
Low Frequencies ◽  
Prototype Tool ◽  
The Difference ◽  
Borehole Seismic ◽  
Seismic Applications

Receiver tests were conducted to compare the responses of downhole geophones and hydrophones. Commercial receiver tools use a maximum of eight geophone levels; however, we use hydrophones because we can record 48 levels simultaneously. For frequencies above 300 Hz, signal‐to‐background‐noise ratios for hydrophones and geophones in a prototype tool were comparable. (This prototype tool is a lightweight, large‐clamping‐force device that can record higher frequencies than commercial geophone tools.) For frequencies below 300 Hz, signal‐to‐noise ratios were greater for the geophones than for the hydrophones. A commercial geophone tool had lower low‐frequency signal‐to‐background‐noise ratios than the prototype tool, but greater than those of the hydrophones. Further analysis was performed to determine why the signal‐to‐background‐noise ratios for geophones were greater than those for hydrophones at low frequencies. The measured signal level for a hydrophone was 2.4 times that for a geophone, compared with a theoretical prediction of 1.8. Thus, the signal levels do not explain the difference in signal‐to‐background‐noise ratios. The low‐frequency background noise was attributed to coherent noise in the form of tube waves, a noise type to which hydrophones are much more susceptible than are geophones. Thus, the low signal‐to‐background‐noise ratios at frequencies below 300 Hz for hydrophones resulted from ambient noise propagating as tube waves in the borehole. The high‐frequency background noise was attributed to random seismic noise in the environment and not to instrument noise. These results show that hydrophones, which do not need to be clamped to the borehole wall, are preferable to geophones for high‐frequency borehole seismic applications using first arrivals. Geophones are preferable to hydrophones for borehole seismic applications using reflector arrivals, because these later‐arriving events are obscured by source‐generated tube waves in hydrophone data. Development of a method to reduce both the source‐generated and ambient tube‐wave noise detected by hydrophones would result in high‐quality borehole seismic data at a greatly reduced cost.

scholarly journals Noise Invariance in Inferior Colliculus Neurons is Dependant on the Input Noisy Conditions

2020 ◽  
Author(s):  
Maryam Hosseini ◽  
Gerardo Rodriguez ◽  
Hongsun Guo ◽  
Hubert H. Lim ◽  
Éric Plourde
Keyword(s):  
Inferior Colliculus ◽  
Neural Activity ◽  
Background Noise ◽  
Neural Mechanisms ◽  
Stationary Noise ◽  
Sound Levels ◽  
Noise Type ◽  
Noisy Conditions ◽  
Audio Information ◽  
Input Level

AbstractThe auditory system is extremely efficient to extract audio information in the presence of background noise. However, the neural mechanisms related to this efficiency is still greatly misunderstood, especially in the inferior colliculus (IC). In fact, while noise processing under different conditions has been investigated at the auditory cortex level, studies in the IC have been much limited. One interesting observation has been that there seems to be some degree of noise invariance in the IC in the presence of white noise. We wish to broaden this knowledge by investigating if there is a difference in the activity of neurons in the IC, when presenting noisy vocalisations with different types of noises, input signal-to-noise ratios (SNR) and signal levels. We do so using a generalized linear model (GLM), which gives us the ability to study the neural activity under these different conditions at a per neuron level. We found that non-stationary noise is the only noise type that clearly contributes to the neural activity in the IC, regardless of the SNR, input level or vocalisation type. However, when presenting white or natural stationary noises, a great diversity of responses was observed for the different conditions, where the activity of some neurons was affected by the presence of noise and the activity of others was not. Therefore, there seems to be some level of background noise invariance as early as the IC level, as reported before, however, this invariance seems to be highly dependent on the noisy conditions.New & NoteworthyThe neural mechanisms of auditory perception in the presence of background noise are still not well understood, especially in the IC. We studied neural activity in the IC when presenting noisy vocalisations using different background noise types, SNRs and input sound levels. We observed that only the non-stationary noise type clearly contributes to the neural activity in the IC. The noise invariance previously observed in the IC thus seems dependent on the noisy conditions.

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