Wide Range Of Characteristic Frequencies Research Articles

A computational model of auditory chirp-velocity sensitivity and amplitude-modulation tuning in inferior colliculus neurons.

We demonstrate a model of chirp-velocity sensitivity in the inferior colliculus (IC) that retains the tuning to amplitude modulation (AM) that was established in earlier models. The mechanism of velocity sensitivity is sequence detection by octopus cells of the posteroventral cochlear nucleus, which have been proposed in physiological studies to respond preferentially to the order of arrival of cross-frequency inputs of different amplitudes. Model architecture is based on coincidence detection of a combination of excitatory and inhibitory inputs. Chirp-sensitivity of the IC output is largely controlled by the strength and timing of the chirp-sensitive octopus-cell inhibitory input. AM tuning is controlled by inhibition and excitation that are tuned to the same frequency. We present several example neurons that demonstrate the feasibility of the model in simulating realistic chirp-sensitivity and AM tuning for a wide range of characteristic frequencies. Additionally, we explore the systematic impact of varying parameters on model responses. The proposed model can be used to assess the contribution of IC chirp-velocity sensitivity to responses to complex sounds, such as speech.

A Computational Model of Auditory Chirp-Velocity Sensitivity and Amplitude-Modulation Tuning in Inferior Colliculus Neurons.

We demonstrate a model of chirp-velocity sensitivity in the inferior colliculus (IC) that retains the tuning to amplitude modulation (AM) that was established in earlier models. The mechanism of velocity sensitivity is sequence detection by octopus cells of the posteroventral cochlear nucleus, which have been proposed in physiological studies to respond preferentially to the order of arrival of cross-frequency inputs of different amplitudes. Model architecture is based on coincidence detection of a combination of excitatory and inhibitory inputs. Chirp-sensitivity of the IC output is largely controlled by the strength and timing of the chirp-sensitive octopus-cell inhibitory input. AM tuning is controlled by inhibition and excitation that are tuned to the same frequency. We present several example neurons that demonstrate the feasibility of the model in simulating realistic chirp-sensitivity and AM tuning for a wide range of characteristic frequencies. Additionally, we explore the systematic impact of varying parameters on model responses. The proposed model can be used to assess the contribution of IC chirp-velocity sensitivity to responses to complex sounds, such as speech.

Interplay between periodic stimulation and GABAergic inhibition in striatal network oscillations.

Network oscillations are ubiquitous across many brain regions. In the basal ganglia, oscillations are also present at many levels and a wide range of characteristic frequencies have been reported to occur during both health and disease. The striatum, the main input nucleus of the basal ganglia, receives massive glutamatergic inputs from the cortex and is highly susceptible to external oscillations. However, there is limited knowledge about the exact nature of this routing process and therefore, it is of key importance to understand how time-dependent, external stimuli propagate through the striatal circuitry. Using a network model of the striatum and corticostriatal projections, we try to elucidate the importance of specific GABAergic neurons and their interactions in shaping striatal oscillatory activity. Here, we propose that fast-spiking interneurons can perform an important role in transferring cortical oscillations to the striatum especially to those medium spiny neurons that are not directly driven by the cortical oscillations. We show how the activity levels of different populations, the strengths of different inhibitory synapses, degree of outgoing projections of striatal cells, ongoing activity and synchronicity of inputs can influence network activity. These results suggest that the propagation of oscillatory inputs into the medium spiny neuron population is most efficient, if conveyed via the fast-spiking interneurons. Therefore, pharmaceuticals that target fast-spiking interneurons may provide a novel treatment for regaining the spectral characteristics of striatal activity that correspond to the healthy state.

Reference-Free Assessment of Speech Intelligibility Using Bispectrum of an Auditory Neurogram.

Sensorineural hearing loss occurs due to damage to the inner and outer hair cells of the peripheral auditory system. Hearing loss can cause decreases in audibility, dynamic range, frequency and temporal resolution of the auditory system, and all of these effects are known to affect speech intelligibility. In this study, a new reference-free speech intelligibility metric is proposed using 2-D neurograms constructed from the output of a computational model of the auditory periphery. The responses of the auditory-nerve fibers with a wide range of characteristic frequencies were simulated to construct neurograms. The features of the neurograms were extracted using third-order statistics referred to as bispectrum. The phase coupling of neurogram bispectrum provides a unique insight for the presence (or deficit) of supra-threshold nonlinearities beyond audibility for listeners with normal hearing (or hearing loss). The speech intelligibility scores predicted by the proposed method were compared to the behavioral scores for listeners with normal hearing and hearing loss both in quiet and under noisy background conditions. The results were also compared to the performance of some existing methods. The predicted results showed a good fit with a small error suggesting that the subjective scores can be estimated reliably using the proposed neural-response-based metric. The proposed metric also had a wide dynamic range, and the predicted scores were well-separated as a function of hearing loss. The proposed metric successfully captures the effects of hearing loss and supra-threshold nonlinearities on speech intelligibility. This metric could be applied to evaluate the performance of various speech-processing algorithms designed for hearing aids and cochlear implants.

Temporal precision of speech coded into nerve-action potentials

The auditory pathway is an excellent system to study temporal aspects of neuronal processing. Unlike other sensory systems, temporal cues cover an extremely wide range of information: for sound localization, interaural time differences with a precision of tens of microseconds are extracted. Phase-locking of auditory nerve responses, which is related to the coding of the temporal fine structure, occurs from the lowest audible frequencies probably up to 3 kHz in humans. Amplitude modulations in speech signals are processed in the ms to tens of ms range. And finally, the energy of spoken speech itself is modulated with a frequency of about 4 Hz, corresponding to a syllable frequency in the order of few hundreds of ms. To extract temporal cues at all timescales, it is important to understand how temporal information is coded. We investigate temporal coding of speech signals using the methods of information theory and a model of the human inner ear. The model is based on a traveling-wave model, a nonlinear compression stage which mimics the function of the amplifier, a model of the sensory cells, the afferent synapse and spike generation (Sumner ) which we extended to replicate offset adaptation (Zhang). We used the action potentials of the auditory nerve to drive Hodgkin-Huxley-type point models of various neurons in the cochlear nucleus. In this investigation we only report data from onset neurons, which exhibit extraordinary fast membrane time-constants below 1 ms. Onset neurons are known for their precise temporal processing. They achieve precisely timed action potentials by coincidence detection: they fire only if at least 10% of the auditory nerve fibers which innervate them fire synchronously. With information theory, we analyzed the transmitted information rate coded in neural spike trains of modeled neurons in the cochlear nucleus for vowels. We found that onset neurons are able to code temporal information with sub-millisecond precision (<0.02 ms) across a wide range of characteristic frequencies. Temporal information is coded by precisely timed spikes per se, not only temporal fine structure. Moreover, the major portion of information (60%) is coded with a temporal precision from 0.2 to 4 ms. Enhancing the temporal resolution from 10 ms to 3 ms and from 3 ms to 0.3 ms is expected to increase the transmitted information by approximately twofold and 2.5 fold, respectively. In summary, our results provide quantitative insight into temporal processing strategies of neuronal speech processing. We conclude that coding of information in the time domain might be essential to complement the rate-place code, especially in adverse acoustical environments. Acknowledgments:Supported by within the Munich Bernstein Center for Computational Neuroscience by the German Federal Ministry of Education and Research (reference numbers 01GQ0441 and 01GQ0443).

Regeneration after tall hair cell damage following severe acoustic trauma in adult pigeons: correlation between cochlear morphology, compound action potential responses and single fiber properties in single animals

The time course of recovery of compound action potential (CAP) thresholds was observed in individual adult pigeons after severe acoustic trauma. Pigeons were overstimulated with a tone of 0.7 kHz and 136–142 dB SPL presented to one ear for 1 h under general anesthesia. Recovery of CAP audiograms was monitored at regular intervals after trauma. A new semi-stereotaxic approach to the peripheral part of the auditory nerve was developed. This permitted activity from single auditory nerve fibers to be recorded over a wide range of characteristic frequencies (CFs), including high CFs, without having to open the inner ear. Single unit recordings were made after three weeks and after 4 or more months of recovery. The time course of recovery, the single unit properties, and the morphological status of the basilar papilla were correlated. The CAP was abolished in all animals after overstimulation. Three groups of animals were identified according to the functional recovery of the CAP thresholds recorded at regular intervals with implanted electrodes: Group 1: Fast functional recovery starting immediately after trauma, followed by recovery to pre-exposure values within 3 weeks. Group 2: Slow functional recovery of threshold starting 1–2 weeks after trauma and ending 4–5 weeks after trauma. A mean residual hearing loss of 26.3 dB at 2 kHz remained. Group 3: No recovery of CAP thresholds up to 8 months after trauma. Three weeks after trauma, very few responsive neurons were found in groups 2 and 3. Tuning curves were very broad and sometimes irregular in shape. Thresholds were very high, around 120 dB SPL. Spontaneous firing rate was much reduced, especially in neurons with high CFs. After 4 or more months of recovery, the response properties of single units in group 1 had only partially recovered. Thresholds and sharpness of tuning of many single units were normal; however, in general they were still poorer than in control animals. Spontaneous firing rate was comparable to control animals. Neurons from animals in group 2 showed less recovery, especially at frequencies above the exposure frequency. Thresholds and sharpness of tuning were normal at frequencies below the exposure frequency, but were much poorer at frequencies above the exposure. Spontaneous firing rate was much reduced in fibers with high CFs. The basilar papilla in animals without recovery showed total loss of the sensory epithelium. The basal lamina of the basilar membrane, however, remained intact and was covered with cuboidal cells. In fast recovering animals, the papilla was repopulated with hair cells after 4 months. In slow recovering animals, short (abneural) hair cells were still missing over large parts of the papilla after 4 months of recovery. Residual short (abneural) hair cell loss was largest at two areas, one more basal and the other more apical to the characteristic place of the traumatizing frequency. The results show that functional recovery from severe damage to both short (abneural) and tall (neural) hair cells occurs in adult birds. However, the onset of recovery is delayed and the time course is slower than after destruction of short (abneural) hair cells alone. Furthermore recovery is incomplete, both functionally and morphologically. There are residual permanent hearing losses and regeneration of short (abneural) hair cells is incomplete.

Moment matching model reduction for multiratc linear systems

Aerospace systems are described by high-order dynamic models which include phenomena covering a wide range of characteristic frequencies and sensor sampling rates. In order to accommodate these multiple information rates, and to complete the control computations within the time available, control systems are designed to operate at multiple sampling rates. Model reduction methods are available for single-rate linear systems to preserve the first q Markov parameters and the first q covariance parameters. This paper extends these ideas to multirate systems.

Peripheral auditory processing in the bobtail lizard Tiliqua rugosa

The present study, aims to provide a more detailed description of the sound-driven activity patterns of the auditory-nerve fibres than was previously available for lizards. Emphasis has been placed on the characterization of responses of fibres with a wide range of characteristic frequencies (CFs) and for stimulation both at the CF and off the CF, in order to identify possible differences. In addition, the patterns of two-tone rate suppression (TTRS) were investigated, with special attention to possible overlap between the single-tone frequency-threshold tuning curve and the TTRS area

Responses of Cat Auditory Nerve Fibers to Biphasic Electrical Current Pulses

Discharge patterns of single auditory nerve fibers were recorded from normal-hearing cats implanted with a 12-band intracochlear electrode array. Stimuli were biphasic current pulses of specifiable width, amplitude, and rate. Acoustic tuning curves were obtained to determine the cochlear positions of the fibers. Response latencies to electrical stimuli formed two groups. Short latency (0.3 to 0.7 ms) responses were attributed to direct activation of spiral ganglion neurons. At high stimulus intensities, these often exhibited abrupt shifts toward even shorter latencies. Long latency (&gt; 1.5 ms) responses were probably caused by electrophonic activation of functional hair cells. Response thresholds to electrical stimuli depended on a fiber's proximity to the stimulating electrodes, and they did not depend on a fiber's acoustic response threshold or spontaneous discharge rate. High intensity (&gt; 1.5 mA) stimuli could excite fibers over a wide range of characteristic frequencies, even for the narrowest (0.45 mm) electrode separations. Response threshold was an exponentially decreasing function of pulse width for widths up to 300 μs/phase. Fiber discharges were highly phase-locked at all suprathreshold intensities, and saturation discharge rates usually equaled stimulus pulse rates for rates up to at least 800 pulses/s. Dynamic ranges were small (1 to 6 dB), increased with pulse rate, and were uncorrelated with electrical response threshold. Within the dynamic range, shapes of poststimulus time and interspike interval histograms resembled those obtained in response to acoustic stimuli. Depolarization block caused fiber activity to cease in 2 to 5 seconds for sustained stimuli presented at high (&gt; 600 pulses/s) pulse rates and intensities.

Speech coding in the auditory nerve: V. Vowels in background noise.

Responses of auditory-nerve fibers to steady-state, two-formant vowels in low-pass background noise (S/N = 10 dB) were obtained in anesthetized cats. For fibers over a wide range of characteristic frequencies (CFs), the peaks in discharge rate at the onset of the vowel stimuli were nearly eliminated in the presence of noise. In contrast, strong effects of noise on fine time patterns of discharge were limited to CF regions that are far from the formant frequencies. One effect is a reduction in the amplitude of the response component at the fundamental frequency in the high-CF regions and for CFs between F1 and F2 when the formants are widely separated. A reduction in the amplitude of the response components at the formant frequencies, with concomitant increase in components near CF or low-frequency components occurs in CF regions where the signal-to-noise ratio is particularly low. The processing schemes that were effective for estimating the formant frequencies and fundamental frequency of vowels in quiet generally remain adequate in moderate-level background noise. Overall, the discharge patterns contain many cues for distinctions among the vowel stimuli, so that the central processor should be able to identify the different vowels, consistent with psychophysical performance at moderate signal-to-noise ratios.

Development and applications of multirate digital control

Multiple sample rate digital control systems are of prominent interest in current control research, development, and applications. Modern aerospace vehicles and systems are described by high-order dynamic models which typically include phenomena covering a wide range of characteristic frequencies and instrumentation measurements available at multiple rates. A multirate control structure allows the designer to accommodate multiple information rates and implement required control computations within the finite computational capabilities of an on-board computer. In this paper the historical development, representative design approaches, and example applications of multirate digital control are outlined. A brief survey of traditional design approaches and techniques currently in development is presented. Potential future areas of research and application of multirate control are suggested and discussed.

Molecular dynamics of solid polymers as revealed by deuteron NMR

Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information about polymer dynamics available now is illustrated by a number of experimental examples. The chain motion in the amorphous regions of linearpolyethylene is discussed in detail and it is shown that it can clearly be distinguished from the chain motion of an amorphous polymer above the glass transition, wherepolystyrene is used as an example. Localized motions in the glassy state are illustrated through the jump motion phenyl groups exhibit both in the main chain (polycarbonate) and as a side group (polystyrene). The latter polymers also serve as examples for detecting motional heterogeneity. Finally, the mobility in novel classes of systems,liquid crystalline polymers andpolymer model membranes as revealed by2H NMR are described.

Single-neuron labeling in the cat auditory nerve.

Single auditory nerve fibers in the cat were labeled intracellularly with horseradish peroxidase. The sample of fibers was selected to represent different response types over a wide range of characteristic frequencies. All 56 labeled neurons were found to be radial fibers innervating inner hair cells, suggesting that none of the single-unit data reported to date has been from the outer hair cell innervation. Differences in rates of spontaneous discharge and thresholds to tones among these labeled neurons were closely correlated with morphological differences in the caliber and location of their unmyelinated terminals on the body of the inner hair cell.

Coding of some consonantal features in the auditory nerve

Responses of auditory‐nerve fibers to computer‐generated stimuli having consonant‐like changes in amplitude and spectral characteristics were obtained for two different sound levels. Experiment I concerned the distinction between two noice bursts differing in the abruptness of their onset: a/č/ stimulus with a 10‐ms rise time, and a /š/ stimulus with a 75‐ms rise time. Response patterns of auditory‐nerve fibers over a wide range of characteristic frequencies (CF) showed a more prominent peak at the onset of the stimulus for /č/ than for /š/. In experiment II the stimuli consisted of /da/‐like formant trajectories preceded a context that was varied to produce stimuli sounding like /da/, /ada/, /na/, /ša/, and /sa/. After the low‐frequency context in /na/, the response of low‐CF fibers during the formant transitions was lower than after a silent context as in /da/ or /ada/, whereas after a high‐frequency context as in /ša/ or /sa/ the response of high‐CF fibers was lower. This dependence of response on context, which was found both for mean discharge rate and for response measures involving fine time patterns of discharge, emphasizes “new” frequency components in the representation of spectrum. [Supported by NIH.]

Representation of speech-like sounds in the discharge patterns of auditory-nerve fibers

It is now possible to study how acoustic characteristics important for speech discrimination are represented in the discharge patterns of single auditory-nerve fibers. Responses to simple tonal stimuli and speechlike sounds (such as one or two formant synthetic stimuli) have been studied in order to elucidate the coding of certain vowel characteristics. At stimulus levels typical of speech, information about formant frequency is carried predominantly by fibers with characteristic frequencies close to the formant frequency, whereas information about fundamental frequency is present in fibers over a wide range of characteristic frequencies. Specific examples will be given for the representation of detailed spectral patterns for vowels and fricative consonants, of rapid changes in intensity and spectrum for stop and nasal consonants, and of speech signals in the presence of background noise. [Supported in part by NIH grants.]