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H Steven Colburn

Publications and source records attributed to H Steven Colburn.

15 recordsLinked to original sources
PubMed2006

Simple models show the general advantages of dendrites in coincidence detection.

Dendrites can influence and improve information processing in single neurons. Here, simple models are used to elucidate mechanisms underlying the dendritic enhancement of coincidence detection. We focus on coincidence-detecting cells in the auditory system, which have bipolar dendrites and show acute sensitivity to interaural time difference (ITD), a critical cue for spatial hearing. A three-compartment model consisting of a single-compartment soma and two single-compartment dendrites is primarily used, although multiple-compartment dendrites are also tested. Two varieties of somata, with and without active ion channels, are studied. Using constant conductance inputs, we show analytically that the somatic response to balanced bilateral inputs is largest, whereas the response monotonically decreases as the input distribution becomes increasingly monolateral. This enhancement is a consequence of the sublinear saturating dendritic voltage response to conductance input and occurs when dendrites are composed of a single compartment or either a finite number or an infinite number (i.e., a cable) of compartments. Longer, thinner dendrites or greater numbers of compartments increase the enhancement of the somatic response to bilateral input. The time-independent dendritic enhancement, moreover, underlies improved coincidence detection of time-varying input. Coincidence sensitivity to a pair of conductance pulses and rate-ITD modulation to low-frequency (400-Hz) periodic inputs increases with dendritic length. These findings are related to the length gradient in the avian system, where low characteristic frequency (CF) cells have long dendrites and high CF cells have short dendrites. We conclude that dendrites fundamentally improve coincidence detection, increasing the computational power of many neurons in the nervous system.

Action Potentials↗
PubMed2006

The perceptual consequences of binaural hearing.

Binaural processing in normal hearing activities is based on the ability of listeners to use the information provided by the differences between the signals at the two ears. The most prominent differences are the interaural time difference and the interaural level difference, both of which depend on frequency. This paper describes the stages by which these differences are estimated by the physiological structures of the auditory system, summarizes the sensitivity of the human listener to these differences, and reviews the nature of the interaural differences in realistic environments.

Acoustics↗
PubMed2006

Binaural detection with narrowband and wideband reproducible noise maskers. III. Monaural and diotic detection and model results.

A single-interval, yes-no, tone-in-noise detection experiment was conducted to measure the proportion of "tone present" responses to each of 25 reproducible noise-alone and tone-plus-noise waveforms under narrowband (100 Hz), wideband (2900 Hz), monotic, and diotic stimulus conditions. Proportions of "tone present" responses (estimates of the probabilities of hits and false alarms) were correlated across masker bandwidths and across monotic and diotic conditions. Two categories of models were considered; one based on stimulus energy or neural counts, and another based on temporal structure of the stimulus envelope or neural patterns. Both categories gave significant correlation between decision variables and data. A model based on a weighted combination of energy in multiple critical bands performed best, predicting up to 90% of the variance in the reproducible-noise data. However, since energy-based models are unable to successfully explain detection under a roving-level paradigm without substantial modification, it is argued that other variations of detection models must be considered for future study. Temporal models are resistant to changes in threshold under roving-level conditions, but explained at most only 67% of the variance in the reproducible-noise data.

Adult↗
PubMed2006

The influence of spectral, temporal, and interaural stimulus variations on the precedence effect.

The precedence effect describes phenomena that are believed to aid localization of sounds in reverberant environments. These phenomena relate to the emphasis given to the first-arriving or preceding sound. In this paper, experiments are described which study precedence using stimulus parametrizations spanning temporal, spectral, and interaural dimensions. Subjects report the sidedness of headphone stimuli comprising a source and single reflection placed symmetrically with respect to midline. Most of the experiments use long-duration noises with the onset and offset time-of-arrival differences windowed out from the combined lead and lag stimulus, thus requiring the subject to lateralize using cues in the ongoing portion of the stimuli where the lead and lag overlap completely. A similar experiment using click stimuli is included for comparison. The influence of spectral content is studied by varying either the bandwidth or the center frequency. Dependence on interaural cues is investigated by using either ITDs or IIDs to induce laterality in the individual lead and lag components. Results indicate that precedence continues into the ongoing portion of long-duration stimuli and is robust to the removal of initial onsets, to reduction of bandwidth, and to the choice of interaural cue used to induce laterality in the lead and lag.

Acoustic Stimulation↗
PubMed2005

A model for interaural time difference sensitivity in the medial superior olive: interaction of excitatory and inhibitory synaptic inputs, channel dynamics, and cellular morphology.

This study reports simulations of recent physiological results from the gerbil medial superior olive (MSO) that reveal that blocking glycinergic inhibition can shift the tuning for the interaural time difference (ITD) of the cell (Brand et al., 2002). Our simulations indicate that the model proposed in the study by Brand et al. (2002) requires precisely timed, short-duration inhibition with temporal accuracy exceeding that described in the auditory system. An alternative model is proposed that incorporates two anatomic observations in the MSO: (1) the axon arises from the dendrite that receives ipsilateral inputs; and (2) inhibitory synapses are located primarily on the soma in adult animals. When the inhibitory currents are activated or blocked, the model cell successfully simulates experimentally observed shifts in the best ITD. The asymmetrical cell structure allows an imbalance between the ipsilateral and contralateral excitatory inputs and shifts the ITD curve such that the best ITD is not at zero. Fine adjustment of the best ITD is achieved by the interplay of somatic sodium currents and synaptic inhibitory currents. The shift of the best ITD in the model is limited to approximately 0.2 ms, which is behaviorally significant with respect to ITDs encountered in perceptual tasks. The model suggests a mechanism for dynamically "fine-tuning" the ITD sensitivity of MSO cells by the opponency between depolarizing sodium currents and hyperpolarizing inhibitory currents.

Animals↗
PubMed2005

Effects of inhibitory feedback in a network model of avian brain stem.

The avian auditory brain stem consists of a network of specialized nuclei, including nucleus laminaris (NL) and superior olivary nucleus (SON). NL cells show sensitivity to interaural time difference (ITD), a critical cue that underlies spatial hearing. SON cells provide inhibitory feedback to the rest of the network. Empirical data suggest that feedback inhibition from SON could increase the ITD sensitivity of NL across sound level. Using a bilateral network model, we assess the effects of SON feedback inhibition. Individual cells are specified as modified leaky-integrate-and-fire neurons with time constants and thresholds that vary with inhibitory input. Acoustic sound level is reflected in the discharge rates of the model auditory-nerve fibers, which innervate the network. Simulations show that with SON inhibitory feedback, ITD sensitivity is maintained in model NL cells over a threefold range in auditory-nerve discharge rate. In contrast, without SON feedback inhibition, ITD sensitivity is significantly reduced as input rates are increased. Feedback inhibition is most beneficial in maintaining ITD sensitivity at high-input rates (simulating high sound levels). With SON inhibition, ITD sensitivity is maintained for both interaurally balanced inputs (simulating an on-center sound source) and interaurally imbalanced inputs (simulating a lateralized source). Further, the empirically observed temporal build-up of SON inhibition and the presence of reciprocal inhibitory connections between the ipsi- and contralateral SON both improve ITD sensitivity. In sum, our network model shows that inhibitory feedback can substantially increase the sensitivity and dynamic range of ITD coding in the avian auditory brain stem.

Action Potentials↗
PubMed2005

Intrinsic oscillations in spike trains indicate non-renewal statistics due to convergence of inputs in dorsal cochlear nucleus neurons.

The occurrence of intrinsic oscillations (IOs) in a unit's discharge is reflected by a prominent peak in the power spectrum (i.e., Fourier transform of the autocorrelation function) of spike trains obtained from single-unit discharge, at a frequency independent of stimulus spectral characteristics. IOs have been reported by researchers in the dorsal cochlear nucleus (DCN) of both the cat and the Mongolian gerbil. It has been hypothesized that IOs are related to inter-spike interval (ISI) regularity (e.g., [Hear. Res. 58 (1992) 153]). This hypothesis is tested in this paper. Responses to multiple presentations of 50-300 ms duration tone bursts, at and near the unit's best frequency (BF) at 20-60 dB re threshold were recorded from DCN units of barbiturate-anesthetized (30 units), as well as decerebrate (53 units) Mongolian gerbils. IOs in the recordings were then compared with the IOs in simulations of spiking-neuron models. The models were selected because: (1) their ISI regularity characteristics follow those of experimental data and (2) their IO properties are completely determined by their ISI regularity. Such comparison reveals that Ghoshal's hypothesis fails for a fraction of the units. These results suggest a re-evaluation of the purported relationship between IOs, ISI regularity, and SAM response. Alternate hypotheses are proposed here using computational models that are based on convergence of multiple neural inputs onto the unit under study. These models produce non-renewal statistics that resemble those of the experimental data, as is evident from IO-based analysis.

Action Potentials↗
PubMed2005

Informational masking for simultaneous nonspeech stimuli: psychometric functions for fixed and randomly mixed maskers.

Sensitivity d' and response bias beta were measured as a function of target level for the detection of a 1000-Hz tone in multitone maskers using a one interval, two-alternative forced-choice (1I-2AFC) paradigm. Ten such maskers, each with eight randomly selected components in the region 200-5000 Hz, with 800-1250 Hz excluded to form a protected zone, were presented under two conditions: the fixed condition, in which the same eight-component masker is used throughout an experimental run, and the random condition, in which an eight-component masker is chosen randomly trial-to-trial from the given set of ten such maskers. Differences between the results obtained with these two conditions help characterize the listener's susceptibility to informational masking (IM). The d' results show great intersubject variability, but can be reasonably well fit by simple energy-detector models in which internal noise and filter bandwidth are used as fitting parameters. In contrast, the beta results are not well fit by these models. In addition to presentation of new data and its relation to energy-detector models, this paper provides comments on a variety of issues, problems, and research needs in the IM area.

Acoustic Stimulation↗
PubMed2004

Infinite-impulse-response models of the head-related transfer function.

Head-related transfer functions (HRTFs) measured from human subjects were approximated using infinite-impulse-response (IIR) filter models. Models were restricted to rational transfer functions (plus simple delays) so that specific models are characterized by the locations of poles and zeros in the complex plane. The all-pole case (with no nontrivial zeros) is treated first using the theory of linear prediction. Then the general pole-zero model is derived using a weighted-least-squares (WLS) formulation of the modified least-squares problem proposed by Kalman (1958). Both estimation algorithms are based on solutions of sets of linear equations and result in efficient computational schemes to find low-order model HRTFs. The validity of each of these two low-order models was assessed in psychophysical experiments. Specifically, a four-interval, two-alternative, forced-choice paradigm was used to test the discriminability of virtual stimuli constructed from empirical and model HRTFs for corresponding locations. For these experiments, the stimuli were 80 ms, noise tokens generated from a wideband noise generator. Results show that sounds synthesized through model HRTFs were indistinguishable from sounds synthesized from original HRTF measurements for the majority of positions tested. The advantages of the techniques described here are the computational efficiencies achieved for low-order IIR models. Properties of the all-pole and pole-zero estimators are discussed in the context of low-order HRTF representations, and implications for basic and applied contexts are considered.

Acoustics↗
PubMed2003

Quantifying the information in auditory-nerve responses for level discrimination.

An analytical approach for quantifying the information in auditory-nerve (AN) fiber responses for the task of level discrimination is described. A simple analytical model for ANT responses is extended to include temporal response properties, including the nonlinear-phase effects of the cochlear amplifier. Use of simple analytical models for AN discharge patterns allows quantification of the contributions of level-dependent aspects of the patterns to level discrimination. Specifically, the individual and combined contributions of the information contained in discharge rate, synchrony, and relative phase cues are explicitly examined for level discrimination of tonal stimuli. It is shown that the rate information provided by individual AN fibers is more constrained by increases in variance with increases in rate than by saturation. As noted in previous studies, there is sufficient average-rate information within a narrow-CF region to account for robust behavioral performance over a wide dynamic range; however, there is no model based on a simple limitation or use of AN information consistent with parametric variations in performance. This issue is explored in the current study through analysis of performance based on different aspects of AN patterns. For example, we show that performance predicted from use of all rate information degrades significantly as level increases above low-medium levels, inconsistent with Weber's Law. At low frequencies, synchrony information extends the range over which behavioral performance can be explained by 10-15 dB, but only at low levels. In contrast to rate and synchrony, nonlinear-phase cues are shown to provide robust information at medium and high levels in near-CF fibers for low-frequency stimuli. The level dependence of the discharge rate and phase properties of AN fibers are influenced by the compressive nonlinearity of the inner ear. Evaluating the role of the compressive nonlinearity in level coding is important for understanding neural encoding mechanisms and because of its association with the cochlear amplifier, which is a fragile aspect of the ear believed to be affected in common forms of hearing impairment.

Animals↗
PubMed2003

Informational masking: counteracting the effects of stimulus uncertainty by decreasing target-masker similarity.

Previous work has indicated that target-masker similarity, as well as stimulus uncertainty, influences the amount of informational masking that occurs in detection, discrimination, and recognition tasks. In each of five experiments reported in this paper, the detection threshold for a tonal target in random multitone maskers presented simultaneously with the target tone was measured for two conditions using the same set of five listeners. In one condition, the target was constructed to be "similar" (S) to the masker; in the other condition, it was constructed to be "dissimilar" (D) to the masker. The specific masker varied across experiments, but was constant for the two conditions. Target-masker similarity varied in dimensions such as duration, perceived location, direction of frequency glide, and spectro-temporal coherence. Group-mean results show large decreases in the amount of masking for the D condition relative to the S condition. In addition, individual differences (a hallmark of informational masking) are found to be much greater in the S condition than in the D condition. Furthermore, listener vulnerability to informational masking is found to be consistent to at least a moderate degree across experiments.

Acoustic Stimulation↗
PubMed2003

Binaural sensitivity as a function of interaural electrode position with a bilateral cochlear implant user.

Experiments were conducted with a single, bilateral cochlear implant user to examine interaural level and time-delay cues that putatively underlie the design and efficacy of bilateral implant systems. The subject's two implants were of different types but custom equipment allowed presentation of controlled bilateral stimuli, particularly those with specified interaural time difference (ITD) and interaural level difference (ILD) cues. A lateralization task was used to measure the effect of these cues on the perceived location of the sensations elicited. For trains of fixed-amplitude, biphasic current pulses at 100 pps, the subject demonstrated sensitivity to an ITD of 300 micros, providing evidence of access to binaural information. The choice of bilateral electrode pair greatly influenced ITD sensitivity, suggesting that electrode pairings are likely to be an important consideration in the effort to provide binaural advantages. The selection of bilateral electrode pairs showing sensitivity to ITD was partially aided by comparisons of the pitch elicited by individual electrodes in each ear (when stimulated alone with fixed-amplitude current pulses at 813 pps): specifically, interaural electrodes with similar pitches were more likely (but not certain) to show ITD sensitivity. Significant changes in lateral position occurred with specific electrode pairs. With five bilateral electrode pairs of 14 tested, ITDs of 300 and 600 micros moved an auditory image significantly from right to left. With these same pairs, ILD changes of approximately 11% of the dynamic range (in microApp) moved an auditory image from the far left to the far right-significantly farther than the nine pairs not showing significant ITD sensitivity. However, even these nine pairs did show response changes as a function of the interaural (or confounding monaural) level cue. Overall, insofar as the access to bilateral cues demonstrated herein generalizes to other subjects, it provides hope that the normal binaural advantages for speech recognition and sound localization can be made available to bilateral implant users.

Acoustic Stimulation↗
PubMed2002

Binaural detection with narrowband and wideband reproducible noise maskers: I. Results for human.

This study investigated binaural detection of tonal targets (500 Hz) using sets of individual masker waveforms with two different bandwidths. Previous studies of binaural detection with wideband noise maskers show that responses to individual noise waveforms are correlated between diotic (N0S0) and dichotic (N0S(pi)) conditions [Gilkey et al., J. Acoust. Soc. Am. 78, 1207-1219 (1985)]; however, results for narrowband maskers are not correlated across interaural configurations [Isabelle and Colburn, J. Acoust. Soc. Am. 89, 352-359 (1991)]. This study was designed to allow direct comparison, in detail, of responses across bandwidths and interaural configurations. Subjects were tested on a binaural detection task using both narrowband (100-Hz bandwidth) and wideband (100 Hz to 3 kHz) noise maskers that had identical spectral components in the 100-Hz frequency band surrounding the tone frequency. The results of this study were consistent with the previous studies: N0S0 and N0S(pi) responses were more strongly correlated for wideband maskers than for narrowband maskers. Differences in the results for these two bandwidths suggest that binaural detection is not determined solely by the masker spectrum within the critical band centered on the target frequency, but rather that remote frequencies must be included in the analysis and modeling of binaural detection with wideband maskers. Results across the set of individual noises obtained with the fixed-level testing were comparable to those obtained with a tracking procedure which was similar to the procedure used in a companion study of rabbit subjects [Zheng et al., J. Acoust. Soc. Am. 111, 346-356 (2002)].

Adolescent↗
PubMed2002

Quantifying the implications of nonlinear cochlear tuning for auditory-filter estimates.

The relation between auditory filters estimated from psychophysical methods and peripheral tuning was evaluated using a computational auditory-nerve (AN) model that included many of the response properties associated with nonlinear cochlear tuning. The phenomenological AN model included the effects of dynamic level-dependent tuning, compression, and suppression on the responses of high-, medium-, and low-spontaneous-rate AN fibers. Signal detection theory was used to evaluate psychophysical performance limits imposed by the random nature of AN discharges and by random-noise stimuli. The power-spectrum model of masking was used to estimate psychophysical auditory filters from predicted AN-model detection thresholds for a tone signal in fixed-level notched-noise maskers. Results demonstrate that the role of suppression in broadening peripheral tuning in response to the noise masker has implications for the interpretation of psychophysical auditory-filter estimates. Specifically, the estimated psychophysical auditory-filter equivalent-rectangular bandwidths (ERBs) that were derived from the nonlinear AN model with suppression always overestimated the ERBs of the low-level peripheral model filters. Further, this effect was larger for an 8-kHz signal than for a 2-kHz signal, suggesting a potential characteristic-frequency (CF) dependent bias in psychophysical estimates of auditory filters due to the increase in strength of cochlear nonlinearity with increases in CF.

Auditory Perception↗