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C Trahiotis

Publications and source records attributed to C Trahiotis.

At least 37 records · Page 2Linked to original sources
PubMed1995

Binaural interference effects measured with masking-level difference and with ITD- and IID-discrimination paradigms.

The results of several studies have demonstrated that the ability to process binaural information within discrete spectral regions may be degraded by the presence of information at other, even remote, spectral loci. This study focused on binaural interference produced by low-frequency noises (centered at 500 Hz) on the processing of interaural disparities within high-frequency bands of noise (centered on 4 kHz). The bandwidths of the interferers and "targets" were either the same (either 100 or 400 Hz) or different (interferer: 100 Hz; target: 400 Hz). Within a single group of listeners, interference was measured with a masking-level difference paradigm (NoSo vs NoS pi), and in ITD- and IID-discrimination tasks. An important feature of the experiments was the utilization, parametrically, in all three tasks, of pulsed and continuous interferers that were either diotic or were interaurally uncorrelated. As reported in previous experiments, the amounts of interference obtained with pulsed interferers were much greater than those obtained with continuous interferers. The present experiment extends that general finding to discrimination of IIDs. In addition, in all three tasks, pulsed, interaurally uncorrelated interferers produced greater amounts of interference than did pulsed, diotic interferers. The patterns of interference effects found across bandwidths and listeners for the four interference conditions (pulsed-diotic, continuous-diotic, pulsed-uncorrelated, and continuous-uncorrelated) in the MLD paradigm were different than those obtained in either the ITD- or IID-discrimination tasks. One factor that may account for the diverging patterns of interference is that the interaural cues produced by adding the S pi signal to the diotic masker fluctuated in magnitude over time. In contrast, the ITDs and IIDs in the discrimination task were static.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Threshold↗
PubMed1995

Neural responses to simple simulated echoes in the auditory brain stem of the unanesthetized rabbit.

1. In most natural environments, sound waves from a single source will reach a listener through both direct and reflected paths. Sound traveling the direct path arrives first, and determines the perceived location of the source despite the presence of reflections from many different locations. This phenomenon is called the "law of the first wavefront" or "precedence effect." The time at which the reflection is first perceived as a separately localizable sound defines the end of the precedence window and is called "echo threshold." The precedence effect represents an important property of the auditory system, the neural basis for which has only recently begun to be examined. Here we report the responses of single neurons in the inferior colliculus (IC) and superior olivary complex (SOC) of the unanesthetized rabbit to a sound and its simulated reflection. 2. Stimuli were pairs of monaural or binaural clicks delivered through earphones. The leading click, or conditioner, simulated a direct sound, and the lagging click, or probe, simulated a reflection. Interaural time differences (ITDs) were introduced in the binaural conditioners and probes to adjust their simulated locations. The probe was always set at the neuron's best ITD, whereas the conditioner was set at the neuron's best ITD or its worst ITD. To measure the time course of the effects of the conditioner on the probe, we examined the response to the probe as a function of the conditioner-probe interval (CPI). 3. When IC neurons were tested with conditioners and probes set at the neuron's best ITD, the response to the probe as a function of CPI had one of two forms: early-low or early-high. In early-low neurons the response to the probe was initially suppressed but recovered monotonically at longer CPIs. Early-high neurons showed a nonmonotonic recovery pattern. In these neurons the maximal suppression did not occur at the shortest CPIs, but rather after a period of less suppression. Beyond this point, recovery was similar to that of early-low neurons. The presence of early-high neurons meant that the overall population was never entirely suppressed, even at short CPIs. Taken as a whole. CPIs for 50% recovery of the response to the probe among neurons ranged from 1 to 64 ms with a median of approximately 6 ms. 4. The above results are consistent with the time course of the precedence effect for the following reasons. 1) The lack of complete suppression at any CPI is compatible with behavioral results that show the presence of a probe can be detected even at short CPIs when it is not separately localizable. 2) At a CPI corresponding to echo threshold for human listeners (approximately 4 ms CPI) there was a considerable response to the probe, consistent with it being heard as a separately localizable sound at this CPI. 3) Full recovery for all neurons required a period much longer than that associated with the precedence effect. This is consistent with the relatively long time required for conditioners and probes to be heard with equal loudness. 5. Conditioners with either the best ITD or worst ITD were used to determine the effect of ITD on the response to the probe. The relative amounts of suppression caused by the two ITDs varied among neurons. Some neurons were suppressed about equally by both types of conditioners, others were suppressed more by a conditioner with the best ITD, and still others by a conditioner with the worst ITD. Because the best ITD and worst ITD presumably activate different pathways, these results suggest that different neurons receive a different balance of inhibition from different sources. 6. The recovery functions of neurons not sensitive to ITDs were similar to those of ITD-sensitive, neurons. This suggests that the time course of suppression may be common among different IC populations. 7. We also studied neurons in the SOC. Although many showed binaural interactions, none were sensitive to ITDs. Thus the response of this population may not be

Acoustic Stimulation↗
PubMed1994

The effect of nonsimultaneous on-frequency and off-frequency cues on the detection of a tonal signal masked by narrow-band noise.

Listeners' detection thresholds were measured for a 125-ms, 1-kHz tonal signal masked by a similarly gated 50-Hz-wide band of noise. A two-interval, adaptive, forced-choice procedure either with or without temporally surrounding cuing intervals containing 50-Hz-wide bands of noise was employed. When the cues were present, their center frequency was either 1 kHz (on-frequency) or 900 or 700 Hz (off-frequency). In the conditions of principal interest, the envelopes and phase modulations of the bands of noise were "frozen" across the four intervals that defined a trial, but were chosen randomly across trials. Thresholds were lowest with cues centered at 1 kHz and increased substantially when the center frequency of the cues was changed to 900 or 700 Hz. With cues centered at 700 Hz, performance was equivalent to that obtained without cues and with the masking noise "frozen" across the two intervals that defined a trial. A similar pattern of results was obtained with high-frequency stimuli, where sensitivity to fine-structure information is greatly reduced. Roving the level of the stimuli over a 40-dB range generally reduced sensitivity but did not greatly affect the overall pattern of the data. Thresholds obtained in the two-interval task with masking waveforms chosen randomly were compared with thresholds obtained when the masking waveform was "frozen" within, but not across trials. Differences in threshold appeared to be accounted for by the listeners' use of changes in the mean slope of the envelope of the noise produced by adding the tonal signal.

Acoustic Stimulation↗
PubMed1994

Detection of interaural delay in high-frequency sinusoidally amplitude-modulated tones, two-tone complexes, and bands of noise.

Listeners' ability to detect interaural temporal disparities (ITDs) was investigated for 160-ms, sinusoidally amplitude modulated (SAM) tones, two-tone complexes, and bands of noise at center frequencies of 4, 8, or 12 kHz. Rates of modulation for the 100%-modulated SAM tones and frequency separation for the equal-amplitude, two-tone complexes ranged from 32-768 Hz, depending on center frequency. Noise bandwidths ranged from 50-2000 Hz, also depending on center frequency. The data indicate, consistent with previous results, that sensitivity to ITD with the SAM and two-tone complexes decreases as the rate of envelope fluctuation increases beyond about 400 Hz. The decline in performance is not due simply to reduced depths of modulation produced by critical-band-like filtering, but is consistent with an inability to "follow" or encode high rates of modulation. For bands of noise, sensitivity to ITD was relatively constant as a function of bandwidth. Generally, sensitivity to ITD decreased as center frequency was increased from 4 to 8 kHz, but the relations among the data were essentially unchanged. Increasing the center frequency to 12 kHz resulted in very poor performance.

Acoustic Stimulation↗
PubMed1994

Detection of interaural delay in bands of noise: effects of spectral interference combined with spectral uncertainty.

This study concerns two situations that could limit a listener's sensitivity to interaural temporal delay (ITD). The first is having to detect a "target" ITD in one spectral region when diotic energy is also present in remote and/or adjacent spectral regions. In such a situation, sensitivity to ITD is typically degraded, as compared to when no remote and/or adjacent diotic energy is present. Both the outcome and the paradigm are commonly termed "spectral interference." In the present study, spectral interference was measured using a broadband (100 Hz to 9 kHz) noise that was diotic, save for a restricted spectral region that was interaurally delayed. The portion of the noise that contained the ITD had a center frequency (CF) of either 300, 1200, 2400, or 4800 Hz and a bandwidth that was 40% of the CF. The second situation of interest was "spectral uncertainty." Here, the center frequency of the portion of the noise containing the ITD was varied (chosen from one of four possible CFs) on a trial-by-trial basis. Consequently, the listener was uncertain about which spectral region could contain the ITD. Data were also collected with one of four narrow bands of noise with the CFs and bandwidths identical to the interaurally delayed spectral regions used in the spectral interference and spectral uncertainty conditions. Within a block of trials, the center frequency of the narrow band of noise was either held constant or was randomly chosen from the set of four CFs.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1994

Lateralization of bands of noise as a function of combinations of interaural intensive differences, interaural temporal differences, and bandwidth.

Listeners indicated the intracranial position of bands of noise (from 50 to 400 Hz in width) for several combinations of interaural intensive differences (IID), and interaural temporal differences (ITD), and/or interaural phase differences (IPD). All ITD and IPD combinations produced an interaural delay of 1500 microseconds at the center frequency of the noise. The interaural phase spectra were constructed to produce several patterns of putative cross-correlation functions. Potency of IIDs depended greatly on particular combinations of bandwidth, ITD and IPD. For some combinations, changing the IID by only 3 dB resulted in large shifts in laterality (sometimes moving the image from near one ear to near the other). The complex interactions observed make the results incompatible with the traditional notion that IIDs simply act as weights or scalars. Rather, IIDs act in two distinct manners: (1) as independent scalar quantities and (2) by interacting with specific combinations of bandwidth and ITD/IPD, which is believed to reflect an action within the cross correlation surface.

Acoustic Stimulation↗
PubMed1993

Interaural temporal discrimination using two sinusoidally amplitude-modulated, high-frequency tones: conditions of summation and interference.

This paper concerns sensitivity to interaural temporal delays (ITD) in the envelopes of two, sometimes simultaneously presented, sinusoidally amplitude-modulated (SAM) tones. The SAM tones were fully modulated (typically at a rate of 250 Hz) and had carrier frequencies of either 2 or 4 kHz. Of particular interest were cases in which the delay to be detected (target ITD) occurred in only one spectral region or in both. The reference ITD, to which the target ITD was added, was either 0, 300, or 600 microseconds. There were three general outcomes: (1) When both regions contained a target ITD, there was an improvement in sensitivity that was quantitatively consistent with an optimal use of independent information. This type of summation was seen even when the target ITDs were added to a pair of SAM tones with two different reference ITDs; (2) when the target ITD was restricted to the higher spectral region, sensitivity was reduced, indicating interference. Interference occurred when the two spectral regions had the same or different reference ITDs and the same or different rates of modulation; (3) sensitivity was unaffected (i.e., no interference occurred) when the target ITD was restricted to the lower spectral region of the pair of SAM tones. These results supplement the observations of Buell and Hafter [J. Acoust. Soc. Am. 90, 1894-1900 (1991)], who used low-frequency tones.

Acoustic Stimulation↗
PubMed1993

Spectral interference in a binaural detection task: effects of masker bandwidth and temporal fringe.

Recently, it was reported that the detectability of a 100-ms, 800-Hz tone (the target) presented antiphasically (S pi) against a background of continuous, broadband, diotic noise could be degraded if a 400-Hz tone (the interferer) was gated simultaneously with the target [L. R. Bernstein, J. Acoust. Soc Am. 89, 1306-1313 (1991)]. This degradation, termed "interference," was reduced by presenting the interferer continuously. In the present study, the amount of such interference was measured when the target was masked by either a broadband or a narrow-band (100-Hz-wide) noise. The narrow-band noise produced a relatively large masking-level difference, thereby allowing about 10 dB of interference to be observed. In other conditions, the interferer was turned on (temporally "fringed") prior to the target. The presence and duration of a forward fringe of the interferer did not reduce the interference, even for forward fringes of 320 ms. This result is consistent with those of Woods and Colburn [W. S. Woods and H. S. Colburn, J. Acoust Soc. Am. 91, 2894-2902 (1992)] who measured the detectability of interaural delay of low-frequency tones. The data from both studies indicate that binaural interference is observed even under conditions where interferers and targets are perceptually segregated in the sense that listeners hear more than one sound object.

Audiometry, Pure-Tone↗
PubMed1992

Detection of antiphasic sinusoids added to the envelopes of high-frequency bands of noise.

Listeners' sensitivities to antiphasic sinusoids added to the envelopes of high-frequency bands of noise were measured as a function of the frequency of the sinusoid and the bandwidth of the masking noise. The stimuli were constructed such that the added sinusoid produced interaural intensive differences (IIDs) that fluctuated at a rate that was equal to the frequency of the sinusoid and was independent of the bandwidth of the masking noise. The data indicated that performance was relatively unaffected by the rate of modulation for rates between 5 and 160 Hz. Greater rates of modulation resulted in substantial degradations of performance. The results are pertinent to Zurek and Durlach's (1987) suggestions concerning the relatively small binaural masking-level differences typically measured with high-frequency signals and broadband maskers in the N0S pi configuration. Specifically, it appears that listeners' performance is greatly affected by an insensitivity to rapidly fluctuating IIDs but is relatively unaffected by any 'spectral interference' produced by masking energy beyond the monaural critical band. Interestingly, the data corroborate Grantham's (1984) insightful proposal that the binaural system may possess two independent averaging mechanisms, one for the processing of interaural temporal disparities (ITDs) and the other for the processing of IIDs.

Acoustic Stimulation↗
PubMed1992

Discrimination of interaural envelope correlation and its relation to binaural unmasking at high frequencies.

Listeners' sensitivity to interaural correlation of the envelope of high-frequency waveforms and whether such sensitivity might account for detectability in a masking-level difference paradigm were assessed. Thresholds of interaural envelope decorrelation (from a reference correlation of 1.0) were measured for bands of noise centered at 4 kHz and bandwidths ranging from 50-1600 Hz. Decorrelation of the envelope was achieved by "mixing" two independent narrow-band noises. Separately, with the same listeners, NoSo and NoS pi detection thresholds were measured for maskers of the same center frequency and bandwidths. For bandwidths of noise up to about 400 Hz, listeners were similarly sensitive to interaural decorrelation in both types of task. However, for bandwidths greater than 400 Hz or so, while sensitivity in the discrimination task was unaffected, sensitivity was reduced in the NoS pi conditions. Additional data suggested that listeners were able to maintain their sensitivity independent of bandwidth in the discrimination task by focusing on binaural information within select spectral regions of the stimuli.

Acoustic Stimulation↗
PubMed1991

Lateralization of low-frequency tones: relative potency of gating and ongoing interaural delays.

Several types of interaural delay can affect the lateral position of binaural signals. Delays can occur within the gating (onset and/or offset) or ongoing portions of the signal, or both. Extent of laterality produced by each of these delays was measured for low-frequency tones with an acoustic pointing task. Relative potency was assessed by presenting the delays singly or in combinations (where the types of delay were consistent or in opposition). Rise/decay time, duration, and frequency of the tonal targets were also varied. The major finding was that ongoing delays were much more potent than gating delays in determining extent of laterality. Gating delays were most effective when the interaural phase of the ongoing portion of the tones was more or less ambiguous with respect to which ear was leading. Many of our findings are qualitatively well described by considering properties of patterns of activity produced within a cross-correlation network by such interaurally delayed signals.

Acoustic Stimulation↗
PubMed1990

Detectability of interaural delays over select spectral regions: effects of flanking noise.

Zurek [P. M. Zurek, J. Acoust. Soc. Am. Suppl. 1 78, S18 (1985)] noted what he termed "spectral dominance" in sensitivity to interaural delay for broadband stimuli. He found that interaural delays presented solely within high-frequency spectral regions were difficult, if not impossible, to detect in the presence of spectrally flanking, gated, diotic noise. In order to see if spectral dominance is a general result of the processing of interaural delays in broadband stimuli, similar experiments were conducted utilizing both gated and continuous flanking noises that were interaurally identical (diotic) or completely uncorrelated. Beyond replicating Zurek's basic findings, the data strongly suggest that the processing of interaural delays was largely unaffected when the flanking sounds were continuous and diotic. When the flanking sounds were interaurally uncorrelated, sensitivity was affected, but not drastically, for both gated and continuous conditions. Consequently, it appears that any inability to cope with conflicting interaural cues across spectral regions may be observed only under restricted conditions.

Acoustic Stimulation↗
PubMed1990

On the use of adaptive procedures in binaural experiments.

Adaptive psychophysical procedures have been routinely used in monaural experiments for many years, but only sparsely used in binaural experiments. In this letter, (1) the increasing use of adaptive procedures in binaural experiments is documented; (2) factors that determine their appropriateness are discussed; and (3) data that attest to their usefulness are presented.

Adaptation, Physiological↗
PubMed1989

Lateralization of bands of noise: effects of bandwidth and differences of interaural time and phase.

The effects of stimulus bandwidth on lateralization of narrow bands of noise were investigated with an acoustic pointing task. Stimuli were narrow bands of noise (centered on 500 Hz with bandwidths ranging from 50-400 Hz) that contained interaural time delays and/or interaural phase shifts. The overall extent of lateralization and sidedness was found to vary greatly as a function of stimulus bandwidth, as insightfully discussed earlier by Jeffress [L. A. Jeffress, Foundations of Modern Auditory Theory, edited by J. V. Tobias (Academic, New York, 1972)]. The data are qualitatively consistent with a weighted-image model [Stern et al., J. Acoust. Soc. Am. 84, 156-165 (1988)] that specifies and utilizes the shapes and locations of patterns of hypothesized neural activity. These patterns are topographically organized along a two-dimensional surface, and they describe the cross-correlation function of the stimuli as a joint function of frequency and the delay parameter of the cross-correlation operation. In this fashion, lateralization depends upon individual modes of such patterns that are weighed with respect to their straightness (consistency of interaural delay over frequency) and centrality (the extent to which interaural delays are small in magnitude).

Acoustic Stimulation↗
PubMed1988

Lateralization of complex binaural stimuli: a weighted-image model.

This article describes a new model that predicts the subjective lateral position of bandpass stimuli. It is assumed, as in other models, that stimuli are bandpass filtered and rectified, and that the rectified outputs of filters with matching center frequencies undergo interaural cross correlation. The model specifies and utilizes the shape and location of assumed patterns of neural activity that describe the cross-correlation function. Individual modes of this function receive greater weighting if they are straighter (describing consistent interaural delay over frequency) and/or more central (describing interaural delays of smaller magnitude). This weighting of straightness and centrality is used by the model to predict the perceived laterality of several types of low-frequency bandpass stimuli with interaural time delays and/or phase shifts, including bandpass noise, amplitude-modulated stimuli with time-delayed envelopes, and bandpass-filtered clicks. This model is compared to other theories that describe lateralization in terms of the relative contributions of information in the envelopes and fine structures of binaural stimuli.

Acoustic Stimulation↗
PubMed1987

A programmable-delay line.

A relatively simple circuit is described which delays audio signals in 5 microseconds steps from 0 microsecond to 4000 microseconds. Delays are programmed via twelve TTL-level data lines. The magnitude response is flat and the phase response is linear from DC to 5 kHz. The gain of the circuit is fixed and independent of the selected delay. Delays are accurate to within 1 microsecond of the programmed value. The device is a nice alternative to other methods which have diverse shortcomings.

Acoustic Stimulation↗
PubMed1987

Some physical and psychological effects produced by selective delays of the envelope of narrow bands of noise.

One can construct narrow bands of noise that contain delays of either the envelope, the phase, or the carrier separately or in combination. Delayed and undelayed noises will have identical spectra if, and only if, both the envelope and the phase undergo delays of the same magnitude. To study lateralization of these signals, an acoustic pointing task was employed in which listeners varied the interaural intensitive disparity of a narrow band of noise (the pointer) so that it matched the position of a second, experimenter-controlled stimulus (the target) which contained symmetric interaural delays of only the envelope. Targets were narrow bands of noise with center frequencies chosen at octave intervals between about 500 Hz and about 4000 Hz. The smallest bandwidth was 100 Hz and the largest was 800 Hz. For high-frequency stimuli, delays of only the envelope of a narrow band of noise appear to mediate lateralization which is greatest for bands centered near 2000 Hz. For low frequencies, delays larger than 800 microseconds were required to produce acoustic images appreciably away from the midline. These findings confirm the notion that listeners are sensitive to interaural temporal disparities in the envelopes of high-frequency, complex stimuli.

Acoustic Stimulation↗