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PubMed1996

Intensity discrimination as a function of stimulus level with electric stimulation.

Difference limens (DLs) for changes in electric current were measured from multiple electrodes in each of eight cochlear-implanted subjects. Stimuli were 200-microseconds/phase biphasic pulse trains delivered at 125 Hz in 300-ms bursts. DLs were measured with an adaptive three-alternative forced-choice procedure. Fixed-level psychometric functions were also obtained in four subjects to validate the adaptive DLs. Relative intensity DLs, specified as Weber fractions in decibels [10 log (delta I/I)] for standards above absolute threshold, decreased as a power function of stimulus intensity relative to absolute threshold [delta I/I = beta (I/I0) alpha] in the same manner as Weber fractions for normal acoustic stimulation reported in previous studies. Exponents (alpha) of the power function for electric stimulation ranged from -0.4 to -3.2, on average, an order of magnitude larger than exponents for acoustic stimulation, which range from -0.07 to -0.11. Normalization of stimulus intensity to the dynamic range of hearing resulted in Weber functions with similar negative slopes for electric and acoustic stimulation, corresponding to an 8-dB average improvement in Weber fractions across the dynamic range. Sensitivity to intensity change ¿10 log beta¿ varied from -0.42 to -13.5 dB compared to +0.60 to -3.34 dB for acoustic stimulation, but on average was better with electric stimulation than with acoustic stimulation. Psychometric functions for intensity discrimination yielded Weber fractions consistent with adaptive procedures and d' was a linear function of delta I. Variability among repeated Weber-fraction estimates was constant across dynamic range. Relatively constant Weber fractions across all or part of the dynamic range, observed in some subjects, were traced to the intensity resolution limits of individual implanted receiver/stimulators. DLs could not be accurately described by constant amplitude changes, expressed as a percentage of dynamic range ¿delta A(% DR)¿. Weber fractions from prelingually deafened subjects were no better or worse than those from postlingually deafened subjects. The cumulative number of discriminable intensity steps across the dynamic range of electric hearing ranged from as few as 6.6 to as many as 45.2. Physiologic factors that may determine important features of electric intensity discrimination are discussed in the context of a simple, qualitative, rate-based model. These factors include the lack of compressive cochlear preprocessing, the relative steepness of neural rate-intensity functions, and individual differences in patterns of neural survival.

Auditory Threshold↗
PubMed1997

Temporal integration of loudness, loudness discrimination, and the form of the loudness function.

Temporal integration for loudness of 5-kHz tones was measured as a function of level between 2 and 60 dB SL. Absolute thresholds and levels required to produce equal loudness were measured for 2-, 10-, 50-, and 250-ms tones using adaptive, two-interval, two-alternative forced-choice procedures. The procedure for loudness balances was new and employed ten interleaved tracks to obtain concurrent measurements for ten tone pairs. Each track converged at the level required to make the variable stimulus just louder than the fixed stimulus. Thus, the data yield estimates of the just-noticeable difference (jnd) for loudness level and temporal integration for loudness. Results for four listeners show that the amount of temporal integration, defined as the level difference between equally loud short and long tones, varies markedly with level and is largest at moderate levels. The effect of level increases as the duration of the short stimulus decreases and is largest for comparisons between the 2- and 250-ms tones. The loudness-level jnds are also largest at moderate levels and, contrary to traditional jnds for the level of two equal-duration tones, they do not appear to depend on duration. The latter finding indicates that loudness discrimination between stimuli that differ along multiple dimensions is not the same as level discrimination between stimuli that differ only in level. An equal-loudness-ratio model, which assumes that the ratio of loudnesses for a long and short tone at equal SPL is the same at all SPLs, can explain the level dependence of temporal integration and the loudness jnds. It indicates that the loudness function [log(loudness) versus SPL] is flatter at moderate levels than at low and high levels in agreement with earlier findings for 1-kHz tones [M. Florentine et al., J. Acoust. Soc. Am. 99, 1633-1644 (1996)].

Female↗
PubMed1997

The relation between gap detection, loudness, and loudness growth in noise-masked normal-hearing listeners.

Gap detection was measured for 50 and 1000-Hz-wide noise markers arithmetically centered on 1000 Hz. The markers were presented in a lowpass background noise having a high-frequency cutoff of 2000 Hz. The pressure spectrum level of the background noise was either 0 or 40 dB/Hz. Gap detection was determined at sensation levels (SLs) of 10, 15, 20, and 30 dB in the 0-dB/Hz background, and at SLs of 10, 15, and 20 dB in the 40-dB/Hz background. Because loudness increased more steeply in the higher level noise background, the markers in the 40-dB/Hz background were at higher loudness (and at a steeper portion of the loudness growth function) than markers in the 0-dB/Hz background, for markers matched in terms of SL. The main goal of the experiment was to determine whether gap detection would be relatively poor at steep portions of the loudness growth function due to the gap being confused with ongoing random dips. Such confusion might be particularly great when the noise bandwidth was narrow (and therefore characterized by prominent fluctuation) and the growth of loudness was steep. Gap detection was poorer for the 50-Hz-wide marker than for the 1000-Hz-wide marker. For a given marker bandwidth at a given SL, gap detection was similar whether the marker was presented in the 0-dB/Hz noise or the 40-dB/Hz noise. Supplementary conditions indicated that (1) gap detection results for 50-Hz-wide markers presented at equal SL's were also similar between a 0-dB/Hz noise background and a 55-dB/Hz noise background, and that (2) gap detection for 50- and 1000-Hz-wide markers was poorer in a 40-dB/Hz background than in a 0-dB/Hz background when markers were matched for loudness. The results generally indicated similar gap detection thresholds for markers presented at similar SLs across a relatively wide range of background noise levels. Gap detection was related more closely to the marker-to-noise ratio than to the loudness relation between markers or the steepness of loudness growth.

Auditory Threshold↗
PubMed1997

Pitch and loudness estimation for single and multiple pulse per period electric pulse rates by cochlear implant patients.

Numerical estimates of loudness and pitch for electric pulse rates were obtained from 14 patients using the 22 electrode cochlear implant manufactured by Cochlear Limited. Six patients were postlinguistically deafened adults, and eight patients were adults and children who became deaf very early in life. Comparisons were made between two types of pulse rate patterns. The SPP pulse pattern presented a single pulse every period, the inverse of the pulse rate. The MPP pulse pattern presented multiple pulses in the first half of the period, using a rate of 1000 pulses/s, with no stimulation in the second half of the period. The pulse rates used for the SPP and MPP pulse patterns were 71.4-500 pulses/s, which corresponded to periods of 14-2 ms. For the SPP pulse pattern, the total number of pulses over the duration of the stimulus increased with increases in pulse rate, while for the MPP pulse pattern, the total number of pulses remained constant. Pitch and loudness estimates were obtained from the postlinguistically deafened patients for the SPP and MPP pulse patterns, and from the early-deafened patients for the MPP pulse pattern. Loudness estimates for the SPP pulse pattern increased with increases in pulse rate for all postlinguistically deafened patients. Loudness estimates for the MPP pulse pattern decreased with increases in pulse rate for three of the six postlinguistically deafened patients and for six of the eight early-deafened patients. For the other patients (three postlinguistically deafened and two early-deafened), loudness estimates marginally increased with increases in pulse rate. Pitch estimates for the SPP and MPP pulse patterns increased with increases in pulse rate for the six postlinguistically deafened patients. For the early-deafened patients, pitch estimates for the MPP pulse patterns increased with increases in pulse rate for only five of the eight patients. For the other three early-deafened patients, pitch estimates were similar to the loudness estimates and decreased with increases in pulse rate.

Adolescent↗
PubMed1997

Loudness adaptation and excitation patterns: effects of frequency and level.

Simple loudness adaptation for pure tones was measured at frequencies from 0.125 to 16 kHz and at sensation levels from 5 to 60 dB. Sixteen young listeners with normal hearing participated in four experiments. Most of the loudness measurements were obtained by the method of successive magnitude estimation; some were also obtained by loudness matching. The two indices of loudness adaptation gave similar results. At all frequencies, loudness adaptation increased as sensation level decreased. After 6 min, average loudness declined at most frequencies by about 20% at 40-dB sensation level (SL) and by between 70% and almost 100% at 5-dB SL. Adaptation also increased with increasing frequency, and was especially marked at 16 kHz, where loudness declined more than 60% at a sensation level as high as 40 dB. Most of the adaptation occurred usually within the first 3 min of exposure, but loudness continued to diminish at a slower rate up to around 6 min. The dependence of loudness adaptation on frequency and level can be largely accounted for by the restricted-excitation-pattern hypothesis. Adaptation is assumed to take place when excitation is restricted to a narrow region of the cochlea. This hypothesis is supported by a quantitative analysis based on excitation patterns derived from measurements of masking.

Adolescent↗
PubMed1997

Changes in evoked otoacoustic emissions in the guinea pig after pure-tone acoustic overstimulation.

To test if click-evoked otoacoustic emissions (CEOAEs) have frequency specificity, continuous changes in CEOAEs (especially frequency components of the CEOAE power spectrum) after pure-tone exposure in guinea pigs were examined. Pure-tone stimuli (0.5 kHz, 120 dB SPL; 2 kHz, 115 dB SPL; 4 kHz, 110 dB SPL) were given in a closed system for 3 min. After exposure, the frequency components in the CEOAE power spectrum decreased maximally at one-half octave or more above the overstimulation frequency. They partially recovered 2 h after exposure. The time course of compound action potential (CAP) thresholds after exposure was similar to that of the frequency components of the CEOAE power spectrum. It was concluded that some local damage caused by outer hair-cell dysfunction in the guinea pig cochlea can be detected by measuring shifts in frequency components in the CEOAE power spectrum.

Animals↗
PubMed1997

Sensitivity to changes in overall level and spectral shape: an evaluation of a channel model.

Two experiments involving level and spectral shape discrimination which test an optimal channel model developed by Durlach et al. [J. Acoust. Soc Am. 80, 63-72 (1986)] are described. The model specifies how the auditory system compares and/or combines intensity information in different frequency channels. In the first experiment, psychometric functions were obtained for the discrimination of changes in level and discrimination of changes in spectral shape for an eight-tone complex sound. A variety of different base spectral shapes were tested. In some conditions, level randomization was introduced to reduce the reliability of across-interval changes in level. Increasing the amount of level variation degraded performance for the level discrimination task but had no effect on the shape discrimination task. In all conditions, sensitivity to changes in spectral shape was superior to sensitivity to changes in level. Consequently, two models of central noise are evaluated in an attempt to explain these results; one in which central noise acts prior to the formation of the likelihood ratio and one in which central noise degrades the likelihood ratio. The former model is more successful in accounting for the data. In a second experiment, the detectability of a level increment to one component of a multitone complex was measured. The frequency content of the complex was varied by systematically removing six components from a 23-component complex. Thresholds were measured for increments at three different signal frequencies. A common trend in the data was that when there was a spectral gap directly above the signal frequency, thresholds were lowest. This result differs from the predictions of a simple channel model, and contrasts with results presented by Green and Berg [Q. J. Exp. Psychol. 43A, 449-458 (1991)].

Adult↗
PubMed1997

Excitation produced by Schroeder-phase complexes: evidence for fast-acting compression in the auditory system.

A series of experiments compared the excitation produced in an auditory filter centered on 1100 Hz by two complexes, both of which consisted of harmonics 2-20 of a 100-Hz fundamental. When the components had a level of 69 dB SPL each, summing them in positive Schroeder phase produced substantially less forward masking of an 1100-Hz signal than when the components were summed in negative Schroeder phase. This difference decreased with decreases in overall masker level. Listeners also reported that the components of the positive-phase masker close to 1100 Hz were quieter than the corresponding components in the negative-phase masker. The data are explained using Kohlrausch and Sander's [J. Acoust. Soc. Am. 97, 1817-1829 (1995)] finding that the response of an 1100-Hz auditory filter to the positive-phase complex shows marked peaks and dips, whereas that to the negative-phase complex does not. It is argued that the peaks in the response to the positive-phase masker are attenuated by fast-acting compression in the auditory system, thereby reducing the excitation produced by that sound. It is also argued that, compared to the power functions commonly used to model "excess masking" and the growth of loudness, the present data reflect greater compression at high levels but less compression at low levels.

Attention↗
PubMed1997

Masking period patterns of Schroeder-phase complexes: effects of level, number of components, and phase of flanking components.

Masking period patterns (MPPs) were obtained for maskers consisting of harmonics 2-20 of a 100-Hz fundamental. The signal was always a 5-ms 1100-Hz sinusoid presented 152, 154, 156, 158, or 160 ms after the start of a 400-ms masker. Experiment 1 replicated the finding that, for a masker level of 69 dB component, the shape of the MPP depended strongly on the phases of the components: Summing them in positive Schroeder phase led to a threshold variation of about 18 dB across the MPP, but summing them in negative Schroeder phase produced a flat MPP [A. Kohlrausch and A. Sander, J. Acoust. Soc. Am. 97, 1817-1829 (1995)]. Reducing the level of the positive-phase masker resulted in a systematic flattening of the MPP, whereas the negative-phase MPPs were flat both at high and at low levels. Experiment 2 showed that removing all components of a positive-phase masker except those close to the signal raised thresholds at the minimum of the MPP. In contrast, a similar manipulation applied to the negative-phase masker produced a uniform elevation of the MPP. Experiment 3 showed that an analogous effect could be obtained by manipulating the phases of masker components remote from the signal. It is shown that several features of the data can be simulated using a nonlinear model of the auditory periphery [C. Giguère and P.C. Woodland, J. Acoust. Soc. Am. 95, 331-342 (1994)].

Auditory Threshold↗
PubMed1997

Auditory filters measured at neighboring center frequencies.

Auditory filters were derived in 20 normal-hearing human listeners at center frequencies (CFs) of 913, 1095, 3651, and 4382 Hz using the roex (p,r) method. Comparisons were made between slopes of the filters' skirts at the neighboring CFs with filter output levels of 45 and 70 dB. The same comparisons were made with regard to filter equivalent rectangular bandwidth (ERB). In the 1000-Hz region, the low-frequency slopes (Pl) of filters centered at 913 and 1095 Hz were significantly correlated at both stimulus levels, while the high-frequency slopes (Pu) were similar only at the high test level. In the 4000-Hz region, for sinusoids of 3651 and 4382 Hz, the level effect was clearer as both Pu and Pl values diverged at the low level but were related at high levels. The ERBs centered at the same CFs displayed a similar level dependence. At the stimulus level most likely to be affected by an active feedback mechanism, auditory filters centered at nearly the same frequency displayed quite distinct frequency selectivity, and this trend was stronger in the 4000-Hz region than the 1000-Hz region. The findings suggest that a saturating, active cochlear mechanism may not be distributed evenly, or contribute to peripheral tuning with equal effectiveness throughout the length of the partition.

Adult↗
PubMed1997

A behavioral measure of basilar-membrane nonlinearity in listeners with normal and impaired hearing.

This paper examines the possibility of estimating basilar-membrane (BM) nonlinearity using a psychophysical technique. The level of a forward masker required to mask a brief signal was measured for conditions where the masker was either at, or one octave below, the signal frequency. The level of the forward masker at masked threshold provided an indirect measure of the BM response to the signal, as follows. Consistent with physiological studies, it was assumed that the BM responds linearly to frequencies well below the characteristic frequency (CF). Thus the ratio of the slopes of the masking functions between a masker at the signal frequency and a masker well below the signal frequency should provide an estimate of BM compression at CF. Results obtained from normally hearing listeners were in quantitative agreement with physiological estimates of BM compression. Furthermore, differences between normally hearing listeners and listeners with cochlear hearing impairment were consistent with the physiological effects of damage to the cochlea. The results support the hypothesis that BM nonlinearity governs the nonlinear growth of the upward spread of masking, and suggest that this technique provides a straightforward method for estimating BM nonlinearity in humans.

Adult↗
PubMed1997

Short-term temporal integration: evidence for the influence of peripheral compression.

Thresholds for a 6.5-kHz sinusoidal signal, temporally centered in a 400-ms broadband-noise masker, were measured as a function of signal duration for normally hearing listeners and listeners with cochlear hearing loss over a range of masker levels. For the normally hearing listeners, the slope of the function relating signal threshold to signal duration (integration function) was steeper at medium masker levels than at low or high levels by a factor of nearly 2, for signal durations between 2 and 10 ms, while no significant effect of level was found for signal durations of 20 ms and more. No effect of stimulus level was found for the hearing-impaired listeners at any signal duration. For signal durations greater than 10 ms, consistent with many previous studies, the slope of the integration function was shallower for the hearing-impaired listeners than for the normally hearing listeners. However, for shorter durations, there was no significant difference in slope between the results from the hearing-impaired listeners and those from the normally hearing listeners in the high- and low-level masker conditions. A model incorporating a compressive nonlinearity, representing the effect of basilar-membrane (BM) compression, and a short-term temporal integrator, postulated to be a more central process, can account well for changes in the short-term integration function with level, if it is assumed that the compression is greater at medium levels than at low or high levels by a factor of about 4. This is in reasonable agreement with physiological measurements of BM compression, and with previous psychophysical estimates.

Adult↗
PubMed1997

Amplitude modulation depth discrimination of a sinusoidal carrier: effect of stimulus duration.

Discrimination of the change in depth of sinusoidal amplitude modulation (AM) was investigated as a function of stimulus duration. The carrier frequency was 4000 Hz, the standard modulation depth (m) was either 0.1, 0.18, or 0.3, and the modulation rate was either 10, 20, 40, or 80 Hz. For all standard depths and modulation rates, threshold (delta m) decreased by more than a factor o two as stimulus duration doubled from the shortest duration used up to a certain duration (critical duration), beyond which the threshold decreased only slightly or remained constant. The critical duration corresponded to about four cycles of modulation. Psychometric functions were measured for different stimulus durations to examine the extent to which a multiple-looks model could explain the present data. This model provided a reasonable prediction of the change in AM depth discrimination threshold as a function of stimulus duration.

Adult↗
PubMed1997

Psychometric functions and temporal integration in electric hearing.

Temporal-integration functions and psychometric functions for detection were obtained in eight users of the Nucleus 22-electrode cochlear implant. Stimuli were 100-Hz, 200-microseconds/phase trains of biphasic pulses with durations ranging from 0.44 to 630.4 ms (1 to 64 pulses). Temporal-integration functions were measured for 21 electrodes. Slopes of these functions were considerably shallower than the 2.5 dB/doubling slopes typically observed in acoustic hearing. They varied widely across subjects and for different electrodes in a given subject, ranging from 0.06 to 1.94 dB/doubling of stimulus pulses, with a mean [standard deviation (s.d.)] value of 0.42 (0.38). Psychometric functions were measured for 11 of the same 21 electrodes. Slopes of psychometric functions also varied across subjects and electrodes, and were 2-20 times steeper than those reported by other investigators for normal-hearing and cochlear-impaired acoustic listeners. Slopes of individual psychometric functions for 1-, 2-, 4-, and 8-pulse stimuli ranged from 0.20 to 1.84 log d'/dB with a mean (s.d.) value of 0.77 (0.45). Psychometric-function slopes did not vary systematically with stimulus duration in most cases. A clear inverse relation between slopes of psychometric functions and slopes of temporal-integration functions was observed. This relation was reasonably well described by a hyperbolic function predicted by the multiple-looks model of temporal integration [Viemeister and Wakefield, J. Acoust. Soc. Am. 90, 858-865 (1991)]. Psychometric-function slopes tended to increase with absolute threshold and were inversely correlated with dynamic range, suggesting that observed differences in psychometric-function slopes across subjects and electrodes may reflect underlying differences in neural survival.

Adult↗
PubMed1997

Comparison between subjective and objective measures of active hearing protector and communication headset attenuation.

A masked-threshold and a loudness-balance method have been developed to estimate the attenuation of communication headsets and hearing protectors with built-in active noise reduction (ANR) systems. Both methods are used to estimate the attenuation of the ANR systems and the masked-threshold method is also used to estimate the total attenuation (active plus passive) of the device. The procedures are designed to be used in the presence of environmental noise, and to minimize the noise exposure of subjects during the measurements. For comparison, physical measurements of insertion loss have also been performed using a miniature microphone in the concha. Experiments showed that the masked-threshold methods tends to give increased estimates of the attenuation if the noise reduction of the left and right earcup ANR systems differs, as commonly occurs in practice. In contrast, the loudness-balance method reduces the estimates of the active attenuation. Insertion loss measurements may be influenced by the position of the microphone, owing to the spatial variability of the sound field under an earmuff when the ANR system is operating. Differences between physical and subjective measurements of up to 20 dB have been obtained in this study at frequencies of 250 Hz and below for a device in which the sound pressure varied substantially near, and within, the ear canal.

Adult↗
PubMed1997

Speech recognition at simulated soft, conversational, and raised-to-loud vocal efforts by adults with cochlear implants.

Ten postlinguistically deaf adults who used the Nucleus Cochlear Implant System and SPEAK speech coding strategy responded to vowels, consonants, words, and sentences presented sound-only at 70, 60, and 50 dB sound-pressure level. Highest group mean scores were at a raised-to-loud level of 70 dB for consonants (73%), words (44%), and sentences (87%); the highest score for vowels (70%) was at a conversational level of 60 dB. Lowest group mean scores were at a soft level of 50 dB for vowels (56%), consonants (47%), words (10%), and sentences (29%); all except subject 7 had some open-set speech recognition at this level. For the conversational level (60 dB), group mean scores for sentences and words were 72% and 29%, respectively. With this performance and sound-pressure level, it was observed that these subjects communicated successfully in a variety of listening situations. Given these subjects' speech recognition scores at 60 dB and the fact that 70 dB does not simulate the vocal effort used in everyday speaking situations, it is suggested that cochlear implant candidates and implantees be evaluated with speech tests presented at 60 dB instead of the customary 70 dB sound-pressure level to simulate benefit provided by implants in everyday life. Analysis of individuals' scores at the three levels for the four speech materials revealed different patterns of speech recognition among subjects (e.g., subjects 1 and 5). Future research on the relation between stimuli, sound processing, and subjects' responses associated with these different patterns may provide guidelines to select parameter values with which to map incoming sound onto an individual's electrical dynamic range between threshold and maximum acceptable loudness level to improve speech recognition.

Adult↗
PubMed1997

Is loudness simply proportional to the auditory nerve spike count?

It is often asserted that the physiological correlate of loudness is the simple sum of the spike activity produced by all neurons in the auditory nerve (the auditory nerve spike count). We will refer to this hypothesis as the spike count hypothesis. The spike count hypothesis has been tested in the past using models of the auditory periphery and in almost all cases, the hypothesis has been supported. Our new technique for recording a compound potential from the chinchilla auditory nerve, the perstimulus compound action potential (PCAP), makes possible the measurement of the growth of the auditory nerve spike count, thus providing data that can be used to test the spike count hypothesis empirically. It was observed that the growth of the auditory nerve spike count in response to a 1-kHz pure tone (in dB/dB) is 33% shallower than the growth of loudness for a 1-kHz tone, and this discrepancy increases to 66% for an 8-kHz tone. In addition, "equal-count" contours were constructed in a manner analogous to equal-loudness contours. It was found that as reference intensity increases, equal-count contours become sharply curved upward at high frequencies whereas equal-loudness contours become increasingly flat. These differences are unlikely to be the result of the cross-species comparison, since the discrepancies are mostly attributable to the skewed pattern of spread of excitation along the basilar membrane, a property shared by humans and chinchillas. Therefore, we conclude that the simple sum of the spike activity in the auditory nerve cannot be the physiological correlate of loudness.

Animals↗
PubMed1997

Detection of silent intervals between noises activating different perceptual channels: some properties of "central" auditory gap detection.

This article describes four experiments on gap detection by normal listeners, with the general goal being to examine the consequences of using noises in different perceptual channels to delimit a silent temporal gap to be detected. In experiment 1, subjects were presented with pairs of narrow-band noise sequences. The leading element in each pair had a center frequency of 2 kHz and the trailing element's center frequency was parametrically varied. Gap detection thresholds became increasingly poor, sometimes by up to an order of magnitude, as the spectral disparity was increased between the noise bursts that marked the gap. These data suggested that gap-detection performance is impoverished when the underlying perceptual timing operation requires a comparison of activity in different perceptual channels rather than a discontinuity detection within a given channel. In experiment 2, we assessed the effect of leading-element duration in within-channel and between-channel gap detection tasks. Gap detection thresholds rose when the duration of the leading element was less than about 30 ms, but only in the between-channel case. In experiment 3, the gap-detection stimulus was redesigned so that we could probe the perceptual mechanisms that might be involved in stop consonant discrimination. The leading element was a wideband noise burst, and the trailing element was a 300-ms bandpassed noise centered on 1.0 kHz. The independent variable was the duration of the leading element, and the dependent variable was the smallest detectable gap between the elements. When the leading element was short in duration (5-10 ms), gap thresholds were close to 30 ms, which is close to the voice onset time that parses some voiced from unvoiced stop consonants. In experiment 4, the generality of the leading-element duration effect in between-channel gap detection was examined. Spectrally identical noises defining the leading and trailing edges of the gap were presented to the same or to different ears. There was a leading-element duration effect only for the between channel case. The mean gap threshold was again close to 30 ms for short leading-element durations. Taken together, the data suggest that gap detection requiring a temporal correlation of activity in different perceptual channels is a fundamentally different task to the discontinuity detection used to execute gap detection performance in the traditional, within-channel paradigm.

Adult↗