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Humans are sensitive to changes in interaural time differences (ITDs) in high‐frequency sounds with fluctuating amplitude envelopes. However, despite noted large individual differences in high‐frequency ITD discrimination ability, to date, most investigations of this performance have employed only a few, typically experienced, listeners. Thus, it is not clear whether the data thus obtained are representative of the general, naive, population. Here, ITD discrimination thresholds with high‐frequency amplitude‐modulated tones were examined in nineteen listeners, all naive to psychoacoustic testing. The large range of performance across these listeners accommodated the collective data previously reported, but was not fully illustrated by any single previous investigation with a small sample size. For these naive listeners, ITD discrimination performance at high frequencies, 1) was much worse than that at low frequencies, 2) was better with a slower (0.15 kHz) than a faster (0.3 kHz) modulation rate with a 4‐k...

The ability to discriminate changes in interaural time differences (ITDs) and interaural level differences (ILDs) varies markedly both within and across individuals. Such variability has been frequently noted, but rarely systematically investigated. Here, both forms of variability, expressed in terms of coefficients of variation (mean divided by standard deviation), were examined across a variety of ITD and ILD conditions in a total of 84 naive listeners. Three consistent patterns emerged. First, across‐listener variability was relatively constant across ITD and ILD discrimination, suggesting that this variability might be determined by factors common to the processing of both cues. Second, compared to across‐listener variability, within‐listener variability was larger for the ITD conditions but smaller for the ILD conditions, suggesting that, within individuals, ITD processing may have a higher level of internal noise than ILD processing. Third, stimulus frequency (ranging from 0.3 to 6 kHz) and stimulus type (pure tones and sinusoidally amplitude modulated tones) had little influence on either type of variability, suggesting that variability was determined by cue‐dependent, rather than stimulus‐dependent mechanisms. The systematic nature of these variability patterns illustrates that examination of variability can provide important insights into the processing of interaural cues. [Work supported by NIH.]

An interesting learning pattern was previously observed for ITD‐discrimination training with a 500‐Hz tone. While the highest of the twelve threshold estimates obtained each day from each listener (n=8) decreased significantly over days, the lowest did not. However, the lowest values averaged ∼6 microseconds, raising the question of whether they represented actual discrimination ability or resulted from random walks in the adaptive testing procedure. In an attempt to address this question, all twelve estimates of each listener were ordered from lowest to highest and the effect of training was examined separately for each rank. There was no improvement for the four lowest ranks, which ranged from ∼6–25 microseconds. These values represent 33% of the data, a seemingly unlikely rate for random walks. In addition, in naive listeners (n=32), despite marked inter‐individual variation in the average and highest thresholds, the lowest thresholds were constant across listeners. Though these analyses do not preclude the potential contribution of random walks within this data set, they keep open the possibility that the invariance in the lowest thresholds through training and across listeners was not an artifact of the adaptive procedure, but rather reflects a stable capacity limit in ITD processing. [Work supported by NIH.]

The two primary cues to the location of sound sources on the horizontal plane are interaural level differences (ILDs) and interaural time differences (ITDs). The malleability of the processing of these two cues in humans was investigated by examining how multiday practice affects the discrimination of different values of ILDs and ongoing ITDs presented over headphones in adults with normal hearing. On average, the listeners improved on both ILD and ITD discrimination, but the learning patterns differed between the two cue types. Improvement was initially rapid for both cue types and appeared to generalize broadly across conditions, suggesting procedural learning. However, a subsequent slower‐improvement stage occurred solely for the ILD cue and showed some specificity to the stimulus used during training. Interestingly, for ILD discrimination, both the best and worst daily threshold estimates decreased with multiday training, indicating an improvement in fundamental processing capacity. In contrast, for ITD discrimination, the best threshold estimates remained unchanged but the worst decreased, suggesting an increased ability to access already existing capacities. One interpretation of these data is that training mediates the processing of ILDs and ITDs at a stage in the auditory pathway, where these two cues are processed separately. [Work supported by NIH/NIDCD.]

Improvement on most perceptual tasks requires active performance of the target task during training. However, there has been little consideration of whether that active performance is necessary throughout the entire practice period. Suggesting that it is not, there is recent evidence that active performance on a simple frequency‐discrimination task, interleaved with passive stimulus exposures, can yield more learning than the active performance alone. The current study examines whether these findings extend to a speech‐learning task, specifically foreign‐accent adaptation. Native‐English speakers transcribed sentences spoken in English by non‐native speakers. Participants who performed the target task for half the training period and received passive stimulus exposures while performing a distracter task for the other half out‐performed participants who received the same amount of active training, but no passive exposures during the distracter task, suggesting that passive exposures enhanced learning. The active‐passive group also out‐performed participants who received only passive exposures—and performed as well as a group who performed only the target task—for the entire training period. Taken together, these results suggest that the combination of active training and passive stimulus exposure may play a key role in real‐world perceptual learning for speech. [Work supported by NIH/NIDCD.]

Sound‐source location on the horizontal plane is primarily determined by two cues: interaural time differences (ITDs) for low‐frequency sounds and interaural level differences (ILDs) for high‐frequency sounds. Though not available in natural listening environments, ILDs in low‐frequency sounds, when artificially delivered to listeners through headphones, also can be used to lateralize sounds. Little is known about the neural processing of such low‐frequency ILDs. Here, the modifiability of this processing was examined by training human adults on ILD discrimination with a 0.5‐kHz tone on the midline. After nine 1‐h daily training sessions, trained listeners (n=6) improved significantly more than untrained controls (n=8) on the trained condition. This learning generalized to a 4‐kHz tone and a 0.5‐kHz tone amplitude modulated at 30 Hz, but appeared not to generalize to a 1‐kHz tone, an off‐midline position, or ITD discrimination with the trained tone. This overall learning pattern differs from those previou...

Performance on many auditory discrimination tasks improves with practice. This learning could result from improvements in fundamental processing capacity (as is implicitly assumed), from improvements in the ability to consistently access already existing capacities, or from a combination of the two. To help distinguish among these types of improvement, we reanalyzed learning data on three basic auditory tasks, examining the best and worst, rather than the mean, thresholds on each of 6–10 days of training. On one task (interaural‐level discrimination), the best and worst thresholds decreased in parallel, indicating an improvement in fundamental processing capacity. On another task (interaural‐time discrimination), the best thresholds remained unchanged but the worst thresholds decreased, suggesting an increased consistency in accessing already existing capacities. Demonstrating a combination of these two types of improvement, on the third task (duration discrimination), both the best and worst thresholds i...

Training‐induced improvements on perceptual skills can be enhanced by increasing the amount of training and by resting between training and testing. However, how these two factors affect the generalization of learning from a briefly trained condition to an untrained one is unknown. Here, listeners were trained on an interaural‐level‐difference (ILD) discrimination condition (4‐kHz tones), then were tested for generalization to an interaural‐time‐difference (ITD) discrimination condition (0.5‐kHz tones). The amount of training and the time between training and testing differed across four groups. Listeners tested 10 hours after training had significantly lower ITD discrimination thresholds than naive listeners (n=94), regardless of whether training lasted for 20 min (n=14) or 2 hs (n=11). Thus, when there was a long time between training and testing, learning generalized from ILD to ITD discrimination regardless of the amount of training. In contrast, listeners tested immediately after training on ILD disc...

Hearing rehabilitation extends beyond simply fitting a hearing aid or cochlear implant. To improve the benefit of these devices, it must be established which auditory abilities can be improved with training. Toward this end, learning in normal‐hearing listeners was examined on five auditory discrimination tasks: frequency, intensity, interaural‐time‐difference (ITD), interaural‐level‐difference (ILD), and duration. Because the same training regimen was used throughout, any differences in the learning patterns across these trained discriminations likely reflect differences in the plasticity of the underlying mechanisms, at least for that regimen. The influence of training was assessed by comparing the improvements in discrimination threshold on trained and untrained conditions between listeners who were given multiple‐hour practice on a single discrimination condition and those who were not. Learning on the five tasks followed one of two general patterns. For ITD and intensity discrimination, multiple‐hour practice did not lead to greater learning than that seen in untrained listeners. In contrast, for ILD, duration, and frequency discrimination, such practice yielded greater learning, but only on a subset of conditions. The differences in the plasticity across these auditory tasks in normal‐hearing listeners imply that cochlear‐implant users may benefit more from training on some tasks than others. [Work supported by NIH.]

Interaural level differences (ILDs) are one of the primary cues to sound source position on the horizontal plane. Most studies on human performance with ILDs use simple sounds such as pure tones. However, naturally occurring acoustic stimuli usually have complex waveforms. Here human learning of ILD discrimination was examined with complex waveforms. Sixteen listeners were trained 1 hr/day for 9 days on ILD discrimination with a 4‐kHz tone sinusoidally amplitude modulated at 0.3 kHz conveyed through headphones. Before and after training, they were tested, together with sixteen untrained controls, on the trained condition and five related untrained conditions (three with amplitude modulated tones, two with pure tones). The trained listeners improved significantly more than controls on all conditions with amplitude‐modulated tones, but not on those with pure tones. The lack of generalization of ILD learning from modulated to pure tones suggests that practice modified ILD processing in a region that encodes ...

Can the processes underlying performance on basic masking tasks be modified with practice? To address this question, 17 listeners completed pre‐ and posttests in which detection thresholds for a 20‐ms 1‐kHz tonal signal were measured in three notched‐noise simultaneous‐masking conditions that differed in the masker duration and relative onset times of the signal and masker, and three forward‐masking conditions that differed in the tonal frequencies of the maskers. For the ∼8 days between tests, eight of these listeners practiced 240 trials/day on each simultaneous‐masking condition. Learning differed across conditions. When the signal and a 20‐ms masker began and ended together, both trained and untrained listeners improved, but trained listeners improved more, learning gradually. When the signal began 400 ms after a 500‐ms masker, only the trained group improved, learning quickly. When the signal and the 500‐ms masker began together, both groups improved equally. Both groups also improved equally on each...

When trying to detect a tonal signal in a continuous broadband noise, listeners attend selectively to both the frequency and the duration of the expected signal. However, it is not known whether they monitor separate, or combined, representations of these two attributes. To investigate this question, a probe‐signal method was used to measure the detectability of signals of expected and unexpected durations at two expected frequencies. Four listeners were led to expect one of two signals to be presented at random: a brief tone at one frequency or a long tone at another frequency. For each signal frequency, the detectability of the signals of unexpected duration decreased to near chance as the difference between the expected and unexpected duration, at that frequency, increased. Thus, signals of each expected duration were rarely detected when they were presented at a frequency not associated with that duration. The frequency specificity of this duration tuning indicates that both the frequency and the dura...

Language‐based learning problems affect approximately one person in twelve with no other obvious signs of disorder. Many of these individuals have accompanying deficits in nonlinguistic perception. To determine whether age influences the magnitude of these deficits, thresholds on a set of auditory masking tasks were measured in individuals with learning problems and controls ranging in age from 6 years to adult. Performance improved with increasing age in both groups. However, the thresholds of the individuals with learning problems were most similar to those of controls approximately 2–4 years younger on every task, suggesting that the perceptual development of the affected individuals was delayed by a constant amount. Further, on the subset of conditions on which controls reached adult levels of performance after 10 years of age, the improvement of affected individuals halted at 10 years of age, suggesting that puberty may play a critical role in human perceptual development. Taken together, these data ...

How does native language experience with a tone or nontone language influence pitch perception? To address this question 12 English and 13 Mandarin listeners participated in an experiment involving three tasks: (1) Mandarin tone identification—a clearly linguistic task where a strong effect of language background was expected, (2) pure‐tone and pulse‐train frequency discrimination—a clearly nonlinguistic auditory discrimination task where no effect of language background was expected, and (3) pitch glide identification—a nonlinguistic auditory categorization task where some effect of language background was expected. As anticipated, Mandarin listeners identified Mandarin tones significantly more accurately than English listeners (Task 1) and the two groups’ pure‐tone and pulse‐train frequency discrimination thresholds did not differ (Task 2). For pitch glide identification (Task 3), Mandarin listeners made more identification errors: in comparison with English listeners, Mandarin listeners more frequently...

Notched‐noise overshoot and two‐tone suppression were measured at 1000 Hz using standard procedures in 40 normal‐hearing, psychoacoustically naive adults, counterbalanced for sex and listening ear. The threshold variability across listeners for the same condition often exceeded 30 dB. In the overshoot conditions, the signal was an average of 7 dB harder to detect when it was presented at the onset of a 500‐ms masker (masker notch width: 1000 Hz) than when signal onset was delayed by 400 ms. Across listeners, this overshoot effect ranged from 1 to 17 dB. In the suppression conditions, for some listeners, the forward‐masked signal was as much as 15 dB easier to detect when the tonal on‐frequency masker (1000 Hz) and suppressor (1150 Hz) were presented together, than when the masker was presented alone, indicating suppression. For other listeners, however, presenting the masker and suppressor together increased thresholds by as much as 13 dB, indicating additional masking (negative suppression). The average amount of suppression was −1.0 dB. ANOVA tests shoed significantly more overshoot and less suppression in females than males, and significantly higher thresholds in left than right ears in the overshoot conditions. Results will be discussed in terms of possible individual, sex, and ear differences in efferent inhibition. [Work supported by NIH.]

Determining the training regimes that do and do not yield improvements in auditory discrimination provides information about the mechanisms underlying the trained task, and about learning itself. In a previous report, training with one standard stimulus yielded improvements in temporal‐interval discrimination that generalized to an untrained frequency at the trained interval [B. A. Wright et al., J. Neurosci. 17, 3956–3963 (1997)]. Here, the impact of training interval discrimination with two standard stimuli, as opposed to one, was investigated. Listeners were trained either with two standard intervals (100 and 350 ms) at one frequency (1 kHz; n=8), or with one standard interval (100 ms) at two frequencies (0.25 and 1 kHz; n=8). On average, listeners in both groups (1) learned less on each trained condition than listeners trained with only one stimulus (n=10), and (2) subsequently performed on the trained interval(s) at an untrained frequency (4 kHz) as though they had trained with only one of the stimuli—in one case, showing no improvement. These results indicate that, at some stage, temporal intervals are processed at frequency‐specific sites, and that training one task with two stimuli sharing all but one feature can interfere with both learning and generalization. [Work supported by NIDCD.]

Does the procedure used to train an auditory skill impact the characteristics of subsequent skill improvement? Here, the effects of multiple‐hour training with either a labeling or discrimination procedure were compared by using a discrimination procedure to examine performance on six conditions. Listeners completed a pretest on the six conditions, trained on one condition for 720 trials/day for 8 days with either a labeling (n=6) or discrimination (n=6) procedure, then completed a post‐test identical to the pretest. The trained condition for labeling‐trained listeners was to determine, for each individual presentation, whether the onsets of two tones were synchronous or asynchronous. The trained condition for discrimination‐trained listeners was to determine which of two presentations of these same tones had asynchronous onsets. All listeners showed significant improvements on the trained condition. Further, there were no significant differences between training groups in the pattern of improvement acros...

The effect of signal duration on the detectability of unexpected tones masked by a continuous wideband noise was assessed using a probe‐signal method. This method encourages the listener to attend to a target frequency by presenting the signal most often at that frequency, and only occasionally at other unexpected probe frequencies. The attention contour (percent correct as a function of probe frequency) was considerably broader with 5‐ms than with 295‐ms signals. However, auditory filter shapes measured using the notched‐noise technique were very similar for those two signal durations, indicating that the results obtained in the attention experiments do not simply reflect peripheral frequency selectivity. Further supporting this interpretation, probe tones having the same frequency but a different duration from the target were poorly detected. It is proposed that the subject listens through a time‐frequency window whose location and shape in the time‐frequency plane is determined by the duration and frequency of the target. [Work supported by the NIDCD and NIH.]

Listeners often show rapid improvements when first performing auditory discrimination tasks. This learning was explored by investigating how training 300–1500 trials on one of three conditions (all 2IFC) influenced interaural‐time‐difference (ITD) discrimination on a target ITD condition (lateralization, 0‐μs ITD, 500 Hz). Listeners trained on ITD or interaural‐level‐difference (ILD) discrimination had equivalent ITD‐discrimination thresholds that were significantly lower than those of naive listeners. However, listeners trained on duration discrimination had ITD‐discrimination thresholds between those of naive and ITD‐trained listeners. These data suggest that rapid decreases in ITD‐discrimination threshold result partly from learning the general procedure (induced by the duration training) and partly from learning the lateralization task (induced by the ILD training). In contrast, compared to naive listeners, final within‐subject standard deviations of the ITD‐discrimination thresholds were significantly smaller for ITD‐trained, somewhat smaller for ILD‐trained, and no smaller for duration‐trained listeners. These data suggest that rapid reductions in threshold variabiilty result partly from learning the lateralization task (induced by the ILD training) and partly from learning something provided, here, only by ITD training. Thus, at least three different types of learning can contribute to initial improvements in performance on auditory discrimination tasks. [Work supported by NIDCD.]

It is not clear which training methods yield the fastest improvement on perceptual skills. To address this issue, performance on a detection task was compared following training on a labeling or detection task. The labeling task was to determine, for each presentation, whether the onsets of two tones were synchronous or asynchronous. Tone onsets were separated by one of six durations. The detection task was to determine which of two presentations contained tones with asynchronous onsets. The duration between tone onsets was varied adaptively to establish the asynchrony‐detection threshold (79% correct detections). In both tasks, the tonal frequencies were 0.25 and 4 kHz. Labeling‐trained listeners (n=11) had detection thresholds lower than those of untrained controls (n=6) following just 600 labeling trials (p=0.008). In contrast, detection‐trained listeners (n=6) had detection thresholds lower than controls only following 3660 detection trials (p=0.027), 2160 trials on the asynchrony‐detection task plus 1500 trials on related temporal‐acuity tasks. Thus, labeling training appears to improve performance on an asynchrony‐detection task more quickly than detection training itself. By increasing our understanding of perceptual learning processes, these data may aid the treatment of individuals with disorders in auditory perception. [Work supported by NIDCD.]

The ability to determine whether the onsets of two tones at different frequencies are asynchronous is a measure of temporal acuity. Learning in this asynchrony‐detection task and its generalization to untrained frequencies and temporal‐acuity tasks was explored. For six listeners, asynchrony‐detection thresholds for tones at 0.25 and 4 kHz improved from 79 to 20 ms with 4320 training trials. A z‐score analysis revealed that trained listeners learned significantly more than untrained controls on the trained condition, but only slightly or no more than controls on: (1) the trained task at two sets of untrained frequencies (0.5 and 1.5 kHz, 0.75 and 1.25 kHz), and (2) three untrained temporal‐acuity tasks at the trained frequencies (offset asynchrony detection, onset temporal order, and offset temporal order). This generalization pattern parallels that seen when the trained task was to determine the onset order of two tones [B. A. Wright and J. A. Mossbridge, J. Acoust. Soc. Am. 107, 2882 (2000)]. Thus, lear...

There is evidence that the learning of tonal‐frequency discrimination is specific to the trained frequency. This study examined whether learning of the discrimination of sinusoidal‐amplitude‐modulation (SAM) rate was also specific to the trained rate, and whether that learning was specific to the trained task. SAM‐rate‐discrimination thresholds of six listeners trained 1 h per day for 6 days with a 150‐Hz rate improved from 24 Hz before to 12 Hz after training. Comparisons between proportional improvements of trained and control listeners revealed that trained listeners learned substantially more than controls on the trained task, but learned only slightly or no more than controls on: (1) the SAM‐rate task at two untrained rates (30 and 300 Hz) and (2) three untrained tasks (tonal‐frequency discrimination, ripple‐noise discrimination, modulation detection) at the trained rate/frequency. Thus, as with tonal‐frequency discrimination, learning of SAM‐rate discrimination is specific to the trained rate. Howev...

It is generally accepted that training on one perceptual task does not yield learning on untrained tasks. If so, interleaved training on two tasks should not affect learning or stimulus generalization on either task. Contrary to this prediction, six listeners trained 2730 trials each on interval‐ and frequency‐discrimination tasks using the same stimulus (100 ms at 1 kHz) learned on the interval task 30% more with the trained stimulus, and 134% more with an untrained stimulus (100 ms at 4 kHz), than ten listeners trained 2934 trials on the interval task alone. Furthermore, listeners trained on both tasks with the same stimulus learned on the trained and untrained stimuli, respectively, (1) 105% and 136% more than 6 listeners trained 2160 trials each on both tasks but with a different stimulus (200 ms at 4 kHz) for the frequency task, (2) 19% and 42% more than 20 listeners trained 9675 trials on the interval task alone, and (3) 71% and 579% more than 6 listeners trained 9000 trials on the frequency task al...

The ability to determine the onset order of two tones at different frequencies is a measure of temporal acuity and an analog of voice‐onset time. Learning in this temporal‐order task and its generalization to untrained frequencies and temporal‐acuity tasks was explored. Temporal‐order thresholds of six listeners trained 1 h per day for 6 days with tones at 0.25 and 4 kHz improved from 58 ms before to 12 ms after training, yielding a proportional improvement greater than on all untrained conditions. Comparisons between proportional improvements of trained and control listeners revealed that trained listeners learned considerably more than controls on the trained condition, and only slightly or no more than controls on: (1) the trained task at two sets of untrained frequencies (0.5 and 1.5 kHz, 0.75 and 1.25 kHz), and (2) three untrained temporal‐acuity tasks (offset temporal order, onset asynchrony, offset asynchrony) at the trained frequencies. The lack of robust generalization to untrained frequencies and tasks suggests learning in onset temporal‐order tasks is mediated by a frequency‐dependent mechanism different from the mechanism(s) underlying performance in other temporal‐acuity tasks. By increasing our understanding of plasticity in temporal‐acuity mechanisms, these data may guide the treatment of related disorders. [Work supported by NIDCD.]

The influence of condition variation on learning rate in an auditory backward‐masking task was assessed by measuring pure‐tone detection thresholds in 24 different trial blocks in five groups of eight normal‐hearing adults assigned to different conditions midway in the testing sequence. Thresholds for a tonal signal (10 ms, 1000 Hz) presented immediately before a noise masker (300 ms, 200–1800 Hz, 40 dB SPL spectrum level) were evaluated in blocks 1–9 and 19–24. The decrease in threshold observed between the means of blocks 1–3 and blocks 19–24 depended upon the condition tested in blocks 10–18. Mean threshold decreased by nearly 20 dB for listeners who detected a backward‐masked tone presented in a temporal gap between two maskers, by around 15 dB for listeners who detected a backward‐masked tone at a higher frequency or a forward‐masked tone, and by around 12 dB for listeners who did the standard backward‐masking task or who rested for 20 min. This information may be useful for the development of interventions for elderly persons and children with language impairment who have been observed to have excessive auditory backward masking. [Work supported by NIDCD and the McDonnell‐Pew Program in Cognitive Neuroscience.]

Approximately 5% of children who are otherwise unimpaired have marked difficulties perceiving and producing spoken language. This disorder is typically labeled specific language impairment. Recent psychoacoustic tests indicate that children with specific language impairment have excessive auditory backward masking, as demonstrated by their extreme difficulties detecting brief tonal signals followed by longer noise maskers. These results are consistent with the hypothesis that specific language impairment results from an auditory perceptual deficit that makes difficult the discrimination of brief, rapidly presented sounds, including phonemes in speech. Subsequent studies using adults with normal hearing and language skills indicate that the interference from a backward masker can be reduced with practice. This learning generalizes from trained to untrained backward‐masking conditions and appears to result from improvements in temporal rather than spectral processing. Taken together, these data imply that t...

Comodulation masking release demonstrated improved detection of pure‐tone signals in amplitude‐comodulated noise bands [Hall et al., J. Acoust. Soc. Am. 76(1), 50–56 (1984)]. However, in most real‐world situations, signals such as speech sounds are comodulated and noises such as cocktail party and traffic noises are not. Two experiments were designed to examine whether comodulation of signals can lead to improved signal detection in noise. Experiment I used a 2AFC method to measure detection threshold of a 2/3‐oct‐spaced, five‐tone complex in pink noise. The complex tones were either amplitude comodulated or randomly modulated. Results from three normal‐hearing listeners showed no difference in detection threshold between amplitude‐comodulated and randomly modulated conditions. Experiment II used a method of constant stimuli to measure the psychometric function of discriminating six vowel‐like stimuli in pink noise. These vowels consisted of three formant‐frequency sinusoids which were unmodulated or amplitude‐comodulated or randomly modulated by a 125‐Hz sinusoid simulating the voice pitch. While no difference was observed between comodulated and randomly modulated conditions, the psychometric function for the nomodulation control condition was shifted by 4–6 dB toward lower signal‐to‐noise ratios. A possible explanation is that auditory fibers phase‐lock to formant‐frequencies of the unmodulated stimuli and to the fundamental frequency of the modulated stimuli.

Excessive auditory backward masking has been observed in elderly persons and in children with language impairments. The purposes of this project were to determine (1) whether practice can improve the ability to detect a backward‐masked signal and, if so, (2) whether this improvement generalizes to other masking tasks. These issues were examined in six normal‐hearing adults using an adaptive, 2IFC procedure. Each subject was asked to detect a tonal signal (10 ms, 1000 Hz) presented immediately before a noise masker (300 ms, 200–1800 Hz, 40‐dB SPL spectrum level), on 900 trials per day for ten days. Before and after the training period, subjects were tested on five other masking tasks in addition to the trained task. A one‐way ANOVA revealed a significant learning curve over the ten days of training [F(9,45)=5.1, p

The ability to hear binaural beats at 200 and 500 Hz was assessed using a tone presented at 20 dB SL to one ear and a tone presented at a variable level ranging from −20 to 20 dB SL in steps of 10 dB to the other ear. A two‐alternative forced‐choice test was used to measure the listener’s ability to detect the beats. In the ‘‘beating’’ interval, the frequencies of the tones at the two ears differed by 6 Hz. In the ‘‘nonbeating’’ interval, the tones at the two ears had the same frequency. Special care was taken to avoid a potential pitch cue by randomly presenting one of four paired frequencies to the two ears. The experiment was conducted in ‘‘burst’’ and ‘‘fringed’’ condition. There was no evidence to suggest that binaural beats were detectable when the intensity of the variable‐level tone was below 0 dB SL. These data fail to replicate a result reported by Groen [Acta Oto‐Laryngol. 57, 224–230 (1964)]. [Work supported by NIH.]

The results of two experiments demonstrated that the detectability of an auditory signal depends on the subject’s expectation about its duration. The signal (a 250‐, 1000‐, or 4000‐Hz tone, or a broadband noise) had one of six durations between 5 and 295 ms. The masker was a continuous, broadband noise (N0=25 dB). Each 2IFC interval was always marked by a fixed‐duration visual display whose onset coincided with the onset of all potential signals. When the signal duration was fixed, each signal was correctly detected on about 85% of the trials. in experiment 1, the six subjects were encouraged to expect a particular signal duration (5 or 295 ms) by presenting the signal most often at that duration, and only occasionally at each of the five remaining unexpected durations. Performance for the unexpected signals decreased from 85% to chance as their durations departed from the expected duration. In experiment 2, the signal was randomly presented at each of the six durations with equal probability, and the sub...

Comodulation masking release (CMR) was measured for a pure‐tone signal (2500 Hz) masked by five narrow‐band (100 Hz wide) noises (2IFC, 3‐down/1‐up paradigm). Nose bands were centered at 1500, 2000, 2500, 3000, and 3500 Hz and had a spectrum level of 50 dB SPL. The stimulus duration was 500 ms. Each band of noise was composed of 51 sinusoids. The noise envelopes were manipulated on two levels. On the first level, the phases and amplitudes of the 51 components were either the same (coherent) or different (incoherent) across the bands. On the second level, the bands were amplitude modulated with 10‐Hz sinusoids and were either comodulated (same starting phase) or uncomodulated (phase shifted). Mean thresholds for three listeners were 69 and 63 dB SPL for incoherent and coherent noise, respectively, yielding a 6‐dB CMR. For both incoherent and coherent noise, thresholds were lower in the presence of modulation. Thresholds were lower by about 3 dB for the uncomodulated noise and 21 dB for the comodulated nois...

Frequency resolution was estimated as a function of masker duration in four masking conditions for three subjects. The signal was a 4‐ms, 1000‐Hz tone. The wideband masker (33‐dB spectrum level) had a spectral notch of variable width centered on the signal. Masker duration was 6 (only in simultaneous masking), 62, or 412 ms. Rise/decay time was 2 ms for all stimuli. In two simultaneous‐masking conditions, signal offset came 1 ms before masker offset (forward‐fringe) or signal onset came 1 ms after masker onset (backward‐fringe). In two nonsimultaneous‐masking conditions, signal onset came immediately after masker offset (forward masking) or signal offset came immediately before masker onset (backward masking). In all conditions, threshold decreased as the width of the masker notch increased. However, the rate of the threshold decrease tended to increase with masker duration. Further, the threshold decrease was more marked in the two ‘‘forward’’ than in the two ‘‘backward’’ conditions. These data indicate ...

The improvement in signal detectability as signal onset is delayed relative to masker onset was measured as a function of masker bandwidth for notched and unnotched maskers. The signal was a 250‐Hz‐wide noise band centered at 2500 Hz. In two conditions, the 20‐ms signal was gated 1 ms or 250 ms after the onset of a 420‐ms masker. Signal thresholds were higher in the short‐delay than in the long‐delay condition. This difference generally increased as masker bandwidth increased and was similar in magnitude across the two masker types. Further, this difference was greatest for maskers whose spectra were symmetric about the signal frequency, and was smaller, and similar, for maskers that extended exclusively above or below the signal frequency. In a third condition, the signal was gated 1 ms after the onset of a 23‐ms masker. Thresholds were highest in this condition, and varied differently as a function of masker bandwidth than in the other two conditions, particularly for the notched maskers. [Work supporte...

The temporal effect, or decrease in simultaneously masked threshold as signal onset is delayed relative to masker onset, was measured for signals centered at 2500 Hz that ranged in width from tonal to 7900 Hz. The masking noises covered the frequency range from 100 to 8000 Hz and either contained a spectral notch that always perfectly complemented the width of the signal, or contained no spectral notch. In the short‐delay and long‐delay conditions, the 20‐ms signal was gated 1 or 250 ms, respectively, after the onset of a 420‐ms masker. In the burst condition, the signal was gated 1 ms after the onset of a 23‐ms masker. Although there were marked individual differences, with the notched masker, thresholds were as much as 7–17 dB higher in the short‐delay condition, and 20–27 dB higher in the burst condition, than in the long‐delay condition. With the unnotched masker burst/short‐delay differences were minimal. Thus, only the magnitude of the temporal effect obtained with notched maskers was strongly influenced by the choice of reference condition. [Work supported by NIDCD.]

In most languages, vowels are longer before voiced than before voiceless consonants. Attempts to explain this vowel-length difference in terms of assumed physical or physiological constraints on speech production have generally been unsuccessful. We propose the alternative hypothesis that language communities intentionally vary vowel length in order to enhance auditorily the closure-duration cue for voicing distinctions. By the principle of durational contrast, a long vowel should make a short closure interval seem even shorter and hence more voiced, whereas a short vowel should make a long closure interval appear longer and hence more voiceless. In support of this auditory hypothesis, we show that, for /aba/–/apa/ stimuli varying in medial closure duration and for square-wave stimuli that temporally mimic these speech stimuli, a longer initial segment causes a reliable shift in subjects’ two-category labeling boundaries toward longer medial gap durations. We also discuss other ways that language communities may exploit durational contrast in order to enhance phonological distinctiveness.

Much debate has been generated in the literature concerning reasons for positive black self-esteem findings. Although some contradiction is found in the literature, findings on black self-esteem suggest a shift to more positive self-images among blacks during the 1970s. This study investigates the relationship between personal and racial self-esteem. These data support the theoretical linkage of racial and personal self-esteem. A positive correlation was found between personal self-esteem and racial self-esteem for black youth in this study.

Perceptual learning is a sustainable improvement in performance on a perceptual task following training. A hallmark of perceptual learning is task specificity – after participants have trained on and learned a particular task, learning rarely transfers to another task, even with identical stimuli. Accordingly, it is assumed that performing a task throughout training is a requirement for learning to occur on that specific task. Thus, interleaving training trials of a target task, with those of another task, should not improve performance on the target task. However, recent findings in audition show that interleaving two tasks during training can facilitate perceptual learning, even when the training on neither task yields learning on its own. Here we examined the role of cross-task training in the visual domain by training 4 groups of human observers for 3 consecutive days on an orientation comparison task (target task) and/or spatial–frequency comparison task (interleaving task). Interleaving small amounts of training on each task, which were ineffective alone, not only enabled learning on the target orientation task, as in audition, but also surpassed the learning attained by training on that task alone for the same total number of trials. This study illustrates that cross-task training in visual perceptual learning can be more effective than single-task training. The results reveal a comparable learning principle across modalities and demonstrate how to optimize training regimens to maximize perceptual learning.

Waveforms that yield comodulation masking release (CMR) when they are presented simultaneously with a signal were used in a standard forward‐masking procedure. The signal was a 25‐ms sample of a 2500‐Hz tone. The masker was a band of noise centered at 2500 Hz, 100 Hz in width, and 200 ms in duration. Presented with the masker were two or four cue bands, each 100 Hz wide and centered at various distances from the masker band. These cue bands either all had the same temporal envelope as the masker band (correlated condition) or their common envelope was different from that of the masker band (uncorrelated condition). In the initial experiments, (1) detectability of the tonal signal was 7–18 dB better when the masker band was accompanied by cue bands than when it was not—an effect that would be expected from past research on lateral suppression—but further, (2) the signal was about 3 dB more detectable in the correlated conditions than in the uncorrelated conditions. In follow‐up experiments, these CMR‐like differences between the correlated and uncorrelated conditions were substantially reduced (although not eliminated) by presenting a contralateral, wideband noise that was gated synchronously with the masker and/or cue bands. The implications are that the initial results were attributable in part to the ‘‘confusion effects’’ known to exist in certain temporal‐masking situations, and that listeners are able to obtain greater information about the temporal extent of a masker band from correlated cue bands than from uncorrelated bands. It is suggested that the small CMR‐like difference that did remain in the face of controls for confusion may be attributable to a form of dynamic lateral suppression, where the magnitude of suppression covaries perfectly with the magnitude of the envelope of the narrow‐band masker. It appears, then, that no explanations beyond confusion and lateral suppression are necessary to account for the reported CMR‐like effects in forward masking.

Detection thresholds were determined for a noise band signal centered at 2500 Hz in the presence of four additional “cue” bands at 1500, 2000, 3000, and 3500 Hz. Contrary to the typical results of comodulation masking release (CMR), subjects were 6–12 dB more sensitive when the signal band's temporal envelope was uncorrelated with the four correlated cue bands than when all five of the bands were correlated. We refer to this difference in detectability as a comodulation detection difference (CDD). Interestingly, when none of the five bands was correlated, performance was essentially the same as when all five of the bands were correlated. The method was two‐interval forced choice. The signal and the cue bands were computer synthesized and were all 100 Hz wide. Different noise samples were presented within and across trials. Results will also be presented for CDD conditions in which different subsets of the four cue bands were correlated, in which the cue bands had different center frequencies, and in which...

Detectability of a 1250‐Hz tonal signal, masked by 50‐Hz‐wide noise bands centered at 850, 1050, 1250, 1450, and 1650 Hz, was determined for two listening conditions (correlated and uncorrelated) under three types of uncertainty about the listening condition. Here, “correlated” means that the temporal envelopes of all five noise bands were the same, and “uncorrelated” means that only the band centered at 1250 Hz had a temporal envelope different from the other noise bands. In the no‐uncertainty condition, all trials of a block consisted of correlated, or uncorrelated, waveforms. In the random‐by‐trial condition, correlated and uncorrelated trials were interleaved at random. In the random‐by‐observation‐interval condition, the nonsignal interval of each trial contained the same type of waveform as the signal interval only by chance. Levels of detectability, and thus the magnitude of the comodulation masking release (CMR), were essentially the same in the first two conditions. However, in the third uncertai...

Vowels are longer before voiced consonants than before voiceless consonants, and a number of studies have demonstrated that perception of voicing, in syllable‐final and intervocalic positions, is in accordance with this production regularity. We present a study, using nonspeech stimuli, that suggests that this agreement between production and perception for segmental duration is grounded in auditory processing of complex stimuli in general. Two types of square‐wave analogs, modeled after a speech series ranging from “aba” to “apa” were constructed. The two nonspeech stimulus series varied in duration of a silent interval from 20–110 ms bounded by frequency transitions out of and into steady‐state segments. One series had an initial segment duration of 155 ms, whereas, the initial segment duration of the other series was 245 ms. Duration of the final segment was 188 ms for both series. Listeners judged significantly more of these nonspeech stimuli to be similar to the short silent interval endpoint when the initial segment was long than when the initial segment was short. This result parallels the finding for speech that listeners perceived more voiced /b/ than voiceless /p/ consonants following longer vowels. These results call into question explanations of this production/perception concordance that suggest either mediation of perception by knowledge of production regularities, or direct perception or articulation. [Work supported by NICHHD.]

The detectability of a 1250‐Hz, 50‐ms signal was assessed in a comodulation masking release (CMR) setting. One 50‐Hz noise band (the “masker”) was centered at 1250 Hz; other noise bands were centered at 850, 1050, 1450, and 1650 Hz (the “cue” bands). The masker and/or cue bands were gated prior to the onset of the signal by an amount (“fringe”) that was varied across blocks of trials. The noise bands and the signal always ended together. The temporal envelopes of the noise bands were all correlated, all correlated except for the masker band, or all uncorrelated. When all of the noise bands were gated synchronously, the CMR grew from 1 dB in the burst condition to 7 dB for a 450‐ms fringe, due to a greater improvement in detectability in the correlated condition compared to the uncorrelated and all‐uncorrelated conditions. When the cue bands were gated before the masker, the average CMR was larger (4–6 dB) than when the masker was gated before the cue bands (2–4 dB). These differences in improvement with increasing fringe duration may be attributable to differences in neural adaptation in the correlated and uncorrelated conditions. [Work supported by NINCDS Grant NS15895.]