摘要:

A conditional‐on‐a‐single‐stimulus (COSS) analysis procedure [B. G. Berg, J. Acoust. Soc. Am.86, 1743–1746 (1989)] was used to measure the weight or relative reliance that normal‐hearing and hearing‐impaired listeners give to different frequencies in the discrimination of the overall level of a multitone complex. On each trial, two multitone‐tone complexes comprised of six octave frequencies from 250 to 8000 Hz were presented to subjects. The levels of the frequencies for each complex were randomly varied. The listeners task was to identify the complex with the higher overall intensity level. Normal‐hearing listeners used a variety of listening strategies to perform the task, showing no general preference to weight one component over another. Hearing‐impaired listeners, however, showed a general tendency to give greatest weight to the spectral information in the region of their hearing loss. Thirteen of the 14 hearing‐impaired listeners, all of whom had a high‐frequency sensorineural hearing loss, weighted one or more of the high‐frequency components in the complex the greatest.

ISSN:0001-4966    

DOI:10.1121/1.414634

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Overshoot—in particular, threshold for a signal near masker onset—can be reduced by presenting a stimulus (precursor) just prior to masker onset. The recovery of overshoot can be examined by varying the delay between the offset of the precursor and the onset of the masker, where ‘‘recovery’’ denotes anincreasein the threshold for a signal near masker onset. The present study examined the effects of stimulus level and relative frequency region on this recovery. In all experiments, the masker was a broadband of noise and the signal was a 4‐kHz sinusoid. The first experiment examined the effects of masker level on overshoot in order to choose two levels (one ‘‘low’’ and one ‘‘high’’) that produced similar amounts of overshoot; these levels were used in the remaining experiments. In the second experiment, the precursor was identical to the masker, and recovery functions were measured for both low and high masker and precursor levels. There was no consistent difference in the recovery functions between the two levels. In the third experiment, the precursor was divided into two bands (one below and one above 4 kHz); one was presented continuously while the other was gated as in experiment 2. The recovery was more complete when the band above 4 kHz was gated, although the recovery was usually less than that observed in experiment 2 when (effectively) both bands were gated. The results suggest that frequency regions on both sides of the signal are important for the recovery of overshoot, but that the frequency region above the signal may be more important than the region below.

ISSN:0001-4966    

DOI:10.1121/1.415232

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Two versions of a cascaded add, attenuate, and delay circuit were used to generate iterated rippled noise (IRN) stimuli. IRN stimuli produce a repetition pitch whose strength relative to the noise can be varied by changing the type of circuit, the attenuation, or the number of iterations in the circuit. Listeners were asked to discriminate between various pairs of IRN stimuli which differed in the type of network used to generate the sounds or the number of iterations (n=1, 2, 3, 4, 7, and 9). Performance was determined for IRN stimuli generated with delays of 2, 4, and 8 ms and for four bandpass filter conditions (0–2000, 250–2000, 500–2000, and 750–2000 Hz). Some IRN stimuli were extremely difficult to discriminate despite relatively large spectral differences, while other IRN stimuli produced readily discriminable changes in perception, despite small spectral differences. These contrasting results are inconsistent with simple spectral explanations for the perception of IRN stimuli. An explanation based on the first peak of the autocorrelation function of IRN stimuli is consistent with the results. Simulations of the processing performed by the peripheral auditory system (i.e., interval histograms and correlograms) produce results which are consistent with the involvement of these temporal processes in the perception of IRN stimuli.

ISSN:0001-4966    

DOI:10.1121/1.414593

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The perceptual dimensions evoked by dual‐electrode stimulation were investigated in four cochlear implantees. The dual‐electrode stimulation consisted of biphasic current pulse trains, such that two intracochlear electrodes each received one pulse in a 250‐Hz cycle. The experiments tested the hypothesis that perceptual qualities would be altered when there was an increased likelihood of interactions occurring between the two electrode places. The parameters of the stimulation which were manipulated to test this hypothesis were the time delay between the pulses on the two electrodes (2 ms and a value between 0.62 and 0.92 ms), the distance between the component electrode rings of each bipolar pair (3.75 mm and either 2.25 or 1.5 mm), and the distance between the two bipolar pairs in the dual‐electrode stimuli (from 0.75 to 12.0 mm). Five sets of 15 loudness balanced stimuli were created, each set having different stimulation parameters.These stimuli consisted of five single‐electrode stimuli (a 250‐Hz pulse train on each of five electrodes) and the ten dual‐electrode stimuli formed by the combinations of those five electrodes. Two perceptual dissimilarity matrices were obtained for each subject and each set, and were analyzed using repeated nonmetric multidimensional scaling techniques. The resultant ‘‘stimulus spaces’’ were then examined to see how many perceptual dimensions the stimuli were best described by, and to what perceptual or stimulus qualities the dimensions might correspond. The results showed that the percept evoked by dual‐electrode stimulation contained two main dimensions. Increasing the width of the current path to create substantially overlapping stimulation areas, or altering the temporal delay between the two electrodes, had very little effect on this percept. The position of the stimuli in the two‐dimensional space was related to the distances of the two component electrodes along the electrode array. These results are relevant to speech processing strategies and electrode design for cochlear implants, as they imply that the creation of discrete, nonoverlapping areas of stimulation may not cause the percepts to be more distinct, and therefore may not necessarily lead to better speech perception.

ISSN:0001-4966    

DOI:10.1121/1.414594

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Temporal gap detection was determined for single 20‐Hz‐wide noise bands having various center frequencies, and for simultaneously presented pairs of noise bands where the spectral separation between center frequencies was varied. In most conditions, each noise band was presented 30 dB above its detection threshold, but in some conditions, each noise band was presented 15 dB above its detection threshold. The results for single noise bands indicated that the gap threshold did not vary significantly across center frequency. Gap detection was significantly better for pairs of noise bands than for single noise bands. The improvement in gap detection when two noise bands were presented instead of one was greater at the 15‐dB presentation level than at the 30‐dB level. In the case where pairs of bands were presented, there was no effect of the spectral separation between bands, even though the spectral separation was varied over a range of 5 oct. Spectral integration for gap detection may be limited only by the audibility curve.

ISSN:0001-4966    

DOI:10.1121/1.414595

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

A two‐dimensional stimulus‐classification paradigm was used to examine the ability of listeners to judge the laterality of an interaurally delayed low‐frequency target component presented concurrently with a distractor component. Of primary interest was the effect on performance of the frequency difference (Δf) between the target and distractor. In one set of conditions, the target was fixed at 753 Hz and the distractor was 353, 553, 653, 703, 803, 853, 953, or 1153 Hz (fixed within a block of trials). In a second set of conditions, the distractor was fixed at 753 Hz and the target frequency was 353, 553, 653, 703, 803, 853, 953, or 1153 Hz. The listeners were presented with a target component with an interaural delay that varied from trial to trial, taking on one of ten values, five leading to the left ear and five leading to the right. A distractor component was simultaneously presented with an interaural delay that also took on one of the same ten values. Delays ranged from −90 to +90 μs in 20‐μs steps. During a block of 100 trials, each of the possible combinations of target and distractor delay was presented once and only once in a random order.Listeners were instructed to make left–right judgments based on the target delay. Each condition was repeated ten times, and the slopes of the best linear boundaries between left and right responses were used to derive the relative weights given to the target and distractor. The duration of the signals was 200 ms. Two of the eight listeners weighted the target heavily when the target and distractor were spectrally remote but gave the two components equal weight when the difference in frequency was small. These two listeners yielded similar target weights regardless of which component was designated as the target. One listener gave nearly equal weight to the target and the distractor regardless of Δf. Five of the listeners gave greater weight to the higher of the two frequencies regardless of which was assigned as the target. This high‐frequency dominance is explained in terms of cross‐correlation functions based on the composite two‐tone waveforms.

ISSN:0001-4966    

DOI:10.1121/1.414670

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The sound localization ability of human observers has been frequently examined in quiet environments, but there have been relatively few studies that have considered the effect of noise on sound localization. In this study, three subjects judged the perceived direction of a broadband click‐train signal in the quiet and in the presence of a broadband noise at nine signal‐to‐noise ratios, which varied over a 23‐dB range. The signal could originate from any of 239 spatial locations that completely surrounded the subjects in azimuth (360°) and ranged from −45° to +90° in elevation; the masker (when present) was always located directly in front of the subjects at 0° azimuth and 0° elevation. The subjects indicated the perceived direction of the signal by pointing at a 20‐cm‐diam spherical model of auditory space. As the signal‐to‐noise ratio was lowered, the accuracy of localization judgments decreased nearly monotonically. However, the accuracy of judgments relative to the median plane (i.e., the left/right dimension) was less strongly influenced by the presence of noise than was the accuracy of judgments relative to the horizontal plane (i.e., the up/down dimension). The accuracy of judgments relative to the frontal plane (i.e., the front/back dimension) was most strongly influenced by noise.

ISSN:0001-4966    

DOI:10.1121/1.415233

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Echo threshold is that critical delay of a lagging signal (the echo) at which the echo is ‘‘suppressed’’—i.e., at which one rather than two events is perceived. It has recently been shown that echo threshold increases in most subjects when they are exposed to a train of redundant information prior to the test stimulus presentation—that is, there isbuildupofechosuppressionin the presence of the preceding train [Cliftonetal., J. Acoust. Soc. Am.95, 1525–1533 (1994)]. The present investigation measured echo threshold in 25 normal‐hearing adult subjects, both for isolated (baseline) test stimuli and for test stimuli preceded by a redundant train of stimuli (buildup conditions). The test stimulus was a 4‐ms wideband noise burst pair, in which the lead burst was presented from either the left or right side (from near −45° or near +45° in different runs), and the lag burst was presented from the opposite side. Echo delay was varied adaptively, and the subject’s task was to indicate on each trial which of two alternative positions (separated by 20°) the lag source was presented from. Average echo threshold in the baseline condition was 11.2 ms (in agreement with previous results) and did not depend on whether the lead burst was on the subject’s left or right side.Average echo threshold in the buildup conditions was significantly elevated. Interestingly, there was a significantly greater buildup effect when the lead stimulus came from the subject’s right side (average echo threshold: 24.4 ms) than when it came from the left side (average: 18.8 ms). This result agrees with informal observations made by Clifton and Freyman [Percept. Psychophys.46, 139–145 (1989)] and suggests that there is more effective suppression of echo information when the lead stimulus originates from the right side (i.e., the side contralateral to the typically dominant hemisphere) than when it originates from the left side. The distribution of the magnitude of buildup effects across subjects (i.e., echo threshold in the presence of the train minus baseline echo threshold) was unimodal and symmetric, both for lag source on left (mean: 14.1 ms) and for lag source on right (mean: 6.7 ms). These results are discussed in relation to other hearing asymmetries that have been reported.

ISSN:0001-4966    

DOI:10.1121/1.414596

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Vibrotactile forward masking experiments were conducted on the thenar eminence of the hand to determine the time course of masking in the Pacinian (P) or a non‐Pacinian (NP I) channel. Brief masking and test stimuli that contained energy centered either below 27 or at 500 Hz were used to preferentially activate the NP I or P channels, respectively. Test thresholds were measured at different fixed delays (Δt) between the masking and test stimuli that ranged from 5 to 995 ms. Masking stimulus level was also varied from 5 to 25 dB above threshold. The masking effect followed an exponential decay with different time constants for each of the channels, but a similar asymptote (residual masking) for both channels. At the higher masking stimulus levels, the time constant for the P channel was about 40 ms, while the time constant for the NP I channel was about 100 ms. Residual masking in both channels increased about 1 dB for every 5‐dB increase of masking stimulus level.

ISSN:0001-4966    

DOI:10.1121/1.414597

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Recent experiments have demonstrated that category goodness influences the perception of vowels [Iverson and Kuhl, J. Acoust. Soc. Am.97, 553–562 (1995)]; listeners show a perceptual magnet effect characterized by shrunken perceptual distances near excellent exemplars of vowel categories and stretched distances near poor exemplars. The present study extends this investigation by examining the relative influence of phonetic identification and category goodness on the perception of American English /r/ and /l/. Eighteen /ra/ and /la/ tokens were synthesized by varyingF2 andF3 frequencies. Adult listeners identified and rated the goodness of individual stimuli, and rated the similarity of stimulus pairs. Multidimensional scaling analyses revealed that the perceptual space was shrunk near the best exemplars of each category and stretched near the category boundary. In addition, individual differences in /r/ identification corresponded to the degree of shrinking near the best exemplars of the /r/ category. The results demonstrate that category goodness and phonetic identification both contribute to the perception of /r/ and /l/.

ISSN:0001-4966    

DOI:10.1121/1.415234

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP