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The ability of the auditory system to maintain high differential sensitivity in the adaptive background was investigated in a beluga whale (Delphinapterus leucas). Adaptive background was a train of tone pips following one another at a rate of 1 kHz. Each pip consisted of eight carrier cycles of 64 kHz. Every 128 ms, the train of pips was interrupted for 16 ms and replaced with a test signal (16-ms series of the same tone pips as in the adaptive background, but of another level). The level of the test signals varied from -15 to + 20 dB relative the level of adaptive background. Evoked potentials (the rate following response, RFR) produced by the test signals were recorded. Increasing of adaptive level led to RFR thresholds growth. The 10-dB rising of adaptive signals intensity level led to 7.8 dB rising of test signal threshold. The response amplitude dependence on the test stimulus level was almost independent of the level of the adaptive background. Thus, the beluga’s auditory system displayed high sensitivity to the change in acoustic signal level in the high-level background. [This study was supported by the Russian Foundation for Basic Research (Grant No. 18-04-00088).]The ability of the auditory system to maintain high differential sensitivity in the adaptive background was investigated in a beluga whale (Delphinapterus leucas). Adaptive background was a train of tone pips following one another at a rate of 1 kHz. Each pip consisted of eight carrier cycles of 64 kHz. Every 128 ms, the train of pips was interrupted for 16 ms and replaced with a test signal (16-ms series of the same tone pips as in the adaptive background, but of another level). The level of the test signals varied from -15 to + 20 dB relative the level of adaptive background. Evoked potentials (the rate following response, RFR) produced by the test signals were recorded. Increasing of adaptive level led to RFR thresholds growth. The 10-dB rising of adaptive signals intensity level led to 7.8 dB rising of test signal threshold. The response amplitude dependence on the test stimulus level was almost independent of the level of the adaptive background. Thus, the beluga’s auditory system displayed high sens...

In general, perceived reverberation strength is related to physical reverberation level present at the two ears; however, this relation depends on listening condition. Pervious work using virtual auditory space techniques has demonstrated that when physical reverberation is reduced in one ear while leaving the other ear unchanged, listeners do not report a change in reverberation strength. Reducing physical reverberation equally in both ears under binaural listening or in the signal ear under monaural listening elicits a decrease in perceived reverberation strength. To better understand the relation between physical and perceived reverberation in different listening conditions, a perceptual weighting experiment was performed. Listeners reported perceived reverberation strength in a test stimulus using a magnitude estimate paradigm relative to a standard while listening over headphones. Test stimuli were generated by jittering reverberation level independently in the two channels of a binaural room impulse...

This paper concerns the extent to which the precedence effect is observed when leading and lagging sounds occupy different spectral regions. Subjects, listening under headphones, were asked to match the intracranial lateral position of an acoustic pointer to that of a test stimulus composed of two binaural noise bursts with asynchronous onsets, parametrically varied frequency content, and different interaural delays. The precedence effect was measured by the degree to which the interaural delay of the matching pointer was independent of the interaural delay of the lagging noise burst in the test stimulus. The results, like those of Blauert and Divenyi [Acustica 66, 267-274 (1988)], show an asymmetric frequency effect in which the lateralization influence of a lagging high-frequency burst is almost completely suppressed by a leading low-frequency burst, whereas a lagging low-frequency burst is weighted equally with a leading high-frequency burst. This asymmetry is shown to be the result of an inherent low-frequency dominance that is seen even with simultaneous bursts. When this dominance is removed (by attenuating the low-frequency burst) the precedence effect operates with roughly equal strength both upward and downward in frequency. Within the scope of the current study (with lateralization achieved through the use of interaural time differences alone, stimuli from only two frequency bands, and only three subjects performing in all experiments), these results suggest that the precedence effect arises from a fairly central processing stage in which information is combined across frequency.

Thresholds for the detection of a 50-ms test stimulus delivered to the thenar eminence were measured as a function of the time interval between the offset of a 500-ms masking stimulus and the onset of the test stimulus (delta t). The frequency of the masker and the test stimulus was the same during a particular testing session and was either 25 or 250 Hz. At all values of delta t, older subjects exhibited significantly more masking than did young subjects. The effects of age were greater for stimuli that primarily affect the Pacinian system (250 Hz) than those that primarily affect non-Pacinian systems (25 Hz). Psychophysical measurements of the apparent duration of tactile sensations suggest that both sensory persistence and adaptation are affected by aging. Since adaptation seemed to be the more dominant factor for stimuli with durations as long as 500 ms, it was concluded that the effects of aging on forward masking seen in our study were due mainly to increased amounts of adaptation produced by the masker.

Listener’s head movement, particularly horizontal rotation, effectively improves sound localization acuity (Wallach, 1939; Thurlow, 1967; Kawaura, 1989). However, few findings have been obtained concerning sound localization during head rotation. In the present study, we directly investigated the minimum audible angle (MAA) at the front during horizontal rotation. A sound stimulus (30-ms noise burst) was presented from a loudspeaker of a circular array (r = 1.1 m), with a loudspeaker separation of 2.5 degrees. The listener, sitting at the center of the circle, was asked to answer whether the sound stimulus was presented from the left or right of the subjective front (2AFC). We designed three listening conditions, static, active rotation and passive rotation. In the static condition, listeners were asked to keep their heads still. For the active rotation condition, listeners were asked to rotate their heads. Meanwhile, for the passive rotation condition, listeners sitting on a revolving chair were rotated by an experimenter. In the latter two conditions, the test stimulus was triggered during head movement. Results showed the MAA to deteriorate significantly in the two rotation conditions. This implies that the improvements in sound localization due to head motion could be explained by the multiple-look model (Viemeister, 1991).

Echo threshold is that critical delay of a logging 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 is buildup of echo suppression in the presence of the preceding train [Clifton et al., 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-microsecond wideband noise burst pair, in which the lead burst was presented from either the left or right side (from near -45 degrees or or near (+)45 degrees 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 degrees) the lag sources was presented from. Average echo threshold in the baseline condition was 11.2 microseconds (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 microseconds) than when it came from the left side (average: 18.8 microseconds). 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) that 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 microseconds) and for lag source on right (mean: 6.7 microseconds). These results are discussed in relation to other hearing asymmetries that have been reported.

The synthetic‐analytic listening task (SALT) developed by Dye and colleagues [Dye et al., J. Acoust. Soc. Am. 96, 2720–2731 (1994)] was applied to a task in which an amplitude‐modulated tonal carrier was presented as a target during the standard stimulus. The standard stimulus was followed by a test stimulus in which the target along with another amplitude‐modulated carrier (the distractor) was presented. The listener determined if in the test stimulus, the target (which was presented along with the distractor) was higher or lower in modulation depth than when the target was presented alone as the standard stimulus. The target and distractor were either 1‐ or 4‐kHz carriers modulated at one of ten depths of modulation during the test stimulus at modulation rates ranging from 4 to 64 Hz. SALT was used to estimate the relative weight listeners assigned to the target and distractor as a function of the difference between their modulation rates, both for target carrier frequencies above and for target carrier frequencies below the distractor carrier frequency. When the target and distractor were modulated at the same rate, the target and distractor weights were equal, indicating synthetic listening. When the target and distractor differed in modulation rate, the listener gave more weight to the target suggesting a form of analytic listening. The result demonstrate the applicability of SALT to studies of modulation and reinforce the claim that different spectral components modulated with the same modulation pattern are processed synthetically.

Natural speech stimuli used in studies of phonological learning usually include several in talkers and phonetic environments because variability aids learning [e.g., Lively, Logan, and Pisoni, J. Acoust. Soc. Am. (1993)]. The present study investigated whether nonphonetic variability in the synthetic test set has a similar effect. First, a perceptual mapping procedure was performed using a synthetic continuum that ranged from the Malayalam voiced, unaspirated, dental stop consonant to the American English alveolar [d], with three F0 contours (low, mid, and high). Subjects identified the stimuli (2AFC) and judged their goodness as exemplars of each category. Subjects then received 15 sessions (one/day) of 2AFC training with feedback using natural stimuli produced by native Malayalam speakers, and performed difference ratings on a subset of pairs from the synthetic stimuli. The perceptual mapping procedure was repeated at 1 and 14 days post‐training and results compared with a parallel experiment that inclu...

Loudness levels were measured for three test stimuli (speech, narrow‐band noise, and square wave) at three levels in three test conditions (test stimulus in quiet, test stimulus in presence of masker, and total loudness of test stimulus plus masker). Loudness levels were measured in the traditional way by matching loudness of the test stimulus to that of a 1‐kHz tone. In addition, loudness levels were measured using a narrow‐band noise as the reference stimulus. The bandwidth of the narrow‐band noise used as test stimulus (NBN‐150) was 150 Hz, and the bandwidth of the narrow‐band reference stimulus (NBN‐120) was 120 Hz. Both stimuli were arithmetically centered at 1 kHz. The loudness level functions for speech and for NBN‐150 have slopes of approximately unity. However, the loudness level function for the square wave has a slope of greater than unity below about 50 dB SL and the slope decreases above about 50 dB SL. Loudness predictions of two models are computed and compared to the experimental measurements.

Localization of a source followed by a delayed version of it from another direction is dominated by the direction of the first wavefront. It has been suggested that this ‘‘precedence’’ effect and its implication of echo suppression is a dynamic process, subject to listeners’ expectations about what a ‘‘plausible’’ echo should be. The present study investigates what makes an echo ‘‘plausible’’ [Rakerd and Hartmann, J. Acoust. Soc. Am. 78, 524–533 (1985); Clifton et al., J. Acoust. Soc. Am. 95, 1525–1533 (1994)]. Synthetic piano tones presented through pairs of speakers in an anechoic room were designed to simulate natural sounds heard in echoic environments. Trials consisted of conditioning stimuli followed by a test stimulus. Each stimulus was made up of a hypothetical source and echo. The spectra of the test echoes could be changed to reflect abrupt changes in the absorption qualities of simulated reflections. As in precedence, conditioning stimuli were localized in the direction of their sources. Attenu...

Recent research on American English /r/ and /l/ has suggested that adult Japanese speakers are more sensitive to changes in F2 frequency than to changes in F3 frequency. In contrast, adult American English speakers seem more sensitive to changes in F3 frequency. To examine the developmental origins of these cue weightings, 7.5‐month‐old infants raised in monolingual English homes were tested. Following the head‐turn conditioning procedure, infants were trained to turn toward a visual reinforcer whenever a continuously repeated background stimulus was changed to a test stimulus. In an initial conditioning phase, infants were trained to discriminate two synthetic /ra/ and /la/ stimuli that differed in both F2 and F3. In the following test phase, infants discriminated these two stimuli along with stimuli that differed from the background along only one of these dimensions. The results demonstrated that infants were more sensitive toF 2 than to F3, suggesting that their cue weightings may better match those o...

The object of this study was to investigate whether subjects are able to compare the prominence caused by different types of accent‐lending pitch movements, and, if so, whether some pitch movements lend more prominence to a syllable than others. These experiments were carried out with the utterance/mamama/, with the second syllable accented by either a rise, a fall, or a rise–fall. Subjects adjusted the variable excursion size of a comparison stimulus to the fixed excursion size of a test stimulus in such a way that the accented syllable in test and comparison stimuli had equal prominence. The rise–fall was only presented in standard position, the fall and the rise were tested for five different positions in the syllable. It is concluded that subjects are well able to equate the prominence of syllables accented by various types of pitch movement, viz., a rise–fall in standard position, a rise starting before the vowel onset, and a fall whatever its position in the syllable. Moreover, when lending equal prominence, the early starting rise and the rise–fall have equal excursion sizes. The fall, however, appears to lend more prominence to a syllable than the rise or the rise–fall of equal excursion size, independent of its position in the syllable. This difference increased with increasing declination of the pitch contour.

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. The masking stimulus, narrow‐band noise centered at 275 Hz, and the test stimulus, a 15‐, 50‐, 80‐, or 300‐Hz sinusoidal burst, were applied to the same site on the thenar eminence of the hand. The intensity of the masker was varied over a range of 0 to 52 dB SL. The results support the hypothesis that the detection of vibrotactile stimuli is mediated by at least two receptor systems which do not mask each other.

The adaptation of a complex and pure-tone pitch was examined, using an adaptation stimulus composed of components of low harmonic number and test stimuli composed of components of high harmonic number, in order to examine separately the effects of pure-tone and complex pitch adaptation. The test stimulus either had the same fundamental as that of the adaptation stimulus, or it had a fundamental lower than that of the adaptation stimulus. Adaptation was measured using a pitch matching method. The adaptation and test stimuli were presented to one ear, and a pure-tone matching stimulus was presented to the opposite ear. Adaptation generally shifted the complex pitch of the test stimulus to a lower pitch. The component pitches, on the other hand, did not change, or shifted upwards slightly. The downward complex pitch changes were consistent with the adaptation of a central complex pitch channel.

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. A 50-ms sinusoidal test stimulus was applied to the thenar eminence of the hand 25 ms after the termination of a 700-ms sinusoidal masker applied to the same site. The frequency of the test stimulus and the frequency of the masker were varied. To eliminate the influence of the Pacinian receptor system, stimuli were delivered through a 0.01-cm2 contactor. The results support the hypothesis that the detection of vibration delivered through a small contactor is determined by two separate populations of non-Pacinian receptors. The study constitutes a psychophysical demonstration of the existence of three receptor systems responsible for the detection of vibration.

Poststimulatory threshold shift has been measured for 1000‐cps stimuli of varying duration and sensation level, turned on and off either without audible transients or abruptly. The measurement was performed by means of test stimuli of varying duration and following the prime stimulus at various time intervals. The results show that the poststimulatory threshold shift depends little on the duration of the test stimulus, but that it depends critically on the time interval between the termination of the prime stimulus and of the test stimulus. The poststimulatory threshold decreases as this time increases. The poststimulatory threshold increases with sensation level and it depends in a complex fashion on the duration of the prime stimulus. The time pattern of the threshold changes radically when a gradual cutoff of the prime stimulus is replaced by an abrupt one. Replacing the 1000‐cps tone by a random noise leads to the same result as an abrupt cutoff.

Evidence is presented which shows that localization aftereffects can be produced not only by an adapting stimulus which has only an intensity differential at the two ears, but also by one which has only a time‐delay differential at the two ears. In general, the displacement of the test stimulus is away from the perceived location of the adapting stimulus. However, exceptions to this rule have been found. It is concluded that the mechanism of these localization aftereffects is not in some final central location corresponding to perceptual space.

Widely divergent amounts of perstimulatory adaptation have been reported previously, possibly due to differences in technique of measurement. One method often used determines perstimulatory adaptation from a series of simultaneous binaural loudness balances between a continuous stimulus in the adapting ear and a stimulus intermittently presented to the test ear. The present study attempts to evaluate the effect of the characteristics of intermittency of the test stimulus upon the measured adaptation in the adapting ear. With a 4000‐cps adapting tone presented at 75‐db sensation level, 16 combinations of on‐ and off‐duration of the test tone were investigated using 11 listeners. For all experimental conditions the adapting curves showed the same general shape, with a rapid initial decline, followed by a more gradual decline reaching asymptote after 5 to 6 min. As the on‐time of the test stimulus increased, less adaptation was seen, except for off‐times of 30 sec or greater where on‐time no longer influence...

The perception of sounds characterized by a moving resonance was investigated a series of experiments. Stimuli were generated by exciting a tuned circuit with a short train of pulses of repetition rate 100/sec. The resonant frequency of the tuned circuit was changed in a piecewise linear manner over a 500‐cps range. Subjects matched the test stimuli by adjusting the resonant frequency of a fixed (i.e., nonvarying in time) resonant circuit until the test and comparison stimuli were judged to be most alike. Results indicate a strong tendency for subjects to adjust the frequency of the fixed resonant circuit until it is close to the terminal resonant frequency of the time‐varying circuit. This tendency depended to some extent on the direction and rate of the frequency change in the test stimulus. The implications of the results for auditory theory and speech perception are discussed briefly.

Ten experienced listeners, eight males and two females, whose hearing sensitivity was within normal limits, participated in a study concerned with an assessment of auditory threshold for a 125‐Hz stimulus as a function of stimulus duration and low‐pass filtering of the test stimulus. Thresholds were obtained with a Bekesy‐type tracking procedure for six stimulus durations (5, 10, 20, 50, 100, 200 msec) in conjunction with three filtering conditions (unfiltered—UNFIL; 200‐Hz low pass—LP‐200; 150‐Hz low pass—LP‐150). Spectral analysis of the stimuli for each duration and filtering condition was performed. Temporal integration occurred for a 125‐Hz stimulus during the LP‐200 and LP‐150 conditions but not when the stimulus was unfiltered (UNFIL). The LP‐150 condition resulted in an average integration of 11.5 dB/decade between 5 and 200 msec and the average integration for the LP‐200 condition was 8.6 dB/decade. Thresholds over the 5‐ to 200‐msec range for the UNFIL condition did not vary by more than 1 dB, t...

Evidence is provided for the existence of at least three feature‐specific channels in the auditory system. Thresholds for the detection of small repetitive or nonrepetitive frequency changes were measured following various adapting stimuli using a 2IFC procedure in two subjects at 1 kHz. Thresholds for single linear upward frequency sweeps (up sweeps) were increased by a factor of 2 to 3 following exposure to repetitive (8 Hz) up sweeps but not following exposure to down sweeps or tone bursts; correspondingly, thresholds for down‐sweep stimuli were increased only by down sweeps. Sinusoidal FM test stimulus thresholds were elevated by both up‐sweeps and down‐sweeps and to a lesser extent by tone bursts. These results suggest the existence in the auditory system of channels specific to upward FM, downward FM, and probably repetition rate.

A series of experiments was conducted to determine the effects of selective adaptation on the perception of linguistic feature contrasts. The test stimulus consisted of a series of synthetic speech sounds, 13 CV syllables which varied in the starting frequency and direction of second‐ and third‐formant transitions. Variations in these formant transitions are sufficient for the perceived consonant distinctions along what linguists have termed the place of articulation dimension; in this case, the perceived distinctions were among the syllables [b ae], [d ae], and [g ae]. It was found that a significant adaptation effect could be obtained for the feature place, as measured by both identification and discrimination responses. For various adapting stimuli, alterations in perception occurred, such that test stimuli lying near a phonetic boundary, normally perceived as having the same place value as the adapting stimulus, were perceived after adaptation as having a systematically different place value. In addition...

The technique of heterofrequency forward masking was used to determine thresholds of three cutaneous receptor systems at the thenar eminence of the hand. A 50‐ms sinusoidal test stimulus was presented 25 ms after the termination of a 700‐ms sinusoidal masking stimulus. Both test and masking stimuli were varied over the frequency range of 15–300 Hz. The stimuli were delivered through a 0.01 cm2 contactor eliminating the influence of the Pacinian receptor system and exposing the threshold characteristics of two non‐Pacinian systems, designated as NPI and NPII. The low‐frequency slopes of the NPI and NPII tuning curves are similar to those measured physiologically from SA and RA receptors, respectively.

Vibrotactile thresholds were measured using a criterion‐free psychophysical method. 200‐Hz signals were presented unmasked and in the presence of three masker types: a 200‐Hz vibration in phase with the signal (experiment 1); a 200‐Hz vibration shifted in phase by 90° (experiment 2); a narrow‐band random noise centered at 200 Hz (experiment 3). The threshold shift was measured as a function of masker SL. The form and position of the masking curves resulting from experiment 1 could be accounted for by an energy‐detection model when a peripheral threshold was assumed. The threshold model described the masking curve over its entire length. Without changing subject‐dependent parameters, the same equation, adjusted only to account for quadrature summation of signal and masker in the stimulus domain, accurately predicted the effects of the sinusoidal masker in quadrature with the test stimulus (experiment 2) as well as the effects of random noise (experiment 3). Although an energy‐detection model without a thre...

An experimental method for the investigation of direction‐specific characteristics of the auditory system is presented. The subjects were exposed to narrowband signals of 100 Hz, 1 kHz, and 6 kHz mean frequency. Directed acoustic motion (adapting stimulus) was presented clockwise/counterclockwise) in three ways: (1) actual sound source motion (loudspeaker rotating around the subject), (2) simulated motion via earphones, varying interaural intensity (ΔI), and (3) simulated motion via earphones, varying interaural‐time delay (Δt). Aftereffects in the opposite direction were observed in all three cases, but in case 3 (Δt) for 6‐kHz signals only. Unlike the visual analogue (waterfall effect) no apparent countermovement occurred, but rather a shift in the localization of the stationary test stimulus (approximately 2°, 1.2 dB, 30 μs, respectively). The results provide evidence for direction specific auditory subsystems in humans, i.e., for null‐point displacements caused by the adaptation of direction‐sensitive movement detectors [cf. J. A. Altman, Exp. Neurol. 22, 13–25 (1968)]. In support of physiological and anatomical findings (cf. Keidel, Neff, and Whitfield), the frequency dependence in case 3 (Δt) may indicate that the observed phenomenon is of cortical origin. [Based on the author's doctoral thesis, University of Gottingen (1977).]

In previous studies we have reported long‐lasting changes in the pitch of a complex sound following its association with a sound of a different pitch. The present study concerned whether a sound altered in pitch would show pitch adaptation effects commensurate with its pitch or frequency status. The test stimulus was the sixth, seventh, eighth, and ninth harmonics of F0 196 Hz. The conditioning tone was the first five harmonics of F0 204 Hz and the adapting stimulus was the first five harmonics of F0 200 Hz. Stimuli F0 196 and 204 Hz were heard in association for 30 min each day for 6 days. This resulted in a shift of F0 196 Hz to a pitch near 204 Hz. The results indicated a pre‐conditioning adaptation of the pitch of F0 196 Hz downward and a post‐conditioning upward shift. While the pitch change was in process and near 200 Hz, no adaptation occurred. The results will be discussed with reference to plasticity of the auditory system.

It has been demonstrated that listeners can identify the intended vowel in n CVC syllable even when the vowel nucleus has been attenuated to silence, leaving only onglides and offglides (Silent‐Center syllables). Verbrugge and Rakerd [Lang. Speech 29, 39–57 (1986)] constructed “hybrid” Silent‐Center syllables by cross‐splicing onglides and offglides of citation‐form CVC syllables spoken by a male and a female talker such that the formant trajectories were discontinuous. Identification of the intended vowel in hybrid syllables was no less accurate than vowel identification of the single‐talker Silent‐Center syllables. The present study replicates this research with syllables spoken in a earlier sentence “I say the word /dVd/ somemore,” using ten American‐English vowels. Hybrid Silent‐Center stimuli were prepared by crossing the stimulus sentences so that the sentence started with one talker and switched to the other talker after the silent portion of the test stimulus. Silent‐Center Control stimuli were al...

A first estimate of the optimum frequency‐gain characteristic for each ear was obtained using psychoacoustic data. The frequency‐gain characteristic was then adjusted systematically so as to obtain an improved estimate of the optimum frequency‐gain characteristic. A paired‐comparison procedure was used with running speech against a noise background as the test stimulus. An estimate of the optimum binaural condition was then obtained by using the estimated optimum monaural condition in each ear. The frequency‐gain characteristics in the two ears were then adjusted systematically and the paired‐comparison procedure was used to compare conditions. For six of the eight hearing‐impaired subjects tested, the best binaural condition was the combination of the two best monaural conditions. This result was found for both the SoNo and SoNπ‐conditions. The two subjects who did not fit this pattern also showed high test‐retest variability in their paired‐comparison judgements. [Research supported by PHS Grant No. P01‐NS 17764.]

Dynamic variations in the strength of echo suppression were investigated through earphone simulation of the free‐field precedence effect. Each test stimulus consisted of two click pairs, with the interaural time parameters of the leading and lagging pairs reflecting stimuli originating from opposite sides of the head. Echo thresholds, the minimum lagging click delay required for subjects to report hearing an echo click, were obtained in two basic conditions: (a) test click presented in isolation, and (b) test click preceded by a train of clicks identical to the test click. The most striking finding was that the presence of the preceding click train usually elevated the echo threshold of the test stimulus relative to its threshold when presented in isolation, suggesting that echo suppression builds up during the click train. The magnitude of the effect was influenced by the number of clicks in the train and the period of silence between the end of the train and the test click. The effect is surprisingly pe...

A series of experiments were conducted in which variations of the selective adaptation procedure were employed with a synthetic /bi/‐/di/ continuum for three female observers in an effort to obtain a systematic mapping of the selective adaptation phenomenon. The first experiment consisted of a series of adaptation sequences each followed by a labeling task in which members of the continuum were randomly presented for identification. Trials were either massed (two minutes between trials) or distributed (20 minutes between trials) in presentation. The degree of adaptation in the two conditions was not significantly different. The second experiment examined adaptation onset and involved varying the number of adaptors presented prior to either a labeling or a random ABX discrimination procedure. Results indicate that labeling and discrimination do not exhibit the same course of adaptation. In the third study, the interval between the last adaptor and the first test stimulus was manipulated to observe the adaptation decay functions for both labeling and discrimination. The results again point to a dissociation between labeling and discrimination with a differential rate of decay for each measure. Findings are discussed in terms of the current hypotheses proposed to account for selective adaptation. [Supported by a grant from NSF.]

A computer was used to generate three different waveforms from the same component frequencies by setting the phases of the components so they were either homophasic (all component sinusoids start at 0°), diphasic (sinusoids alternate between − and +45°), or heterophasic (starting phase randomly selected). The pitches evoked by these waveforms were investigated by asking listeners to match a pure tone to all the pitches they could distinguish in a test stimulus, and to rate the saliency of each pitch. Data from three listeners indicated that the pitch of the test stimuli could generally be matched by pure tones whose frequencies are around the fundamental (f1) or the octaves 2f1 and 4f1. Waveform patterning had no significant effect on the overall distributions of periodicity pitch matching responses. However, clear trends could be discerned from the ratings listeners assigned to the saliency of the pitches. A major finding was that the highest ratings of f1 pitch “strength” were always obtained for homoph...

Vibrotactile thresholds were measured at a single site on the thenar eminence in the presence of maskers set at different sensation levels. Measurements were made using a two‐interval, forced‐choice tracking paradigm. Maskers, either narrow‐band random noise or sinusoids, were presented simultaneously with test stimuli of different frequencies. Predictions of threshold shifts as a function of masker intensity were made for individual subjects based on their absolute vibrotactile thresholds and a duplex model of mechanoreception. The results showed that masking occurred within either the Pacinian or non‐Pacinian receptor system, but masking virtually disappeared when masker and test stimulus occurred in different channels. [Work supported by NIH.]

Vibrotactile thresholds for the detection of a 50‐ms vibratory stimulus on the thenar eminence of the hand were measured in the presence of and in the absence of a 700‐ms suprathreshold vibratory masking stimulus. When thresholds were measured in the presence of the masking stimulus, stimulus‐onset‐asynchrony was varied so that backward, simultaneous, and forward masking could be measured. The amount of masking, expressed as the difference between thresholds for detecting the test stimulus in the presence of and in the absence of the masking stimulus, was greatest when the test stimulus was presented near the onset or offset of the masking stimulus. For both backward and forward masking, the amount of masking decreased as a function of increasing stimulus‐onset‐asynchrony with the decay rate being greater for backward than for forward masking. Comparisons were made of the amounts of masking measured when the test and masking stimuli were both sinusoids, when the test and masking stimuli were both noise, a...

The common measures used in evaluating the magnitude of a noise (Lx, Leq, and etc.) correspond to first‐ and second‐order statistics of the distribution of sound levels. There are, however, perceived differences between sounds that have the same values of these statistics. It is therefore necessary to consider the spectral properties of the waveform envelope which correspond to higher‐order statistics. In the present experiments the subject compares a test stimulus and a reference stimulus and selects the one which appears to be fluctuating more rapidly. The reference stimulus is a noise whose waveform envelope is a noise with a low‐pass cutoff which varies from 0.125 to 8 Hz. The point of subjective equality is determined by adjusting the modulation frequency of the test stimulus, a sinusoidally modulated noise, in an adaptive procedure. The results indicate that when the median frequency of the spectrum of the envelope is above 1 Hz, it is a reasonably good predictor of the subjective rate, when the med...

The results of this study indicated that the interval between the standard and the test stimulus has little, if any, effect on the listener's ability to perceive an intensity‐produced lateral shift in a binaurally fused auditory image at frequencies of 1 and 4 kHz.

This research represented an attempt to clarify the relations between loudness changes and threshold shifts following the cessation of an auditory stimulus. A 400‐msec, 1000‐Hz sinusoid served as the “fatiguer” and, following a specified recovery time, a 50‐msec, 1000‐Hz test stimulus was presented. The test stimulus was always delivered to the ear stimulated by the 400‐msec signal, but in the case of loudness judgments, simultaneous with the test stimulus, a comparison stimulus was presented to the opposite ear. The entire stimulus sequence was recycled every 4 sec. Thresholds were obtained by varying the level of the test stimulus while loudness was determined by adjusting the level of the comparison stimulus so that loudness in the two ears was equal. In general, threshold shifts were much greater than loudness shifts when both were measured in decibels. Loudness recovery proceeded more slowly than did the recovery of threshold. The sound pressure of the 400‐msec stimulus produced marked changes in the...

A test stimulus consisting of square waves repeated 200 times/sec and filtered so as to bandpass 1000–1250 Hz, was presented once each 5 sec. Other stimuli—a 200‐Hz tone, a 1000‐Hz tone, or a train of filtered signals identical to the test stimulus—intervened once per second between successive test stimuli. The question asked was, “What is the influence of each intervening stimulus condition on the responsiveness to the test stimulus?” The results showed that the 1000‐Hz tone and the filtered square waves suppressed greatly the evoked response (N1P2 component) to the test stimulus. The 200‐Hz tone did not. These data suggest that the N1P2 component of the evoked response reflected the acoustic spectrum of the filtered signal, not its modulation rate. If N1P2 can be taken validly as an index of auditory cortex activity, one can infer from these results that periodicity differences in stimulation at the periphery are not converted into place differences at the level of the auditory cortex.

This paper presents the results of subjective tests related to hearing in concert halls. The influence of nonexponential decay on the subjectively felt reverberation was investigated by comparing non‐exponentially reverberated sound signals with exponentially reverberated ones with different reverberation times. Two types of nonexponential reverberation were investigated: (1) reveration with different initial and final decay rates and (2) reverberation with increased or decreased energies in the direct sound and early reflections. Subjects were asked, in paired‐comparison tests, which stimulus in each pair sounded more reverberant. In another experiment, low frequencies (below 300 cps) were eliminated from the direct component in the test stimulus and added, with a delay, to the reverberation. The test stimuli were compared with reference stimuli whose low‐frequency components were attenuated by specified amounts. The subjects were asked which of the two stimuli had more low frequencies. Speech and music were used as test signals. The different reverberators and filters used were simulated on a digital computer.

Previous studies have demonstrated that central masking depends on the time pattern of stimulus presentation. When both the masking and masked stimuli are pulsed simultaneously, the masking effect amounts to about 10 dB, when the masker is continuous and the test stimulus pulsed the effect decreases to a few decibels. In order to study the temporal course of central masking more analytically, the contralateral threshold shift was investigated by means of 10‐msec tone bursts. The masker consisted of 250‐msec bursts of tone or random noise, repeated at a rate of one per second, and the test bursts were presented at various time intervals from the onset of masking bursts. The results show that the contralateral threshold shift may exceed 10 dB at the onset of masking bursts. It decreases rapidly within about 15 msec and more slowly thereafter. In a matter of 200 msec, it is reduced to a few decibels. When the intermittent masking and test stimuli are turned on simultaneously, the threshold shift gradually de...