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PubMed1984

Interaural intensity discrimination: insensitivity at 1000 Hz.

Recent data from three laboratories have replicated Mills' [J. Acoust. Soc. Am. 32, 132-134 (1960)] finding that interaural intensity discrimination is relatively poorer for tones of 1000 Hz than for tones of either higher or lower frequencies. To get a finer look at this frequency effect, interaural intensity difference thresholds were obtained from four subjects for tones of several frequencies around 1000 Hz. An adaptive two-interval forced-choice procedure was employed, in which the overall intensity of the signals was varied randomly in order to prevent subjects from listening to monaural loudness changes. Despite large intersubject differences in overall sensitivity to interaural intensity differences, all four subjects showed a local peak in their threshold functions at or near 1000 Hz. This curious "1000-Hz effect" might be explained by imagining that an interaural intensity comparator operates more efficiently as frequency increases, but that a peripheral interaural intensity difference to interaural-time difference conversion contributes to laterality judgments for low-frequency tones, thus acting to lower thresholds again for frequencies below 1000 Hz.

Auditory Threshold↗
PubMed1984

Speech recognition in a special case of low-frequency hearing loss.

Recognition of speech stimuli consisting of monosyllabic words, sentences, and nonsense syllables was tested in normal subjects and in a subject with a low-frequency sensorineural hearing loss characterized by an absence of functioning sensory units in the apical region of the cochlea, as determined in a previous experiment [C. W. Turner, E. M. Burns, and D. A. Nelson, J. Acoust. Soc. Am. 73, 966-975 (1983)]. Performance of all subjects was close to 100% correct for all stimuli presented unfiltered at a moderate intensity level. When stimuli were low-pass filtered, performance of the hearing-impaired subject fell below that of the normals, but was still considerably above chance. A further diminution in the impaired subject's recognition of nonsense syllables resulted from the addition of a high-pass masking noise, indicating that his performance in the filtered quiet condition was attributable in large part to the contribution of sensory units in basal and midcochlear regions. Normals' performance was also somewhat decreased by the masker, suggesting that they also may have been extracting some low-frequency speech cues from responses of sensory units located in the base of the cochlea.

Adult↗
PubMed1984

Reference threshold sound pressure levels for the Welch Allyn AudioScope.

The Welch Allyn AudioScope has been evaluated as an audiometer screening instrument using a threshold, loudness balancing technique. Two sets of eartips have been compared to determine which eartip configuration would yield the most reliable audiometric data. The AudioScope has also been evaluated by the American National Standard Method for Coupler Calibration of Earphones using both sets of eartips, and reference threshold sound pressure levels for the AudioScope were developed by combining the coupler and loudness balance data. The most reliable eartip configuration for audiometric purposes is identified and guidelines for use of the audiometric screening instrument are proposed.

Audiometry↗
PubMed1984

Temporal gap resolution in masked normal ears as a function of masker level.

Recent studies of temporal resolution in hearing-impaired listeners indicate that many ears with cochlear damage exhibit elevated temporal gap thresholds. The deviations from normal may be large, for equivalent-SPL comparisons, but are often small or absent for equivalent-SL comparisons. In the present experiment, we examine the premise that SL effects in gap resolution are independent of sound pressure level. Normal hearing subjects used a Békésy procedure to track the minimum level of an octave-band signal at 1 kHz needed to keep a periodic temporal gap at threshold. Performance functions were generated to show stimulus intensity as a function of gap duration, for gaps from 25 ms to the smallest detectable value. In separate conditions, the level of a white-noise background was varied to shift the subject's audibility threshold. Results indicate that the limits of resolution are largely invariant with SPL, but criterion sensation levels for resolution are progressively reduced at higher SPL. It is concluded that gap thresholds from normal and impaired ears should be compared for equivalent SPL; comparisons made with SL equated are likely to underestimate the consequence of cochlear damage on resolving capacity.

Audiometry, Pure-Tone↗
PubMed1984

Discrimination of dynamic interaural intensity differences.

An experiment was conducted to measure observers' ability to detect time-varying interaural intensity differences (IIDs). In a two-interval forced-choice task, observers discriminated a binaural amplitude modulated (AM) noise in which the modulating sinusoid was interaurally in-phase from the same AM noise in which the modulator was interaurally phase-reversed. The latter stimulus produces a sinusoidally varying IID whose rate and peak IID depend on the frequency (fm) and depth (m) of modulation. The carrier was a narrow-band noise, interaurally uncorrelated, centered at 500, 1000, or 4000 Hz. Presentation level was 75 dB SPL; duration was 1.0 s. For a given fm, m was varied in an adaptive procedure to estimate the depth required for 71% discriminability (mthr). Three of the four observers displayed "low-pass" modulation functions: at 500 Hz, as fm increased from 0-50 Hz, mthr increased from 0.08 (IID = 1.3 dB) to 0.50 (peak IID = 9.5 dB). At 1000 and 4000 Hz observers were more sensitive to IID and the functions (mthr vs fm) were flatter than at 500 Hz. Comparison of these data to previously published data indicates that the binaural system can follow fluctuations in IID more efficiently than it can follow fluctuations in interaural time difference, although there are large individual differences in subjects' capacity to process these two types of binaural cues.

Auditory Threshold↗
PubMed1984

Phase relationship between bone and air conducted impulse signals in the human head.

Using the cancellation method we investigated the phase relationship as well as the amplitude ratio between impulse signals transmitted simultaneously via both bone and air conduction channels. The psychophysical findings indicated a phase difference corresponding to a time delay of about 0.9 ms by which the air input led the bone input in the case of frontal bone stimulation. Changing the polarity of the bone conduction signal a maximum in the loudness sensation was found just in the same phase difference. The psychophysical findings, predicted mathematically, were verified with brainstem evoked potentials elicited to similar signals. Preliminary results showed that the time lag observed relied on the location of the bone vibrator on the head and furthermore on the frequency used. This suggests different transmissions of vibratory energy reaching the inner ear along the skull.

Bone Conduction↗
PubMed1984

Infants' discrimination of intensity variation in multisyllabic stimuli.

Two groups of 5- to 11-month-old infants were tested for their ability to discriminate within-utterance intensity variations similar to those associated with linguistic stress. A visually reinforced discrimination procedure was used to determine sensitivity to increments in peak intensity for a final position, synthetic CVC syllable within either a bisyllabic (CVCVC) or a trisyllablic (CVCVCVC) context. Discrimination performance was above chance for a 2-dB increment, and improved for 4- and 6-dB increments. In addition, infants were more sensitive to intensity increments in the bisyllablic as compared to the trisyllabic context. Infant sensitivity for within-utterance intensity variations is sufficient for the detection of some linguistic stress contrasts.

Cues↗
PubMed1984

The role of monaural frequency selectivity in binaural analysis.

The relation between the monaural critical band and binaural analysis was examined using an NoSm MLD paradigm, in order to resolve ambiguities about the width of the masking spectrum important for binaural detection. A 500-Hz pure-tone signal was presented with a 600-Hz-wide band of masking noise to the signal ear. Bands of noise ranging in width from 25 to 600 Hz, or noise notches (imposed on a 600-Hz-wide band centered on the signal frequency) ranging in width from 0 to 600 Hz were presented to the nonsignal ear. All noise bands and notches were centered on 500 Hz, the frequency of the signal. The effects of varying bandwidth were radically different from those of varying notchwidth: the MLD changed from zero to approximately 8 dB over a bandwidth range of 400 Hz; for notchwidths, however, the MLD changed 8 dB over a range of only 50 Hz. The results support an interpretation that the fine frequency selectivity of monaural analysis is preserved in peripheral binaural interaction, but that a relatively wide frequency range of critical bands is scanned at a later stage of binaural processing. It was suggested that the wide spectral range of binaural analysis may provide a background against which binaural differences due to the signal are detected.

Attention↗
PubMed1984

Behavioral vocal response thresholds to mating calls in the bullfrog, Rana catesbeiana.

Male bullfrogs will vocalize in response to playbacks of the mating (advertisement) calls of conspecifics. This behavior was studied in response to playbacks of bullfrog mating calls presented at six different sound intensity levels. The lowest sound intensity level tested (50 dB SPL) was insufficient to evoke calling from any of the animals. Calling was evoked by playback levels of 60 dB SPL and higher. The data suggest that behavioral evoked calling thresholds lie between 50-60 dB SPL for these animals. Playback intensity levels of 80 dB SPL were more effective in evoking responses than were intensity levels up to 20 dB higher or lower. This was true both in terms of the total number of evoked responses and the trial number at which responding ceased. Moreover, significantly less habituation of evoked calling occurred at levels of 80 dB SPL than at higher or lower levels. The data suggest that a sound pressure level of 80 dB represents a behaviorally preferred intensity level for evoked calling in the bullfrog. Field recordings of bullfrog choruses show that the intensity produced by an individual calling male reaches a level of 80 dB SPL at a distance of 1 m. This intensity level is identical to that producing maximal evoked calling in the laboratory.

Animals↗
PubMed1984

On the growth of masking asymmetry with stimulus intensity.

Masking asymmetry was investigated over a wide range of stimulus intensities for two signal frequencies, fo = 1.0 and 4.0 kHz, using both fixed-masker and fixed-signal paradigms. The masker was a notched noise with the upper and lower edges of the notch, fu and fl, respectively, placed asymmetrically about fo. For various notch widths, the asymmetry of masking was measured as the difference between the masked threshold obtained when fl was nearer fo and that obtained when fu was nearer fo. For maskers with wide notches, (fu - fl)/fo greater than 0.15, masking asymmetry changed with stimulus level; at the highest level, masked threshold was greatest when fl was nearer fo, and, at the lowest level the asymmetry reversed slightly for fo = 1.0 kHz so that masked threshold was actually greater when fu was nearer fo. Nonparallel growth of masking functions reveal changes in masking asymmetry with signal level as well as with masker level. It is concluded that the nonlinear growth of masking with level is due primarily to changes in the auditory filter, rather than changes in the detector following the filter.

Auditory Threshold↗
PubMed1984

Monaural and binaural auditory brainstem responses in relation to the psychophysical loudness growth function.

Electrophysiological measures of the brainstem response to auditory stimuli permit comparisons to be made between latency shifts across intensity increments and psychophysical measures of loudness growth. Monaural comparisons leave much room for uncertainty in the interpretation of the nature of the relationship between the two response modes. A more definitive method for examining this relationship is to compare the monaural and binaural data obtained from psychophysical and electrophysiological measures. It is shown here that, while the brainstem electrophysiological response to intensity changes can be described by a power function, the latency of the neural response does not provide a direct link to the process of loudness summation or to the psychophysical response to loudness growth.

Adult↗
PubMed1984

Noise levels and hearing thresholds in the drop forging industry.

A-weighted equivalent continuous noise levels for hammer and press operations in a drop-forging industry were determined using both tape recordings of the noise and personal noise dosimeters. The results indicated average A-weighted Leq values of 108 dB for hammer operators and 99 dB for press operators. Comparison of hearing level statistics for 716 hammer and press operators and 293 control subjects indicated the severe hazard to hearing of impact noise exposures. For mean exposure times of less than 10 years, hearing levels for the press (99 dB) and hammer (108 dB) operator age groups are nearly identical, and in the latter case are less than those predicted for exposure to equivalent continuous noise. For long-term exposures of 10 years or more, the results of this study indicate that hearing losses resulting from impact noise in the drop-forging industry are as great or greater than those resulting from continuous noise.

Adolescent↗
PubMed1984

Intensity discrimination: a severe departure from Weber's law.

These experiments were designed to assess the importance of different types of information which might be used in detecting intensity changes for pure tones. Thresholds for detecting an intensity change, expressed as 10 log (delta I/I), were measured over a wide range of frequencies and levels under conditions where one or more sources of information was either present or was removed. Spread of excitation was restricted by using bandstop noise centered at the signal frequency. Information conveyed by dynamic responses to signal onsets and offsets was eliminated by masking onsets and offsets with bursts of bandpass noise. Phase-locking information was eliminated by using high-frequency signals (above 5 kHz). Dynamic responses to signal onsets and offsets appear to play little role in intensity discrimination. Phase locking does appear to be important since Weber's law or a near-miss to it was observed at low frequencies, whereas at high frequencies performance deteriorated at moderate sound levels, and improved again at high levels. A preliminary experiment, using 225-ms stimuli revealed only a small midlevel deterioration at high frequencies. However, when 30-ms stimuli were used a large deterioration was observed, performance being worse when bandstop noise was presented with the tone. Hence at short durations and high frequencies spread of excitation seems to be important: When it is restricted by bandstop noise values of 10 log (delta I/I) observed at moderate levels it can be as large as 14 dB. The results of the experiments are consistent with a bimodal distribution of thresholds in primary auditory neurons; at intermediate levels neither population will operate effectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1984

Dynamic range and asymmetry of the auditory filter.

This experiment was designed to measure the shape and asymmetry of the auditory filter over a wider dynamic range than has been measured previously. Thresholds were measured for 2-kHz sinusoidal signals in the presence of two 800-Hz-wide noise bands, one above and one below the signal frequency. The spectrum level of the noise was 45 dB (re: 20 muPa), and the noise bands were placed both symmetrically and asymmetrically about the signal frequency. The deviation of the signal frequency from the nearer edge of each noise band varied from 0 to 0.8 times the signal frequency. Each ear of six subjects was tested, and the subjects' ages ranged from 22 to 74 years. The auditory filters derived from the data were somewhat asymmetric, with steeper slopes on the high-frequency side; the degree of asymmetry varied across subjects. The asymmetry could be characterized as a uniform stretching of the (linear) frequency scale on one side of the filter. The dynamic range of the auditory filter exceeded 60 dB in the younger listeners, but the dynamic range and sharpness of the filter tended to decrease with increasing age.

Adult↗
PubMed1984

An evaluation of the effectiveness of three hearing protection devices at an industrial facility with a TWA of 107 dB.

Three hearing protection devices [Siebe Norton Com-fit earplug, Flents Silenta model 080 earmuff, and E-A-R foam earplug] were compared for their effectiveness in preventing both daily temporary threshold shifts (TTS) and threshold variability between sequential annual audiograms for workers in an industrial environment with a TWA of 107 dB. Com-fit wearers showed significant TTS at 500-4000 Hz from the beginning to the end of the workday. Silenta wearers displayed significant TTS at 500 Hz and nonsignificant improvement at 6000 Hz. E-A-R wearers showed significant TTS at 1000-2000 Hz and nonsignificant improvement at 3000-6000 Hz. Statistical analysis indicated that the protection provided by the E-A-R plug was significantly better than that of the Com-fit plug at 500-4000 Hz, and significantly better than the protection of the Silenta muff at 500, 3000, and 4000 Hz. Employees' last four annual audiograms prior to the start of the TTS study were evaluated to compare the wearer groups' mean values of the %BWs statistic (sequential percent better or worse). Previous research indicates that the %BWs statistic for a properly protected population with past audiometric test experience will be less than 30%. The E-A-R group showed an acceptable %BWs value (26%), but the Silenta wearers (45%) and Com-fit wearers (53%) showed excess threshold variability in threshold measurements from year to year.

Adult↗
PubMed1985

Thresholds for the detection of inharmonicity in complex tones.

Thresholds were measured for the detection of inharmonicity in complex tones. Subjects were required to distinguish a complex tone whose partials were all at exact harmonic frequencies from a similar complex tone with one of the partials slightly mistuned. The mistuning which allowed 71% correct identification in a two-alternative forced-choice task was estimated for each partial in turn. In experiment I the fundamental frequency was either 100, 200, or 400 Hz, and the complex tones contained the first 12 harmonics at equal levels of 60 dB SPL per component. The stimulus duration was 410 ms. For each fundamental the thresholds were roughly constant when expressed in Hz, having a mean value of about 4 Hz (range 2.4-7.3 Hz). In experiment II the fundamental frequency was fixed at 200 Hz, and thresholds for inharmonicity were measured for stimulus durations of 50, 110, 410, and 1610 ms. For harmonics above the fifth the thresholds increased from less than 1 Hz to about 40 Hz as duration was decreased from 1610-50 ms. For the lower harmonics (up to the fourth) threshold changed much less with duration, and for the three shorter durations thresholds for each duration were roughly a constant proportion of the harmonic frequency. The results suggest that inharmonicity is detected in different ways for high and low harmonics. For low harmonics the inharmonic partial appears to "stand out" from the complex tone as a whole. For high harmonics the mistuning is detected as a kind of "beat" or "roughness," presumably reflecting a sensitivity to the changing relative phase of the mistuned harmonic relative to the other harmonics.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Threshold↗
PubMed1985

Perceived magnitude of two-tone-noise complexes: loudness, annoyance, and noisiness.

An investigation of the perceived effects of tonal components was undertaken to establish a broader data base for quantification and prediction of annoyance of sounds containing added tones. The current study was concerned with two-tone-noise complexes. The stimuli were tone pairs added to a low-pass noise that was attenuated by 5 dB/oct above 600 Hz. Overall perceived magnitude is shown to be a function of the frequency separation (delta F) between the tonal components, tone-to-noise ratio, and the overall SPL of the noise-tone complex. Results obtained with two tones are compared to those obtained in an earlier study with single tones [R. P. Hellman, J. Acoust. Soc. Am. 75, 209-218 (1984)]. The observed effects appear relevant to the rules governing loudness summation across frequency, to measurements of psychoacoustic consonance and roughness, and to the issue of mutual masking among the component stimuli. The implications of the findings in relation to proposed tone-correction procedures are also discussed.

Acoustic Stimulation↗
PubMed1985

Steps in loudness summation.

The dependence of binaural loudness summation on interaural phase of tones ranging between 250 and 1400 Hz was investigated in a series of experiments using a loudness-matching procedure. Observers matched loudness of monaural-binaural and binaural-binaural pairs of alternating tones by adjusting the amplitude of one of the two. Adjustable and reference components of each tone pair were equal in frequency and were varied independently in interaural phase angle through the range +/- 177 degrees. For each tone frequency, steps in loudness summation of approximately 3 dB were obtained in the vicinity of a constant value of phase angle, theta t, which depends on the Hornbostel-Wertheimer constant (tau H) according to the relations theta t = 2 pi f tau H for tones of low frequency (f less than or equal to 1/2 tau H), and theta t = 2 pi(1 - f tau H) for tones of higher frequency (1/2 tau H less than or equal to f less than or equal to 1/tau H). Spatial relationships among alternating tones observed in the above conditions covaried with relative loudness in a complex manner, but exhibited qualitative changes in the vicinity of theta t.

Dominance, Cerebral↗