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PubMed1985

Auditory profile analysis: frequency, phase, and Weber's law.

This paper reports three separate experiments on different aspects of performance in auditory profile analysis. The first experiment deals with the effects of the frequency and position of an increment in a single component of a multitonal complex. The general results indicate that detection of the signal is easier for components in the mid-frequency range (around 1000 Hz) independent of signal position within the complex. The second experiment investigates the effects of relative phase of the individual components of the complex. Regardless of the number of components, our results indicate that phase has very little effect, even when different phases are selected for each presentation. The third experiment compares the detection of an increment in intensity of a single component, the traditional Weber fraction experiment, and conditions where additional components are present, a profile experiment. The detection of the increment is measured as a function of the level of the standard. The single-tone condition shows the usual near miss to Weber's law whereas the multitone condition does not. In addition, threshold for the increment is better for the multitone condition than for the single tone condition for levels of the standard up to 70 dB SPL. This last result is investigated for ten observers, five of whom were experienced in profile tasks and five of whom were not. Using a low level standard, the five experienced observers replicate the results described above. The inexperienced observers show the opposite result. On average, they are better able to detect the increment in the single-component condition.

Auditory Threshold↗
PubMed1985

Development of absolute thresholds in chickens.

Absolute auditory thresholds were estimated in chickens at 0 and 4 days after hatching. Momentary suppressions of the chicks' regular peeping, following the onset of a tone, were used as indications of stimulus detection. In the first experiment a staircase procedure was used to estimate thresholds. The absolute thresholds of both ages were the same at low frequencies (250-500 Hz), but at higher frequencies (1-2 kHz) 4-day-old chicks had lower thresholds than the 0-day-old chicks. The estimates of thresholds at 1 kHz were corroborated in the second experiment with a method of constant stimuli. A more efficient modified method of limits was used to replicate the age by frequency interaction in the third experiment. These changing thresholds are likely to reflect a developmental process somewhere in the auditory system and not some nonsensory artifact for two reasons: similar thresholds at low frequencies show that developmental differences are not due to differences in the sensitivity of the testing procedure at the two ages and thresholds obtained from the 4-day-old birds are similar to estimates from mature birds. In conclusion, responsiveness to low frequencies develops before responsiveness to higher frequencies, showing that the development of absolute thresholds is correlated with other measures of functional maturation in the auditory system.

Aging↗
PubMed1985

Gap detection in chinchillas with temporary high-frequency hearing loss.

Estimates of auditory temporal acuity were obtained from normal chinchillas by measuring their gap-detection thresholds using wideband noise over a range of intensities. Afterwards, the animals were exposed to high-intensity noise whose low-frequency cutoff was progressively lowered towards the low frequencies in five 1-oct steps. The five exposures resulted in a temporary high-frequency hearing loss that progressively spread towards the low frequencies. In addition, there was a systematic and orderly increase in the gap-detection thresholds. These results indicate that gap resolution is strongly dependent on the audibility of the high-frequency energy in the test signal.

Animals↗
PubMed1985

Thresholds for primary auditory fibers using statistically defined criteria.

The discharge behavior of auditory-nerve fibers near "threshold" was investigated in anesthetized cats using low-intensity sinusoidal stimuli presented at the respective characteristic frequencies. Particular attention was paid to fibers with "low" and "medium" rates. Estimates of threshold derived from statistically significant increases in discharge rate indicate that the average threshold values for low-spontaneous fibers are only slightly higher (ca. 5 dB) than the averages for the corresponding high-spontaneous fibers, with the medium-spontaneous fibers having intermediate averages. The difference between these average values is considerably less than the more than 20-dB difference obtained using threshold criteria based on an absolute increment in discharge rate [e.g., M. C. Liberman, J. Acoust. Soc. Am. 63, 442-455 (1978)]. The main reason for the difference between the results of the two techniques is the fact that the slopes of the rate-intensity functions for the high-spontaneous fibers are considerably steeper near "threshold" than those for fibers of the other two classes. The results are taken as supportive of a recent model of primary-fiber discharge [C. D. Geisler, Brain Res. 212, 198-201 (1981)].

Animals↗
PubMed1985

A scale for rate of tactual vibration.

Observers were asked to make estimates of the rate of mechanical vibrations presented to the finger as pulses ranging from 2 to about 300 pps. From the functions generated by this study, a set of ten values of mechanical vibration rate was selected. In a second experiment additional observers were asked to learn to identify these values of rate. Information analysis of the data showed that, when rate alone is varied, observers can identify between three and five items correctly; when rate and intensity are covaried redundantly, between five and eight items can be identified correctly. These results are viewed as supporting those from studies of the DL for rate, and as evidence for a limited but useful role of rate discrimination in tactile displays of acoustic signals.

Adolescent↗
PubMed1985

Additivity of simultaneous masking, revisited.

Lutfi [J. Acoust. Soc. Am. 73, 262-267 (1983)] compared simultaneous masking functions (signal threshold versus masker level) for individual sinusoidal and narrow-band noise maskers, and for those maskers presented in pairs. Lutfi found that the pairs of maskers produced 10-17 dB "excess" masking over that predicted from the linear sum of their individual masking and explained the results in terms of a model in which the effects of the maskers are summed after undergoing independent compressive transformations. This paper describes experiments similar to those of Lutfi, and presents evidence suggesting that Lutfi's results may have been influenced by two factors: (1) combination-product detection, and (2) the use of different detection cues for single maskers and for pairs of maskers. Experiment I showed that when the stimulus conditions were chosen so as to minimize the likelihood of combination-product detection, "excess" masking was only 3-5 dB. Experiment II supported the idea that for a single narrow-band noise masker, subjects make use of the relatively slow envelope fluctuations to enhance performance. When two independent narrow-band noise maskers are added, the effectiveness of this cue is reduced, and between 3 and 9 dB of "excess" masking occurs. When the two noises are derived from the same source, and have correlated envelope fluctuations, no "excess" masking occurs. The results indicate that Lufti's compressive-nonlinearity model clearly fails in some situations.

Auditory Threshold↗
PubMed1985

Intensity difference limens at high frequencies.

Thresholds for amplitude modulation detection were obtained from four subjects at frequencies of 2, 4, 6, 8, and 10 kHz for sensation levels of 15, 30, 45, and 60 dB and modulation rates of 2, 4, and 8 Hz. High-frequency difference limens calculated from amplitude modulation thresholds were found to change nonmonotonically as a function of sensation level, independent of modulation rate. This nonmonotonic relation stemmed mainly from a gradual reduction of the difference limen at the lowest sensation level with increasing frequency. Difference limens for pulsed tone discrimination were also measured in two of the subjects at 2, 6, and 10 kHz and sensation levels of 15, 30, 45, and 60 dB. The relation between intensity discrimination and sensation level was similar to that found for amplitude modulation detection. These findings are interpreted as indicating that the nonmonotonic relation between sensation level and intensity resolution is a general characteristic of stimulus processing at higher frequencies.

Adult↗
PubMed1985

Lateralization of sinusoidally amplitude-modulated tones: effects of spectral locus and temporal variation.

It has long been recognized that listeners are sensitive to interaural temporal disparities (ITDs) of low-frequency (i.e., below 1600 Hz) stimuli. Within the last three decades, it has often been demonstrated that listeners are also sensitive to ITDs within the envelope of high-frequency, complex stimuli. Because these studies, for the most part, employed discrimination tasks, few data exist concerning the extent of laterality produced by ITDs as a function of the spectral locus of the stimulus. To this end, we employed an acoustic "pointing" task in which listeners varied the interaural intensity difference of a 500-Hz narrow-band noise (the pointer) so that it matched the intracranial position of a second, experimenter-controlled stimulus (the target). Targets were sinusoidally amplitude-modulated tones centered on 500 Hz, 1, 2, 3, or 4 kHz and modulated at rates ranging from 50 to 800 Hz. Targets were presented with either the entire waveform delayed or with only the envelope delayed. Our results suggest that: (1) for low-frequency targets, lateralization is influenced by ITDs in the envelope but is dominated by ITDs in the fine structure; (2) for high-frequency targets, envelope-based delays produce displacements of the acoustic images which are affected greatly by the rate of modulation; rather large extents of laterality could be produced with high rates of modulation; these data are consistent with those obtained previously in discrimination experiments; (3) for low rates of modulation (e.g., 100 Hz), delays of the entire waveform (both envelope and fine structure) produce much greater displacements of the acoustic image for low-frequency than for high-frequency targets (where fine-structure-based cues are not utilizable); (4) there appear to be no consistent relations among extent of laterality, rate of modulation, and the frequency of the carrier within and across listeners.

Adult↗
PubMed1985

Masking-period patterns: presentation of a model compatible with an enlarged set of psychophysical and physiological results.

Masking-period patterns (MPP) have been regarded by Zwicker [J. Acoust. Soc. Am. 59, 166-175 (1976)] as psychoacoustic equivalents of period histograms (PH) measured in auditory neurons. Various models have been proposed in the literature to account for his results. We present here a set of results on the MPP produced by a 40-Hz triangular masker that cannot be reproduced by any of these models. This leads to the elaboration of a new model for predicting MPP assuming the existence of nonlinearities in the basilar membrane, and based on neural fast adaptation and rectification, and a simple detection device. This model is shown to be able to account for the whole set of available results, and thus to provide a good basis for the use of MPP as a psychoacoustic tool for the study of PH.

Humans↗
PubMed1986

Loudness summation, masking, and temporal interaction for sensations produced by electric stimulation of two sites in the human cochlea.

Three psychophysical studies were conducted on two multichannel cochlear implant patients. The first study investigated the amount of loudness summation as a function of the spatial separation between two bipolar electrode pairs in the cochlea. Summation was found to increase in an orderly way with the separation between the two electrode pairs. This observation suggested that loudness was related to the distribution of discharge rate of auditory neurons along the cochlea for electric stimulation, and a model of loudness summation formulated on the basis of a functional relationship between loudness and the discharge rate distribution was proposed. The second study investigated the possibility of estimating the discharge rate distribution by means of masking. The amount of masking was found to decrease in an orderly fashion with the spatial separation between the masker and probe electrode pairs. This pattern of masking is consistent with the physiological and modeling observation that the current and neural discharge rate distributions produced by an electrode pair (masker) in the cochlea are approximately bell shaped with gradually decaying borders. The third study investigated the just-discriminable changes in the temporal delay between two interleaving pulse trains delivered, respectively, to two electrode pairs in the cochlea. Discrimination performance was found to decrease with the spatial separation between the two electrode pairs.

Cochlea↗
PubMed1986

Frequency selectivity of single cochlear-nerve fibers based on the temporal response pattern to two-tone signals.

The physiological basis of auditory frequency selectivity was investigated by recording the temporal response patterns of single cochlear-nerve fibers in the cat. The characteristic frequency and sharpness of tuning was determined for low-frequency cochlear-nerve fibers with two-tone signals whose frequency components were of equal amplitude and starting phase. The measures were compared with those obtained with sinusoidal signals. The two-tone characteristic frequency (2TCF) is defined as the arithmetic-center frequency at which the fiber is synchronized to both signal frequencies in equal measure. The 2TCF closely corresponds to the characteristic frequency as determined by the frequency threshold curve. Moreover, the 2TCF changes relatively little (2%-12%) over a 60-dB intensity range. The 2TCF generally shifts upward with increasing intensity for cochlear-nerve fibers tuned to frequencies below 1 kHz and shifts downward as a function of intensity for units with characteristic frequencies (CF's) above 1 kHz. The shifts in the 2TCF are considerably smaller than those observed with sinusoidal signals. Filter functions were derived from the synchronization pattern to the two-tone signal by varying the frequency of one of the components over the fiber's response area while maintaining the other component at the 2TCF. The frequency selectivity of the two-tone filter function was determined by dividing the vector strength to the variable frequency signal by the vector strength to the CF tone. The filter function was measured 10 dB down from the peak (2T Q 10 dB) and compared with the Q 10 dB of the frequency threshold curve. The correlation between the two measures of frequency selectivity was 0.72. The 2T Q 10 dB does change as a function of intensity. The magnitude and direction of the change is dependent on the sharpness of tuning at low and moderate sound-pressure levels (SPL's). The selectivity of the more sharply tuned fibers (2T Q 10 dB greater than 3) diminishes at intensities above 60 dB SPL. However, the broadening of selectivity is relatively small in comparison to discharge rate-based measures of selectivity. The selectivity of the more broadly tuned units remains unchanged or improves slightly at similar intensity levels. The present data indicate that the frequency selectivity and tuning of low-frequency cochlear-nerve fibers are relatively stable over a 60-dB range of SPL's when measured in terms of their temporal discharge properties.

Animals↗
PubMed1986

Critical modulation frequency based on detection of AM versus FM tones.

The ratios between the modulation index (eta) for just noticeable FM of a sinusoidally modulated pure tone and the degree of modulation (m) for just noticeable AM at the same carrier and the same modulation frequency were measured at carrier frequencies of 0.125, 0.25, 0.5, 1, 2, 4, and 8 kHz. Signal levels were 20 dB SL and 50 dB SPL or 80 dB SPL. At low modulation frequencies, for example, 8 Hz, AM and FM elicit very different auditory sensations (i.e., a fluctuation in loudness or pitch, respectively). In this case, eta and m show different values for just noticeable modulation. Since both stimuli have almost equal amplitude spectra if eta equals m (m less than 0.3), the difference in detection thresholds reflects differences in the phase relation between carrier and sidebands in AM and FM. With increasing modulation frequency, the eta-m ratio decreases and reaches unity at a modulation frequency called the "critical modulation frequency" (CMF). At modulation frequencies above the CMF, the same modulation thresholds are obtained for AM and FM. Therefore, it can be concluded that the difference in phase between the two types of stimuli is not perceived in this range. At center frequencies below 1 kHz, where phase errors caused by headphones and ear canal presumably are small, the CMF is useful in estimating critical bandwidth.

Adult↗
PubMed1986

Development of auditory-evoked potentials in the cat. I. Onset of response and development of sensitivity.

Auditory-evoked potentials, originating from the brain stem and the forebrain, were studied in 30 unanesthetized kittens during the first 3 months of postnatal life, and from a smaller set of animals before and after surgical exposure of their tympanic membranes. In intact animals, responses to 135-dB peak SPL clicks were first reliably discernible on the seventh postnatal day; when stimuli were presented directly to the exposed tympanic membrane, responses were observed several days earlier. Responses progressed through three stages during maturation: an early period of gross insensitivity during which responses are evoked only by high-intensity stimuli and whose response thresholds remain essentially constant (week 1); a middle period characterized by rapid acquisition of sensitivity to near-adult values (week 2); and a late period during which adult thresholds and latencies are acquired. A sequential stage model of threshold maturation is proposed, in which thresholds decline linearly during stage two and exponentially during stage three. It is hypothesized that mechanical reorganization of the cochlea during the first 2 to 3 postnatal weeks and development of the stria vascularis are primarily responsible for the linear stage, and that neural factors primarily underlie the exponential stage and account for the gradual acquisition of adult thresholds. Rates of maturation for brain stem responses are frequency dependent, with responses to high frequencies achieving adult thresholds earlier than those to low frequencies.

Aging↗
PubMed1986

Development of auditory-evoked potentials in the cat. II. Wave latencies.

Brain stem and forebrain auditory-evoked potentials were studied parametrically during the first 90 postnatal days in unanesthetized kittens using tonal and click stimuli. This paper describes changes that occur in transmission time through the auditory pathway during development by analyses of the maturational time courses of latencies associated with waves of both auditory brain stem responses (ABR's) and late-occurring auditory-evoked potentials (AER's), recorded subdermally from the vertex. In response to click stimuli, ABR latencies were found to decay rapidly early in postnatal life and more slowly after the third postnatal week. Those trends were modeled as a two-stage sequential process, with a linear stage occurring between 7 and 18 postnatal days followed by an exponential stage during which adult latencies were achieved. AER latencies changes during development were less complicated, and followed a single-stage exponential time course. When threshold influences were taken into account--that is, when data were adjusted so that sensation level (SL) was constant across age--the latency-maturation curves associated with all ABR waves were adequately described by a single exponential, and latencies recorded from young animals were substantially shorter than latencies associated with the same aged animals when analyses were carried out with constant sound-pressure level (SPL) stimuli across age. In addition, the difference function, generated when isoasymptotic SPL and SL latency versus age functions were subtracted from one another, was also represented by an exponential curve, suggesting that at least two processes underlie the latency decay that occurs during postnatal development. Evoked responses to tonal stimuli throughout development were consistent with the basoapical developmental gradient that is observed anatomically.

Aging↗
PubMed1986

Development of auditory-evoked potentials in the cat. III. Wave amplitudes.

Amplitudes of auditory-evoked brain stem response (ABR) and late-occurring auditory-evoked potential (AER) components were recorded from kittens between birth and 90 postnatal days. All ABR and AER wave amplitudes increased during the first postnatal month. Wave amplitudes exhibited nonmonotonic growth with increasing age, attaining a maximum at 40-60 days of age, after which amplitudes decreased. Amplitudes of waves originating in the auditory nerve matured somewhat faster than waves originating in the brain stem and forebrain, and the order in which waves reached maturity was roughly the reverse order of the latencies of their peaks. Input-output curves for ABR and AER waves displayed nonmonotonic behavior that varied as a function of postnatal age. Wave amplitudes recorded from adult cats increased between threshold and 70 dB SPL, then decreased between 70 and 100 dB SPL, and rapidly increased above 100 dB SPL. The intensity corresponding to the change from increasing to decreasing amplitudes was higher for younger animals and achieved adult values during the first postnatal month.

Aging↗
PubMed1986

Absolute intensity discrimination using two responses.

The observer was asked to judge whether a comparison sound was more or less intense than a standard sound of 60 dB SPL. The sounds were broadband noises of 100-ms duration. The independent variables were the range of intensities used in the set of comparison sounds and the presence or absence of feedback. The main dependent variable was the variability of such judgments, which was measured from the psychometric function. The variability, measured in terms of the Weber function, increased from about 1.5 to 4 dB when the stimulus range changed from 10 to 60 dB. Increases in stimulus range increased the variability of the binary judgments in this task, as they had in previous experiments where multiple responses were required. Feedback improved performance primarily at the largest ranges. Only a small fraction of these changes in variability stems from sequential effects.

Acoustic Stimulation↗
PubMed1986

On the relations of intensity jnd's to loudness and neural noise.

It is shown experimentally that, in contradiction of the fundamental concept of Fechner's law, the intensity jnd for auditory sinusoidal signals follows loudness, rather than its derivative with respect to sound intensity. The evidence is obtained by comparing the jnd's of a population with normal hearing to those of a population with hearing loss accompanied by loudness recruitment. Although the recruitment increases the slope of the loudness function, the jnd's of both populations were found to be practically equal when the loudness were equal. The phenomenon is accounted for mathematically by assuming that psychophysically relevant neural noise depends not only on the magnitude of loudness, but also on its derivative with respect to sound intensity. A related derivation accounts for the near miss to Weber's law.

Adult↗
PubMed1986

Level discrimination of tones as a function of duration.

Difference limens for level [delta Ls (dB) = 20 log[p + delta p)/p), where p is the pressure] were measured as a function of duration for tones at 250, 500, and 8000 Hz. Stimulus durations ranged from 2 ms to 2 s, and the stimulus power was held constant. Rise and fall times were 1 ms. The interstimulus interval was 250 ms. At each frequency, three levels were tested: 85, 65, and approximately 40 dB SPL. An adaptive two-alternative forced-choice procedure with feedback was used. For three normal listeners, delta Ls decreased as duration increased, up to at least 2 s, except at 250 Hz. At 250 Hz, delta L stopped decreasing at durations between 0.5 and 1 s. In a double logarithmic plot of delta L versus duration, the rate of decrease is generally well fitted by a sloping line. The average slope is -0.28; it is steeper at high levels than at low levels. Because the average slope is shallower than the -0.5 slope predicted for an optimum detector, it may be that fast adaptation of auditory-nerve activity and/or memory effects interfere with level discrimination of long-duration tones. Finally, the delta Ls at 8 kHz decreased nonmonotonically with increasing level.

Adult↗