Psychoacoustical Tuning Curves Research Articles

The effects of preceding sound on psychoacoustic tuning curves measured in simultaneous and forward masking

The medial olivocochlear reflex (MOCR) decreases the gain of the cochlear active process in response to sound. We have used psychoacoustic techniques to show behavioral effects of gain reduction, which could be consistent with the MOCR. We have used paradigms understood to measure frequency selectivity and the input/output function at the level of the cochlea using stimuli (masker and signal) that should be too short to evoke the MOCR. A precursor sound is then presented before these stimuli to evoke the MOCR. Our most recent studies have used forward masking, to avoid the complicating effects of suppression. The current study was designed to examine the effects of suppression, by comparing the effects of a precursor on frequency selectivity measured using forward masking and simultaneous masking. Psychoacoustic tuning curves were measured using simultaneous and forward masking, with and without a precursor. This allowed us to measure the change in tuning with and without the presence of suppression. Broadband precursors and tonal precursors at masker frequencies were measured because previous studies have shown broadening with broadband precursors and sharpening when tonal maskers are the precursors. Results will be discussed in the context of current understanding of the MOCR.

Relationship between irregularities in spontaneous otoacoustic emissions suppression and psychophysical tuning curves.

The suppression of spontaneous otoacoustic emissions (SOAEs) allows the objective evaluation of cochlear frequency selectivity by determining the suppression tuning curve (STC). Interestingly, some STCs have additional sidelobes at the high frequency flank, which are thought to result from interaction between the probe tone and the cochlear standing wave corresponding to the SOAE being suppressed. Sidelobes are often in regions of other neighboring SOAEs but can also occur in the absence of any other SOAE. The aim of this study was to compare STCs and psychoacoustic tuning curves (PTCs). Therefore, STCs and PTCs were measured in: (1) subjects in which the STC had a sidelobe, and (2) subjects without STC sidelobes. Additionally, PTCs were measured in subjects without SOAEs. Across participant groups, the quality factor Q10dB of the PTCs was similar, independently from whether SOAEs were present or absent. Thus, the presence of an SOAE does not provide enhanced frequency selectivity at the emission frequency. Moreover, both PTC and STC show irregularities, but these are not related in a straightforward way. This suggests that different mechanisms cause these irregularities.

Cochlear Implant: Effect of the Number of Channel and Frequency Selectivity on Speech Understanding in Noise Preliminary Results in Simulation with Normal-Hearing Subjects

The cochlear implant is the most successful implantable device for the rehabilitation of profound deafness. However, in some cases, the electrical stimulation delivered by the electrode can spread inside the cochlea creating overlap and interaction between frequency channels. By using channel-selection algorithms like the “nofm” coding-strategy, channel interaction can be reduced. This paper describes the preliminary results of experiments conducted with normal hearing subjects (n = 9). Using a vocoder, the present study simulated the hearing through a cochlear implant. Speech understanding in noise was measured by varying the number of selected channels (“nofm”: 4, 8, 12 and 16of20) and the degree of simulated channel interaction (“Low”, “Medium”, “High”). Also, with the vocoder, we evaluated the impact of simulated channel interaction on frequency selectivity by measuring psychoacoustic tuning curves. The results showed a significant average effect of the signal-to-noise ratio (p < 0.0001), the degree of channel interaction (p < 0.0001) and the number of selected channels, (p = 0.029). The highest degree of channel interaction significantly decreases intelligibility as well as frequency selectivity. These results underline the importance of measuring channel interaction for cochlear implanted patients to have a prognostic test and to adjust fitting methods in consequence. The next step of this project will be to transpose these experiments to implant users, to support our results.

The Physiologic and Psychophysical Consequences of Severe-to-Profound Hearing Loss.

Substantial loss of cochlear function is required to elevate pure-tone thresholds to the severe hearing loss range; yet, individuals with severe or profound hearing loss continue to rely on hearing for communication. Despite the impairment, sufficient information is encoded at the periphery to make acoustic hearing a viable option. However, the probability of significant cochlear and/or neural damage associated with the loss has consequences for sound perception and speech recognition. These consequences include degraded frequency selectivity, which can be assessed with tests including psychoacoustic tuning curves and broadband rippled stimuli. Because speech recognition depends on the ability to resolve frequency detail, a listener with severe hearing loss is likely to have impaired communication in both quiet and noisy environments. However, the extent of the impairment varies widely among individuals. A better understanding of the fundamental abilities of listeners with severe and profound hearing loss and the consequences of those abilities for communication can support directed treatment options in this population.

Contralateral efferent reflex effects on threshold and suprathreshold psychoacoustical tuning curves at low and high frequencies.

Medial olivocochlear efferent neurons can control cochlear frequency selectivity and may be activated in a reflexive manner by contralateral sounds. The present study investigated the significance of the contralateral medial olivocochlear reflex (MOCR) on human psychoacoustical tuning curves (PTCs), a behavioral correlate of cochlear tuning curves. PTCs were measured using forward masking in the presence and in the absence of a contralateral white noise, assumed to elicit the MOCR. To assess MOCR effects on apical and basal cochlear regions over a wide range of sound levels, PTCs were measured for probe frequencies of 500 Hz and 4 kHz and for near- and suprathreshold conditions. Results show that the contralateral noise affected the PTCs predominantly at 500 Hz. At near-threshold levels, its effect was obvious only for frequencies in the tails of the PTCs; at suprathreshold levels, its effects were obvious for all frequencies. It was verified that the effects were not due to the contralateral noise activating the middle-ear muscle reflex or changing the postmechanical rate of recovery from forward masking. A phenomenological computer model of forward masking with efferent control was used to explain the data. The model supports the hypothesis that the behavioral results were due to the contralateral noise reducing apical cochlear gain in a frequency- and level-dependent manner consistent with physiological evidence. Altogether, this shows that the contralateral MOCR may be changing apical cochlear responses in natural, binaural listening situations.

Associations and Dissociations Between Psychoacoustic Abilities and Speech Perception in Adolescents With Severe-to-Profound Hearing Loss

To clarify the relationship between psychoacoustic capabilities and speech perception in adolescents with severe-to-profound hearing loss (SPHL). Twenty-four adolescents with SPHL and young adults with normal hearing were assessed with psychoacoustic and speech perception tests. The psychoacoustic tests included gap detection (GD), difference limen for frequency, and psychoacoustic-tuning curves. To assess the perception of words that differ in spectral and temporal cues, the speech tests included the Hebrew Early Speech Perception test and the Hebrew Speech Pattern Contrast test (L. Kishon-Rabin et al., 2002). All tests were conducted for the listeners with normal hearing at low and high presentation levels and for the participants with SPHL at 20 dB SL. Only GD thresholds were comparable across the 2 groups at similar presentation levels. Psychoacoustic performance was poorer in the group with SPHL, but only selected tests were correlated with speech perception. Poor GD was associated with pattern perception, 1-syllable word identification, and final voicing subtests. Speech perception performance in adolescents with SPHL could not be predicted solely on the basis of spectral and temporal capabilities of the auditory system. However, when the GD threshold was greater than 40 ms, speech perception skills were predictable by psychoacoustic abilities.

Use of a high-level language in high performance biomechanics simulations

Distortion product otoacoustic emission (DPOAE) iso-suppression tuning curves (STC) were generated in 15 normal-hearing adults and 16 healthy term-born neonates for three f2 frequencies. The 2f1-f2 DPOAE was elicited using f2f1 = 1.2, L1 = 65 and L2 = 50 dB SPL. A suppressor tone was presented at frequencies ranging from 1 octave below to 1/4 octave above f, and varied in level until DPOAE amplitude was reduced by 6 dB. The suppressor level required for 6 dB suppression was plotted as function of suppressor frequency to generate a DPOAE STC. Forward-masked psychoacoustic tuning curves (PTO were obtained for three of the adult subjects. Results indicate that DPOAE STCs are stable and show minimal inter- and intea-subject variability. The tip of the STC is consistently centered around the f, region and STCs are similar in shape, width (Q10) and slope to VIIlth-nerve TCs. PTCs and STCs measured in the same subject showed similar trends, although PTCs had narrower width and steeper slope. Neonatal STCs were recorded at 3000 and 6000 Hz only and were comparable in shape, width and slope to adult STCs. Results suggest: (1) suppression of the 2f1-f2 DPOAE may provide an indirect measure of cochlear frequency resolution in humans and (2) cochlear tuning, and associated active processes in the cochlea, are mature by term birth for at least mid- and high-frequencies. These results provide significant impetus for continued study of DPOAE suppression as a means of evaluating cochlear frequency resolution in humans.

Effects of efferent acoustic reflex activation on psychoacoustical tuning curves in humans

ConclusionsThe results show that, in humans, activation of the contralateral EAR makes the PTC narrower at 1 kHz but wider at 4 kHz. These data are consistent with those reported previously in animals and demonstrate that, during medial efferent stimulation in humans, frequency resolution is improved at low frequencies but impaired at high frequencies.ObjectiveTo evaluate, in humans, the effect of activation of the contralateral efferent acoustic reflex (EAR) on the psychoacoustical tuning curves (PTCs) recorded for 1- and 4-kHz probe tones.Material and methodsTen young (20–30 years) volunteers served as subjects. They had normal hearing (thresholds<20 dB HL in the frequency range 0.25–8 kHz) and a functioning EAR (contralateral suppression of transient-evoked otoacoustic emissions≥0.8 dB). Frequency resolution was evaluated using PTCs. PTCs were recorded at 1 and 4 kHz using a simultaneous masking method. Q10 and Q20 were calculated as the ratio between the test frequency and the bandwidth of the PTC at 10 and 20 dB above the tip of the curve, respectively. The EAR was activated with a 40-dB SL contralateral narrow-band noise centered on the characteristic frequency of the PTC (1 or 4 kHz). Q10 and Q20 were measured in the presence and absence of the contralateral noise.ResultsActivation of the EAR led to a significant increase (p<0.001) in Q10 at 1 kHz and a significant decrease (p<0.001) at 4 kHz. Changes in the value of Q20 were not significant.

Perception of speech and non-speech sounds by listeners with real and simulated sensorineural hearing loss

The effects of sensorineural and simulated hearing loss on the perception of speech and non-speech sounds are evaluated and compared. Two simulations of hearing loss are considered: one introduces additive masking noise to elevate the detection thresholds of listeners with normal hearing, the other applies multiband dynamic expansion to attenuate sound components towards these detection thresholds. Measures of speech perception are derived from intelligibility tests for consonant-vowel syllables presented in a background of speech-spectrum noise. The perception of non-speech sounds was evaluated through measurements of the detection of tones in quiet and in the presence of broadband and narrowband masking noise, psychoacoustic tuning curves measured under forward masking conditions, and intensity discrimination for tone pulses. For mild and moderate hearing losses, both types of simulation alter the perception of speech in noise in a manner similar to sensorineural impairment. These simulations also produce effects similar to sensorineural impairment on the detection of tones in quiet and on simultaneous and forward masking. The expansion simulation tends to improve the ability to discriminate tone intensities, an effect generally not seen in listeners with sensorineural impairments.

Evaluation of simulations of the effects of hearing loss produced by combinations of dynamic expansion and spectral smearing

By processing sounds with combinations of multiband expansion (MBE) and spectral smearing (SS), listeners with normal hearing can experience the elevated thresholds, abnormal growth of loudness, and reduced frequency selectivity similar to those of listeners with sensorineural hearing impairments. The effects of simulations of flat 40-dB losses produced by such combinations on masking patterns and loudness summation, and of simulations of a more severe loss on speech perception in noise, were studied. Both MBE and SS reduce frequency selectivity as measured by masking patterns for tones produced by narrow-band noise, and both broaden forward-masked tuning curves for tones. However, for equally loud probe tones, MBE elevates the tips of psychoacoustic tuning curves much more than SS. As measured by loudness balances between narrow-band and wideband noises, MBE reduces loudness summation much more than SS. The effects of MBE and SS simulations of a severe hearing loss on consonant identification in speech-shaped noise depend on the SNR, with MBE more detrimental at high SNR and SS more detrimental at low SNR. MBE tends to degrade reception of cues for voicing; SS, cues for place of articulation; both degrade cues for manner of articulation. [Work supported by NIH.]

Effects of changes of the spectral masking slope on sound quality and clarity of music sounds in the normal and impaired ear

Reduced frequency selectivity as occurs in the cochlear impaired ear has been shown to be a main factor for degraded speech perception [J. M. Festen and R. Plomp, J. Acoust. Soc. Am. 76, 652–662 (1983)]. It is also assumed to have negative effects on music perception. In this paper the hypothesis is tested that the loudness relations between spectral peaks and nonmasked lower-level components, which depend on the individual fre- quency selectivity, are important for (a) subjective sound quality (listening comfort) and (b) clarity, as measured in terms of detectability of altered notes in music excerpts. In order to test this hypothesis a signal processing algorithm has been utilized which enhances or suppresses the lower-level spectral components of a complex signal according to a masking function. Processed signals have been presented to normal-hearing and cochlear-impaired subjects. Results revealed that subjects with reduced frequency selectivity—as measured with psychoacoustical tuning curves—tend to prefer music signals with enhanced lower-level components. In the clarity experiment, results obtained with hearing-impaired subjects show improved detectability with suppression of the lower-level components (increase of spectral contrasts). [Work supported by Austrian Academy of Sciences.]

Distortion product otoacoustic emission suppression tuning curves in human adults and neonates

Distortion product otoacoustic emission (DPOAE) iso-suppression tuning curves (STC) were generated in 15 normal-hearing adults and 16 healthy term-born neonates for three f 2 frequencies. The 2f 1-f 2 DPOAE was elicited using f 2 f 1 = 1.2 , L1 = 65 and L2 = 50 dB SPL. A suppressor tone was presented at frequencies ranging from 1 octave below to 1/4 octave above f, and varied in level until DPOAE amplitude was reduced by 6 dB. The suppressor level required for 6 dB suppression was plotted as function of suppressor frequency to generate a DPOAE STC. Forward-masked psychoacoustic tuning curves (PTO were obtained for three of the adult subjects. Results indicate that DPOAE STCs are stable and show minimal inter- and intea-subject variability. The tip of the STC is consistently centered around the f, region and STCs are similar in shape, width ( Q 10) and slope to VIIlth-nerve TCs. PTCs and STCs measured in the same subject showed similar trends, although PTCs had narrower width and steeper slope. Neonatal STCs were recorded at 3000 and 6000 Hz only and were comparable in shape, width and slope to adult STCs. Results suggest: (1) suppression of the 2f 1-f 2 DPOAE may provide an indirect measure of cochlear frequency resolution in humans and (2) cochlear tuning, and associated active processes in the cochlea, are mature by term birth for at least mid- and high-frequencies. These results provide significant impetus for continued study of DPOAE suppression as a means of evaluating cochlear frequency resolution in humans.

The development of frequency resolution in humans as revealed by the auditory brain-stem response recorded with notched-noise masking

Studies of tuning in infants have reported that auditory brain-stem response (ABR) tuning curves generated using low-frequency probes are adultlike by 3 months of age while high-frequency tuning curves remain immature [Folsom and Wynne, J. Acoust. Soc. Am. 81, 412-417 (1987)]. Behavioral studies have similarly reported adultlike low-frequency psychoacoustic tuning curves by 3 months with high-frequency tuning curves immature until approximately 6 months of age [L. Olsho, Infant Behav. Dev. 8, 371-384 (1985); Spetner and Olsho, Child Dev. 61, 632-652 (1990); Schneider et al., J. Exp. Psych.: Human Percept. Perform. 16, 642-652 (1990)]. Prior to this experiment, there have been no ABR studies of the development of frequency resolution for infants older than 3 months. In this study, notched-noise tuning functions were constructed from wave-V amplitude data for 3-month-old, 6-month-old, and adult subjects. Tone-pip stimuli at 1000, 4000, and 8000 Hz (50 dB nHL) were presented simultaneously with notched-noise masking centered at frequencies related to the tone-pip frequency (1/3-oct intervals above and below the probe frequency). By plotting wave-V amplitude across notched-noise center frequency, isointensity tuning functions were generated for the three subject groups at the three probe frequencies. Auditory filter width (Q) and slope (dB/oct) were measured from each notched-noise tuning function in order to qualify degree of tuning. Consistent with previous studies, results showed that 3-month-old infants do not have adultlike tuning for high-frequency stimulation (8000 Hz). In contrast, by 6 months of age, tuning-function width (Q) is adultlike for both high- and low-frequency probes. These results, combined with previously reported evidence that the human cochlea is fully tuned at birth [Abdala et al., submitted to Hear. Res. (1995); Bargones and Burns, J. Acoust. Soc. Am. 83, 1809-1816 (1988)], suggest that immaturities in the auditory-neural system contribute to the broad high-frequency tuning consistently observed in 3-month-old human infants.

Effects of Cochlear Impairment and Equivalent-Threshold Masking on Psychoacoustic Tuning Curves: Courbes d'accord psychoacoustiques chez les mal-entendants et chez les normaux en écoute masquée

Psychoacoustic tuning curves in simultaneous masking were measured in three groups: listeners with hearing impairment of primarily cochlear origin, normal listeners with equivalent-threshold masking (ETM) and normal listeners tested in the quiet. ETM was produced by presenting a continuous background noise that was spectrally shaped to yield masked thresholds within 3 dB of each impaired listener's quiet thresholds. For the tuning curves, the level of a 50-Hz-wide noise band necessary to mask a 10-dB SL tone was measured for six masker frequencies. Results under ETM indicate that the shape of the tuning curve depends not only on masked threshold at the probe frequency but also on the spectral shape of the masker. Tuning curves are abnormally broad in some impaired listeners even when the effects of their elevated thresholds, audiometric configuration and altered intensity perception are taken into account by comparisons with normal listeners with ETM.

Frequency selectivity and psychoacoustic tuning curves in old age

Frequency selectivity represents an important contributory factor in the understanding of human speech. It refers to the ability of the ear to discriminate between two simultaneously occurring sounds of different spectral composition. The capabilities of frequency selection, time pattern analysis, and information processing can be determined generally only by speech audiometry. Schorn and co-workers (1977) published a simplified method for audiological investigations whereby results obtained at two different frequency values are sufficient. The test tone frequencies of 0.5 and 4 kHz were selected because they are representative of the frequency range of normal speech. To determine the influence of ageing on frequency selectivity we investigated three groups of patients between the ages of 20-30, 40-50 and 60-70 years. All of the subjects had normal hearing according to ISO 7029 standards. The measurements of pure-tone audiometry, speech audiometry, and the psychoacoustic tuning curves were performed sequentially on the same day. The influence of ageing on frequency selectivity mainly concerns frequencies above 2 kHz. This is related to the progressive loss of outer hair cells in the basal parts of the cochlea in old age. Our investigations show that particular attention must be paid to a loss of frequency selectivity in old age. This becomes evident mainly after the 60th year. Frequency selectivity is not significantly disturbed before that age, although pure tone audiograms show high frequency inner ear hearing loss earlier in life.

The Effect of Quinine on Psychoacoustic Tuning Curves, Stapedius Reflexes and Evoked Otoacoustic Emissions in Healthy Volunteers

Quinine causes reversible hearing loss, closely related to the quinine plasma concentration. The effects of quinine on psychoacoustic tuning curves, stapedius reflex thresholds and evoked otoacoustic emissions were studied in healthy volunteers. The tuning curves became shallower, whereas reflex thresholds were unaffected. The shift in the emission thresholds paralleled that of the pure-tone thresholds. There were also qualitative changes in the emissions: 1) the exponent of the stimulus-response function changed from 0.34 to 0.56; 2) decay time shortened; 3) the power spectrum shifted towards lower frequencies. The results are discussed in relation to various aspects of cochlear performance and are suggested to depend on an outer hair cell dysfunction.

Frequency resolution as a function of hearing threshold level and age

Frequency resolution ability was measured using a psychoacoustical tuning curve (PTC) or a notch-noise technique in two population samples. The first sample incorporated 1764 subjects with various degrees of sensorineural hearing impairment and ranging in age from 17-80 years. The second sample included 240 subjects aged between 50 and 75 years, carefully balanced in terms of impairment and age to avoid confounding between these two variables. In both samples, frequency resolution ability declined with increasing hearing threshold level (HTL), as measured by either method. In a subsample tested with both methods, the correlation between the two was only modest. After accounting for HTL, there was a minor dependence of frequency resolution on age, older subjects having poorer frequency resolution once HTL had been accounted for. No addition to the explained variance was achieved by taking sex, occupational group, or audiogram slope into account. Despite the documented reproducibility of the measures, much of the variance in the frequency resolution measurements remained unrelated to HTL or age.

Speech Recognition in Noise, Temporal and Spectral Resolution in Normal and Impaired Hearing.

A battery of tests for the evaluation of temporal (forward masking) and spectral (detection of frequency change; critical band for masking; psychoacoustic tuning curve) resolution in hearing with regard to the importance for speech recognition in noise has been applied to two groups of subjects. One group of 10 listeners had normal hearing, while the other consisted of 11 subjects with moderate, sloping sensorineural hearing loss. Significant differences were found between the two groups in all parameters except critical bandwidth for masking. Correlation analysis on the test results from the combined groups of subjects showed that speech recognition in noise was best corrected with the average hearing threshold levels at 2 and 4 kHz, followed by forward masking and psychoacoustic tuning curves at 4 kHz. The correlation coefficients were approximately 0.7, 0.6 and 0.55, respectively. Detection of frequency change and critical bandwidth show the lowest correlations to speech recognition in noise.

Residual frequency selectivity in the profoundly hearing-impaired listener

The extent to which auditory frequency analysis is retained in profoundly hearing-impaired listeners has major implications for hearing aid design. We have measured simplified psychoacoustic tuning curves in nine such listeners, using sinusoidal probes at 125 and 250 Hz, and 80-Hz wide narrow-band noise maskers. Two listeners showed PTCs at 125 and 250 Hz whose shapes were independent of probe frequency and parallel to their absolute thresholds, indicating the complete absence of frequency selectivity. Seven listeners showed evidence of frequency selectivity at 125 or 250 Hz or at both frequencies; at 250 Hz, frequency selectivity was evident in the six listeners whose 250-Hz hearing level was 95 dB or less, but not in the listeners with 250 Hz hearing levels above 95 dB. Where conventional 'v'-shaped PTCs were observed, estimated 3-dB auditory filter bandwidths were two to three times larger than those typically found in normal listeners. Notched-noise masking results at 250 Hz from the least hearing-impaired listener gave an estimated 3-dB bandwidth in reasonable agreement with that from the same listener's PTC data. Listeners who retain some frequency selectivity are able to make some use of first formant information in vowel identification, and preliminary results from one patient showed the ability to distinguish a variety of noise spectra. Both of these abilities could be of potential importance as a basis for the recoding of speech spectral patterning through stimulation matched to the listener's residual frequency selectivity.

Auditory frequency selectivity and tinnitus.

In the majority of cases tinnitus has a high pitch and can be matched rather precisely to an objective high frequency sound. However, it is well known that tinnitus can be masked by different tones without any frequency selectivity. We wondered whether objective tones matched to tinnitus would show a more significant deterioration of frequency selectivity than could be expected from any associated hearing loss. Psychoacoustic tuning curves were obtained using simultaneous pure-tone masking and revealed a broadening of frequency selectivity. In cases of comparable bilateral hearing losses with unilateral tinnitus, the broadening associated with the tinnitus was particularly conspicuous. This broadening strongly suggests that tinnitus originates in the cochlea, although some involvement of central pathways may also occur. Tinnitus-induced broadening of frequency selectivity as a possible sign of cochlear origin deserves further consideration in future studies.