Frequency Difference Limens Research Articles

Frequency difference limens of pure tones and harmonics within complex stimuli in Mongolian gerbils and humans

Frequency difference limens (FDLs) for pure tones between 200 and 6400 Hz and for the first, the second, or the eighth harmonic of an 800 Hz complex in four Mongolian gerbils (Meriones unguiculatus) were determined using a Go/NoGo-procedure. The 12 harmonics of the complex started either in sine phase or at a random phase. Gerbils showed very high pure tone FDLs ranging from 17.1% Weber fraction (200 Hz) to 6.7% (6400 Hz). They performed much better in detecting mistuning of a harmonic in the complex in the sine phase condition with FDLs decreasing from 0.07% for the first harmonic to 0.02% for the eighth harmonic. FDLs were about one order of magnitude higher when temporal cues were degraded by randomizing the starting phase of every component in the harmonic complex for every stimulus. These results are strikingly different from those obtained in four human subjects who needed about four times higher frequency shifts than gerbils for detecting a mistuned component in a sine phase complex and showed similar detection of mistuning in the random phase condition. The results are discussed in relation to possible processing mechanisms for pure tone frequency discrimination and for detecting mistuning in harmonic complex stimuli.

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.

Generalization to Untrained Conditions Following Training with Identical Stimuli

It has recently been documented that perceptual learning occurs in the absence of perceived differences between stimuli. This finding supports the notion that stimuli do not have to be highly discriminable in order to elicit learning effects. It is not clear, however, whether additional characteristics of perceptual learning, such as generalization of the learning gains, will be demonstrated in this type of training. Thus, the goals of the present study were to compare the effects of type of training, i.e. adaptive versus fixed with identical stimuli on (1) difference limen for frequency (DLF) thresholds; and (2) the extent of generalization of the learning gains to an untrained frequency and the untrained ear. Twelve adult participants with normal hearing were randomly assigned into two experimental groups: an 'adaptive' group and a 'fixed' group. A single-session frequency discrimination training/testing protocol was conducted in which participants were assessed using three 1,000 Hz DLF testing intervals separated by two training intervals. In the 'adaptive' group, each training interval consisted of tone pairs that varied in a 2-down 1-up adaptive procedure. In the 'fixed' group, each training interval consisted of identical 1,000 Hz tone pairs. Following the training/testing protocol, two untrained conditions were tested: a 2,000 Hz untrained frequency and the untrained ear. Results show that: (1) training on a DLF task with identical stimuli improved performance; (2) the type of training (i.e., 'adaptive' versus 'fixed' with identical stimuli) did not influence the amount of gains in performance; (3) learning generalized to an untrained frequency but to a lesser extent in the 'fixed' group with identical stimuli compared to the 'adaptive' group; and (4) learning generalized to the untrained ear for both groups. Thus, training with identical stimuli appears to promote auditory perceptual learning in a frequency discrimination task that generalizes, to some extent, to untrained conditions. These findings support the hypothesis that top-down attention processes and not only bottom-up processes may play an important role in auditory perceptual learning.

Hearing of note: An electrophysiologic and psychoacoustic comparison of pitch discrimination between vocal and instrumental musicians

Cortical auditory evoked potentials of instrumental musicians suggest that music expertise modifies pitch processing, yet less is known about vocal musicians. Mismatch negativity (MMN) to pitch deviances and difference limen for frequency (DLF) were examined among 61 young adult women, including 20 vocalists, 21 instrumentalists, and 20 nonmusicians. Stimuli were harmonic tone complexes from the mid-female vocal range (C4-G4). MMN was elicited by multideviant paradigm. DLF was obtained by an adaptive psychophysical paradigm. Musicians detected pitch changes earlier and DLFs were 50% smaller than nonmusicians. Both vocal and instrumental musicians possess superior sensory-memory representations for acoustic parameters. Vocal musicians with instrumental training appear to have an auditory neural advantage over instrumental or vocal only musicians. An incidental finding reveals P3a as a sensitive index of music expertise.

Sound quality evaluation of the booming sensation for passenger cars

Automotive booming noise due to powertrain occurs when pure or narrow band tones related to the firing frequency of engine and its harmonics excite the passenger cavity, which entails a prominent increase of sound intensity. The booming sensation has been considered as very important to the acoustic comfort of passengers. In this study, a sound quality index which can objectively evaluate the booming sensation was derived. Because of the tonal nature of powertrain booming noise, subjective pitch was employed to find only aurally relevant tonal components which influence booming sensation as well as loudness. Using the empirical data and the frequency difference limen for just-noticeable change of booming sensation obtained from the listening test, an existing pitch extraction algorithm could be modified. The modified pitch model was applied to the interior noises of accelerating passenger cars together with a loudness analysis for representing the objective features of booming feeling. Subjective tests using the magnitude estimation method were conducted to evaluate the degree of booming sensation. Finally, booming strength was proposed for quantifying the booming sensation, which was validated by subjective results. The correlation coefficient between the derived booming strength and the degree of booming sensation obtained by the subjective test was 0.926.

Current Steering and Results From Novel Speech Coding Strategies

Advanced Bionics' cochlear implants have independent current sources that can share stimulation current between 2 contacts (Current Steering). By stimulating 2 adjacent electrodes with different weights, different pitches can be evoked, allowing to increase the number of processing channels. A counterbalanced crossover design was used to compare 3 different current steering implementations to the clinical HiRes strategy. The study was a prospective, within-subject, repeated-measure experiment. The study group consisted of 8 postlingually deaf subjects with a minimum of 12-month experience in HiRes. The following programs were evaluated: 1) a Fast Fourier Transformation (FFT)-based current steering implementation with 120 stimulation sites; 2) the same current steering implementation but with 16,000 stimulation sites; and 3) a current steering implementation based on a sinusoidal decomposition of the original signal with 16,000 stimulation sites. Speech perception tests in quiet and in Comité Consultatif International Télégraphique et Téléphonique (CCITT) noise, as well as with competing talker; an adaptive test of the frequency difference limen; a Quality Assessment Questionnaire. Current results do not show any improvement in speech perception for a certain current steering strategy compared with HiRes. However, when selecting the optimal current steering strategy, subjects could achieve a significant benefit compared with the clinical HiRes. In addition, the frequency difference limen could be reduced significantly at 1,280 Hz. Current steering seems to have the potential to improve both understanding in adverse listening situations and frequency resolution. However, the optimal implementation needs further investigation.

Sample discrimination of frequency by hearing-impaired and normal-hearing listeners

In a multiple observation, sample discrimination experiment normal-hearing (NH) and hearing-impaired (HI) listeners heard two multitone complexes each consisting of six simultaneous tones with nominal frequencies spaced evenly on an ERB(N) logarithmic scale between 257 and 6930 Hz. On every trial, the frequency of each tone was sampled from a normal distribution centered near its nominal frequency. In one interval of a 2IFC task, all tones were sampled from distributions lower in mean frequency and in the other interval from distributions higher in mean frequency. Listeners had to identify the latter interval. Decision weights were obtained from multiple regression analysis of the between- interval frequency differences for each tone and listeners' responses. Frequency difference limens (an index of sensorineural resolution) and decision weights for each tone were used to predict the sensitivity of different decision-theoretic models. Results indicate that low-frequency tones were given much greater perceptual weight than high-frequency tones by both groups of listeners. This tendency increased as hearing loss increased and as sensorineural resolution decreased, resulting in significantly less efficient weighting strategies for the HI listeners. Overall, results indicate that HI listeners integrated frequency information less optimally than NH listeners, even after accounting for differences in sensorineural resolution.

Effect of Age on F0Difference Limen and Concurrent Vowel Identification

To investigate the effect of age on voice fundamental frequency (F0) difference limen (DL) and identification of concurrently presented vowels. Fifteen younger and 15 older adults with normal audiometric thresholds in the speech range participated in 2 experiments. In Experiment 1, F0 DLs were measured for a synthesized vowel. In Experiment 2, accuracy in identifying concurrently presented vowel pairs was measured. Vowel pairs were formed from 5 synthesized vowels with F0 separations ranging from 0 to 4 semitones. Younger adults had smaller (better) F0 DLs than older adults. For the older group, age was significantly correlated with F0 DLs. Younger adults identified concurrent vowels more accurately than older adults. When the vowels in the pairs had different formants, both age groups benefited similarly from F0 separation. Interestingly, when both constituent vowels had identical formants, F0 separation was deleterious, especially for older adults. Pure-tone average threshold did not correlate significantly with either F0 DL or accuracy in concurrent vowel identification. Age-related declines were confirmed for F0 DLs, identification of concurrently spoken vowels, and benefit from F0 separation between vowels with identical formants. This pattern of findings is consistent with age-related deficits in periodicity coding.

Enhanced frequency discrimination in hearing-impaired individuals: A review of perceptual correlates of central neural plasticity induced by cochlear damage

Cochlear damages have been shown to induce changes in tonotopic maps in the central auditory system of animals; neurons deprived from peripheral inputs start to respond to stimuli with frequencies close to the cutoff frequency (Fc) or “edge” of the hearing loss, which then become over-represented at the neural level. Here, we review findings, which reveal a possible psychophysical correlate of such central over-representation in human listeners with sensorineural hearing loss. These findings concur to demonstrate a local improvement in difference limens for frequency (DLFs) at or near Fc. This effect has now been observed in several studies and subjects with varied audiometric characteristics, including high- and low-frequency, and symmetric and asymmetric hearing losses. The presence of cochlear dead region or a steeply sloping hearing loss appear as a necessary condition for its occurrence. The effect cannot be explained simply by more prominent loudness cues or spontaneous otoacoustic emissions (SOAEs) near the audiogram edge. Overall, the data are consistent with local changes in pitch discrimination performance near the hearing-loss cutoff frequency being a result of the neural over-representation of that frequency region in the central auditory system. Further work is needed to confirm this hypothesis, and investigate other possible perceptual correlates of injury-related cortical plasticity in both humans and animals.

Accuracy of Cochlear Implant Recipients on Pitch Perception, Melody Recognition, and Speech Reception in Noise

The purposes of this study were to (a) examine the accuracy of cochlear implant recipients who use different types of devices and signal processing strategies on pitch ranking as a function of size of interval and frequency range and (b) to examine the relations between this pitch perception measure and demographic variables, melody recognition, and speech reception in background noise. One hundred fourteen cochlear implant users and 21 normal-hearing adults were tested on a pitch discrimination task (pitch ranking) that required them to determine direction of pitch change as a function of base frequency and interval size. Three groups were tested: (a) long electrode cochlear implant users (N = 101); (b) short electrode users that received acoustic plus electrical stimulation (A+E) (N = 13); and (c) a normal-hearing (NH) comparison group (N = 21). Pitch ranking was tested at standard frequencies of 131 to 1048 Hz, and the size of the pitch-change intervals ranged from 1 to 4 semitones. A generalized linear mixed model (GLMM) was fit to predict pitch ranking and to determine if group differences exist as a function of base frequency and interval size. Overall significance effects were measured with Chi-square tests and individual effects were measured with t-tests. Pitch ranking accuracy was correlated with demographic measures (age at time of testing, length of profound deafness, months of implant use), frequency difference limens, familiar melody recognition, and two measures of speech reception in noise. The long electrode recipients performed significantly poorer on pitch discrimination than the NH and A+E group. The A+E users performed similarly to the NH listeners as a function of interval size in the lower base frequency range, but their pitch discrimination scores deteriorated slightly in the higher frequency range. The long electrode recipients, although less accurate than participants in the NH and A+E groups, tended to perform with greater accuracy within the higher frequency range. There were statistically significant correlations between pitch ranking and familiar melody recognition as well as with pure-tone frequency difference limens at 200 and 400 Hz. Low-frequency acoustic hearing improves pitch discrimination as compared with traditional, electric-only cochlear implants. These findings have implications for musical tasks such as familiar melody recognition.

Release from interference in auditory working memory for pitch

The purpose of this study was to quantify the effect of interpolated tones upon a pitch standard held within auditory working memory through measurement of the difference limen (just noticeable difference) for frequency and the usefulness of “Where” cues to ameliorate the interference produced by these intervening stimuli. To this end, we measured the degree to which tones, containing identical and disparate localization cues, presented within the retention interval altered differential sensitivity for frequency via the method of constant stimuli. The difference limen for frequency nearly tripled when tones were presented within the retention interval and sound localization cues produced a significant partial release from interference within the short-term pitch store. Interference produced by “Where” cues ranged from 4.0 to 5.2 Hz. These findings indicate that there is a possible integrative use of the “What” and “Where” pathways in forming and maintaining pitch information within the pitch array within auditory working memory.

Psychophysical Performance and Mandarin Tone Recognition in Noise by Cochlear Implant Users

The present study was aimed to examine the relationship between psychophysical performance in temporal and spectral resolution and Mandarin tone recognition in noise by cochlear-implant (CI) listeners. Seventeen Nucleus-24 implant users, 10 postlingually deafened and 7 prelingually deafened, participated in the experiments. A 3-interval, forced-choice procedure was used to measure gap detection and pure-tone frequency discrimination at 250 to 4,000 Hz in octave steps. A 4-alternative forced-choice procedure was used to measure Mandarin tone recognition in quiet and in noise. Signal-to-noise ratios (SNRs) varied from +10 to -10 dB. All stimuli were delivered to the clinical processor via a speaker in a sound free field. The obtained data were compared to data collected from normal-hearing control subjects, as well as cochlear-implant users who performed similar tasks using single-electrode stimulation via a research interface. Postlingually-deafened CI subjects generally performed better than prelingually-deafened subjects. The average gap detection threshold was 30 ms with a range from 4 to 128 ms. The average frequency difference limen was 100 Hz with a range from 12 to 192 Hz, regardless of the standard frequency. The average tone recognition was 80% correct in quiet, which dropped to 55% at +10 dB SNR and essentially chance performance at -5 dB SNR. In comparison, the normal-hearing control subjects maintained essentially perfect performance over this SNR range. Only frequency discrimination at 1,000 Hz was significantly correlated with tone recognition in quiet but all psychophysical measures were correlated to tone recognition in noise. The present result suggests that the CI users can rely on either temporal or spectral cues to perform tone recognition in quiet, but need both cues for tone recognition in noise. Future CI processors need to extract and encode these acoustic cues to achieve better performance in tone perception and production.

Effect of duration on the frequency discrimination of individual partials in a complex tone and on the discrimination of fundamental frequency

Thresholds for the discrimination of fundamental frequency (FODLs) and frequency difference limens (FDLs) for individual partials within a complex tone (F0=250 Hz, harmonics 1-7) were measured for stimulus durations of 200, 50, and 16 ms. The FDLs increased with decreasing duration. Although the results differed across subjects, the effect of duration generally decreased as the harmonic number increased from 1 to 4, then increased as the harmonic number increased to 6, and finally decreased for the seventh harmonic. For each duration, FODLs were smaller than the smallest FDL for any individual harmonic, indicating that information is combined across harmonics in the discrimination of FO. FODLs predicted from the FDLs corresponded well with observed FODLs for the 200- and 16-ms durations but were significantly larger than observed FODLs for the 50-ms duration. A supplementary pitch-matching experiment using two subjects indicated that the contribution of the seventh harmonic to the pitch of the 16-ms complex tone was smaller than would be predicted from the FDL for that harmonic. The results are consistent with the idea that the dominant region shifts upward with decreasing duration, but that the weight assigned to individual harmonics is not always adjusted in an optimal way.

Individual differences in the sensitivity to pitch direction

It is commonly assumed that one can always assign a direction-upward or downward-to a percept of pitch change. The present study shows that this is true for some, but not all, listeners. Frequency difference limens (FDLs, in cents) for pure tones roved in frequency were measured in two conditions. In one condition, the task was to detect frequency changes; in the other condition, the task was to identify the direction of frequency changes. For three listeners, the identification FDL was about 1.5 times smaller than the detection FDL, as predicted (counterintuitively) by signal detection theory under the assumption that performance in the two conditions was limited by one and the same internal noise. For three other listeners, however, the identification FDL was much larger than the detection FDL. The latter listeners had relatively high detection FDLs. They had no difficulty in identifying the direction of just-detectable changes in intensity, or in the frequency of amplitude modulation. Their difficulty in perceiving the direction of small frequency/pitch changes showed up not only when the task required absolute judgments of direction, but also when the directions of two successive frequency changes had to be judged as identical or different.

The relationship between frequency selectivity and pitch discrimination: Effects of stimulus level

Three experiments tested the hypothesis that fundamental frequency (fo) discrimination depends on the resolvability of harmonics within a tone complex. Fundamental frequency difference limens (fo DLs) were measured for random-phase harmonic complexes with eight fo's between 75 and 400 Hz, bandpass filtered between 1.5 and 3.5 kHz, and presented at 12.5-dB/component average sensation level in threshold equalizing noise with levels of 10, 40, and 65 dB SPL per equivalent rectangular auditory filter bandwidth. With increasing level, the transition from large (poor) to small (good) fo DLs shifted to a higher fo. This shift corresponded to a decrease in harmonic resolvability, as estimated in the same listeners with excitation patterns derived from measures of auditory filter shape and with a more direct measure that involved hearing out individual harmonics. The results are consistent with the idea that resolved harmonics are necessary for good fo discrimination. Additionally, fo DLs for high fo's increased with stimulus level in the same way as pure-tone frequency DLs, suggesting that for this frequency range, the frequencies of harmonics are more poorly encoded at higher levels, even when harmonics are well resolved.

The relationship between frequency selectivity and pitch discrimination: Sensorineural hearing loss

This study tested the relationship between frequency selectivity and the minimum spacing between harmonics necessary for accurate fo discrimination. Fundamental frequency difference limens (fo DLs) were measured for ten listeners with moderate sensorineural hearing loss (SNHL) and three normal-hearing listeners for sine- and random-phase harmonic complexes, bandpass filtered between 1500 and 3500 Hz, with fo's ranging from 75 to 500 Hz (or higher). All listeners showed a transition between small (good) fo DLs at high fo's and large (poor) fo DLs at low fo's, although the fo at which this transition occurred (fo,tr) varied across listeners. Three measures thought to reflect frequency selectivity were significantly correlated to both the fo,tr and the minimum fo DL achieved at high fo's: (1) the maximum fo for which fo DLs were phase dependent, (2) the maximum modulation frequency for which amplitude modulation and quasi-frequency modulation were discriminable, and (3) the equivalent rectangular bandwidth of the auditory filter, estimated using the notched-noise method. These results provide evidence of a relationship between fo discrimination performance and frequency selectivity in listeners with SNHL, supporting "spectral" and "spectro-temporal" theories of pitch perception that rely on sharp tuning in the auditory periphery to accurately extract fo information.

Audiological Evaluation of Affected Members from a Dutch DFNA8/12 (TECTA) Family

In DFNA8/12, an autosomal dominantly inherited type of nonsyndromic hearing impairment, the TECTA gene mutation causes a defect in the structure of the tectorial membrane in the inner ear. Because DFNA8/12 affects the tectorial membrane, patients with DFNA8/12 may show specific audiometric characteristics. In this study, five selected members of a Dutch DFNA8/12 family with a TECTA sensorineural hearing impairment were evaluated with pure-tone audiometry, loudness scaling, speech perception in quiet and noise, difference limen for frequency, acoustic reflexes, otoacoustic emissions, and gap detection. Four out of five subjects showed an elevation of pure-tone thresholds, acoustic reflex thresholds, and loudness discomfort levels. Loudness growth curves are parallel to those found in normal-hearing individuals. Suprathreshold measures such as difference limen for frequency modulated pure tones, gap detection, and particularly speech perception in noise are within the normal range. Distortion otoacoustic emissions are present at the higher stimulus level. These results are similar to those previously obtained from a Dutch DFNA13 family with midfrequency sensorineural hearing impairment. It seems that a defect in the tectorial membrane results primarily in an attenuation of sound, whereas suprathreshold measures, such as otoacoustic emissions and speech perception in noise, are preserved rather well. The main effect of the defects is a shift in the operation point of the outer hair cells with near intact functioning at high levels. As most test results reflect those found in middle-ear conductive loss in both families, the sensorineural hearing impairment may be characterized as a cochlear conductive hearing impairment.

Auditory memory for frequency in sequential interference

Percepts within working memory are weakened by the presence of intervening stimuli that lie along the same perceptual dimension. To this end, the effect of sequential interference on the storage of frequency information within auditory working memory was measured. The difference limen for frequency was measured by the method of constant stimuli for two diotic and two dichotic conditions. The first diotic condition served as a control and consisted of two 300-ms stimuli separated by 5 s. The frequency of the referent (first tone) was roved over a 100-Hz range centered at 435 Hz. Listeners indicated whether the target (second tone) was higher or lower in frequency than the referent. The second diotic condition added four interfering tones between the referent and the target. In the third condition, the interferers and referent/target pair were lateralized to opposite ears via the Stenger effect. In condition four, the phase of the interferers differed between ears by 180 deg. Results indicate (1) the addition of interferers increased the difference limen for frequency, and (2) when the interferer and target/referent pair differed along a single localization dimension, the effect of the interferers was reduced.

Pitch discrimination in children using cochlear implants

Research in pitch perception by cochlear implant users has focused primarily on postlingually deafened adults. Little is currently known regarding the pitch perception abilities of those who are implanted at a very early age, yet many children receive cochlear implants when they are less than 2 years old. Given the effects of brain plasticity, it is conceivable that pitch perception by early cochlear implant users may be much better than that of their older counterparts. This study examines pitch discrimination thresholds in young cochlear‐implant users between the ages of 4 and 16. A computer game was developed to determine difference limens for fundamental frequency in vowellike stimuli at three referent frequencies: 100, 200, and 400 Hz. Two different tasks were employed: pitchdiscrimination, in which subjects were asked whether two stimuli are same or different, and pitch ranking, in which participants determine which of two stimuli is higher in pitch. Normal‐hearing matches were tested to control for maturational effects, and adult cochlear implant users were also tested to compare findings with other studies. [Work supported by the Nova Scotia Health Research Foundation.]

Dead regions in the cochlea and enhancement of frequency discrimination: Effects of audiogram slope, unilateral versus bilateral loss, and hearing-aid use

Following a restricted lesion of the cochlea, which produces a “dead region” (DR), animal experiments have revealed an increase in the cortical representation of frequencies just below the edge frequency ( f e) of the DR. This may result in improved difference limens for frequency (DLFs) just below f e. In previous studies to assess this, the value of f e was not determined precisely. We measured DLFs using human subjects with DRs for whom the values of f e had been determined precisely using psychophysical tuning curves. To prevent use of loudness cues, stimuli for the measurement of DLFs had a mean level falling along an equal-loudness contour and levels were roved over a 12-dB range. DLFs were measured for thirteen subjects with a DR in at least one ear. Almost all subjects with bilateral hearing loss exhibited enhanced DLFs near f e, consistent with cortical reorganisation. This occurred for subjects whose audiograms had both steep and shallow slopes, regardless of hearing aid use, and for two subjects with low-frequency DRs. One subject with a high-frequency DR in one ear and good hearing in the other ear showed an enhanced DLF in her better ear.