Frequency Difference Limens Research Articles

Frequency and practice interactions in frequency discrimination

Differences between human infants and adults in frequency discrimination resemble differences between untrained and trained adults: frequency difference limens (FDL's) tend to be relatively worse for infants and untrained adults at low frequencies [L. W. Olsho, Inf. Behav. Dev. 7, 27–35 (1984)]. To demonstrate directly that the effect of training in frequency discrimination depends on frequency, the course of improvement in frequency discrimination was examined in adults at 500, 1000, and 4000 Hz. Stimuli were pure tones presented at a 40‐dB sensation level. A two‐alternative forced‐choice procedure was used, and FDL was tracked using a one‐up, two‐down adaptive procedure. Four subjects completed 200–250 trials of training at each frequency. For these subjects not only was initial FDL much higher relative to final FDL at the two lower frequencies, but tracking width decreased progressively with increasing frequency. Four additional subjects were tested for a total of 20 h each to make certain that asymptotic performance was reached. The final FDL's obtained by these listeners were similar to those reported by other investigators [e.g., C. C. Weir et al., J. Acoust. Soc. Am. 61, 178–184 (1977)], and the same practice effects were observed as in the first group. [Work supported by NIH.]

Frequency discrimination as a function of tonal duration and excitation-pattern slopes in normal and hearing-impaired listeners.

Frequency difference limens were determined as a function of stimulus duration in five normal-hearing and seven hearing-impaired subjects. The frequency DL duration functions obtained from normal-hearing subjects were similar to those reported by Liang and Chistovich [Sov. Phys. Acoust. 6, 75-80 (1961)]. As duration increased, the DL's improved rapidly over a range of short durations, improved more gradually over a middle range of durations, and reached an asymptote around 200 ms. The functions obtained from the hearing-impaired subjects were similar to those from normal subjects over the middle and longer duration, but did not display the rapid changes at short durations. The paper examines the ability of a variation of Zwicker's excitation-pattern model of frequency discrimination to explain these duration effects. Most, although not all, of the effects can be adequately explained by the model.

Vibrotactile frequency discrimination at short durations.

This experiment investigated how frequency discrimination of a sinusoidal, mechanical vibration applied to the tip of the right index finger is affected by shortening the duration of the stimuli from 200 ms to 30 ms. Using a standard stimulus of 100 Hz at 30 dB above threshold, seven comparison frequencies (at intervals of 10 Hz) were judged as higher or lower in frequency according to the method of constant differences. Vibrotactile stimuli were matched for subjective intensity across both frequency and duration. Difference limens for vibrotactile frequency were found to decline slightly from 200 ms to 50 ms (attributable to practice) and to increase noticeably at 30 ms. This result is discussed in relation to the seemingly contradictory results for auditory pitch discrimination.

Psychometric functions for frequency discrimination from listeners with sensorineural hearing loss.

Psychometric functions for pulsed pure-tone frequency discrimination were obtained from hearing-impaired listeners at frequencies with normal hearing and at frequencies with mild or moderate hearing losses. The general form of psychometric functions at hearing-impaired frequencies was found to be the same as at normal-hearing frequencies, i.e.,d' was linear with the frequency difference between tones, in Hz. For all but one psychometric function, the addition of an intercept term to the fitting equation did not account for significantly more variance than did the slope term alone. Therefore, it was concluded that psychometric functions for frequency discrimination can be adequately described with only one parameter: the slope of the psychometric function. Deficits in discrimination at hearing-loss frequencies were manifested by more gradual slopes of psychometric functions. Procedures for normalizing psychometric functions are presented, which facilitate comparisons of normal and impaired frequency discrimination data across studies and frequencies. Comparisons of dlf's (difference limen for frequency) obtained with adaptive and fixed procedures show a bias toward larger dlf's with adaptive procedures, but only at higher frequencies. A discussion of equal-interval and equal-ratio adaptive stepping rules indicates that an equal-ratio rule may be preferable.

Frequency and Rate Discrimination by Menière Patients

Discrimination tests were conducted for each ear of 6 patients with unilateral Menière's disease. Differential sensitivity to changes in pure-tone frequency (presumably containing temporal and place cues) was compared to differential sensitivity to changes in rate of sinusoidally amplitude-modulated noise (presumably containing only a temporal cue) at common low frequencies and modulation rates (less than 400 Hz). An adaptive forced-choice psychophysical procedure was used. The better-ear results for the Menière patients generally were similar to findings for normally hearing listeners. For the impaired ears, pure-tone frequency discrimination typically was impaired relatively more than was the rate discrimination up to 200 Hz. However, rate discrimination was difficult or impossible above 250-300 Hz. Absolute frequency difference limens (DLs) were, on average, smaller than or at least equivalent to absolute rate DLs. Moreover, frequency discrimination always was possible for the Menière patients.

On measuring the frequency-difference limen for short tones

The standard deviation of the distribution of matching frequencies in a two-interval pitch-matching experiment and the width of the psychometric function in a two-interval frequency-discrimination experiment both provide measures of the frequency-difference limen (DL). We compared DLs as measured by these two methods for tones of short duration, using all nine pairings of durations 12, 25, and 50 msec, at nominal frequencies of 200, 342,584, and 1000 Hz. We found that the two experiments gave qualitatively different results. In frequency discrimination, the DL decreased as the duration of either the standard or the comparison tone increased, as expected from statistical decision theory in one dimension. In pitch matching, the DL was smallest whenever the standard and comparison tones had equal durations. To explain this dichotomy, we suggest that, for tones of short duration, a pitch-matching experiment permits a multidimensional comparison of two tones, but that a frequency-discrimination experiment forces a comparison along a single perceptual dimension.

Variability in frequency difference limens from newborn animals

Young chickens suppress their regular peeping when they hear a change in the frequency of a tone. Gray and Rubel [J. Acoust. Soc. Am. Suppl. 1 76, S13 (1984)] estimated frequency difference limens in newborn chickens using peep suppressions and a nonstandard adaptive procedure. The definition of a correct response depended on an initial series of control trials used to estimate the distribution of suppressions expected when there was no change in frequency. Consistent improvement in frequency difference limens, approximately 1% in 4 days, was observed. A more controlled procedure involves the presentation of a stimulus and a control trial in pairs. When the duration of suppression is greater on the stimulus than control trial then the response is defined as correct, and transformed up-down rules can be applied as usual. Unfortunately, the data from this procedure are inconsistent. Any increase in frequency selectivity over age is probably greater at high than low frequencies. Difference limens appear to be affected by intensity, but not by the direction of delta F nor temporal characteristics of the stimulus. In conclusion, high variability makes frequency difference limens difficult to estimate in neonates. [Work supported by NIH.]

Extension of a temporal model of frequency discrimination: intensity effects in normal and hearing-impaired listeners.

The effects of intensity on the difference limen for frequency (DLF) in normal-hearing and in hearing-impaired listeners are incorporated into the temporal model of frequency discrimination proposed by Goldstein and Srulovicz [Psychophysics and Physiology of Hearing, edited by E. F. Evans and J.P. Wilson (Academic, New York, 1977)]. A simple extension of the temporal mode, which includes the dependence of phase locking on intensity, is sufficient to predict the effects of intensity on the DLF in normal-hearing listeners. To account for elevated DLFs in hearing-impaired listeners the impairment is modeled as a reduction in the synchrony of the discharge from VIIIth-nerve fibers that innervate the region of hearing loss. Constraints on the optimal processor and the validity of the temporal model at high frequencies are discussed.

Investigations of the residual hearing capacity of severely hearing-impaired and profoundly deaf subjects.

Speech reception functions (maximum discrimination score for phonemes, speech reception threshold) and auditory functions (pure-tone audiogram, difference limens for frequency and intensity, temporal modulation transfer function, critical ratio and temporal integration) have been investigated in a group of severely hearing-impaired and deaf subjects (median Fletcher index: 80 dB), for different frequency regions (250, 1 000 and 2 000/4 000 Hz). The correlations between the different functions were calculated on the basis of characteristic numbers, derived from the originally measured functions, in the indicated frequency regions. The residual hearing capacities could be described best with two factors, one reflecting the distortion term in the speech reception threshold and the other representing the frequency discrimination for high-frequency tones. It was found that residual hearing capacities are present, at least up to a Fletcher index of 105 dB.

The spatial frequency discrimination function at low contrasts.

Spatial frequency difference thresholds for sinewave gratings near contrast threshold were measured using a two-alternative forced-choice technique, and the threshold frequency differences were plotted as a proportion of standard frequency for standards from 2 to 7 cycles/degree. This function shows reliable local maxima and minima, and these features are more pronounced than they are when stimuli of 30% contrast are used. This result is consistent with the notion that at low contrasts, fewer spatial frequency channels are above threshold in the area of the visual field covered by the stimulus than when the stimulus is at high contrast.

Frequency difference limens of C57BL/6 and DBA/2 mice: relationship to auditory neuronal response properties and hearing impairment.

Frequency difference limens (DLs) were measured in DBA/2 and C57BL/6 mice using an avoidance conditioning procedure and were viewed in relation to previously obtained neurophysiological data. DRA mice had significantly smaller DLs at 12 and 16 kHz, despite progressive sensorineural hearing loss and disrupted tonotopic organization characteristic of this strain. C57 mice had smaller DLs at 8 kHz. Several inferior colliculus (IC) neuronal response properties, that may be related to DL performance, differ between strains. Compared to C57s, a large proportion of DBA neurons respond to 12 and 16 kHz, many more best frequencies (BF, the frequency for which a neuron is most sensitive) fall between 10 and 20 kHz, response ranges are narrow, and neural intensity functions are steep. For C57 mice, a large proportion of neurons respond to 8 kHz, and more neurons have BFs between 5 and 10 kHz.

Neonatal development of frequency difference limens in chickens

Young chickens will suppress their regular peeping when they hear a change in the frequency of pulsing pure tones. The duration of this peep suppression grows with increasing amounts of frequency change. Various adaptive tracking procedures can thus use this response to estimate frequency difference limens in neonatal chickens. These estimates in chickens as young as 4 days of age are close to others available in the literature from mature subjects. Despite large variability in the results from these “staircases,” frequency difference limens generally decrease by approximately one percent over the first 4 days of post-natal life. As expected from human studies, variability in this discrimination task is greater than previously reported in a comparable detection task [L. Gray and E. W. Rubel, J. Acoust. Soc. Am. Suppl 1 71, S31 (1983)]. In conclusion, there is a significant increase in responsiveness to small changes in the frequency of pure tones as animals mature over the first few post-natal days. [Work supported by NIH.]

Stimulus Duration and Frequency Discrimination for Normal-Hearing and Hearing-Impaired Subjects

Frequency discrimination for 500- and 2000-Hz pure tones at durations of 5, 10, 20, 50, and 200 ms was determined for 10 normal-hearing and 10 cochlear-impaired listeners. Listeners from both groups demonstrated monotonic increases in frequency difference limens as stimulus duration decreased. The functions of the hearing-impaired listeners were parallel to those of the normal-hearing listeners for stimulus durations between 10 and 200 ms, but the overall performance of the hearing-impaired group was poorer than that of the normal-hearing group. The functions of many of the cochlear-impaired subjects were less steep than normal for the shortest durations tested (between 5 and 10 ms). There appeared to be no relation between temporal integration for frequency discrimination and temporal integration for detection threshold. The results are discussed in terms of processes of temporal integration and frequency selectivity.

Frequency discrimination for conditions of roving standard and random interstimulus interval

A two‐interval forced‐choice adaptive tracking procedure was used to estimate the frequency difference limen (DL). In one condition, the frequency of the standard tone was constant for every trial with the frequency of the comparison tone varied according to the adaptive procedure. The interval between standard and comparison stimuli (ISI) was fixed. In contrast to this “fixed‐standard fixed‐ISI” condition, other conditions were tested in which the standard frequency and/or the ISI were chosen on each trial according to pseudo‐random algorithms. The results indicate that the frequency DL may increase by as much as a factor of 2 for some roving‐standard and random ISI conditions. In addition, a trial‐by‐trial record of each run was used to assess discrimination performance as a function of frequency and ISI. The decay of the sensory trace with increasing ISI, and uncertainty about signal frequency and timing appear to account for the changes in discrimination. [Supported by NIH.]

Frequency and intensity difference limens for harmonics within complex tones.

A two-interval, two-alternative forced choice task was used to estimate frequency difference limens (DLs) for individual harmonics within complex tones, and DLs for the periodicity (i.e., number of periods per s) of the whole complexes. For complex tones with equal-amplitude harmonics, the DLs for the lowest harmonics were small (less than one percent). The DLs increased rather abruptly around the fifth to seventh harmonic. The highest harmonic in each complex was also well discriminated, and the discriminability of a single high harmonic was markedly improved by increasing its level relative to the other components. The DL for a complex tone was generally smaller than the frequency DL of its most discriminable component. The DL for a complex was found to be predictable from the DLs of the harmonics comprising the complex, using a formula derived by Goldstein [J. Acoust. Soc. Am. 54, 1496-1516 (1973)] from his optimum processor theory for the formation of the pitch of complex tones. The DL for a complex is sometimes primarily determined by high harmonics, such as the highest harmonic, or a harmonic whose level exceeds that of adjacent harmonics. We also measured intensity DLs for individual harmonics within complex tones. The intensity DLs were smallest for low harmonic numbers, and for the highest harmonic in a complex. An excitation-pattern model was used to determine whether the frequency DLs of harmonics within complex tones could be explained in terms of place mechanisms, i.e., in terms of changes in the amount of excitation at appropriate frequency places. We conclude that place mechanisms are not adequate, and that information about the frequencies of individual harmonics is probably carried in the time patterning of neural impulses.

Reliability of auditory function tests in severely hearing-impaired and deaf subjects.

The test-retest variability of a series of auditory functions has been investigated in a group of severely hearing-impaired and deaf subjects (64 ears, median Fletcher index: 80 dB) and in a group of 10 controls with normal hearing. An adaptive forced-choice procedure was used for both groups. The functions were: tone audiogram, difference limen for intensity, difference limen for frequency, modulation transfer function and critical ratio. In spite of sometimes strongly deviating function values within the hearing-impaired group, the test-retest variability of the two groups was found to be of the same order of magnitude, except for the tone audiogram where the variability in the hearing-impaired group was twice that for the control group.

Infant frequency discrimination

Frequency difference limens were determined for infants aged 5 to 8 months and for adults, at six tonal frequencies ranging from 250 to 8000 Hz, using the visually reinforced head-turn procedure. The relative difference threshold (threshold divided by frequency) was a nonmonotonic function of frequency with a minimum around 1000 Hz for both infants and adults. However, infant thresholds were twice those of adults at low frequencies but did not differ from adult values at high frequencies. Previously reported differences in absolute sensitivity at low frequencies are not great enough to account for the age difference in low frequency discrimination ability. These findings suggest that the auditory mechanisms responsible for frequency discrimination mature first at high frequencies, paralleling the base to apex sequence of prenatal development of hair cells and associated auditory nerve fibers.

Generalization of learning in auditory pattern discrimination

Frequency discrimination for tones embedded in a varying sequence of ten brief tones can be extremely poor. Yet after repeated exposure to a constant tonal sequence, listeners demonstrate discrimination of changes in a target component almost as fine as for the target tone presented alone [e.g., C. S. Watson et al., J. Acoust. Soc. Am. 60, 1176–1186 (1976)]. It is clear, however, which aspects of the constant pattern are learned, thereby allowing the listener to overcome the effects of the surrounding tonal context on discrimination of the target. This experiment investigated generalization to new patterns of the learned target and learned context to assess their contributions to pattern discrimination. Four listeners were trained in a same‐different task to discriminate small frequency changes in a 920‐Hz target tone, which was the second element in a ten‐tone pattern. Frequency difference limens were subsequently determined for the learned target tone embedded in a different tonal context, and for diffe...

Asymmetrical frequency discrimination in primates

Auditory frequency difference limens at 0.5, 1.0, 2.0, and 4.0 kHz were measured monaurally in humans and in four Old World monkey species: Japanese and rhesus macaques (Macaca fuscata, Macaca mulatta) and vervet and deBrazza monkeys (Cercopithecus aethiops, Cercopithecus neglectus). A go, no‐go, repetitive‐standard discrimination procedure was employed with positive reinforcement. At certain frequencies and sensation levels, humans and macaques exhibit superior discrimination for frequency increments, while under these same conditions the Cercopithecus species exhibit superior discrimination for frequency decrements. Possible coding mechanisms to account for these results will be discussed, including monitoring rate increases versus rate decreases in asymmetrically tuned auditory nerve fibers. In one species, the Japanese macaque, there is some evidence that superior discrimination of frequency increments may relate to the design features of the animal's vocal communication system. [Supported by NSF, Sloan Foundation, and Deafness Research Foundation.]

Incorporating intensity effects into a temporal model of frequency discrimination

The effects of duration and of frequency on frequency discrimination are consistent with a neural-based model that used the temporal information present in the phase-locked response of VIIIth nerve units to estimate the frequency of a pure-tone stimulus [J. L. Goldstein and P. Srulovicz, “Auditory-nerve spike intervals as an adequate basis for aural frequency measurement” in Psychophysics and Physiology of Hearing, edited by E. F. Evans and J. P. Wilson (Academic, London, 1977), pp. 337–346]. We have extended this model to include the effects of intensity on the frequency difference limen by incorporating (1) the functional dependence of the synchronization index on intensity [D. H. Johnson, doctoral dissertation, MIT, 1974] and (2) an appropriate dependence of average discharge rate on intensity. When fit to the psychophysical data, the extended model accounts for much of the effect of intensity on the frequency DL above 10 dB SL. At levels lower than this, the model does not exhibit the same rapid increase in the DL observed in the human data. We will discuss this discrepancy as well as our attempts to generalize the model to account for the effects of hearing impairment on frequency discrimination. [Work supported by NINCDS Grant NS12125.]