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PubMed2005

Psychophysical design influences frequency discrimination performance in young children.

We investigated how different psychophysical procedures affect frequency discrimination performance in children. Four studies used a design in which listeners heard two tone pairs and had to identify whether the first or second pair contained a higher frequency target tone. Thresholds for 6- and 7-year-olds were higher than those for 8- and 9-year-olds and adults. Two manipulations led to lower (better) thresholds in young children: (a) moving the standard comparison tone before the target tone and (b) using three target comparison tone pairs. It is suggested that young children benefit from designs that help cue them to when they need to attend to a target tone. The two-interval, forced-choice procedure that is widely used in studies of developmental disorders led to variable performance even in adults and did not give a realistic picture of the perceptual capabilities of children under 8 years of age.

Adult↗
PubMed1978

Frequency discrimination in the chinchilla.

Chinchillas were trained with shock-avoidance procedures to discriminate or detect pure-tone frequency differences. Inital attempts at determining frequency-difference thresholds utilized a complex discrimination paradigm and a go-no-go response. Although discriminations of large frequency differences were obtained from chinchillas after considerable training, discriminations of small frequency differences could not be trained. Therefore, determinations of frequency-difference thresholds could not be made with the complex discrimination paradigm and the go-no-go response task. A simple detection paradigm, involving the detection of frequency alternation in an ongoing train of tone bursts proved to be a more successful technique. Frequency-alternation detection was quickly learned by six chinchillas, and frequency-difference thresholds were obtained with an adaptive sequential procedure. Psychometric functions were reconstructed from the threshold tracking data of chinchillas, and comparisons were made with differential frequency thresholds from cats and humans obtained by previous investigators. Differential frequency thresholds from chinchillas paralleled those from cats and were about twice as large. Differential frequency thresholds from humans were considerably smaller than from chinchillas, especially for low-frequency tones. When a constant detectability index was used to specify differential frequency sensitiviy in chinchillas, chinchilla and human differential sensitivity functions paralleled one another. Human differential sensitivity was about ten times better than that of the chinchilla.

Animals↗
PubMed2003

Interaural time difference discrimination thresholds for single neurons in the inferior colliculus of Guinea pigs.

Sensitivity to changes in the interaural time difference (ITD) of 50 msec tones was measured in single units in the inferior colliculus of urethane-anesthetized guinea pigs. ITD functions were measured with 100 repeats and fine spacing (100 points per cycle). The just noticeable difference (jnd) for ITD was determined using receiver operating characteristic (ROC) analysis of the spike-count distribution at each ITD. The jnd became progressively smaller as the signal frequency increased from 50 to 800 Hz but became unmeasurable above 1 kHz. The lowest jnds (30 microsec) were comparable with human jnds, indicating that there is sufficient information in the firings of individual neurons to permit discrimination without obligatory pooling. ROC analysis requires the choice of a reference ITD from which the jnd may be found by stepping the target ITD through the ITD function. For each neuron the reference was chosen to minimize the jnd. The lowest jnd was usually for ipsilateral leading references, near the minimum of the ITD function where the variance was also low, but where the slope was nearing its steepest. This was despite the peak of the ITD function occurring for contralateral leading stimuli. When the reference ITD was on midline, a jnd could be obtained by looking for firing rates either greater or smaller than the firing rate at midline. The lower jnd was usually obtained by looking for a decrease in firing rate. As duration increased, jnds either decreased or increased, depending on unit type, whereas when level increased, jnds generally increased.

Animals↗
PubMed2002

Auditory stream segregation on the basis of amplitude-modulation rate.

In this study, auditory stream segregation based on differences in the rate of envelope fluctuations--in the absence of spectral and temporal fine structure cues--was tested. The temporal sequences to segregate were composed of fully amplitude-modulated (AM) bursts of broadband noises A and B. All sequences were built by the reiteration of a ABA triplet where A modulation rate was fixed at 100 Hz and B modulation rate was variable. The first experiment was devoted to measuring the threshold difference in AM rate leading subjects to perceive the sequence as two streams as opposed to just one. The results of this first experiment revealed that subjects generally perceived the sequences as a single perceptual stream when the difference in AM rate between the A and B noises was smaller than 0.75 oct, and as two streams when the difference was larger than about 1.00 oct. These streaming thresholds were found to be substantially larger than, and not related to, the subjects' modulation-rate discrimination thresholds. The results of a second experiment demonstrated that AM-rate-based streaming was adversely affected by decreases in AM depth, but that segregation remained possible as long as the AM of either the A or B noises was above the subject's AM-detection threshold. The results of a third experiment indicated that AM-rate-based streaming effects were still observed when the modulations applied to the A and B noises were set individually, either at a constant level in dB above AM-detection threshold, or at levels at which they were of the same perceived strength. This finding suggests that AM-rate-based streaming is not necessarily mediated by perceived differences in AM depth. Altogether, the results of this study indicate that sequential sounds can be segregated on the sole basis of differences in the rate of their temporal fluctuations in the absence of other temporal or spectral cues.

Adult↗
PubMed1981

Signal and masker uncertainty in intensity discrimination.

Intensity discrimination thresholds were assessed in a series of experiments. Signals were in-phase increments in the level of one component of a multitone masker. The main parameters of interest were the effects of signal uncertainty (which frequency is tested on a given trial) and masker uncertainty (which components were selected as the multitone masker on a given trial). Thresholds were measured as a function of signal frequency, number of components, and amount of overall changes in masker level. The results suggest a form of profile processing, in which the signal is detected by comparing levels in adjacent critical bands. Such a mechanism will account for the relatively small effects generally observed with signal uncertainty, for masker uncertainty showing larger effects on thresholds than signal uncertainty, and for the near constancy of signal threshold despite large (60 dB) fluctuations in overall level of the stimulus in the two intervals of the forced-choice trial.

Acoustic Stimulation↗
PubMed2002

A comparison of the effects of differences in temporal gating and ear of presentation on profile discrimination.

The aim of the study was to examine the effects of differences in temporal gating and ear of presentation (both separately and in combination) on listeners' ability to detect an increment in the level of a 1 kHz component (the target) relative to that of four spectrally flanking components. The flanking components were always presented to the listeners' right ear, while the target component was either presented to the same ear (monaural presentation) or to the left ear (dichotic presentation). Similarly, the target and flanking components were either gated on and off at the same time (synchronous presentation), or else the target component began 100 ms before and terminated 100 ms after the four flanking components (asynchronous presentation). On average, thresholds were lowest in the synchronous, monaural condition, and highest in the two asynchronous conditions. Ear differences alone did result in elevated thresholds for most listeners. However, combining differences in gating and ear of presentation produced thresholds that were indistinguishable from those obtained when gating differences alone were employed. These results are consistent with the suggestion that differences in temporal gating lead to more complete segregation of concurrent frequency components than differences in spatial location.

Acoustic Stimulation↗
PubMed2005

Encoding of vowel-like sounds in the auditory nerve: model predictions of discrimination performance.

The sensitivity of listeners to changes in the center frequency of vowel-like harmonic complexes as a function of the center frequency of the complex cannot be explained by changes in the level of the stimulus [Lyzenga and Horst, J. Acoust. Soc. Am. 98, 1943-1955 (1995)]. Rather, a complex pattern of sensitivity is seen; for a spectrum with a triangular envelope, the greatest sensitivity occurs when the center frequency falls between harmonics, whereas for a spectrum with a trapezoidal envelope, greatest sensitivity occurs when the center frequency is aligned with a harmonic. In this study, the thresholds of a population model of auditory-nerve (AN) fibers were quantitatively compared to these trends in psychophysical thresholds. Single-fiber and population model responses were evaluated in terms of both average discharge rate and the combination of rate and timing information. Results indicate that phase-locked responses of AN fibers encode phase transitions associated with minima in these amplitude-modulated stimuli. The temporal response properties of a single AN fiber, tuned to a frequency slightly above the center frequency of the harmonic complex, were able to explain the trends in thresholds for both triangular- and trapezoidal-shaped spectra.

Acoustic Stimulation↗
PubMed2001

Binaural processing model based on contralateral inhibition. II. Dependence on spectral parameters.

This and two accompanying articles [Breebaart et al., J. Acoust. Soc. Am. 110, 1074-1088 (2001); 110, 1105-1117 (2001)] describe a computational model for the signal processing in the binaural auditory system. The model consists of several stages of monaural and binaural preprocessing combined with an optimal detector. In the present article the model is tested and validated by comparing its predictions with experimental data for binaural discrimination and masking conditions as a function of the spectral parameters of both masker and signal. For this purpose, the model is used as an artificial observer in a three-interval, forced-choice adaptive procedure. All model parameters were kept constant for all simulations described in this and the subsequent article. The effects of the following experimental parameters were investigated: center frequency of both masker and target, bandwidth of masker and target, the interaural phase relations of masker and target, and the level of the masker. Several phenomena that occur in binaural listening conditions can be accounted for. These include the wider effective binaural critical bandwidth observed in band-widening NoS(pi) conditions, the different masker-level dependence of binaural detection thresholds for narrow- and for wide-band maskers, the unification of IID and ITD sensitivity with binaural detection data, and the dependence of binaural thresholds on frequency.

Auditory Threshold↗
PubMed1995

Auditory event-related magnetic fields in a tone-duration discrimination task. Source localization for the mismatch field and for a new component M2".

Auditory event related magnetic fields were measured using an odd-ball paradigm in which the rare event was a tone of short duration, D2, and the frequent one a tone of longer duration, D1. The subjects were required to attend to and count the number of rare stimuli. In the average across target stimuli a mismatch field (MMF) occurs and the dependence of the MMF, especially its latency, on the tone duration D2 is examined in detail. The location of an equivalent current dipole for the MMF-source is found and turns out to be at variance with earlier results. In addition to the MMF we propose a new component, here called M2", which in time overlaps the magnetic equivalent of the P200 signal and which has a source location (equivalent current dipole) lying rather close to the MMF-source. The two sources are, however, active at latencies differing by a time equal to D2. We speculate that M2" indicates the onset of the process: "evaluation of tone-duration" while the MMF indicates the end of this process.

Acoustic Stimulation↗
PubMed1987

Level and age effects in infant frequency discrimination.

Frequency difference limens (FDLs) were estimated for 3-, 6-, and 12-month-old infants and for adults using pure tones at 500, 1000, and 4000 Hz. Each listener provided an FDL at 40 dB and at a higher (80 dB, in most cases) sensation level (SL). An observer-based behavioral testing technique was used. The FDLs of 3-month-olds were worse than those of adults at all three frequencies, and increased with increasing frequency. The FDLs of 6- and 12-month-olds were worse than those of adults at 500 and 1000 Hz, but not at 4000 Hz. Decreasing the SL led to an increase in the FDL of about the same magnitude at all ages, and the same age differences were found at both SLs. Thus infant-adult differences in FDL are not a simple consequence of differences in absolute sensitivity. Infant FDLs at one SL were also found to be significantly correlated with the FDL at the other SL. The FDLs at one age were, in general, predictive of the FDL at a later age in a longitudinal sample of infants. Models that might account for these age-related differences are discussed.

Adult↗
PubMed2002

Decision strategies of hearing-impaired listeners in spectral shape discrimination.

The ability to discriminate between sounds with different spectral shapes was evaluated for normal-hearing and hearing-impaired listeners. Listeners detected a 920-Hz tone added in phase to a single component of a standard consisting of the sum of five tones spaced equally on a logarithmic frequency scale ranging from 200 to 4200 Hz. An overall level randomization of 10 dB was either present or absent. In one subset of conditions, the no-perturbation conditions, the standard stimulus was the sum of equal-amplitude tones. In the perturbation conditions, the amplitudes of the components within a stimulus were randomly altered on every presentation. For both perturbation and no-perturbation conditions, thresholds for the detection of the 920-Hz tone were measured to compare sensitivity to changes in spectral shape between normal-hearing and hearing-impaired listeners. To assess whether hearing-impaired listeners relied on different regions of the spectrum to discriminate between sounds, spectral weights were estimated from the perturbed standards by correlating the listener's responses with the level differences per component across two intervals of a two-alternative forced-choice task. Results showed that hearing-impaired and normal-hearing listeners had similar sensitivity to changes in spectral shape. On average, across-frequency correlation functions also were similar for both groups of listeners, suggesting that as long as all components are audible and well separated in frequency, hearing-impaired listeners can use information across frequency as well as normal-hearing listeners. Analysis of the individual data revealed, however, that normal-hearing listeners may be better able to adopt optimal weighting schemes. This conclusion is only tentative, as differences in internal noise may need to be considered to interpret the results obtained from weighting studies between normal-hearing and hearing-impaired listeners.

Adult↗
PubMed1997

Sensitivity to changes in overall level and spectral shape: an evaluation of a channel model.

Two experiments involving level and spectral shape discrimination which test an optimal channel model developed by Durlach et al. [J. Acoust. Soc Am. 80, 63-72 (1986)] are described. The model specifies how the auditory system compares and/or combines intensity information in different frequency channels. In the first experiment, psychometric functions were obtained for the discrimination of changes in level and discrimination of changes in spectral shape for an eight-tone complex sound. A variety of different base spectral shapes were tested. In some conditions, level randomization was introduced to reduce the reliability of across-interval changes in level. Increasing the amount of level variation degraded performance for the level discrimination task but had no effect on the shape discrimination task. In all conditions, sensitivity to changes in spectral shape was superior to sensitivity to changes in level. Consequently, two models of central noise are evaluated in an attempt to explain these results; one in which central noise acts prior to the formation of the likelihood ratio and one in which central noise degrades the likelihood ratio. The former model is more successful in accounting for the data. In a second experiment, the detectability of a level increment to one component of a multitone complex was measured. The frequency content of the complex was varied by systematically removing six components from a 23-component complex. Thresholds were measured for increments at three different signal frequencies. A common trend in the data was that when there was a spectral gap directly above the signal frequency, thresholds were lowest. This result differs from the predictions of a simple channel model, and contrasts with results presented by Green and Berg [Q. J. Exp. Psychol. 43A, 449-458 (1991)].

Adult↗
PubMed1996

Auditory event-related potentials to a two-tone discrimination paradigm in attention deficit hyperactivity disorder.

Auditory event-related potentials (ERPs) were recorded from 10 children diagnosed with attention deficit hyperactivity disorder (ADHD) and 10 age-, sex-, and IQ-matched control children. ERPs were recorded from 17 electrodes during an auditory two-tone discrimination ("oddball') paradigm. Subjects were instructed to press a hand-held response button to infrequently presented target tones. ERP components elicited to target and non-target stimuli were analyzed for between-group differences. Results indicated that for the children with ADHD relative to control children, an N2 component to non-target stimuli was larger in the posterior region and smaller in the frontal region. The P3b component to target stimuli was smaller in the posterior region and larger in the frontal region for the ADHD group compared with the control group. The between-group differences in P3b scalp distribution are indicative of a between-group difference in the neural generators of P3b. It is proposed that the ADHD group, relative to controls, utilizes an additional cognitive process when processing task-relevant stimuli. This process is more frontally distributed and may reflect an attentional compensation mechanism in the ADHD group.

Adolescent↗
PubMed1990

The role of single-channel cues in synchrony perception: the summed waveform.

Human observers are able to discriminate between simultaneously presented bands of noise having envelopes that are identical (synchronous) rather than statistically independent (asynchronous). The possibility that the detection of envelope synchrony is based on cues available in a single critical band, rather than on a simultaneous comparison of envelopes extracted via independent critical bands, is examined. Two potential single-channel cues were examined, both relying on the assumption that information present in the envelope of the summed bands is available to the listener. One such single-channel cue is the rms of the envelope of the summed waveform; the envelope is more deeply modulated for the summed synchronous bands than for the summed asynchronous bands. The second cue examined was envelope regularity; the envelope of the summed synchronous bands has periodic envelope minima, while the summed asynchronous bands exhibit aperiodic envelope minima. Psychophysical results suggest that such within-channel cues may be both available to, and utilized by, the listener when the component bands are separated by less than one-third of an octave.

Attention↗
PubMed1980

Aspects of frequency discrimination in passerine birds and pigeons.

With the use of a positive reinforcement operant technique, pulsed-tone, frequency difference limens (DLs) were measured in two Icterid passerine species, the redwing blackbird (Agelaius phoeniceus) and the brown-headed cowbird (Molothrus ater). Direct comparisons were made with two nonpasserine control (pigeon) subjects. Blackbirds were more sensitive than pigeons to frequency changes above 1.0 kHz but less sensitive below 1.0 kHz. Measured DLs in all these birds were within the range of nonhuman mammals but higher than those of humans. The lowest delta f/f ratio for all birds occurred at 4.0 kHz, a frequency for which they exhibit minimal absolute auditory thresholds and which is a dominant component in the song of the redwing. As in humans, blackbird sensitivity at 1.0 and 2.0 kHz declined as sensation level (SL) was decreased, but at 4.0 kHz, sensitivity showed no clear dependence on SL. At 8.0 kHz, near the upper limit of blackbird hearing, sensitivity increased with a decrease in SL. This latter frequency is a dominant component in the song of the cowbird. Differences in frequency sensitivty were also found as a function of the direction of frequency shift from the standard: Upward shifts produced lower DLs at 1.0 and 2.0 kHz, and downward shifts produced lower DLs at 8.0 kHz.

Animals↗
PubMed1994

Discrimination of interaural envelope delays: the effect of randomizing component starting phase.

The goal of this study was to examine the nature of envelope extraction in the discrimination of high-frequency waveforms on the basis of envelope delay. Threshold interaural envelope delays were measured for complexes consisting of three or five components for which the starting phases of all sinusoids were either sine phase or randomized between intervals of a two-alternative forced-choice (2-AFC) task. The center frequency was 4 kHz and the frequency separation was varied from 25 to 500 Hz. The results showed that thresholds were greater for the phase-randomized conditions than the sine-phase conditions. The phase effect tended to diminish with increasing frequency separation for three-component complexes but not for the five-component complexes. Sensitivity to envelope delay was better for five-component complexes than for three-component complexes at most frequency separations. In general, the results showed superior lateralization performance for conditions in which the envelope fluctuations were greater, a finding that is consistent with models of high-frequency binaural processing that include envelope extraction prior to binaural comparison.

Adult↗
PubMed2003

Auditory temporal order discrimination and backward recognition masking in adults with dyslexia.

The ability of 20 adult dyslexic readers to extract frequency information from successive tone pairs was compared with that of IQ-matched controls using temporal order discrimination and auditory backward recognition masking (ABRM) tasks. In both paradigms, the interstimulus interval (ISI) between tones in a pair was either short (20 ms) or long (200 ms). Temporal order discrimination was better for both groups of listeners at long than at short ISIs, but no group differences in performance were observed at either ISI. Performance on the ABRM task was also better at long than at short ISIs and was influenced by variability in masker frequency and by the spectral proximity of target and masker. The only significant group difference was found in one condition of the ABRM task when the target-masker interval was 200 ms, but this difference was not reliable when the measure was of optimal performance. Moderate correlations were observed between auditory thresholds and phonological skill for the sample as a whole and within the dyslexic and control groups. However, although a small subgroup of dyslexic listeners with poor phonology was characterized by elevated thresholds across the auditory tasks, evidence for an association between auditory and phonological processing skills was weakened by the finding of a subgroup of control listeners with poor auditory processing and normal phonological processing skills.

Adult↗
PubMed2004

Verbal memory in schizophrenia: additional evidence of subtypes having different cognitive deficits.

A prior study found a selective deficit in verbal working memory in a subgroup of patients with schizophrenia who performed as well as healthy controls on a screening test of attention and auditory perception [Arch. Gen. Psychiatry 55 (1998) 1093]. Given the importance of defining pathophysiologically distinct subtypes of schizophrenia, the present study aimed to replicate and extend this finding. Patients with schizophrenia who passed the screening test (discriminators or Dsz patients) were compared to those who did not (nondiscriminators, NDsz patients), and healthy controls on a word serial position test (WSPT) and on other tests of verbal and nonverbal cognitive function. Dsz patients performed more poorly than controls on the WSPT and showed serial position effects consistent with a verbal memory deficit. They also showed a deficit in verbal memory but not visual memory on the Wechsler Memory Scale-Revised. In contrast, the NDsz patients showed overall poor performance on both verbal and nonverbal tests, consistent with a generalized deficit. Verbal working memory deficits were not related to education, gender, severity of symptoms, medication status, or hemispheric dominance for perceiving dichotic words. The findings add to growing evidence for the existence of a subgroup of schizophrenia having a specific verbal memory deficit that is not limited to working memory, but extends to learning and recall of verbal material.

Adult↗