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PubMed1992

Auditory processing of complex sounds: an overview.

The past 30 years has seen a remarkable development in our understanding of how the auditory system--particularly the peripheral system--processes complex sounds. Perhaps the most significant has been our understanding of the mechanisms underlying auditory frequency selectivity and their importance for normal and impaired auditory processing. Physiologically vulnerable cochlear filtering can account for many aspects of our normal and impaired psychophysical frequency selectivity with important consequences for the perception of complex sounds. For normal hearing, remarkable mechanisms in the organ of Corti, involving enhancement of mechanical tuning (in mammals probably by feedback of electro-mechanically generated energy from the hair cells), produce exquisite tuning, reflected in the tuning properties of cochlear nerve fibres. Recent comparisons of physiological (cochlear nerve) and psychophysical frequency selectivity in the same species indicate that the ear's overall frequency selectivity can be accounted for by this cochlear filtering, at least in bandwidth terms. Because this cochlear filtering is physiologically vulnerable, it deteriorates in deleterious conditions of the cochlea--hypoxia, disease, drugs, noise overexposure, mechanical disturbance--and is reflected in impaired psychophysical frequency selectivity. This is a fundamental feature of sensorineural hearing loss of cochlear origin, and is of diagnostic value. This cochlear filtering, particularly as reflected in the temporal patterns of cochlear fibres to complex sounds, is remarkably robust over a wide range of stimulus levels. Furthermore, cochlear filtering properties are a prime determinant of the 'place' and 'time' coding of frequency at the cochlear nerve level, both of which appear to be involved in pitch perception. The problem of how the place and time coding of complex sounds is effected over the ear's remarkably wide dynamic range is briefly addressed. In the auditory brainstem, particularly the dorsal cochlear nucleus, are inhibitory mechanisms responsible for enhancing the spectral and temporal contrasts in complex sounds. These mechanisms are now being dissected neuropharmacologically. At the cortical level, mechanisms are evident that are capable of abstracting biologically relevant features of complex sounds. Fundamental studies of how the auditory system encodes and processes complex sounds are vital to promising recent applications in the diagnosis and rehabilitation of the hearing impaired.

Animals↗
PubMed2003

"Out-of-pitch" but still "in-time". An auditory psychophysical study in congenital amusic adults.

Congenital amusia is a lifelong disability, commonly known as tone deafness, that prevents afflicted individuals from developing basic musical skills despite normal audiometry and above-average intellectual, memory, and language skills. Although it is estimated that 4% of the general population would be born with such a musical handicap, the underlying cause is presently unknown. Recently, we proposed that this disorder could be traced to a deficit in pitch perception on the basis of a single case. Here we provide psychophysical evidence for the existence of a generalized defect that is both fine grained and specific to pitch because time is unaffected.

Female↗
PubMed2004

Pitch estimation of a deeply inserted cochlear implant electrode.

In this short communication, we evaluate the place-pitch relation of a newly designed, deeply inserted, cochlear implant electrode. The insertion depths ranged from 471 degrees to 662 degrees. Pitch perception was measured in eight subjects with monopolar stimulation on each electrode contact at intensities of 50% and 80% of the dynamic range. We observed a monotonic reduction of pitch estimate with insertion depth. For about half of the subjects, a flattening of the pitch estimate at the basal end of the electrode was seen, while for the other half, pitch continued to decrease monotonically up to the most apical part of the array. We conclude that deeper insertion could increase pitch range for at least some cochlear implant recipients, and could hence potentially increase group performance.

Adult↗
PubMed1988

Perception of the missing fundamental in nonhuman primates.

In preparation for neurophysiological experiments aimed at mechanisms of pitch perception, four rhesus monkeys were trained to press a button when the fundamental frequencies (missing or present) of two complex tones in a tone pair matched. Both tones were based on a five-component harmonic series. Zero to three of the lowest components could be missing in the first tone, while the second (comparison) tone contained all five harmonics. The range of fundamentals tested varied from 200 to 600 Hz. Three monkeys learned to match tones missing their fundamentals to comparison harmonic complexes with the same pitch, whereas the fourth monkey required the physical presence of the fundamental. Consideration of several cues available to the monkeys suggests that the animals could perceive the missing fundamental.

Animals↗
PubMed2002

Chimaeric sounds reveal dichotomies in auditory perception.

By Fourier's theorem, signals can be decomposed into a sum of sinusoids of different frequencies. This is especially relevant for hearing, because the inner ear performs a form of mechanical Fourier transform by mapping frequencies along the length of the cochlear partition. An alternative signal decomposition, originated by Hilbert, is to factor a signal into the product of a slowly varying envelope and a rapidly varying fine time structure. Neurons in the auditory brainstem sensitive to these features have been found in mammalian physiological studies. To investigate the relative perceptual importance of envelope and fine structure, we synthesized stimuli that we call 'auditory chimaeras', which have the envelope of one sound and the fine structure of another. Here we show that the envelope is most important for speech reception, and the fine structure is most important for pitch perception and sound localization. When the two features are in conflict, the sound of speech is heard at a location determined by the fine structure, but the words are identified according to the envelope. This finding reveals a possible acoustic basis for the hypothesized 'what' and 'where' pathways in the auditory cortex.

Auditory Perception↗
PubMed2004

Frequency discrimination at different frequency levels as indexed by electrophysiological and behavioral measures.

The present study systematically compared the neural and behavioral accuracy of discriminating a frequency change ("deviant") in a repetitive tone ("standard") across a frequency range of 250-4000 Hz. The sound structure (pure sinusoidal vs. harmonically rich tones) and the magnitude of frequency change (2.5%, 5%, 10%, 20%) were also varied. The accuracy of neural frequency-change detector was determined by comparing the auditory event-related potentials (ERP) elicited by deviant and standard stimuli in the absence of attention. In a separate behavioral task, subjects were to indicate when they noticed a frequency change. The ranges of the across-subject means of ERP parameters across the conditions were: the mismatch negativity (MMN) amplitude -0.9 to -4.9 microV, latency 125-218 ms, the P3a amplitude 0.3-3.2 microV, latency 239-304 ms. The ERP latency was shortest for the standard-stimulus frequency from 1000 to 2000 Hz suggesting that automatic frequency discrimination was the most accurate in that range. The ERP latencies and amplitudes correlated with the hit rate (HR) and reaction time (RT), with highest correlation found between the MMN amplitude and the HR (r=0.8). The harmonical tones elicited MMN and P3a with shorter latencies and larger amplitudes, than did pure sinusoidal tones in all frequency bands. The results may have implication to pitch-perception theories.

Acoustic Stimulation↗
PubMed2005

Structural, functional, and perceptual differences in Heschl's gyrus and musical instrument preference.

The musical pitch of harmonic complex sounds, such as instrumental sounds, is perceived primarily by decoding either the fundamental pitch (keynote) or spectral aspects of the stimuli, for example, single harmonics. We divided 334 professional musicians, including symphony orchestra musicians, 75 amateur musicians, and 54 nonmusicians, into either fundamental pitch listeners or spectral pitch listeners. We observed a strong correlation between pitch perception preference and asymmetry of brain structure and function in the pitch-sensitive lateral areas of Heschl's gyrus (HG), irrespective of musical ability. In particular, fundamental pitch listeners exhibited both larger gray matter volume measured using magnetic resonance imaging (MRI) and enhanced P50m activity measured using magnetoencephalography (MEG) in the left lateral HG, which is sensitive to rapid temporal processing. Their chosen instruments were percussive or high-pitched instruments that produce short, sharp, or impulsive tones (e.g., drums, guitar, piano, trumpet, or flute). By contrast, spectral pitch listeners exhibited a dominant right lateral HG, which is known to be sensitive to slower temporal and spectral processing. Their chosen instruments were lower-pitched melodic instruments that produce rather sustained tones with characteristic changes in timbre (e.g., bassoon, saxophone, french horn, violoncello, or organ). Singers also belonged to the spectral pitch listeners. Furthermore, the absolute size of the neural HG substrate depended strongly on musical ability. Overall, it is likely that both magnitude and asymmetry of lateral HG, and the related perceptual mode, may have an impact on preference for particular musical instruments and on musical performance.

Acoustic Stimulation↗
PubMed1985

Perceptual learning in frequency discrimination.

This study was concerned with the effects of training on the frequency discrimination ability of human listeners. Frequency discrimination at 200 Hz was tested before and after training. Four groups of listeners received training in four different frequency regions, 200, 360, 2500, and 6000 Hz. It was found that training at 200, 360, and 2500 Hz all provided comparable improvement in discrimination performance at 200 Hz whereas training at 6000 Hz provided less improvement. This result is consistent with the idea that frequency discrimination and pitch perception are mediated by different processes at high (greater than 5000 Hz) and low (less than 5000 Hz) frequencies.

Adult↗
PubMed1997

Representation of periodicity pitch in the primary auditory cortex of the Mongolian gerbil.

Responses of single and multi-units in the primary auditory cortex (AI) of the Mongolian gerbil to tones and amplitude modulations (AMs) were studied. Two types of AM stimuli were used: i) those which were spectrally inside the unit's frequency response range (FRR) and ii) those that were spectrally completely outside a unit's FRR. In response to AMs spectrally within a unit's FRR, a minority of units showed phase-locked responses tuned to a certain range of modulation frequencies (envelope periodicities) of the AM. Phase-locking was confined to frequencies up to 65 Hz, the range best modulation frequencies covered by this synchrony code (sync-BMFs) contained values between 5 and 30 Hz. In response to AMs completely outside a unit's FRR, 69% of the units in the low frequency area of AI (up to 3 kHz best frequency) exhibited phasic or tonic responses tuned to certain envelope periodicities with rate-BMFs ranging from 50 to about 3000 Hz, a range that might be sufficient to account for a representation of periodicity pitch. Topographic reconstruction of the recording sites of such units revealed that, in contrast to the sync-BMFs described above, the rate-BMF values were systematically distributed within AI, therefore reflecting a periodotopic organization. We suggest that the temporal quality of the percept (rhythm) might be coded via a temporal (synchrony) code whereas the non-temporal quality of the percept (pitch) is coded via a non-temporal (rate-place) code.

Animals↗
PubMed1982

Frequency and intensity effects on ear dominance for tone bursts.

Normal-hearing Ss (N = 20) listened to dichotic pairs of 20-msec tones at 0.4, 1.5, or 3 kc/s differing by 76, 224, or 376 c/s between the two ears and also differing by 0, 15, or 35 db in SPL (the more intense tone always at 80 db SPL). S judged each pair "high-low" or "low-high" in pitch. Earlier investigations have shown that many normal-hearing Ss demonstrate a dominance for pitch perception of one ear over the other which is unaltered by large interaural intensity differences. In this study, ear dominance could be modified by a change in frequency location or interaural frequency difference of the dichotic stimuli. The effect of interaural level differences could be seen at all frequency conditions, but was strongest at low frequencies. It was suggested that ear dominance on this perceptual task is governed by several characteristics of the auditory system, including loudness perception, dichotic fusion, and frequency selectivity, as well as some as-yet ill-defined binaural processes.

Acoustic Stimulation↗
PubMed1984

Representation of voice pitch in discharge patterns of auditory-nerve fibers.

Responses of populations of auditory-nerve fibers were measured for synthesized consonant-vowel stimuli. This paper explores the encoding of fundamental frequency (pitch) in these responses. Post-stimulus time (PST) histograms were computed from 25 ms segments of the spike trains. Discrete Fourier transforms with a 40 Hz resolution were computed from the histograms. Two representations of pitch are considered. The first representation is based on the pitch-related temporal properties of the speech signal. Histograms for individual units can show envelope modulations directly related to the pitch period. These modulations reflect the responses of these fibers to a number of stimulus harmonics near fiber CF. Responses of fibers near formant frequencies are dominated by a single large harmonic component, and thus show small or no pitch-related enveloped modulations. Envelope modulations are reduced in the presence of background noise. The second representation uses both temporal properties of auditory-nerve responses and cochlear place to encode the pitch-related harmonic structure of speech. As a measure of the response of the population of fibers to each harmonic of 40 Hz the magnitude of the component of the Fourier transform at that frequency was averaged across all fibers whose characteristic frequencies were within one-fourth octave of that harmonic. We call this measure the average localized synchronized rate (ALSR). The ALSR provides a good representation of stimulus spectrum, even in the presence of background noise. From the harmonic structure of the ALSR, we are able to extract the stimulus pitch frequency. The relationship of these two representations to pitch perception in both acoustic and electrical stimulation (via cochlear implants) is discussed.

Acoustic Stimulation↗
PubMed2000

On the dichotic pitch of simultaneously presented interaurally delayed white noises. Implications for binaural theory.

A dichotic pitch known as Fourcin Pitch (FP) is perceived when two independent interaurally delayed white noises are presented simultaneously. Experiments in the past mainly dealt with stimulus situations where one interaural delay was smaller than 4 ms and the other was in the range 0-10 ms. Here, experiments are reported showing a novel pitch percept that occurs when one noise is interaurally delayed at the left ear and the other noise is about equally delayed at the right ear, for delays in the range of 4-10 ms. It is shown that, for both the previously reported FP and the novel pitch, the Central Spectrum (CS) theory [Raatgever and Bilsen, J. Acoust. Soc. Am. 80, 429-441 (1986)] provides a correct prediction of both the pitch value and the lateral position of the pitch image, where other current theories partly or completely fail. Further experiments indicate that the lateralized position of the pitch image is essentially not influenced by an interaural intensity difference (IID). This is also predicted by the CS model and leads to the generalized conclusion that interaural time and intensity differences are processed separately in the auditory system until, at least, the level where the dichotic pitch is generated.

Dichotic Listening Tests↗
PubMed1979

Tone-segregation by phase: on the phase sensitivity of the single ear.

A monaural complex tone is synthesized from 12 harmonically related pure tones, played in phase. In each of 12 segments, one of the tones (the target) is played out of phase so that the sequence of targets is increasing or decreasing in frequency. If the target is at least 30 degrees out of phase, the targets are perceptually segregated. This tone-segregation by phase raises doubts concerning several current theories of pitch perception. The phenomenon is conjectured to be caused by the ear's nonlinear compressive transfer characteristic or by a temporal analysis of the stimulus.

Acoustic Stimulation↗
PubMed1995

The effect of voice lessons on the clinical and perceptual skills of graduate students in speech-language pathology.

Two groups of 10 speech-language pathology graduate students were each given 7 weeks of singing lessons to determine whether voice lessons could have an effect on their clinical and perceptual skills. Pre-, mid-, and posttests to measure various skills were designed and implemented. With use of paired sample statistical testing, statistically significant results were obtained. In addition, the subjective responses of the students show that the lessons were effective in improving pitch perception, breath control, and legato production or easy onset. This study supports efforts to integrate curricula in vocal performance and speech-language pathology.

Adult↗
PubMed2005

Pitch of complex tones: rate-place and interspike interval representations in the auditory nerve.

Harmonic complex tones elicit a pitch sensation at their fundamental frequency (F0), even when their spectrum contains no energy at F0, a phenomenon known as "pitch of the missing fundamental." The strength of this pitch percept depends upon the degree to which individual harmonics are spaced sufficiently apart to be "resolved" by the mechanical frequency analysis in the cochlea. We investigated the resolvability of harmonics of missing-fundamental complex tones in the auditory nerve (AN) of anesthetized cats at low and moderate stimulus levels and compared the effectiveness of two representations of pitch over a much wider range of F0s (110-3,520 Hz) than in previous studies. We found that individual harmonics are increasingly well resolved in rate responses of AN fibers as the characteristic frequency (CF) increases. We obtained rate-based estimates of pitch dependent upon harmonic resolvability by matching harmonic templates to profiles of average discharge rate against CF. These estimates were most accurate for F0s above 400-500 Hz, where harmonics were sufficiently resolved. We also derived pitch estimates from all-order interspike-interval distributions, pooled over our entire sample of fibers. Such interval-based pitch estimates, which are dependent on phase-locking to the harmonics, were accurate for F0s below 1,300 Hz, consistent with the upper limit of the pitch of the missing fundamental in humans. The two pitch representations are complementary with respect to the F0 range over which they are effective; however, neither is entirely satisfactory in accounting for human psychophysical data.

Acoustic Stimulation↗
PubMed2006

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.

Adult↗
PubMed2006

The case of the missing delay lines: synthetic delays obtained by cross-channel phase interaction.

Temporal models of pitch and harmonic segregation call for delays of up to 30 ms to cover the full range of existence of musical pitch. To date there is little anatomical or physiological evidence for delays that long. We propose a mechanism by which delays may be synthesized from cross-channel phase interaction. Phases of adjacent cochlear filter channels are shifted by an amount proportional to frequency and then combined as a weighted sum to approximate a delay. Synthetic delays may be used by pitch perception models such as autocorrelation, segregation models such as harmonic cancellation, and binaural processing models to explain sensitivity to large interaural delays. The maximum duration of synthetic delays is limited by the duration of the impulse responses of cochlear filters, itself inversely proportional to cochlear filter bandwidth. Maximum delay is thus frequency dependent. This may explain the fact, puzzling for temporal pitch models such as autocorrelation, that pitch is more salient and easy to discriminate for complex tones that contain resolved partials.

Auditory Cortex↗
PubMed2001

Coding of the fundamental frequency in continuous interleaved sampling processors for cochlear implants.

In this study the perception of the fundamental frequency (F0) of periodic stimuli by cochlear implant users is investigated. A widely used speech processor is the Continuous Interleaved Sampling (CIS) processor, for which the fundamental frequency appears as temporal fluctuations in the envelopes at the output. Three experiments with four users of the LAURA (Registered trade mark of Philips Hearing Implants, now Cochlear Technology Centre Europe) cochlear implant were carried out to examine the influence of the modulation depth of these envelope fluctuations on pitch discrimination. In the first experiment, the subjects were asked to discriminate between two SAM (sinusoidally amplitude modulated) pulse trains on a single electrode channel differing in modulation frequency ( deltaf = 20%). As expected, the results showed a decrease in the performance for smaller modulation depths. Optimal performance was reached for modulation depths between 20% and 99%, depending on subject, electrode channel, and modulation frequency. In the second experiment, the smallest noticeable difference in F0 of synthetic vowels was measured for three algorithms that differed in the obtained modulation depth at the output: the default CIS strategy, the CIS strategy in which the F0 fluctuations in the envelope were removed (FLAT CIS), and a third CIS strategy, which was especially designed to control and increase the depth of these fluctuations (F0 CIS). In general, performance was poorest for the FLAT CIS strategy, where changes in F0 are only apparent as changes of the average amplitude in the channel outputs. This emphasizes the importance of temporal coding of F0 in the speech envelope for pitch perception. No significantly better results were obtained for the F0 CIS strategy compared to the default CIS strategy, although the latter results in envelope modulation depths at which sub-optimal scores were obtained in some cases of the first experiment. This indicates that less modulation is needed if all channels are stimulated with synchronous F0 fluctuations. This hypothesis is confirmed in a third experiment where subjects performed significantly better in a pitch discrimination task with SAM pulse trains, if three channels were stimulated concurrently, as opposed to only one.

Acoustic Stimulation↗