Mistuned Component Research Articles

On mistuning detection and beat perception for harmonic complex tones at low and very high frequencies.

This study assessed the detection of mistuning of a single harmonic in complex tones (CTs) containing either low-frequency harmonics or very high-frequency harmonics, for which phase locking to the temporal fine structure is weak or absent. CTs had F0s of either 280 or 1400 Hz and contained harmonics 6-10, the 8th of which could be mistuned. Harmonics were presented either diotically or dichotically (odd and even harmonics to different ears). In the diotic condition, mistuning-detection thresholds were very low for both F0s and consistent with detection of temporal interactions (beats) produced by peripheral interactions of components. In the dichotic condition, for which the components in each ear were more widely spaced and beats were not reported, the mistuned component was perceptually segregated from the complex for the low F0, but subjects reported no "popping out" for the high F0 and performance was close to chance. This is consistent with the idea that phase locking is required for perceptual segregation to occur. For diotic presentation, the perceived beat rate corresponded to the amount of mistuning (in Hz). It is argued that the beat percept cannot be explained solely by interactions between the mistuned component and its two closest harmonic neighbours.

Effect of Mistuning on the Detection of a Tone Masked by a Harmonic Tone Complex

The human auditory system is sensitive in detecting “mistuned” components in a harmonic complex, which do not match the frequency pattern defined by the fundamental frequency of the complex. Depending on the frequency configuration, the mistuned component may be perceptually segregated from the complex and may be heard as a separate tone. In the context of a masking experiment, mistuning a single component decreases its masked threshold. In this study we propose to quantify the ability to detect a single component for fixed amounts of mistuning by adaptively varying its level. This method produces masking release by mistuning that can be compared to other masking release effects. Detection thresholds were obtained for various frequency configurations where the target component was resolved or unresolved in the auditory system. The results from 6 normal-hearing listeners show a significant decrease of masked thresholds between harmonic and mistuned conditions in all configurations and provide evidence for the employment of different detection strategies for resolved and unresolved components. The data suggest that across-frequency processing is involved in the release from masking. The results emphasize the ability of this method to assess integrative aspects of pitch and harmonicity perception.

Noise‐induced increase in human auditory evoked neuromagnetic fields

Noise is usually detrimental to auditory perception. However, recent psychophysical studies have shown that low levels of broadband noise may improve signal detection. Here, we measured auditory evoked fields (AEFs) while participants listened passively to low-pitched and high-pitched tones (Experiment 1) or complex sounds that included a tuned or a mistuned component that yielded the perception of concurrent sound objects (Experiment 2). In both experiments, stimuli were embedded in low or intermediate levels of Gaussian noise or presented without background noise. For each participant, the AEFs were modeled with a pair of dipoles in the superior temporal plane, and the effects of noise were examined on the resulting source waveforms. In both experiments, the N1m was larger when the stimuli were embedded in low background noise than in the no-noise control condition. Complex sounds with a mistuned component generated an object-related negativity that was larger in the low-noise condition. The results show that low-level background noise facilitates AEFs associated with sound onset and can be beneficial for sorting out concurrent sound objects. We suggest that noise-induced increases in transient evoked responses may be mediated via efferent feedback connections between the auditory cortex and lower auditory centers.

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.

Distortion product otoacoustic emissions generated by mistuned harmonic stimuli

Psychoacoustic research in humans [Lee and Green, J. Acoust. Soc. Am. 95, 718–725 (1994)] suggests that the detection of the mistuning of an harmonic when the harmonic complex and a mistuned component were presented simultaneously to the same ear stems, at least in part, from the resulting envelope interactions on the basilar membrane. Neurophysiological research in chinchillas [Sinex et al., Hear. Res. 168, 150–162 (2002)], provides evidence that such envelope interactions can be detected at the level of the inferior colliculus. The potential role of cochlear nonlinearites in determining the nature of the signal on the basilar membrane is explored by evaluating the DPOAE generated by multicomponent harmonic and inharmonic complexes. When harmonic complexes are used, the DPOAE all fall at harmonic frequencies. When inharmonic complexes are used, many nonharmonic DPOAE are detected.

Further explorations of the contribution of a nonsimultaneous mistuned harmonic to residue pitch

Ciocca and Darwin [V. Ciocca and C.J. Darwin, J. Acoust. Soc. Am. 105, 2421–2430 (1999)] reported a surprising finding: The shift in residue pitch caused by mistuning a harmonic was the same when the mistuned harmonic was presented after the remainder of the complex as when it was simultaneous. The present study tried to replicate this result, and investigated the role of the presence of the nominally mistuned harmonic in the matching sound. Subjects adjusted a matching sound so that its pitch equaled that of a subsequent 90-ms complex tone (12 harmonics of a 155-Hz F0), whose mistuned (±3%) 3rd harmonic was presented either simultaneously with or after the remainder. In experiment 1, the matching sound was a harmonic complex whose 3rd harmonic was either present or absent. In experiment 2, it was a sinusoid. In experiment 3, the target and matching sound contained non-overlapping harmonics. In all experiments, a non-simultaneous mistuned component produced significantly smaller pitch shifts than a simultaneous one. In the absence of the nominally mistuned harmonic in the matching sound, the pitch shift with simultaneous presentation was about five times larger than that with non-simultaneous presentation of the mistuned component. [Work supported by EPSRC Grant GR/R65794/01.]

Neural mechanisms for spectral segregation

Humans exhibit a remarkable ability to segregate sounds produced by multiple sources that overlap in frequency and in time. It is likely that other species that use hearing also have this ability. To investigate the neural mechanisms that contribute to spectral segregation, responses of auditory nerve fibers (ANFs) and inferior colliculus (IC) neurons to harmonic complex tones and to the same tones with a mistuned component were measured. Mistuning leads to the perception of a new sound source and also produces dramatic qualitative changes in the temporal discharge patterns of IC neurons. In contrast, the same stimulus manipulation produces only modest quantitative changes in the responses of ANFs. These results indicate that the processing of complex tones undergoes a major transformation in the lower brainstem that is likely to contribute to perceptual segregation based on harmonicity. A computational model has been developed to investigate integrative mechanisms that may underlie this transformation. The model reproduces the distinctive discharge patterns of IC neurons, and suggests that these patterns arise as a result of narrow-band envelope extraction, followed by broadband excitatory–inhibitory interactions. Specific predictions of the model have been confirmed in subsequent electrophysiological experiments, providing further support for this interpretation. [Work supported by NIDCD.]

Responses of inferior colliculus neurons to harmonic and mistuned complex tones

Responses of inferior colliculus neurons to simplified stimuli that may engage mechanisms that contribute to auditory scene analysis were obtained. The stimuli were harmonic complex tones, which are heard by human listeners as single sounds, and the same tones with one component ‘mistuned’, which are heard as two separate sounds. The temporal discharge pattern elicited by a harmonic complex tone usually resembled the same neuron’s response to a pure tone. In contrast, tones with a mistuned component elicited responses with distinctive, stereotypical temporal patterns that were not obviously related to the stimulus waveform. For a particular stimulus configuration, the discharge pattern was similar across neurons with different pure-tone frequency selectivity. A computational model that compared response envelopes across multiple narrow bands successfully reproduced the stereotypical response patterns elicited by different stimulus configurations. The results suggest that mistuning created a temporally synchronous distributed representation of the mistuned component that could be identified by higher auditory centers in the presence of the ongoing response produced by the remaining components; this kind of representation might facilitate the identification of individual sound sources in complex acoustic environments.

Temporal aspects of pitch perception at high and low S/N ratios

The study investigated the integration of nonsimultaneous frequency components into a single pitch in quiet and in noise. Using a pitch matching paradigm, the shifts produced by a mistuned harmonic in the pitch of a target complex were measured either with a pre-target component (when the mistuned component stopped as the target started) or with a post-target component (when the mistuned component immediately followed the target tone) [J. Acoust. Soc. Am. 98, 2946(A) (1995)]. The stimuli were presented in quiet or in the presence of a band of noise, low-pass filtered at a frequency cutoff of 3 kHz (approx. −23-dB S/N ratio around the frequency of the mistuned component). In quiet, post-target and simultaneous mistuned components produced larger pitch shifts than pre-target components. In noise, shifts in the pre-target condition were identical to those produced by simultaneous and post-target components. The duration of the interval which separated the nonsimultaneous components and the target tone was varied in a second experiment. The results suggest that the period over which nonsimultaneous components contribute to the pitch of the target is longer in noise than in quiet for both pre- and post-target conditions. [Work supported by HKRGC Grant No. HKU362/94M.]

The role of temporal factors in pitch perception

This study investigated how pitch perception mechanisms integrate acoustic information over time. The pitch matching procedure developed by Moore etal. [J. Acoust. Soc. Am. 77, 1853–1860 (1985)] was used in order to measure pitch shifts in a harmonic series (target complex) produced by mistuning a harmonic that either preceded or followed the target complex. In the first experiment, the mistuned component could either stop as the target complex started (pretarget condition) or start as the target stopped (post-target condition). The results showed that pitch shifts were significantly larger in the post-target than in the pretarget condition. In the second experiment, the duration of the silent period, which separated the mistuned component and the target complex, was varied in both the pre- and the post-target conditions. Pitch shifts were virtually eliminated by a delay longer than 20 ms in the pretarget condition. By contrast, a delay of 160 ms was necessary to eliminate pitch shifts in the post-target condition. These results suggest that pitch perception mechanisms take into account the order of occurrence of acoustic information for calculating the pitch of a complex sound. [Work supported by Hong Kong RGC, Grant HKU 362/94M.]

Comparison of the effect of onset asynchrony on auditory grouping in pitch matching and vowel identification.

Previous experiments have shown that when a slightly mistuned harmonic of a complex tone starts more than about 80 msec before the remaining components, it makes a reduced contribution to the pitch of the complex. This contribution decreases to zero by about 300-msec onset asynchrony. In vowel perception, however, analogous experiments have shown that a much shorter asynchrony (around 40 msec) is enough to ensure that a component does not influence a vowel's phonemic category. The three experiments reported here demonstrate that this difference in the utility of onset time as a grouping cue does not arise because of differences in stimulus structure, but rather is due to the perceptual task. They show that the onset asynchrony needed in a pitch-matching experiment to remove the contribution that a mistuned component makes to the pitch of a vowel is the same as that needed to remove the contribution to the pitch of a flat-spectrum complex tone. They further show that a much smaller onset asynchrony is needed to perceptually remove the same harmonic from a vowel for the calculation of vowel quality. The implication of this result for models of auditory grouping is discussed.

Detection of a mistuned component in a harmonic complex.

The ability to detect a mistuned component in a harmonic complex was measured as a function of harmonic number under three different stimulus procedures: simultaneous monotic, successive monotic, and simultaneous dichotic. In the first experiment, the fundamental frequency was 200 Hz, and the stimulus duration was 410 ms. The threshold obtained in the simultaneous-monotic procedure was lower than those obtained in the other two procedures, especially for harmonics above the third. It is argued that an envelope cue associated with lower-frequency components in the power spectrum of the envelope was the primary cue for the detection of a mistuned component in a harmonic complex in the simultaneous-monotic procedure. Thresholds did not differ for successive-monotic and simultaneous-dichotic procedures, suggesting that the detection of the mistuning was mediated above the level of the cochlea. In the second and third experiments, the stimulus duration and the fundamental frequency of the complex was altered. The envelope cue seemed to be weakened by decreasing the stimulus duration and by increasing the fundamental frequency.

Detection of a mistuned component in a harmonic complex

The ability to detect a mistuned component in a harmonic complex was measured as a function of harmonic number using three different stimulus procedures. The harmonic complex and target component were presented either simultaneously to the same ear (simultaneous monotic), successively to the same ear (successive monotic), or simultaneously to different ears (simultaneous dichotic). For harmonic numbers above the third, the thresholds obtained in the simultaneous-monotic procedure were much lower than those obtained in the other two procedures. It is argued that detection in the simultaneous-monotic procedure is primarily based on a cue associated with the lower-frequency components in the power spectrum of the stimulus envelope. The envelope cue seemed to be weakened by either decreasing the stimulus duration from 410 ms or increasing the fundamental frequency from 200 Hz. Thresholds did not differ for successive-monotic and simultaneous-dichotic procedures, suggesting that the detection of the mistuned component was mediated above the level of the cochlea. [Work supported by NIH.]

Effects of onset asynchrony on pitch perception: adaptation or grouping?

A previous paper by Darwin and Ciocca [J. Acoust. Soc. Am. 91, 3381-3390 (1992)] showed that a slightly mistuned frequency component of a (target) harmonic complex produced smaller pitch shifts in the target if it started 160 ms or more before the other components than if all the components were simultaneous. Three experiments investigated whether this effect of onset asynchrony is due to peripheral adaptation to the leading portion of the mistuned component or to perceptual grouping. The first two experiments showed that the effect of asynchrony could be influenced by grouping mechanisms without changing the amount of adaptation produced by the leading portion of the mistuned component. In the first experiment, the effect of asynchrony was reduced by the presence of an additional (captor) complex which was harmonically related to the mistuned component and synchronous with just its leading portion. In experiment 2, the effect of asynchrony was increased by presenting a captor that was synchronous with the entire mistuned component. This capturing effect was independent of the harmonic relation between the captor and the mistuned component at 40-ms asynchrony; at 160 ms the effect of asynchrony increased further only if the captor and the mistuned component were harmonically related. In the third experiment, the expected amount of adaptation was increased (relative to that produced by a single sine precursor) by presenting several components that were close in frequency to the mistuned component and synchronous with its leading portion.(ABSTRACT TRUNCATED AT 250 WORDS)

Grouping in pitch perception: effects of onset asynchrony and ear of presentation of a mistuned component.

Three experiments investigated how the onset asynchrony and ear of presentation of a single mistuned frequency component influence its contribution to the pitch of an otherwise harmonic complex tone. Subjects matched the pitch of the target complex by adjusting the pitch of a second similar but strictly periodic complex tone. When the mistuned component (the 4th harmonic of a 155 Hz fundamental) started 160 ms or more before the remaining harmonics but stopped simultaneously with them, it made a reduced contribution to the pitch of the complex. It made no contribution if it started more than 300 ms before. Pitch shifts and their reduction with onset time were larger for short (90 ms) sounds than for long (410 ms). Pitch shifts were slightly larger when the mistuned component was presented to the same ear as the remaining 11 in-tune harmonics than to the opposite ear. Adding a "captor" complex tone with a fundamental of 200 Hz and a missing 3rd harmonic to the contralateral ear did not augment the effect of onset time, even though the captor was synchronous with the mistuned harmonic, the mistuned component was equal in frequency to the missing 3rd harmonic of the captor complex tone and it was played to the same ear as the captor. The results show that a difference in onset time can prevent a resolved frequency component from contributing to the pitch of a complex tone even though it is present throughout that complex tone.

Matching the pitch of a mistuned harmonic in an otherwise periodic complex tone

Listeners adjusted the frequency of a sine tone to match the pitch of a single mistuned harmonic in a complex tone consisting of 16 harmonics. Fundamental frequencies were 200, 400, or 800 Hz, and mistunings ranged from 0.5% to 8.0%. The successful matches, those close to the actual mistuned harmonic, show highly consistent and unexpected pitch shift effects; the pitch shifts can be twice as large as the frequency shifts, for both positive and negative frequency shifts. The percentage of matches which are successful provides an estimate of a listener's ability to segregate the mistuned component from the complex tone. Best performance occurs for mistuned harmonics in the region of spectral dominance. The highest frequency which can be segregated is a decreasing function of the fundamental frequency. The latter result suggests that the segregation operation depends upon both place and time coding in the auditory system. [Work supported by the NIH, the NSF, and the CHRS—France.]