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K Krumbholz

Publications and source records attributed to K Krumbholz.

16 recordsLinked to original sources
PubMed2006

From noise to pitch: transient and sustained responses of the auditory evoked field.

In recent magnetoencephalographic studies, we established a novel component of the auditory evoked field, which is elicited by a transition from noise to pitch in the absence of a change in energy. It is referred to as the 'pitch onset response'. To extend our understanding of pitch-related neural activity, we compared transient and sustained auditory evoked fields in response to a 2000-ms segment of noise and a subsequent 1000-ms segment of regular interval sound (RIS). RIS provokes the same long-term spectral representation in the auditory system as noise, but is distinguished by a definite pitch, the salience of which depends on the degree of temporal regularity. The stimuli were presented at three steps of increasing regularity and two spectral bandwidths. The auditory evoked fields were recorded from both cerebral hemispheres of twelve subjects with a 37-channel magnetoencephalographic system. Both the transient and the sustained components evoked by noise and RIS were sensitive to spectral bandwidth. Moreover, the pitch salience of the RIS systematically affected the pitch onset response, the sustained field, and the off-response. This indicates that the underlying neural generators reflect the emergence, persistence and offset of perceptual attributes derived from the temporal regularity of a sound.

Acoustic Stimulation↗
PubMed2004

Interaction between the neuromagnetic responses to sound energy onset and pitch onset suggests common generators.

The pitch-onset response (POR) is a negative component of the auditory evoked field which is elicited when the temporal fine structure of a continuous noise is regularized to produce a pitch perception without altering the gross spectral characteristics of the sound. Previously, we showed that the latency of the POR is inversely related to the pitch value and its amplitude is correlated with the salience of the pitch, suggesting that the underlying generators are part of a pitch-processing network [Krumbholz, K., Patterson, R.D., Seither-Preisler, A., Lammertmann, C. & Lütkenhöner, B. (2003) Cereb. Cortex,13, 765-772]. The source of the POR was located near the medial part of Heschl's gyrus. The present study was designed to determine whether the POR originates from the same generators as the energy-onset response (EOR) represented by the N100m/P200m complex. The EOR to the onset of a noise, and the POR to a subsequent transition from noise to pitch, were recorded as the time interval between the noise onset and the transition varied from 500 to 4000 ms. The mean amplitude of the POR increased by approximately 5.9 nA.m with each doubling of the time between noise onset and transition. This suggests an interaction between the POR and the EOR, which may be based on common neural generators.

Acoustic Stimulation↗
PubMed2003

Localization of primary auditory cortex in humans by magnetoencephalography.

Brief auditory stimuli activate the primary auditory cortex (PAC) earlier than any other cortical area so, within a certain latency range, the PAC is the only cortical source contributing to the auditory evoked field (AEF). Nevertheless, there is no AEF component specific to PAC that can be reliably detected in all individuals. The present study suggests that a peak in the first temporal derivative of the magnetic field at about 20 ms (dP20m) is a genuine correlate of PAC activity. AEFs in response to clicks presented to the right ear were recorded with a 37-channel axial gradiometer system positioned over the left hemisphere in nine normal-hearing subjects. More than 8500 stimuli were presented in each of two independent sessions at a rate of approximately 3/s. The dipole coordinates for the dP20m derived from the two sessions typically differed by only a few millimeters. Coregistration of the dipoles with structural magnetic resonance images suggests that dP20m arises from an area close to the retroinsular origin of Heschl's gyrus. Although the dP20m is simply the point of steepest slope on the well-known middle-latency peak, P30m or Pam, it would appear that dP20m and P30m do not have the same cortical origin. Evidence is provided that P30m receives major contributions from at least two distinct cortical areas, only one of which is PAC.

Acoustic Stimulation↗
PubMed2003

Studies of tonotopy based on wave N100 of the auditory evoked field are problematic.

There is still dissension as to whether the auditory evoked field (AEF) reflects tonotopy in the auditory cortex. That notwithstanding, particularly the pronounced AEF wave occurring about 100 ms after stimulus onset (N100 m) is increasingly used for the investigation of issues such as cortical reorganization and representation of virtual pitch. Thus, it appears to be time for a critical revaluation of the supposed tonotopic organization of the N100 m generator. In the present magnetoencephalography study, the response to tonebursts of 500 ms duration, monaurally presented 60 dB above threshold, was recorded with a 37-channel axial gradiometer system over the hemisphere contralateral to the side of stimulation. The stimulus frequencies were 250, 500, 1000, and 2000 Hz. About 250 stimuli of each type were presented in random order in four independent sessions at intervals uniformly distributed between 2 and 2.8 s. An analysis of 19 hemispheres in 10 normal-hearing subjects showed a high intraindividual reproducibility, but also a substantial interindividual variability. In most cases, the dipole location either exhibited no significant frequency dependence at all, the dipoles for the four frequencies were not orderly aligned, or the data disagreed with the single-dipole model. In the few cases showing an arrangement of dipoles consistent with the assumption of an orderly tonotopic cortical map, the most relevant coordinate varied from subject to subject. Regarding theses results, it seems crucial to understand wave N100 m on the basis of individual subjects, whereas conclusions relying on mean dipole locations for groups of subjects are problematic.

Acoustic Stimulation↗
PubMed2003

Neuromagnetic evidence for a pitch processing center in Heschl's gyrus.

There have been several attempts to use the neuromagnetic response to the onset of a tonal sound (N100m) to study pitch processing in auditory cortex. Unfortunately, a large proportion of the N100m is simply a response to the onset of sound energy, independent of whether the sound produces a pitch. The current study describes a novel stimulus paradigm designed to circumvent the energy-onset response and thereby isolate the response of those neural elements specifically involved in pitch processing. The temporal resolution of magnetoencephalography enables us to show that the latency and amplitude of this pitch-onset response (POR) vary with the pitch and pitch strength of the tone. The spatial resolution is sufficient to show that its source lies somewhat anterior and inferior to that of the N100m, probably in the medial part of Heschl's gyrus.

Acoustic Stimulation↗
PubMed2001

Evidence for an analytic perception of multiharmonic sounds in the bat, Megaderma lyra, and its possible role for echo spectral analysis.

For echolocation, the gleaning bat Megaderma lyra relies on short and broadband calls consisting of multiple harmonic components, each of which is downward frequency modulated. The harmonic components in M. lyra's calls have a relatively small frequency excursion and do not overlap spectrally. Broadband calls of other bat species, on the other hand, often consist of only a few harmonics which are modulated over broad and sometimes overlapping frequency ranges. A call consisting of narrow and nonoverlapping harmonic components may provide a less complete representation of target structure than a call which consists of broadly modulated components. However, a multiharmonic call may help the bats to perceive local spectral changes in the echo from shifts in the peak frequencies of single harmonics, and thereby to extract additional information about the target. To assess this hypothesis, the accuracy with which M. lyra can analyze frequency shifts of single partials in multiharmonic complex tones was investigated. A two-alternative, forced-choice behavioral task was used to measure M. lyra's frequency discrimination threshold for the third partial in complex tones whose spectral composition resembled that of the bat's sonar calls. The discrimination threshold for the third partial in a 21.5-kHz harmonic tone amounted to about 2% and was similar to the bat's pure-tone discrimination threshold at 64.5 kHz. Discrimination performance was essentially unaffected by random frequency changes of the other partials and by reducing stimulus duration from 50.5 to 1.5 ms. Both findings are in accordance with predictions made on the basis of the shape of M. Ivra's cochlear filters. The comparison between the observed frequency discrimination performance and a computational estimate of the expected frequency shift in the third harmonic of an echo reflected by a simple, two-front target showed that M. lyra's frequency resolution is sufficient for analyzing the target-specific information conveyed by shifts in the peak frequency of single echo components.

Animals↗
PubMed2001

The lower limit of melodic pitch.

An objective melody task was used to determine the lower limit of melodic pitch (LLMP) for harmonic complex tones. The LLMP was defined operationally as the repetition rate below which listeners could no longer recognize that one of the notes in a four-note, chromatic melody had changed by a semitone. In the first experiment, the stimuli were broadband tones with all their components in cosine phase, and the LLMP was found to be around 30 Hz. In the second experiment, the tones were filtered into bands about 1 kHz in width to determine the influence of frequency region on the LLMP. The results showed that whenever there was energy present below 800 Hz, the LLMP was still around 30 Hz. When the energy was limited to higher-frequency regions, however, the LLMP increased progressively, up to 270 Hz when the energy was restricted to the region above 3.2 kHz. In the third experiment, the phase relationship between spectral components was altered to determine whether the shape of the waveform affects the LLMP. When the envelope peak factor was reduced using the Schroeder phase relationship, the LLMP was not affected. When a secondary peak was introduced into the envelope of the stimuli by alternating the phase of successive components between two fixed values, there was a substantial reduction in the LLMP, for stimuli containing low-frequency energy. A computational auditory model that extracts pitch information with autocorrelation can reproduce all of the observed effects, provided the contribution of longer time intervals is progressively reduced by a linear weighting function that limits the mechanism to time intervals of less than about 33 ms.

Adult↗
PubMed2001

Asymmetry of masking between noise and iterated rippled noise: evidence for time-interval processing in the auditory system.

This study describes the masking asymmetry between noise and iterated rippled noise (IRN) as a function of spectral region and the IRN delay. Masking asymmetry refers to the fact that noise masks IRN much more effectively than IRN masks noise, even when the stimuli occupy the same spectral region. Detection thresholds for IRN masked by noise and for noise masked by IRN were measured with an adaptive two-alternative, forced choice (2AFC) procedure with signal level as the adaptive parameter. Masker level was randomly varied within a 10-dB range in order to reduce the salience of loudness as a cue for detection. The stimuli were filtered into frequency bands, 2.2-kHz wide, with lower cutoff frequencies ranging from 0.8 to 6.4 kHz. IRN was generated with 16 iterations and with varying delays. The reciprocal of the delay was 16, 32, 64, or 128 Hz. When the reciprocal of the IRN delay was within the pitch range, i.e., above 30 Hz, there was a substantial masking asymmetry between IRN and noise for all filter cutoff frequencies; threshold for IRN masked by noise was about 10 dB larger than threshold for noise masked by IRN. For the 16-Hz IRN, the masking asymmetry decreased progressively with increasing filter cutoff frequency, from about 9 dB for the lowest cutoff frequency to less than 1 dB for the highest cutoff frequency. This suggests that masking asymmetry may be determined by different cues for delays within and below the pitch range. The fact that masking asymmetry exists for conditions that combine very long IRN delays with very high filter cutoff frequencies means that it is unlikely that models based on the excitation patterns of the stimuli would be successful in explaining the threshold data. A range of time-domain models of auditory processing that focus on the time intervals in phase-locked neural activity patterns is reviewed. Most of these models were successful in accounting for the basic masking asymmetry between IRN and noise for conditions within the pitch range, and one of the models produced an exceptionally good fit to the data.

Adult↗
PubMed2000

The lower limit of pitch as determined by rate discrimination.

This paper is concerned with the lower limit of pitch for complex, harmonic sounds, like the notes produced by low-pitched musical instruments. The lower limit of pitch is investigated by measuring rate discrimination thresholds for harmonic tones filtered into 1.2-kHz-wide bands with a lower cutoff frequency, F(c), ranging from 0.2 to 6.4 kHz. When F(c) is below 1 kHz and the harmonics are in cosine phase, rate discrimination threshold exhibits a rapid, tenfold decrease as the repetition rate is increased from 16 to 64 Hz, and over this range, the perceptual quality of the stimuli changes from flutter to pitch. When F(c) is increased above 1 kHz, the slope of the transition from high to low thresholds becomes shallower and occurs at progressively higher rates. A quantitative comparison of the cosine-phase thresholds with subjective estimates of the existence region of pitch from the literature shows that the transition in rate discrimination occurs at approximately the same rate as the lower limit of pitch. The rate discrimination experiment was then repeated with alternating-phase harmonic tones whose envelopes repeat at twice the repetition rate of the waveform. In this case, when F(c) is below 1 kHz, the transition in rate discrimination is shifted downward by almost an octave relative to the transition in the cosine-phase thresholds. The results support the hypothesis that in the low-frequency region, the pitch limit is determined by a temporal mechanism, which analyzes time intervals between peaks in the neural activity pattern. It seems that temporal processing of pitch is limited to time intervals less than 33 ms, corresponding to a pitch limit of about 30 Hz.

Adult↗
PubMed1999

Perception of complex tones and its analogy to echo spectral analysis in the bat, Megaderma lyra.

The gleaning bat Megaderma lyra emits broadband echolocation sounds consisting of multiple frequency components. The present study investigates into which perceptual qualities the spectral characteristics of echoes may be translated in the auditory system of M. lyra. Three bats were trained in a 2-AFC behavioral experiment to classify nine complex tones, which spectrally resembled M. lyra's sonar calls, into two perceptual categories. Then the bats' spontaneous responses to unknown complex tones were recorded. The results show that the animals based their classifications of the complex tones on a sound quality which was mediated by their broadband frequency spectra. The bats used the training stimuli as spectral templates and classified the test stimuli according to their broadband spectral similarity with the learned patterns. Assuming that passive hearing and echo processing are governed by similar perceptual qualities and subject to similar limitations, the perceptual mode which was used by the bats to compare the multicomponent spectral patterns in the reported experiments could serve as a powerful tool for the spectral analysis of M. lyra's multicomponent echoes. The analogy between the perception of complex tones and echo spectral analysis in M. lyra is theoretically elaborated in the "formant-mode" model.

Animals↗
PubMed1999

Temporal resolution and temporal masking properties of transient stimuli: data and an auditory model.

Temporal resolution is often measured using the detection of temporal gaps or signals in temporal gaps embedded in long-duration stimuli. In this study, psychoacoustical paradigms are developed for measuring the temporal encoding of transient stimuli. The stimuli consisted of very short pips which, in two experiments, contained a steady state portion. The carrier was high-pass filtered, dynamically compressed noise, refreshed for every stimulus presentation. The first experiment shows that, with these very short stimuli, gap detection thresholds are about the same as obtained in previous investigations. Experiments II and III show that, using the same stimuli, temporal-separation thresholds and duration-discrimination thresholds are better than gap-detection thresholds. Experiment IV investigates the significance of residual spectral cues for the listeners' performance. In experiment V, temporal separation thresholds were measured as a function of the signal-pip sensation level (SL) in both forward- and backward-masking conditions. The separation thresholds show a strong temporal asymmetry with good separation thresholds independent of signal-pip SL in backward-masking conditions and increasing separation thresholds with decreasing signal-pip SL in forward-masking conditions. A model of the auditory periphery is used to stimulate the gap-detection and temporal-separation thresholds quantitatively. By varying parameters like auditory-filter width and transduction time constants, the model provides some insight into how the peripheral auditory system may cope with temporal processing tasks and thus represents a more physiology-related complement to current models of temporal processing.

Adult↗
PubMed1998

Detection thresholds for brief sounds--are they a measure of auditory intensity integration?

The present study measured how the detection thresholds for two very brief tone or noise bursts depend on the delay between them. The thresholds for the tone burst pairs systematically increase for increasing delays up to a few milliseconds and then reach a constant value. The tone burst thresholds thus reflect a very short-term interaction between the brief signals. Strikingly, the time constant of the interaction appears to scale inversely to the frequency of the tone bursts. The thresholds for the noise burst pairs, on the other hand, remain approximately constant down to the shortest measured delay of less than 1 ms. In contrast to the concept of intensity integration, these results are interpreted in terms of a temporal overlap of the auditory filter responses elicited by two brief, successively presented signals. In a second experiment it was shown that the observed short-term interaction between two brief signals is sensitive to their relative phases, corroborating the conjecture that the interaction takes place at a level prior to the mechanical to neural transduction in the inner ear.

Acoustic Stimulation↗
PubMedDate not supplied

Sensitivity of the neuromagnetic N100m deflection to spectral bandwidth: a function of the auditory periphery?

The amplitude of the auditory evoked field (AEF) component N100m in response to tonal stimuli of varying spectral bandwidth and periodicity was compared with simulated peripheral activity patterns of the auditory nerve (AN). The AEF of ten subjects was recorded with a 37-channel axial gradiometer system (four independent measurement sessions per hemisphere). The simulated peripheral activity was characterized using measures derived from spike probabilities of the AN. Stimuli were pure tones, narrow-band harmonic complex tones (spectrum: 4-4.8 kHz), and broad-band harmonic complex tones (spectrum: 800 Hz-4.8 kHz) with periodicities of 100, 200, and 400 Hz. The intensity of all stimuli was set to 65 dB above the absolute thresholds. Both the simulated AN activity and measured cortical response amplitudes increased consistently with spectral bandwidth. This suggests that the enhanced sensitivity of the N100m amplitude to broad-band complex tones is to some extent a function of the auditory periphery.

Acoustic Stimulation↗