Biomedical subjects

Katrin Krumbholz

Publications and source records attributed to Katrin Krumbholz.

10 recordsLinked to original sources

PubMed2006

Cortical response to auditory motion suggests an asymmetry in the reliance on inter-hemispheric connections between the left and right auditory cortices.

The aim of the current study was to measure the brain's response to auditory motion using electroencephalography (EEG) to gain insight into the mechanisms by which hemispheric lateralization for auditory spatial processing is established in the human brain. The onset of left- or rightward motion in an otherwise continuous sound was found to elicit a large response, which appeared to arise from higher-level nonprimary auditory areas. This motion onset response was strongly lateralized to the hemisphere contralateral to the direction of motion. The response latencies suggest that the ipsilateral response to the leftward motion was produced by indirect callosal projections from the opposite hemisphere, whereas the ipsilateral response to the rightward motion seemed to receive contributions from direct thalamocortical projections. These results suggest an asymmetry in the reliance on inter-hemispheric projections between the left and right auditory cortices for auditory spatial processing.

Acoustic Stimulation↗

PubMed2006

Hemispheric asymmetry for auditory processing in the human auditory brain stem, thalamus, and cortex.

We report evidence for a context- and not stimulus-dependent functional asymmetry in the left and right human auditory midbrain, thalamus, and cortex in response to monaural sounds. Neural activity elicited by left- and right-ear stimulation was measured simultaneously in the cochlear nuclei, inferior colliculi (ICs), medial geniculate bodies (MGBs), and auditory cortices (ACs) in 2 functional magnetic resonance imaging experiments. In experiment 1, pulsed noise was presented monaurally to either ear, or binaurally, simulating a moving sound source. In experiment 2, only monaural sounds were presented. The results show a modulation of the neural responses to monaural sounds by the presence of binaural sounds at a time scale of tens of seconds: In the absence of binaural stimulation, the left and right ICs, MGBs, and ACs responded stronger to stimulation of the contralateral ear. When blocks of binaural stimuli were interspersed in the sound sequence, the contralateral preference vanished in those structures in the right hemisphere. The resulting hemispheric asymmetry was similar to the asymmetry demonstrated for spatial sound processing. Taken together, the data demonstrate that functional asymmetries in auditory processing are modulated by context. The observed long time constant suggests that this effect results from a "top-down" mechanism.

Acoustic Stimulation↗

PubMed2006

Evidence of pitch processing in the N100m component of the auditory evoked field.

The latency of the N100m component of the auditory evoked field (AEF) is sensitive to the period and spectrum of a sound. However, little attention was paid so far to the wave shape at stimulus onset, which might have biased previous results. This problem was fixed in the present study by aligning the first major peaks in the acoustic waveforms. The stimuli were harmonic tones (spectral range: 800-5000 Hz) with periods corresponding to 100, 200, 400, and 800 Hz. The frequency components were in sine, alternating or random phase. Simulations with a computational model suggest that the auditory-nerve activity is strongly affected by both the period and the relative phase of the stimulus, whereas the output of the more central pitch processor only depends on the period. Our AEF data, recorded from the right hemisphere of seven subjects, are consistent with the latter prediction: The latency of the N100m depends on the period, but not on the relative phase of the stimulus components. This suggests that the N100m reflects temporal pitch extraction, not necessarily implying that the underlying generators are directly involved in this analysis.

Acoustic Stimulation↗

PubMed2006

Vowel processing evokes a large sustained response anterior to primary auditory cortex.

The present study uses electroencephalography (EEG) and a new stimulation paradigm, the 'continuous stimulation paradigm', to investigate the neural correlate of phonological processing in human auditory cortex. Evoked responses were recorded to stimuli consisting of a control sound (1000 ms) immediately followed by a test sound (150 ms). On half of the trials, the control sound was a noise and the test sound a vowel; to control for unavoidable effects of spectral change at the transition, the roles of the stimuli were reversed on the other half of the trials. The acoustical properties of the vowel and noise sounds were carefully matched to isolate the response specific to phonological processing. As the unspecific response to sound energy onset has subsided by the transition to the test sound, we hypothesized that the transition response from a noise to a vowel would reveal vowel-specific processing. Contrary to this expectation, however, the most striking difference between vowel and noise processing was a large, vertex-negative sustained response to the vowel control sound, which had a fast onset (30-50 ms) and remained constant throughout presentation of the vowel. The vowel-specific response was isolated using a subtraction technique analogous to that commonly applied in neuroimaging studies. This similarity in analysis methodology enabled close comparison of the EEG data collected in the present study with relevant functional magnetic resonance (fMRI) literature. Dipole source analysis revealed the vowel-specific component to be located anterior and inferior to primary auditory cortex, consistent with previous data investigating speech processing with fMRI.

Adult↗

PubMed2005

Hierarchical processing of sound location and motion in the human brainstem and planum temporale.

Horizontal sound localization relies on the extraction of binaural acoustic cues by integration of the signals from the two ears at the level of the brainstem. The present experiment was aimed at detecting the sites of binaural integration in the human brainstem using functional magnetic resonance imaging and a binaural difference paradigm, in which the responses to binaural sounds were compared with the sum of the responses to the corresponding monaural sounds. The experiment also included a moving sound condition, which was contrasted against a spectrally and energetically matched stationary sound condition to assess which of the structures that are involved in general binaural processing are specifically specialized in motion processing. The binaural difference contrast revealed a substantial binaural response suppression in the inferior colliculus in the midbrain, the medial geniculate body in the thalamus and the primary auditory cortex. The effect appears to reflect an actual reduction of the underlying activity, probably brought about by binaural inhibition or refractoriness at the level of the superior olivary complex. Whereas all structures up to and including the primary auditory cortex were activated as strongly by the stationary as by the moving sounds, non-primary auditory fields in the planum temporale responded selectively to the moving sounds. These results suggest a hierarchical organization of auditory spatial processing in which the general analysis of binaural information begins as early as the brainstem, while the representation of dynamic binaural cues relies on non-primary auditory fields in the planum temporale.

Acoustic Stimulation↗

PubMed2005

The effect of cross-channel synchrony on the perception of temporal regularity.

Temporal models of pitch are based on the assumption that the auditory system measures the time intervals between neural events, and that pitch corresponds to the most common time interval. The current experiments were designed to test whether time intervals are analyzed independently in each peripheral channel, or whether the time-interval analysis in one channel is affected by synchronous activity in other channels. Regular and irregular click trains were filtered into narrow frequency bands to produce target and flanker stimuli. The threshold for discriminating a regular target from an irregular distracter click train was measured in the presence of an irregular masker click train in the target band, as a function of the frequency separation between the target band and a flanker band. The flanker click train was either regular or irregular. The threshold for detecting the regular target was 5-7 dB lower when the flanker was regular. The data indicate that the detection of temporal regularity (and thus, pitch) involves cross-channel processes that can operate over widely separated channels. Model simulations suggest that these cross-channel processes occur after the time-interval extraction stage and that they depend on the similarity, or consistency, of the time-interval patterns in the relevant channels.

Acoustic Stimulation↗

PubMed2004

Representation of interaural temporal information from left and right auditory space in the human planum temporale and inferior parietal lobe.

The localization of low-frequency sounds mainly relies on the processing of microsecond temporal disparities between the ears, since low frequencies produce little or no interaural energy differences. The overall auditory cortical response to low-frequency sounds is largely symmetrical between the two hemispheres, even when the sounds are lateralized. However, the effects of unilateral lesions in the superior temporal cortex suggest that the spatial information mediated by lateralized sounds is distributed asymmetrically across the hemispheres. This paper describes a functional magnetic resonance imaging experiment, which shows that the interaural temporal processing of lateralized sounds produces an enhanced response in the contralateral planum temporale (PT). The response is stronger and extends further into adjacent regions of the inferior parietal lobe (IPL) when the sound is moving than when it is stationary. This suggests that the interaural temporal information mediated by lateralized sounds is projected along a posterior pathway comprising the PT and IPL of the respective contralateral hemisphere. The differential responses to moving sounds further revealed that the left hemisphere responded predominantly to sound movement within the right hemifield, whereas the right hemisphere responded to sound movement in both hemifields. This rightward asymmetry parallels the asymmetry associated with the allocation of visuo-spatial attention and may underlie unilateral auditory neglect phenomena.

Adult↗

PubMed2004

Mechanisms determining the salience of coloration in echoed sound: influence of interaural time and level differences.

This study investigates whether the salience of the pitch associated with a single reflection of a broadband sound, such as noise, is determined by the monaural information mediated by the stimuli at the two ears, or by the relative locations of the primary sound and the reflection. Pitch strength was measured as a function of the reflection delay and the lateral displacement between the primary sound and the reflection. Thereby, lateral displacement was produced by means of interaural time differences (ITDs) in experiment 1 and interaural level differences (ILDs) in experiment 3. The results from both experiments are in accordance with the assumption that the strength of the pitch associated with a reflection is based on a central average of the internal representations of the stimuli at the two ears. This notion was corroborated by experiment 2, which showed that the results from experiment 1 could be mimicked by simply adding the stimuli from the two ears and presenting the merged stimulus identically to both ears.

Acoustic Stimulation↗

PubMed2003

Microsecond temporal resolution in monaural hearing without spectral cues?

The auditory system encodes the timing of peaks in basilar-membrane motion with exquisite precision, and perceptual models of binaural processing indicate that the limit of temporal resolution in humans is as little as 10-20 microseconds. In these binaural studies, pairs of continuous sounds with microsecond differences are presented simultaneously, one sound to each ear. In this paper, a monaural masking experiment is described in which pairs of continuous sounds with microsecond time differences were combined and presented to both ears. The stimuli were matched in terms of the excitation patterns they produced, and a perceptual model of monaural processing indicates that the limit of temporal resolution in this case is similar to that in the binaural system.

Adult↗

PubMed2002

Buildup and breakdown of echo suppression for stimuli presented over headphones-the effects of interaural time and level differences.

The current study investigates buildup and breakdown of echo suppression for stimuli presented over headphones. The stimuli consisted of pairs of 120-micros clicks. The leading click (lead) and the lagging click (lag) in each pair were lateralized on opposite sides of the midline by means of interaural level differences (ILDs) of +/-10 dB or interaural time differences (ITDs) of +/-300 micros. Echo threshold was measured with an adaptive one-interval, two-alternative, forced-choice procedure with a subjective decision criterion, in which listeners had to report whether they heard a single, fused auditory event on one side of the midline, or two separate events on both sides. In the control conditions, referred to as the "single" conditions, echo threshold was measured for a single click pair, the test pair, presented in isolation. In addition to the control conditions, two kinds of test conditions were investigated, in which the test pair was preceded by 12 identical conditioning pairs: in the "same" conditions, the interaural configuration (ILDs or ITDs) of the conditioning pairs was identical to that of the test pair; in the "switch" conditions, the interaural configuration of lead and lag was reversed between the conditioning pairs and the test pair, in order to produce a switch in the lateralizations of the stimuli between the conditioning train and the test pair. No matter whether the lateralization of the clicks was produced by ILDs or by ITDs, most listeners experienced a buildup of echo suppression in the "same" conditions, manifested by a prolongation of echo threshold relative to the respective "single" conditions. However, the breakdown of echo suppression was much stronger in the ILD-switch than in the ITD-switch conditions. In five out of six listeners, the ITD switch had hardly any effect on echo threshold, although the ITDs (+/-300 micros) produced roughly the same degree of lateral displacement as the ILDs (+/-10 dB). These results suggest that the dynamic processes in echo suppression operate differentially in pathways responsible for the processing of interaural time and level differences.

Adult↗