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PubMed2002

Magnetoencephalographic correlates of audiotactile interaction.

To seek for correlates of an interaction between auditory and somatosensory processing, the brain's magnetic field in response to simultaneously presented auditory (A) and tactile (T) stimuli was compared with the sum of the respective unimodal responses (A+T). The stimuli were binaural 1047-Hz tone bursts of 60 dB sensation level and tactile pressure pulses to the right thumb. The mean interval between two stimuli of the same modality was 1.95 s. The magnetic field was recorded using a 306-channel whole-scalp neuromagnetometer. A clear audiotactile interaction was revealed in the hemisphere contralateral to the side of tactile stimulation in six of eight subjects, whereas in the ipsilateral hemisphere an interaction was noticed in only three subjects. The time courses of these audiotactile interaction fields typically showed major deflections of opposite polarities around 140 and 220 ms. The first deflection appeared to arise in the region of the secondary somatosensory cortex (SII). The polarity of this interaction was consistent with the view that the auditory stimulus resulted in a partial inhibition in SII. In two subjects, strong indications of auditory contributions to the interaction were available, although in different hemispheres. The relatively high interindividual variability of the observed interaction, which represents potential neural substrates for multisensory integration, could indicate that the way subjects perceive the simultaneous presentation of auditory and tactile stimuli differs.

Attention↗
PubMed2002

Is it tonotopy after all?

In this functional MRI study the frequency-dependent localization of acoustically evoked BOLD responses within the human auditory cortex was investigated. A blocked design was employed, consisting of periods of tonal stimulation (random frequency modulations with center frequencies 0.25, 0.5, 4.0, and 8.0 kHz) and resting periods during which only the ambient scanner noise was audible. Multiple frequency-dependent activation sites were reliably demonstrated on the surface of the auditory cortex. The individual gyral pattern of the superior temporal plane (STP), especially the anatomy of Heschl's gyrus (HG), was found to be the major source of interindividual variability. Considering this variability by tracking the frequency responsiveness to the four stimulus frequencies along individual Heschl's gyri yielded medio-lateral gradients of responsiveness to high frequencies medially and low frequencies laterally. It is, however, argued that with regard to the results of electrophysiological and cytoarchitectonical studies in humans and in nonhuman primates, the multiple frequency-dependent activation sites found in the present study as well as in other recent fMRI investigations are no direct indication of tonotopic organization of cytoarchitectonical areas. An alternative interpretation is that the activation sites correspond to different cortical fields, the topological organization of which cannot be resolved with the current spatial resolution of fMRI. In this notion, the detected frequency selectivity of different cortical areas arises from an excess of neurons engaged in the processing of different acoustic features, which are associated with different frequency bands. Differences in the response properties of medial compared to lateral and frontal compared to occipital portions of HG strongly support this notion.

Adult↗
PubMed2002

Human cortical dynamics determined by speech fundamental frequency.

Evidence for speech-specific brain processes has been searched for through the manipulation of formant frequencies which mediate phonetic content and which are, in evolutionary terms, relatively "new" aspects of speech. Here we used whole-head magnetoencephalography and advanced stimulus reproduction methodology to examine the contribution of the fundamental frequency F0 and its harmonic integer multiples in cortical processing. The subjects were presented with a vowel, a frequency-matched counterpart of the vowel lacking in phonetic contents, and a pure tone. The F0 of the stimuli was set at that of a typical male (i.e., 100 Hz), female (200 Hz), or infant (270 Hz) speaker. We found that speech sounds, both with and without phonetic content, elicited the N1m response in human auditory cortex at a constant latency of 120 ms, whereas pure tones matching the speech sounds in frequency, intensity, and duration gave rise to N1m responses whose latency varied between 120 and 160 ms. Thus, it seems that the fundamental frequency F0 and its harmonics determine the temporal dynamics of speech processing in human auditory cortex and that speech specificity arises out of cortical sensitivity to the complex acoustic structure determined by the human sound production apparatus.

Adult↗
PubMed2002

Visualization of auditory habituation by fMRI.

The aim of this study was to measure and quantify habituation phenomena within the auditory cortex of 18 healthy subjects by means of fMRI. Auditory stimulation was done by digitally generated pulsed (nu = 5 Hz) 800-Hz sine tones with three alternating ON (duration 2 min) and OFF (1 min) periods. Binaural stimulation resulted in symmetrical bihemispheric activation of the auditory cortex. Our data revealed a characteristic signal decay to repeated acoustic stimulation: the response to the second was even more pronounced, and the third stimulation block significantly lower compared to the first. Thus, our data clearly demonstrate habituation phenomena, probably due to reduced neuronal activity with increased duration and/or frequency of stimuli.

Acoustic Stimulation↗
PubMed2002

Independent components of magnetoencephalography: single-trial response onset times.

Werecently demonstrated that second-order blind identification (SOBI), an independent component analysis (ICA) method, can separate the mixture of neuronal and noise signals in magnetoencephalographic (MEG) data into neuroanatomically and neurophysiologically meaningful components. When the neuronal signals had relatively higher trial-to-trial variability, SOBI offered a particular advantage in identifying and localizing neuronal source activations with increased source detectability (A. C. Tang et al., 2002, Neural Comput. 14, 1827-1858). Here, we explore the utility of SOBI in the analysis of temporal aspects of neuromagnetic signals from MEG data. From SOBI components, we were able to measure single-trial response onset times of neuronal populations in visual, auditory, and somatosensory modalities during cognitive and sensory activation tasks, with a detection rate as high as 96% under optimal conditions. Comparing the SOBI-aided detection results with those obtained directly from the sensors, we found that with SOBI preprocessing, we were able to measure, among a greater proportion of trials, single-trial response onset times that are above background neuronal activity. We suggest that SOBI ICA can improve our current capability in measuring single-trial responses from human subjects using the noninvasive brain imaging method MEG.

Algorithms↗
PubMed1993

Periodicity extraction in the anuran auditory nerve. I. "Pitch-shift" effects.

1. Activity of individual eight nerve fibers in the bullfrog, Rana catesbeiana, was measured in response to complex, multiple-frequency stimuli differing in both frequency composition and harmonic structure. Stimuli were chosen to parallel types of stimuli producing "pitch-shift" effects in humans. 2. The fundamental frequency of harmonic stimuli can be extracted from the autocorrelation of fiber firing, whether the fundamental is physically present in the stimulus or is a "missing" fundamental. The spectral fine-structure of harmonic stimuli is not robustly represented in fiber temporal response. These effects are seen in both AP and BP fibers. 3. The pseudoperiod of inharmonic stimuli is represented by synchronization to successive high-amplitude peaks in the stimulus envelope. Temporal responses to stimuli with high center frequencies are similar regardless of whether their frequency components are harmonically or inharmonically related. Responses remain dominated by the envelope periodicity, and no "pitch-shift" is signaled. In response to stimuli with low center frequencies, temporal responses signal a "pitch-shift" between harmonic and inharmonic complexes. Both AP and BP fibers show these effects. 4. These data suggest that bullfrog peripheral fibers extract the periodicity of complex stimuli by time-domain rather than frequency-domain coding.

Animals↗
PubMed1984

Inhibitory contours in the inferior colliculus as revealed by the 2-deoxyglucose method.

2-Deoxyglucose experiments were carried out during which tone bursts were presented to one ear of cats, while white noise bursts were presented to the other ear. Autoradiography revealed that the tones had produced clear bands of reduced labelling in the ipsilateral inferior colliculus, in addition to the expected band of increased labelling in the contralateral inferior colliculus. The positions of the bands or contours appeared to be organized tonotopically into iso-frequency inhibitory contours.

Animals↗
PubMed1981

Neuronal mechanisms for pitch analysis in the time domain.

Many units in the auditory midbrain nucleus (MLD) of the Guinea fowl are found to be tuned to amplitude modulated tones (AM). For a given response maximum the relationship of the period tau m of the modulation frequency fm and the period tau c of the carrier frequency fc may be given by an empirical equation: m . tau m + n . tau c = 1 . tau l, where m, n and l are small integers typical for a unit. tau l is a time constant of 0.4 ms. The temporal pattern of the neuronal response support these findings. The averages of spike trains oscillate with periods multiple to tau l. These oscillations are elicited by stimulus onsets and zero crossings of fm and may by coupled strongly to fm depending on fc. Variation of fm or fc shifts the mean delay of the phase coupled activity proportional to m . tau m and n . tau c, respectively. These effects may be explained with activity phase coupled to fc which coincides at the level of the recorded units with oscillations coupled to fm. This is expressed by the above given periodicity equation. Psychophysical results with AM-stimuli indicate that the mechanisms described and the periodicity equation are adequate for the explanation of the analysis of periodicity pitch in humans. Hence the period corresponding to pitch is defined by tau p = n . tau c-1 . tau l, where n and 1 are integers and tau l = 0.4 ms. Plots of tau p as a function of tau c reveal steps at 0.4 ms intervals indicating that the neuronal time constant is the same in both species.

Animals↗
PubMed1984

Acoustic sensitivity and bimodal properties of cells in the anterior suprasylvian gyrus of the cat.

The properties of acoustically responsive neurons were studied in the anterior part of the gyrus suprasylvius (ASG) of the cat. The most important features of the responses given to pure tones of different frequencies were: short latency, sharp tuning curves with well definable best frequency (BF). In these respects the cells showed a close resemblance to those of primary acoustic area (AI), and at the same time they proved to be true bimodal cells (responding to somatosensory stimuli, too) like those of the associative areas.

Animals↗
PubMed1982

Calculating psychoacoustic parameters of amplitude modulated narrow noise bands.

A simple model is suggested enabling the comprehensive calculation of pschoacoustic parameters (absolute modulation thresholds, modulation difference limens, and the subjective magnitude of supraliminal modulation differences) for amplitude modulated narrow noise bands. A comparison of experimental and model data reveals good agreement.

Adult↗
PubMed1996

The cognitive representation of action: automatic integration of perceived action effects.

Actions have been assumed to be cognitively represented by codes of relevant action features. Six experiments investigated whether irrelevant action features--conditioned response-contingent auditory events--are also coded and integrated into action codes. Subjects responded to visual stimuli by pressing a left-versus right-hand button or by touching a single key once versus twice. Responses produced certain action effects: tones on the left versus the right or tones of low versus high pitch. After subjects had some practice, an "inducing stimulus" was presented together with the reaction stimulus; this inducing stimulus shared features with the action effect of the correct or incorrect response. If action effects were integrated into action codes, inducing stimuli should activate or prime the associated response. Indeed, substantial effects of correspondence or compatibility between inducing stimuli and irrelevant action effects were found in a variety of tasks. Results are interpreted as evidence for an automatic integration of information about action effects and taken as support of an action-concept model of action-effect integration and stimulus-response compatibility.

Adult↗
PubMed1983

Registration of spontaneous cochlear emissions by means of Fourier transformation.

Fourier transformation is a suitable procedure for the detection of spontaneous cochlear emissions. In the setup used, the microphone lies unsupported at the entrance to the external auditory canal; after amplification and optional filtering, the signal is processed digitally. The frequency distribution of the emissions is considerably narrow and shows alterations in frequency and intensity. Emissions seem to occur in slightly damaged cochleas.

Adolescent↗
PubMed1985

Dissociation of the cochlear microphonics and endocochlear potential after injection of ethacrynic acid.

The cochlear microphonics (CM), endocochlear potential (EP) and summating potential (SP) were simultaneously recorded for 60 min after injection of 30 mg/kg body weight of ethacrynic acid. The EP decreased parallel with the CM for about 20 min after injection, but they differed in the recovery stage. Even when the EP was still negative, the output of CM for 500 Hz acoustic stimulus recovered to its original level and was supernormal. A large SP observed in the recovery stage of CM and EP seemed to suggest that some functional change in the hair cells might be connected with the supernormal CM. Four minutes of anoxia during the supernormal CM decreased CM to only 68% of its level prior to anoxia. A cathodal polarization of the scala media, to change the polarity of the dc potential gradient, reversed the polarity of CM in the anoxic guinea-pig cochlea but not in the guinea-pig cochlea administered ethacrynic acid. These results suggest that supernormal CM observed in this experiment may not be dependent on the dc potential gradient, but due to some functional change in the hair cells after the injection of ethacrynic acid, although CM is essentially dependent on the dc potential gradient between the scala media and the inside of the hair cells.

Acoustic Stimulation↗
PubMed1985

Temporary threshold shift frequency profiles after low-tone exposure.

Low-tone exposure elicits four distinct dips in hearing thresholds: one octave above the exposure frequency, in the permanent threshold shift (PTS) range, at about 10-11 kHz, and at 14-15 kHz. While dips 1, 2 and 3 decay as a function of the time log, dip 4 has a much longer decay time.

Adolescent↗
PubMed1986

Physiology and tonotopic organization of auditory receptors in the cricket Gryllus bimaculatus DeGeer.

Physiological recordings were obtained from identified receptors in the tympanal organ of Gryllus bimaculatus. By immersing the prothoracic leg in Ringer solution and removing the anterior tympanic membrane the auditory receptors were exposed without significantly altering the frequency response of the auditory organ (Fig. 1). Each receptor was tuned to a specific sound frequency. For sound frequencies below this characteristic frequency the roll-off in sensitivity decreased from 20-30 dB/octave to 10-15 dB/octave as the characteristic frequency of receptors increased from 3-11 kHz (Fig. 4A). For each individual receptor the slope, dynamic range and maximum spike response were similar for different sound frequencies (Fig. 9A). The receptors were tonotopically organized with the characteristic frequency of the receptors increasing from the proximal to the distal end of the array (Figs. 5, 6). Several receptors had characteristic frequencies of 5 kHz. These receptors were divided into two groups on the basis of their maximum spike response produced in response to pure tones of increasing intensity (Fig. 7). Independent of the tuning of the receptor no two-tone inhibition was observed in the periphery, thus confirming that such interactions are a property of central integration.

Adaptation, Physiological↗
PubMed1989

Ontogenesis of tonotopy in inferior colliculus of a hipposiderid bat reveals postnatal shift in frequency-place code.

The postnatal development of midbrain tonotopy was investigated in the inferior colliculus (IC) of the south Indian CF-FM bat Hipposideros speoris. The developmental progress of the three-dimensional frequency representation was determined by systematic stereotaxic recordings of multiunit clusters from the 1st up to the 7th postnatal week. Additional developmental measures included the tuning characteristics of single units (Figs. 3f; 4f; 5f), the analysis of the vocalised pulse repertoire (Figs. 3e, 4e, 5e), and morphometric reconstructions of the brains of all experimental animals (Fig. 1). The maturation of auditory processing could be divided into two distinct, possibly overlapping developmental periods: First, up to the 5th week, the orderly tonotopy in the IC developed, beginning with the low frequency representation and progressively adding the high frequency representation. With regard to the topology of isofrequency sheets within the IC, maturation progresses from dorsolateral to ventromedial (Figs. 3c, 4c). At the end of this phase the entire IC becomes specialised for narrowly tuned and sensitive frequency processing. This includes the establishment of the 'auditory fovea', i.e. the extensive spatial representation of a narrow band of behaviorally relevant frequencies in the ventromedial part of the IC. In the 5th postnatal week the auditory fovea is concerned with frequencies from 100-118 kHz (Fig. 4c, d). During subsequent development, the frequency tuning of the auditory fovea increases by 20-25 kHz and finally attains the adult range of ca. 125-140 kHz. During this process, neither the bandwidth of the auditory fovea (15-20 kHz) nor the absolute sensitivity of its units (ca. 50 dB SPL) were changed. Further maturation occurred at the single unit level: the sharpness of frequency tuning increased from the 5th to the 7th postnatal weeks (Q-10-dB-values up to 30-60), and upper thresholds emerged (Figs. 4f, 5f). Although in the adult the frequency of the auditory fovea matches that of the vocalised pulses, none of the juvenile bats tested from the 5th to the 7th weeks showed such a frequency match between vocalisation and audition (Figs. 4e, 5e). The results show that postnatal maturation of audition in hipposiderid bats cannot be described by a model based on a single developmental parameter.

Acoustic Stimulation↗
PubMed1984

Effects of noncontingent feedback on EMG training, EMG responses, and subjective experience.

Various types of noncontingent feedback have been used as control procedures in EMG training; however, their effects on such training have received little attention. Experiment 1 in the present study examined the effects of noncontingent feedback on EMG training, and Experiment 2 assessed the effects of feedback characteristics on EMG responses. In Experiment 1, three noncontingent feedback groups (yoked control, randomly fluctuating tones, and decreasing tones) and one contingent group underwent 20 minutes of training for frontal EMG decreases. Procedures in Experiment 2 were identical to those in Experiment 1 except that subjects were instructed merely to listen to the feedback tones. Results of Experiment 1 indicated that contingent and noncontingent fluctuating feedback groups achieved significantly lower EMG levels than noncontingent decreasing and yoked control groups. In Experiment 2, however, no differences in EMG activity were found among groups. In both experiments, groups did not differ in terms of subjective variables such as frustration, suspiciousness about the tone, or length of time attending to the tone. Results of these two experiments suggest that differences in EMG responses to various types of noncontingent feedback result from interactions between characteristics of the feedback stimulus and instructions to decrease the stimulus.

Adolescent↗