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D Poeppel

Publications and source records attributed to D Poeppel.

13 recordsLinked to original sources
PubMed1998

Auditory evoked M100 reflects onset acoustics of speech sounds.

Magnetoencephalography (MEG) was used to investigate the response to speech sounds that differ in onset dynamics, parameterized as words that have initial stop consonants (e.g., /b/, /t/) or do not (e.g., /m/, /f/). Latency and amplitude of the M100 auditory evoked neuromagnetic field, recorded over right and left auditory cortices, varied as a function of onset: stops had shorter latencies and higher amplitudes than no-stops in both hemispheres, consistent with the hypothesis that M100 is a sensitive indicator of spectral properties of acoustic stimuli. Further, activation patterns in response to stops/no-stops differed in the two hemispheres, possibly reflecting differential perceptual processing for the acoustic-phonetic cues at the onset of spoken words.

Adult↗
PubMed1998

Latency of evoked neuromagnetic M100 reflects perceptual and acoustic stimulus attributes.

The latency of components of the auditory evoked neuromagnetic field has been shown to reflect, or encode, stimulus attributes. In particular, the M100 component, occurring approximately 100 ms post stimulus onset has a latency that depends on stimulus pitch, spectral complexity and presentation level. This study used magnetoencephalography to record neuromagnetic fields evoked by presentation of two-tone complexes consisting of various proportions of 100 Hz and 1 kHz energy. These are perceived categorically, as evidenced by classification and reaction time measurements. It is found that the M100 latency also varies categorically, that is, characterized by two plateau regions with a sharp interface. Thus, we find that not only does the M100 latency reflect acoustic attributes of a stimulus, but also such perceptual characteristics.

Acoustic Stimulation↗
PubMed1998

Peri-threshold encoding of stimulus frequency and intensity in the M100 latency.

Recent work has suggested that, in addition to spatial tonotopy, pitch and timbre information may be encoded in the temporal activity of the auditory cortex. Specifically, the post-stimulus latency of the maximal cortical evoked neuromagnetic field (M100 or N1m) is a function of stimulus frequency. We investigated the additional effect of varying the stimulus intensity on the M100 response. A 37-channel biomagnetometer recorded neuromagnetic fields over the temporal lobe of healthy volunteers in response to monaurally presented tones. The frequency dependence of the M100 latency remained remarkably invariant even at low stimulus intensity. Thus, for peri-threshold stimuli, frequency information appears encoded in the temporal form of the evoked response.

Acoustic Stimulation↗
PubMed1998

Comparison of covariance-based and waveform-based subtraction methods in removing the interference from button-pressing finger movements.

A covariance matrix-based subtraction method has recently been proposed to remove interference using two MEG measurements: The first has both target and interfering activities and the second only has the interference. This paper compared covariance matrix-based subtraction with conventional waveform-based subtraction, which requires that the waveforms of interference be equal at every time point between the two measurements. Our analysis showed that covariance-subtraction only requires that the time-average of the squared intensity of interference be equal between the two measurements. As a result, the method is still effective when the onset of interference differs or even their measured waveforms differ between the two measurements. The covariance- and waveform-subtraction methods were both applied to remove the interference caused by response-button-pressing finger movements in auditory-evoked MEG measurements. The results of this application demonstrated the superiority of the covariance-subtraction method over the conventional waveform-subtraction method.

Algorithms↗
PubMed1998

MEG covariance difference analysis: a method to extract target source activities by using task and control measurements.

A method is proposed for extracting target dipolesource activities from two sets of evoked magnetoencephalographic (MEG) data, one measured using task stimuli and the other using control stimuli. The difference matrix between the two covariance matrices obtained from these two measurements is calculated, and a procedure similar to the MEG-multiple signal classification (MUSIC) algorithm is applied to this difference matrix to extract the target dipole-source configuration. This configuration corresponds to the source-configuration difference between the two measurements. Computer simulation verified the validity of the proposed method. The method was applied to actual evoked-field data obtained from simulated task-and-control experiments. In these measurements, a combination of auditory and somatosensory stimuli was used as the task stimulus and the somatosensory stimulus alone was used as the control stimulus. The proposed covariance difference analysis successfully extracted the target auditory source and eliminated the disturbance from the somatosensory sources.

Algorithms↗
PubMed1998

Magnetoencephalography and magnetic source imaging.

Current brain imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI), provide noninvasive, high-resolution images that depict fine anatomic structure and delineate pathology by control of image contrast and sensitivity to the physicochemical microenvironment. These methods, although invaluable for the identification, characterization, and localization of lesions, do not provide any assessment of the functional viability of brain tissues, nor of the spatial organization of sensory, motor, and cognitive systems. However, such additional functional information is of great significance to the clinician in the determination of treatment strategies and patient management.

Brain Mapping↗
PubMed1997

Learning transfer and neuronal plasticity in humans trained in tactile discrimination.

Adult humans were unilaterally trained in a tactile discrimination task of sequentially applied multi-finger stimuli. Magnetic source imaging (MSI) was performed before and after the training to evaluate use-dependent neuronal plasticity. All subjects showed fast improvements in performance and complete transfer of the learned task. MSI recordings revealed an unilateral decrease in current dipole strength in the somatosensory system contralateral to the trained hand. Attenuation of sensory evoked fields and a complete learning transfer indicate learning in associative and secondary cortices rather than perceptual plasticity operating on neuronal populations involved in early sensory processing. This findings are discussed with respect to an equivalent animal model and to learning specificity and generalization.

Adult↗
PubMed1997

Processing of vowels in supratemporal auditory cortex.

The auditory evoked neuromagnetic fields elicited by synthesized vowels of two different fundamental frequencies F0 were recorded in six subjects over the left and right temporal cortices using a 37-channel biomagnetometer. Single equivalent current dipole modeling of the fields elicited by all vowel types localized activity to a well-circumscribed area in supratemporal auditory cortex in both hemispheres. There were hemisphere asymmetries in the amplitude and latency of the M100 response. We also observed changes in M100 latency related to vowel type, but not to F0. There was no clear effect of vowel type or F0 on dipole localization for the M100, but a possible vowel type by latency interaction. These M100 data provide further evidence that vowels are processed independently of their pitch.

Adult↗
PubMed1997

Noise covariance incorporated MEG-MUSIC algorithm: a method for multiple-dipole estimation tolerant of the influence of background brain activity.

This paper proposes a method of localizing multiple current dipoles from spatio-temporal biomagnetic data. The method is based on the multiple signal classification (MUSIC) algorithm and is tolerant of the influence of background brain activity. In this method, the noise covariance matrix is estimated using a portion of the data that contains noise, but does not contain any signal information. Then, a modified noise subspace projector is formed using the generalized eigenvectors of the noise and measured-data covariance matrices. The MUSIC localizer is calculated using this noise subspace projector and the noise covariance matrix. The results from a computer simulation have verified the effectiveness of the method. The method was then applied to source estimation for auditory-evoked fields elicited by syllable speech sounds. The results strongly suggest the method's effectiveness in removing the influence of background activity.

Algorithms↗
PubMed1996

Latency of auditory evoked M100 as a function of tone frequency.

This study investigated post-stimulus latency of the M100 component of auditory evoked fields as a function of tone frequency. A 37-channel biomagnetometer was used to record neuromagnetic fields over the temporal lobe in response to monaurally presented tones. M100 peaks in evoked field amplitude were found for each subject. The post-stimulus latency was observed to vary parabolically with tone frequency. Latencies as short as 99 ms were found in response to mid-audio range frequencies (1000-2000 Hz), whereas lower (100-500 Hz) and higher (3000-5000 Hz) frequencies were associated with longer latencies (up to 153 ms). All fields gave M100 dipole localizations in auditory cortex. Although it was not possible to resolve spatial tonotopy, it appears that frequency information is encoded in the temporal evoked response.

Acoustic Stimulation↗
PubMed1996

A critical review of PET studies of phonological processing.

The use of positron emission tomography to identify sensory and motor systems in humans in vivo has been very successful. In contrast, studies of cognitive processes have not always generated results that can be reliably interpreted. A metaanalysis of five positron emission tomography studies designed to engage phonological processing (Petersen, Fox, Posner, Mintun, & Raichle, 1989; Zatorre, Evans, Meyer, & Gjedde 1992; Sergent, Zuck, Levesque, & MacDonald, 1992; Demonet, Chollet, Ramsay, Cardebat, Nespoulous, Wise, & Frackowiak, 1992; and Paulesu, Frith, & Frakowiak, 1993) reveals that the results do not converge as expected: Very similar experiments designed to isolate the same language processes show activation in nonoverlapping cortical areas. Although these PET confirm the importance of left perisylvian cortex, the experiments implicate distinct, nonoverlapping perisylvian areas. Because of the divergence of results, it is premature to attribute certain language processes or the elementary computations underlying the construction of the relevant linguistic representations to specific cerebral regions on the basis of positron emission tomographic results. It is argued that this sparse-overlap result is due (1) to insufficiently detailed task decomposition and task-control matching, (2) to insufficient contact with cognitive psychology, psycholinguistics, and linguistic theory, and (3) to some inherent problems in using substractive PET methodology to study the neural representation and processing of language.

Brain↗
PubMed1996

Task-induced asymmetry of the auditory evoked M100 neuromagnetic field elicited by speech sounds.

The auditory evoked neuromagnetic fields elicited by synthesized speech sounds (consonant-vowel syllables) were recorded in six subjects over the left and right temporal cortices using a 37-channel SQUID-based magnetometer. The latencies and amplitudes of the peaks of the M100 evoked responses were bilaterally symmetric for passively presented stimuli. In contrast, when subjects were asked to discriminate among the same syllabic stimuli, the amplitude of the M100 increased in the left and decreased in the right temporal cortices. Single equivalent current dipole modeling of the activity elicited by all stimulus-types localized to a well-circumscribed area in supratemporal auditory cortex. The results suggest that attentional modulation affects the two supratemporal cortices in a differential manner. Task-conditioned attention to speech sounds is reflected in lateralized supratemporal cortical responses possibly concordant with hemispheric language dominance.

Acoustic Stimulation↗