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D Poeppel

Publications and source records attributed to D Poeppel.

24 records · Page 2Linked to original sources
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↗