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David Poeppel

Publications and source records attributed to David Poeppel.

24 records · Page 2Linked to original sources

The effect of spectral manipulations on the identification of affective and linguistic prosody.

We investigated the effect of various spectral manipulations on the identification of sentential prosody. Two main categories of prosody--affective (happy, angry, sad) and linguistic (statement, question, continuation)--were studied. Thirty-six subjects were presented with stimuli that were recorded by a female native speaker of American English. The stimuli were digitally manipulated to create synthesized, band-pass filtered (F0-range and F2/F3-range) and re-entrant (pitch only version of stimulus is convolved with a steady-state signal) conditions. Results of a forced-choice discrimination paradigm showed that, in general, performance is remarkably robust despite spectral manipulation, even when there is relatively little spectral information. However, performance was significantly degraded in the low band-pass and re-entrant conditions. These observations are discussed in light of the relevance of the fundamental frequency as well as syllabification for the analysis of prosodic information.

Adolescent↗

Application of an MEG eigenspace beamformer to reconstructing spatio-temporal activities of neural sources.

We have applied the eigenspace-based beamformer to reconstruct spatio-temporal activities of neural sources from MEG data. The weight vector of the eigenspace-based beamformer is obtained by projecting the weight vector of the minimum-variance beamformer onto the signal subspace of a measurement covariance matrix. This projection removes the residual noise-subspace component that considerably degrades the signal-to-noise ratio (SNR) of the beamformer output when errors in estimating the sensor lead field exist. Therefore, the eigenspace-based beamformer produces a SNR considerably higher than that of the minimum-variance beamformer in practical situations. The effectiveness of the eigenspace-based beamformer was validated in our numerical experiments and experiments using auditory responses. We further extended the eigenspace-based beamformer so that it incorporates the information regarding the noise covariance matrix. Such a prewhitened eigenspace beamformer was experimentally demonstrated to be useful when large background activity exists.

Evoked Potentials, Auditory↗

Performance of an MEG adaptive-beamformer technique in the presence of correlated neural activities: effects on signal intensity and time-course estimates.

The influence of temporarily correlated source activities on neuromagnetic reconstruction by adaptive beamformer techniques was investigated. It is known that the spatial filter weight of an adaptive beamformer cannot perfectly block correlated signals. This causes two major influences on the reconstruction results: time course distortions and reductions in reconstructed signal intensities. Our theoretical analysis and numerical experiments both showed that the reduction in signal intensity for sources with a medium degree of correlation is small. The time-course distortion for such sources, however, may be discernible. Our analysis also showed that the magnitude correlation coefficient between two correlated sources can be accurately estimated by using the beamformer outputs. A method of retrieving the original time courses using estimated correlation coefficients was developed. Our numerical experiments demonstrated that reasonably accurate time courses can be retrieved from considerably distorted time courses even when the signal-to-noise ratio is low.

Algorithms↗

Dorsal and ventral streams: a framework for understanding aspects of the functional anatomy of language.

Despite intensive work on language-brain relations, and a fairly impressive accumulation of knowledge over the last several decades, there has been little progress in developing large-scale models of the functional anatomy of language that integrate neuropsychological, neuroimaging, and psycholinguistic data. Drawing on relatively recent developments in the cortical organization of vision, and on data from a variety of sources, we propose a new framework for understanding aspects of the functional anatomy of language which moves towards remedying this situation. The framework posits that early cortical stages of speech perception involve auditory fields in the superior temporal gyrus bilaterally (although asymmetrically). This cortical processing system then diverges into two broad processing streams, a ventral stream, which is involved in mapping sound onto meaning, and a dorsal stream, which is involved in mapping sound onto articulatory-based representations. The ventral stream projects ventro-laterally toward inferior posterior temporal cortex (posterior middle temporal gyrus) which serves as an interface between sound-based representations of speech in the superior temporal gyrus (again bilaterally) and widely distributed conceptual representations. The dorsal stream projects dorso-posteriorly involving a region in the posterior Sylvian fissure at the parietal-temporal boundary (area Spt), and ultimately projecting to frontal regions. This network provides a mechanism for the development and maintenance of "parity" between auditory and motor representations of speech. Although the proposed dorsal stream represents a very tight connection between processes involved in speech perception and speech production, it does not appear to be a critical component of the speech perception process under normal (ecologically natural) listening conditions, that is, when speech input is mapped onto a conceptual representation. We also propose some degree of bi-directionality in both the dorsal and ventral pathways. We discuss some recent empirical tests of this framework that utilize a range of methods. We also show how damage to different components of this framework can account for the major symptom clusters of the fluent aphasias, and discuss some recent evidence concerning how sentence-level processing might be integrated into the framework.

Aphasia↗

Towards a new functional anatomy of language.

The classical brain-language model derived from the work of Broca, Wernicke, Lichtheim, Geschwind, and others has been useful as a heuristic model that stimulates research and as a clinical model that guides diagnosis. However, it is now uncontroversial that the classical model is (i) empirically wrong in that it cannot account for the range of aphasic syndromes, (ii) linguistically underspecified to an extent that prohibits contact with the language sciences, and (iii) anatomically underspecified. We briefly summarize some of the central issues that motivate why a new functional anatomy of language is necessary, in the context of introducing a collection of articles that describe systematic new attempts at specifying the new functional anatomy. The major convergent observations are highlighted and the emergent conceptual and empirical trends are identified.

Brain↗