Deficient Speech Repaired : Evidence from Event Related Brain Responses

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HANNEMANN, Ronny, 2008. Deficient Speech Repaired : Evidence from Event Related Brain Responses

@phdthesis{Hannemann2008Defic-10626, title={Deficient Speech Repaired : Evidence from Event Related Brain Responses}, year={2008}, author={Hannemann, Ronny}, address={Konstanz}, school={Universität Konstanz} }

2011-03-25T09:20:12Z eng Deficient Speech Repaired : Evidence from Event Related Brain Responses 2008 deposit-license 2011-03-25T09:20:12Z Hannemann, Ronny Reparatur unzureichender Sprachsignale: Evidenz ereigniskorrelierter Hirnantworten The comprehension of speech is an extraordinary ability of the human cognitive system. Listeners are capable of recognizing speech efficiently and rapidly under an exceedingly broad range of acoustic environmental conditions. Even if segments of the speech signal are acoustically not present or heavily distorted these disturbances may not impede the comprehension of speech.<br />In a series of EEG experiments different repair processes in speech perception using lexical top-down information were examined. It was hypothesized that a successful recovery of deficient speech results in resonant states which are reflected in the induced gamma band activity (GBA). Instead, if the general conditions of an ambiguous speech event prevent the repair process, this failure should be reflected in an error signal, i.e. the mismatch negativity (MMN). All these processes were expected to be influenced by the overall structure of representations in the mental lexicon.<br />The findings of the present thesis revealed a direct correlate for the facilitating influence of top-down knowledge on speech comprehension under adverse listening conditions in the induced GBA. Twice, a modulation in the 40 Hz range over left anterior temporal electrode sites was reported. Further, the present results evinced deep insights in the general conditions that allow for a repair of deficient speech. Only if the expected phonemic information matches somewhat the characteristics of the incoming stimulus a successful repair was evident. On the contrary, an explicit difference between the sensory and the expected information prevent the recovery of deficient speech and revealed a distinct MMN over frontal electrode sites. Moreover, at least for the phonemic restoration illusion, the induced GBA as well as the MMN responses corroborated the hypothesis of sparse representations in the mental lexicon (Lahiri and Reetz, 2002).<br />Taken together, the present data show experimentally how comprehending speech and the bottom-up brain processes mediating it depend highly on memory-driven (i.e., top-down) expectancies. Finally, the present data are in line with recent models of speech perception relying on Bayesian statistics (Friston, 2005; Norris and McQueen, 2008) by demonstrating how the cognitive system adapts in an optimal way to a complex and constant changing environment. Hannemann, Ronny application/pdf

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