@mastersthesis{Hartmann2006TopDo-10337,
  year={2006},
  title={Top-Down Modulation of the auditory Steady-State Response},
  author={Hartmann, Thomas}
}

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    <dcterms:abstract xml:lang="eng">The classification of sensory processes into bottom-up and top-down mech- anisms is generally accepted but the impact of top-down processes on elec- trophysiological measurements is not well understood today. The follow- ing study proposes a design which tries to examine the influence of top- down processes on the auditory steady-state response which is elicited by an amplitude-modulated tone. Therefore the EEG of twelve subjects was mea- sured while they believed they were solving a very difficult frequency discrim- ination task. In reality however this task was impossible because only one tone was used, thus eliminating the bottom-up influences that would come from differences of the stimuli. In order to manipulate expectancies two dif- ferent kinds of auditory feedback were given being organized pseudorandomly so that a defined number of repetitions of equal feedback was achieved fol- lowing the work of Perruchet (1985) [31]. As only one tone was used any changes in the behavioral and the electrophysiological data could only come from cognitive, and thus top-down processes. The analysis of the behav- ioral data showed similar trends as Perruchet (1985) [31] who found that the subjects' rating of the likelihood of the occurance of an aversive stimu- lus depended on the amount of repeated presentation of this stimulus in the past. The electrophysiological data was projected on a source-montage and analyzed using three approaches. First the classical event-related-potentials approach was conducted. This revealed effects of the amplitude at the right frontal source and for the latency at the anterior cingulum. The analysis of the amplitude of the aSSR did not show any significant effects at the tem- poral sources although this was expected, but turned out to be significant at the anterior cingulum. These effects show a good resemblance with the behavioral data. The absence of amplitude-effects in temporal regions, which contrasts with preceding studies showed that activities in primary auditory areas cannot be modulated by one single tone but only with the use of two actually different stimuli. The phase-coherences showed a large involvement of the right parietal source especially in combination with the cingulum. To conclude the proposed design was able to modulate many parameters of the aSSR although the same stimulus was used in all trials. Therefore it can be assumed that the aSSR can be modulated by top-down processes.</dcterms:abstract>
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    <dcterms:title>Top-Down Modulation of the auditory Steady-State Response</dcterms:title>
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