Abstract
The present study investigated event-related brain potentials elicited by true and false negated statements to evaluate if discrimination of the truth value of negated information relies on conscious processing and requires higher-order cognitive processing in healthy subjects across different levels of stimulus complexity. The stimulus material consisted of true and false negated sentences (sentence level) and prime-target expressions (word level). Stimuli were presented acoustically and no overt behavioral response of the participants was required. Event-related brain potentials to target words preceded by true and false negated expressions were analyzed both within group and at the single subject level. Across the different processing conditions (word pairs and sentences), target words elicited a frontal negativity and a late positivity in the time window from 600–1000 msec post target word onset. Amplitudes of both brain potentials varied as a function of the truth value of the negated expressions. Results were confirmed at the single-subject level. In sum, our results support recent suggestions according to which evaluation of the truth value of a negated expression is a time- and cognitively demanding process that cannot be solved automatically, and thus requires conscious processing. Our paradigm provides insight into higher-order processing related to language comprehension and reasoning in healthy subjects. Future studies are needed to evaluate if our paradigm also proves sensitive for the detection of consciousness in non-responsive patients.
Highlights
The question of what constitutes consciousness has fascinated researchers from different research disciplines for years and centuries
To explore the potential of our paradigm for later use in DOC the following open questions were addressed: (1) Which brain potentials vary as a function of the truth value of negated language content when healthy individuals are provided with sufficient processing time to reflect and evaluate the meaning of the presented material and integrate the negation into the semantic context? (2) Are these brain potentials reliable indicators of higher-order cognitive and conscious processing? Stimulusdriven modulations of brain potentials are merely short-lived and elicited within the first 100–200 msec after stimulus presentation
analysis of variance (ANOVA) calculated separately for each electrode group showed that target words preceded by negated, but semantically congruent primes elicited larger cortical negativity at the frontal electrode cluster compared to target words preceded by negated, but semantically incongruent primes, F(1,17) = 10.1, p =
Summary
The question of what constitutes consciousness has fascinated researchers from different research disciplines for years and centuries. To explore the potential of our paradigm for later use in DOC the following open questions were addressed: (1) Which brain potentials vary as a function of the truth value of negated language content when healthy individuals are provided with sufficient processing time to reflect and evaluate the meaning of the presented material and integrate the negation into the semantic context? We were interested in the modulation of later event-related brain potentials that are sensitive to contextual violations and stimulus evaluation If modulations of these later ERPs map conscious processes required for the truth value evaluation of a negated expression their amplitudes should reliable differentiate between false and true negated expressions. To explore the stability of the ERP patterns we report both group and single-subject data
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