Poster C41, Wednesday, August 21, 2019, 10:45 am – 12:30 pm, Restaurant Hall
Towards an Optimized Paradigm for N400-Effect Elicitation in Single-Subject Applications
Carsten Eulitz1, Anna-Maria Waibel1;1University of Konstanz, Germany
Event-related potentials (ERPs) provide insight into cognitive processing without requiring an overt response from the subject. This supports, for example, clinical applications in non-responsive as well as non-communicative, low-responsive patients. For patients with disorders of consciousness, research has shown that the N400-effect might be predictive of recovery. To this end, the data have to be interpretable on a single-subject basis. Only a few studies have investigated N400-effects in single subjects. Passive paradigms are particularly suitable for this target group, due to an inability to follow commands. However, using passive paradigms, detection rates in healthy control subjects have been reported to be only around 50 %. The present study was aimed to maximize a possible N400-effect by controlling linguistic factors in the stimulus materials as well as to further enhance the detection rate by using two different types of expectancy violations (high cloze sentence-final nouns and antonyms). The final words of semantically congruous and incongruous German sentences were matched on linguistic parameters (length, word class, countability, phonological properties, concreteness, animacy). The final set of sentences was then selected in cloze probability and acceptability rating studies. To determine the sensitivity in an ERP study, 19 healthy subjects passively listened to the sentences while watching a film without sound. In an initial data analysis using t-tests and ANOVAs on a single-subject basis, we identified clusters of at least three electrodes showing a significant difference between the congruous and incongruous conditions in the N400-latency range. We were able to measure an N400-effect for at least one of the two types of expectancy violations in 79 % of the healthy subjects. This is a considerable improvement of the detection rate compared to previous studies. In addition, measurements with brain-damaged but communicative patients have demonstrated the design’s applicability in a clinical setting. More sophisticated single-subject analysis methods will be explored to possibly even further enhance the reported detection rate for N400-effects in single subjects.
Themes: Methods, Meaning: Lexical Semantics
Method: Electrophysiology (MEG/EEG/ECOG)