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Free keywords:
Coherence; Component definition; Event-related potentials (ERP); Half wave encoding; Symbolic dynamics; Word statistics
Abstract:
In most experiments using event-related brain poten-
tials (ERPs), there is a straightforward way to define—on theoret-
ical grounds—which of the conditions tested is the experimental
condition and which is the control condition. If, however, theoret-
ical assumptions do not give sufficient and unambiguous informa-
tion to decide this question, then the interpretation of an ERP effect
becomes difficult, especially if one takes into account that certain
effects can be both a positivity or a negativity on the basis of the
morphology of the pattern as well as with respect to peak latency
(regard for example, N400 and P345). Exemplified with an ERP
experiment on language processing, we present such a critical case
and offer a possible solution on the basis of nonlinear data analysis.
We show that a generalized polarity histogram, the word statistics
of symbolic dynamics, is in principle able to distinguish negative
going ERP components from positive ones when an appropriate
encoding strategy, the half wave encoding is employed. We pro-
pose statistical criteria which allow to determine ERP components
on purely methodological grounds
