Brief article The P600 as an indicator of syntactic ambiguity Stefan Frisch * , Matthias Schlesewsky, Douglas Saddy, Annegret Alpermann Institute of Linguistics, University of Potsdam, P.O. Box 60 15 53, 14415 Potsdam, Germany Received 5 September 2001; received in revised form 1 February 2002; accepted 19 June 2002 Abstract In a study using event-related brain potentials, we show that the current characterization of the P600 component as an indicator of revision processes (reanalysis and repair) in sentence compre- hension must be extended to include the recognition of syntactic ambiguity. By comparing the processing of ambiguous and unambiguous sentence constituents in German, we show that the P600 is elicited when our language processing system has syntactic alternatives at a certain item given in the input string. That the P600 is sensitive to syntactic ambiguity adds crucial evidence to current debates in psycholinguistic modelling, as the results clearly favour parallel models of syntactic processing which assume that ambiguity is recognized and costly. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Event-related brain potentials; Language processing; P600 component; Syntactic ambiguity; Serial processing; Parallel processing 1. Introduction 1.1. Serial versus parallel parsing One of the key issues in sentence processing is the question of how the human sentence parser deals with syntactic ambiguity, and this is so for at least two reasons. Firstly, the processing of the ambiguous region itself can tell us whether the parser acknowledges – at least temporarily – the presence of more than one syntactic analysis, which would allow us to distinguish between serial and parallel approaches to parsing (cf. Lewis, 2000; Mitchell, 1994). Secondly, the disambiguating region is of interest since it is crucial for deciding whether one alternative is preferred over others or whether all continuations are consid- ered to be equally likely (cf. Mitchell, 1994). On the one hand, serial models (Frazier & S. Frisch et al. / Cognition 85 (2002) B83–B92 B83 Cognition 85 (2002) B83–B92 www.elsevier.com/locate/cognit 0010-0277/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S0010-0277(02)00126-9 COGNITION * Corresponding author. E-mail address: frisch@rz.uni-potsdam.de (S. Frisch).