WORKING-MEMORY CONSTRAINTS ON SYNTACTIC AMBIGUITY RESOLUTION AS REVEALED BY ELECTRICAL BRAIN RESPONSES

Parsing strategies in temporarily ambiguous sentences were investigate d in readers with different sentence memory capacities using event-rel ated brain potentials (ERPs). Readers with a high memory span as well as readers with a low memory span were required to read subject and ob ject relative sentences which were either ambiguous until the last wor d (late disambiguation) or were disambiguated by case marking either t he clause initial pronoun (immediate disambiguation) or the noun phras e following it (early disambiguation). ERPs registered during sentence reading elicited the following effects. In the late disambiguation co ndition, high span readers, but not low span readers, displayed a more positive going wave at the disambiguating number marked auxiliary for the object relative sentences than for the subject relative sentences . This positivity is taken to reflect processes of revision that becom e necessary at the disambiguating element if the initial structure con sidered is a subject relative clause. When case marking was available in the clause initial at the relative pronoun, both high and low span readers showed a positivity at the disambiguating element for the obje ct relative sentences, suggesting the immediate use of case marking in formation for revision. When case marking was available in the noun ph rase following an ambiguous pronoun both groups showed no clear effect of revision at the disambiguating element, but only at the sentence f inal number marked auxiliary. This non-immediate use of the case marki ng information seems to be due to an inherent ambiguity in the German case marking system which interacts with the disambiguating element's position in the sentence. The combined data indicate that morphologica l information can be used immediately by high and low span readers to resolve syntactic ambiguity during sentence processing whenever the in formation given is clearly unambiguous. In addition they suggest that possible processing differences in ambiguity resolution between high a nd low span readers may only appear when the ambiguous regions are lon g. (C) 1998 Elsevier Science B.V. All rights reserved.