This study focuses on the processing of fronted auxiliaries in Basque negative sentences. Basque auxiliaries are a good source of morphological information since (apart from tense, number and mood) they encode argument structure information. They therefore make it possible to anticipate the argument structure of the upcoming verbal heads in the sentence. Even if the more detailed lexical content of the verb is not available to the parser, we predict that the morphological information encoded in the auxiliary about the subcategorization of the verb could help interpreting the structure ahead of the main subcategorizer and could give some cues for the processing of upcoming material, (e.g.: whether the sentence contains more than one clause).

By means of using a morphological mismatch between the auxiliary's information and the NP immediately following the fronted auxiliary, we tried to create expectations in the parser and we examined what takes place when these expectations are not immediately fulfilled.

Results of the online experiment suggest that information prior to encountering the head is being used by the parser and that it tries to accommodate every new word in the input incrementally. In sum, we take our results to be evidence of the use of incremental structure building prior to the head in head-final languages.