Syntactic features in reanalysis: positive and negative symptoms

Meng and Bader have presented evidence that a Case conflict is a more effective cue for garden-path reanalysis than a number conflict is, for German wh-sentences with subject-object ambiguities. The preferred first-pass analysis has the wh-trace in subject position, although object position is correct. In a speeded grammaticality judgment task, perceivers accepted Case-disambiguated examples more often and more rapidly than number-disambiguated examples, although comprehension questions indicated that both were eventually understood correctly. For ungrammatical sentences, a Case mismatch error resulted in more false positive grammaticality judgments than a number mismatch error. We offer an explanation for why Case and number features differ in these two ways in their effects on sentence processing. We propose, within the Diagnosis Model of garden-path processing, that reanalysis triggered by a Case mismatch guides the parser more effectively toward the correct structure. Case is a positive symptom, which carries information about the new structure that must be built. By contrast, a number mismatch is a negative symptom; it invalidates the incorrect structure without showing how to rebuild it. This difference in the transparency of garden-path repair can also account for the greater overacceptance of Case-disambiguated ungrammatical sentences. The speeded grammaticality judgment task is designed to encourage hasty responses. Usually, these are hasty rejections of garden path sentences that, on calmer reflection, the parser would find acceptable. Conversely, over-hasty acceptance could occur if some initial progress is made in resolving a grammatical problem. Thus, a higher rate of false positives on ungrammaticals is to be expected where reanalysis proceeds successfully for a while before blocking.