Electrophysiological evidence for two steps in syntactic analysis. Early automatic and late controlled processes.

In this study we examined the properties of the processes involved in the structural analysis of sentences using event-related brain potential measures (ERP). Previous research had shown two ERP components to correlate with phrase structure violations: an early left anterior negativity (ELAN), which is assumed to reflect first-pass parsing processes, and a late parietally distributed positivity (P600), assumed to reflect second-pass parsing processes. We hypothesized that the first-pass parsing processes are highly automatic, whereas second-pass parsing processes are more controlled. To test this hypothesis we varied the proportion of correct sentences and sentences containing phrase structure violations with incorrect sentences being either of a low (20% violation) or a high (80% violation) proportion. Results showed that the early left anterior negativity was elicited and equally pronounced under both proportion conditions. By contrast, the late positivity was elicited for a low proportion of incorrect sentences only. This data pattern suggests that first-pass parsing processes are automatic, whereas second-pass parsing processes are under participants' strategic control.