Attentional effects on the processing of syntactic violations during listening two simultaneous speech streams
The notion of automatic syntactical analysis for linguistic stimuli received support from some event-related studies. Here we provide a stronger test of this issue by presenting to listeners two concurrent continuous speech streams and manipulating in a fully crossed design two variables that can potentially affect speech processing: the direction of attention (focused vs. divided) × task (lexical – detecting numerals vs. syntactical – detecting syntactic violations). By recording EEG, we could thus compare between the event-related potentials (ERP) elicited by syntactic violations and numerals as targets (task-relevant events in the attended speech stream) with those for distractor (task-relevant events in the unattended speech stream) and attended and unattended task-irrelevant events with attention focused on one or divided between the two streams. Both task-relevant and task-irrelevant syntactic violations elicited the ELAN or possibly the N400 ERP component for the attended but not for the unattended speech stream, irrespective of the direction of attention. P600 was only elicited by target syntactic violations. Numeral targets elicited the N2b and P3 irrespective of the direction of attention, whereas none of the non-target numerals elicited either of these ERPs. The N2b amplitude was associated with the participant’s performance in recognizing information from the speech material. The results provide no support for the notion of automatic syntactic analysis, because unattended syntactic violations failed to elicit any detectable ERP response.