Do saccades and attention shifts interfere with concurrent language perception? An ERP dual-task study

The present study investigated whether saccadic eye movements and the accompanying shifts of visuospatial attention interfere with the concurrent processing of spoken language. For this, a language task and an eye movement task were combined in a dual-task experiment. In the language task, subjects classified synonymous or non-synonymous spoken noun pairs according to their semantic relatedness. The N400 brain potential elicited by the second noun was used as an index for the time course of semantic processing. In the eye movement task, subjects made a choice reaction to a visual stimulus that appeared 10° from the fixation point on half of the trials, forcing the subjects to make a saccade. Temporal overlap (SOA) between both tasks was varied. As eye movements cause large artifacts in the EEG, the data was corrected with the MSEC spatial filter developed by Berg & Scherg (1994). Experiment 1 showed that the need for a saccade in the visual task in combination with high task overlap strongly delayed the N400 component. However, Experiment 2 demonstrated that this interference was not due to the saccade itself, but to the additional change in the effective SOA caused by the saccadic RT. This confirms an earlier finding that task overlap as such has a strong influence on the latency of the N400 in a dual-task situation (Hohlfeld, Sangals & Sommer, JEP:LMC, in press). In summary, our results indicate that eye movements and shifts of visuospatial attention in an additional task do not interfere with concurrent semantic processing.