Processing syntax with two hemispheres

Hoeks, J. C. J.1, Stowe, L. A.1, Prinsen, I.1, and Wijers, A. A.2
1BCN Neuroimaging Center, University of Groningen, The Netherlands; 2Experimental Psychology, University of Groningen, The Netherlands

In the present experiment we investigate the processing of category and morphosyntactic violations, using sentences such as (1) and (2).

1) Category Violation: Het brood werd door de bakkers in gebakken. (lit. The bread was by the bakers in baked)

2) Morphosyntactic Violation: Het brood werd door de bakkers bakte. (lit. The bread was by the bakers baked (past tense))

Final words of these sentences were briefly presented in either the right visual field (directly connected to Left Hemisphere = LH) or the left visual field (connected to Right Hemisphere = RH), while ERPs were recorded. We were especially interested to find out how the RH copes with ungrammaticality.

Morphosyntactic violations presented to the LH elicited a LAN (Left Anterior Negativity) and a P600, which have been commonly reported in the literature for this sort of violation. When presented to the RH morphosyntactic violations elicited a "RAN" which was so broadly distributed (and especially large at parietal sites) that it looked more like an N400 effect; the P600 was evident in the RH too, though it started later.

The results for category violations were rather unexpected. For stimuli initially presented to the LH, a highly lateralized frontal positivity was apparent -- starting as early as 175 ms post onset -- which was largest at RIGHT frontal electrodes; no P600 was observed. For the RH, the early positivity was largest at left frontal electrodes. Again, no P600 was observed.

Implications for theories of sentence processing will be discussed.