Theoretical considerations and diverse empirical data from clinical, psycholinguistic, and developmental studies suggest that language comprehension processes are decomposable into separate subsystems, including distinct systems for semantic and grammatical processing. Here we report that event-related potentials (ERPs) to syntactically well-formed but semantically anomalous sentences produced a pattern of brain activity that is distinct in timing and distribution from the patterns elicited by syntactically deviant sentences, and further, that different types of syntactic deviance produced distinct ERP patterns. Forty right-handed young adults read sentences presented at 2 words/sec while ERPs were recorded from over several positions between and within the hemispheres. Half of the sentences were semantically and grammatically acceptable and were controls for the remainder, which contained sentence medial words that violated (1) semantic expectations, (2) phrase structure rules, or (3) WH-movement constraints on Specificity and (4) Subjacency. As in prior research, the semantic anomalies produced a negative potential, N400, that was bilaterally distributed and was largest over posterior regions. The phrase structure violations enhanced the N125 response over anterior regions of the left hemisphere, and elicited a negative response (300-500 msec) over temporal and parietal regions of the left hemisphere. Violations of Specificity constraints produced a slow negative potential, evident by 125 msec, that was also largest over anterior regions of the left hemisphere. Violations of Subjacency constraints elicited a broadly and symmetrically distributed positivity that onset around 200 msec. The distinct timing and distribution of these effects provide biological support for theories that distinguish between these types of grammatical rules and constraints and more generally for the proposal that semantic and grammatical processes are distinct subsystems within the language faculty.

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We explore the language production process by eliciting subject-verb agreement errors. Participants were asked to create complete sentences from sentence beginnings such as The elf's/elves' house with the tiny window/windows and The statue in the elf's/elves' gardens. These are subject noun phrases containing a head noun and controller of agreement (statue) and two nonheads, a “local noun” (window(s)/garden(s)), and a possessor noun (elf's/elves'). Past research has shown that a plural nonhead noun (an “attractor”) within a subject noun phrase triggers the production of verb agreement errors, and further, that the nearer the attractor to the head noun, the greater the interference. This effect can be interpreted in terms of relative hierarchical distance from the head noun, or via a processing window account, which claims that during production, there is a window in which the head and modifying material may be co-active, and an attractor must be active at the same time as the head to give rise to errors. Using possessors attached at different heights within the same window, we are able to empirically distinguish these accounts. Possessors also allow us to explore two additional issues. First, case marking of local nouns has been shown to reduce agreement errors in languages with “rich” inflectional systems, and we explore whether English speakers attend to case. Secondly, formal syntactic analyses differ regarding the structural position of the possessive marker, and we distinguish them empirically with the relative magnitude of errors produced by possessors and local nouns. Our results show that, across the board, plural possessors are significantly less disruptive to the agreement process than plural local nouns. Proximity to the head noun matters: a possessor directly modifying the head noun induce a significant number of errors, but a possessor within a modifying prepositional phrase did not, though the local noun did. These findings suggest that proximity to a head noun is independent of a “processing window” effect. They also support a noun phrase-internal, case-like analysis of the structural position of the possessive ending and show that even speakers of inflectionally impoverished languages like English are sensitive to morphophonological case-like marking.