Verifying simple sentences generally involves a process wherein the meanings of individual words are combined to form the meaning of the entire sentence. In this paper we investigated the combination process by asking subjects to decide whether sentences of the form S-V-Adj-O (e.g., Pines have green needles) were true or false. Such sentences can be factored into three component propositions: (1) a proposition formed from the adjective and object noun (e.g., Needles can be green); (2) a proposition formed from the subject noun, verb, and object noun (Pines have needles); and (3) a proposition formed from the subject noun, verb, and adjective (Pines have green [parts]). In Experiment 1, we varied the truth value and semantic relatedness of Propositions (1) and (2) in an effort to determine which of these components plays a role in the semantic composition process. Reaction time results indicated reliable effects of truth and relatedness for both propositions. Experiment 2 employed the same task and extended it by testing all three of the above propositions. This time, the results exhibited significant effects of the truth of Propositions (2) and (3). Finally, Experiment 3 applied the same method to sentences of a new syntactic type: cleft sentences of the form It's-Adj-O-that-S-V (e.g., It's green needles that pines have). The effects of the truth value of Propositions (2) and (3) were once more in evidence, although syntactic form differentially influenced the size of these effects.
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