Reduced relatives judged hard require constraint-based analyses

The processing difficulty of sentences with reduced relative clauses (RRs) is strongly determined by the inherent lexical semantic class of the verbs used as passive participles in RRs: namely, the unaccusative vs. unergative class (see Stevenson and Merlo, 1997). Our main claim is that among the linguistic variables responsible for the relevant differences a crucial role is played by semantic variables, rather than just category-level syntactic complexity and/or complexity associated with word-internal lexical structure of verbs (see Hale and Keyser, 1993). First, we observe a considerable overlap in the distributions of acceptability judgments between sentences with RRs based on unaccusative verbs and those based on unergative verbs, and even more importantly, clear gradient effects with respect to acceptability judgments for both types of sentences that are influenced by the lexical semantics of the main verb in the matrix clause. Second, such data can be successfully motivated, if we characterize the crucial unaccusative-unergative distinction in terms of thematic Proto-Role properties (Dowty, 1988, 1991). Third, the linguistic analysis is consistent with recent constraint-based grammars, most notably HPSG, and our constraint-based model that uses the integration-competition architecture developed by Spivey (1996) and applied to reduced relatives by McRae et al. (1998) and Spivey and Tanenhaus (1998).