Modeling the Role of Plausibility and Verb-bias in the Direct Object/Sentence Complement Ambiguity

We provide a computational account of the integration of various constraints proposed to be involved in the resolution of the direct object/sentence complement ambiguity. In the first part, competition-integration simulations show that a constraint-based model accounts for the results of Garnsey, Pearlmutter, Myers, and Lotocky (1997) at least as well as the garden-path model. In the second part, we compare the efficacy of norming techniques for capturing plausibility effects. Simulations show that norms designed to tap people's conceptual knowledge of events better capture plausibility effects than do norms that are biased toward tapping linguistic knowledge. We conclude that local information concerning event plausibility is an important constraint for understanding ambiguity resolution. Part 1: Distinguishing Between Theories of Sentence Processing The human language comprehension system is impressive in its ability to integrate multiple sources of information when comprehending sentences (Marslen-Wilson, 1975). Most theories of sentence comprehension include the idea that understanding sentences involves the rapid integration of general syntactic information (Frazier & Rayner, 1982), lexically-specific syntactic information (MacDonald, Pearlmutter, & Seidenberg, 1994; Garnsey et al., 1997), discourse information (Spivey & Tanenhaus, 1998), and knowledge of thematic roles (McRae, Ferretti, & Amyote, 1997; Trueswell, Tanenhaus, & Garnsey, 1994). They differ, however, in their claims about precisely when the comprehension system exploits various types of information. Two prominent theories of sentence processing have emerged in this debate. The garden-path model (Frazier, 1987; Frazier & Rayner, 1982) claims the comprehension system naively constrains initial interpretation by using a limited subset of the relevant information, reserving other information sources for evaluating and, if necessary, revising the initial interpretation. The first stage of comprehension uses only the major syntactic category of each word (noun, verb, etc.), phrase-structure rules, and a small set of syntactic decision principles. One of these principles, minimal attachment, states that the initial interpretation always corresponds to the simplest structure that can be built. The second stage of comprehension temporally lags behind the first, with all potentially relevant sources of knowledge being used to evaluate, and if necessary, revise the initial structure. In contrast, the constraint-based approach views syntactic ambiguity resolution as a continuous process in which the most likely syntactic alternatives are evaluated with respect to all available evidence (MacDonald et al., 1994; McRae, Spivey-Knowlton, & Tanenhaus, 1998). Thus, the distinguishing features of this model are that multiple constraints are combined to compute alternative interpretations in parallel, and that these alternatives compete with one another during processing. Unlike the garden-path model, lexically-specific knowledge and relevant discourse information is available to guide initial interpretations rather than solely to revise the initial interpretation if it is incorrect. The Direct Object/Sentence Complement Ambiguity The direct object/sentence complement ambiguity occurs when a noun phrase (NP) following a main verb is temporarily ambiguous with respect to its relationship to the verb. Consider the following examples: 1a) The gossipy neighbor heard (that) the story had never actually been true. 1b) The gossipy neighbor heard (that) the house would never be flooded again. In (1), the NPs "the story" and "the house" are ambiguous as to whether they are the direct object of the verb (i.e., something that someone has heard), or the subject of a sentence complement (something that someone has heard about). In (1a), for example, when the complementizer "that" is removed from these sentences, readers receive confirmation that the gossipy neighbor has not directly heard the story when they read the auxiliary verb "had" or "would". Readers' use of verb-bias and plausibility information to constrain resolution of the direct object/sentence complement ambiguity has recently been investigated by Garnsey et al. (1997). They manipulated the plausibility of the post-verbal noun as a direct object. For example, in (1a) “the story” is a plausible direct object of the verb “heard” (i.e., people tend to hear stories directly), whereas “the house” is not as plausible (people do not commonly hear houses directly). Of particular interest to Garnsey et al. was how this type of plausibility 3 0 2 0 1 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 the story had never EQ Implausible DO EQ Plausible DO