Meaning in gestures : What event-related potentials reveal about processes underlying the comprehension of iconic gestures

When people create linguistic expressions, they should avoid ambiguity. Current evidence on this is mixed. In two experiments, subjects read sentences including passive relative clauses, which can be written in full or reduced form (The team (that was) defeated in the Super Bowl vowed revenge); when reduced (without the that was), ambiguity is a threat. Subjects were told about the optional material, and instructed to include or omit it to make the sentence “easier to understand. ” One experiment manipulated past participle ambiguity (The team defeated. is ambiguous, whereas The team beaten. is not). Another experiment also manipulated plausibility (The winning team defeated. is more ambiguous relative to The losing team defeated.). Past-participle ambiguity failed to influence whether subjects wrote full embedded clauses, but plausibility tended to. A third experiment verified that the ambiguous fragments are consistent with main-verb interpretations. Thus, when instructed to edit sentences to make them easy to understand, subjects avoid ambiguity not based on morphological ambiguity, but (perhaps) only as conditioned upon pragmatic, real-world knowledge.highlight certain common, but problematic, methodological practices in patient research, and alternative approaches are suggested. It’s right there in the Gricean maxim of manner (Grice, 1975): Avoid ambiguity. The reason for this directive is obvious: An ambiguous linguistic expression is difficult to understand, and so to produce one is to be uncooperative (unless of course the aim is to flout the maxim of manner, but that’s a different matter entirely). Therefore, speakers -or, more relevantly in the present context, writers -should avoid ambiguity when they can. The “avoid ambiguity” component of the Gricean maxim of manner is obviously important when full ambiguity is at stake. Full ambiguity arises when a complete linguistic expression can be interpreted in more than one way. The recommendation, “I can’t say enough good things about this candidate,” is fully ambiguous. (Is the candidate stronger than words can express? Or is the candidate not worthy of positive description? ) However, temporary ambiguity too is likely to be problematic for linguistic communication. Temporary ambiguity arises when part-way through, a linguistic expression can be interpreted in more than one way, but by the end of the expression, the inappropriate interpretation becomes impossible. Temporary ambiguities are called garden paths when, at the point of ambiguity, linguistic or contextual factors encourage the ultimately incorrect interpretation. “The team defeated in the Super Bowl vowed revenge next season” is a garden path, because after reading “The team defeated. ,” the main-verb interpretation (whereby defeat is a main verb and so the team did the defeating) is especially likely; however, by the end of the expression, this main verb interpretation proves incorrect, because defeat is actually a passive verb in a relative clause (implying that the team got defeated). Garden paths pose demonstrable problems for readers (as shown by the last few decades of research on language comprehension), and so, by the logic described above, writers should avoid them too. (In fact, once the wider contexts of utterances in natural language use are taken into account, this distinction between full and temporary ambiguity is likely to collapse. “I can’t say enough good things” is likely unambiguous in its larger context, though its tolerance of an inappropriate [here opposite] interpretation might pose temporary comprehension difficulties.) So, do speakers avoid full ambiguities or garden paths? Many investigations have explored this question. Two early (and conflicting) observations relevant to this point come from Elsness (1984). He looked at naturally occurring text from the Brown corpus (a variety of written forms, including books, periodicals, government documents, etc.), investigating “that” omission in fully ambiguous sentences like “The newspaper reported (that) yesterday (that) the politician had lied” (without one of the “thats,” it is uncertain whether the reporting or the lying happened yesterday). He found that sentences with such medial adverbials (“yesterday”) indeed included “thats” more often than other similar sentences, suggesting a disambiguating function for CRL Technical Reports, Vol. 18 No. 2, December 2006 4 the “that. ” (Note, however, that it may be the presence of the adverbial per se, rather than its ambiguity, that may compel “that” inclusion.) In the same report, Elsness also assessed sentences like “The newspaper reported (that) you had lied. ” Such sentences can include a temporary ambiguity, because upon its comprehension, “you” might either be the direct object of the preceding main verb, or the subject of an upcoming embedded-clause verb. Including the optional “that” eliminates this ambiguity. However, the ambiguity only arises for case-ambiguous pronouns (or noun phrases in general) like “you” or “it”; for a case-unambiguous pronouns like “she” or “he,” the sentence is never ambiguous (“The newspaper reported she.” can only be interpreted with “she” as the subject of an upcoming embedded verb). Elsness found no tendency to use “thats” more often in sentences with ambiguous pronouns, in which the “that” can disambiguate, than in sentences with unambiguous pronouns, in which the “that” need not disambiguate. This suggests that the optional “that” does not serve a disambiguating function. Another observation from a corpus analysis comes from Temperley (2003). He also examined the Brown corpus, and suggested that optional “thats” were used to avoid temporary ambiguities (which were likely garden paths as well) that arise with relative clause structures like “the lawyer companies like. ” (because “lawyer companies” could be a compound noun). A number of laboratory studies have also investigated ambiguity avoidance. Ferreira and Dell (2000) explored a contrast similar to Elsness’s (ambiguous versus unambiguous pronouns), by having subjects say sentences from memory. Like Elsness, we found no tendency for speakers to use “thats” to avoid garden paths. Similarly, Arnold, Wasow, Asudeh, and Alrenga (2004) had subjects say sentences like “The judge sent the letter to the president to the members of the congressional subcommittee,” which include a temporary ambiguity (momentarily, “to the president” sounds like where the letter is sent -as if it attaches ‘high’ to the verb phrase -rather than what kind of letter was sent -attaching ‘low’ to the noun phrase). The ambiguity can be avoided by phrasing the sentence as, “The judge sent the members of the congressional subcommittee the letter to the president. ” When speakers rephrased paraphrases of sentences like these with the instruction to create maximally understandable new sentences, no tendency for them to use the unambiguous rather than the ambiguous forms of these sentences was observed. On the other hand, Haywood, Pickering, and Branigan (2005) found that when speakers took turns instructing each other to carry out actions with utterances like “put the penguin (that’s) in the cup (that’s) on the plate,” they used “that’s” more in ambiguous circumstances (when either instruction was possible) than in unambiguous circumstances (when only one instruction was possible). (However, see Kraljic & Brennan, 2005 described below.) Ferreira, Slevc, and Rogers (2005) looked at ambiguity avoidance by investigating speakers’ object descriptions in a communication task. The objects were made ambiguous either by including in the same displays other different objects that happened to have the same name (e.g., a flyingmammal bat was to be described in displays also including a baseball bat), or by including objects of the same type that differed in some describable way (e.g., a flying-mammal bat accompanied by a larger flying-mammal bat). Results showed that this latter nonlinguistic form of ambiguity was easily avoided (the ambiguity is nonlinguistic because it arises from the conceptual similarity between objects of the same type, not directly because they happen to be described with the same words). However, the former linguistic ambiguity was avoided very weakly, and only under specific circumstances (the ambiguity is linguistic because the only reason for the ambiguity is that the otherwise distinct objects happen to have the same name). These results suggest that speakers strive to avoid ambiguity in general, as shown by their avoidance of nonlinguistic ambiguity, but they nonetheless have greater difficulty avoiding linguistic ambiguity, and they seem to do so only under specific circumstances. (Note that the ambiguities under scrutiny throughout this paper are linguistic in nature.) A number of reports have looked at whether speakers alter the prosody of sentences to avoid ambiguity, and most have found this not to be the case. Kraljic and Brennan (2005) had speakers describe displays to listeners, and found that they did not use different prosody for sentences like “put the dog in the basket on the star” when describing ambiguous displays (when either instruction was possible) versus unambiguous displays (when only one instruction was possible). (And, unlike Haywood et al. described above, they did not find that speakers used additional lexical material more often in ambiguous rather than unambiguous situations.) Schafer, Speer, Warren, and White (2000) also found that speakers failed to use disambiguating prosody specifically in CRL Technical Reports, Vol. 18 No. 2, December 2006 5 ambiguous situations in a scripted game-playing tasks. Allbritton, McKoon, and Ratcliff (1996) had subjects read aloud ambiguous sentences of a number of different types, and found that they used disambiguating prosody only when explicitly told about the possible ambiguity of the sentences. Similarly, Snedeker and Trueswell (2003)