Learning from speaker word choice by assuming adjectives are informative

Learning from speaker word choice by assuming adjectives are informative Alexandra Horowitz Michael C. Frank ahorowit@stanford.edu Department of Psychology Stanford University mcfrank@stanford.edu Department of Psychology Stanford University Abstract The goal in our studies was thus to investigate whether chil- dren can learn from how speakers choose to express them- selves. We focused on adjective use as a case study be- cause adjectives are optional and may signify cues to con- trast and noteworthy features. As an extension of the princi- ple of contrast—that a contrast in form signifies a contrast in meaning (E. Clark, 1987)—children should interpret that ref- erential expressions modified with adjectives convey different types of information than expressions with bare nouns. This makes adjective interpretation a useful domain for examining how children form implicit inferences from a speaker’s word choices. We began by looking at color and size terms because they are some of the earliest-learned and most commonly- used adjectives. Adults perceive adjective use as marking contrast, but there are differences between their comprehension and production. Grice’s maxim of quantity—that speakers should be only as informative as is necessary—predicts that modifiers should be used selectively to disambiguate target referents from con- trast sets (Grice, 1975). Indeed, in comprehension, visual search findings reveal that adults process color and size in- formation as it comes online and are faster to locate a modi- fied referent (e.g. “big comb”) when a contrasting competitor item is present (e.g. a small comb) than when a distractor item is present (e.g. a spoon) (Sedivy, Tanenhaus, Chambers, & Carlson, 1999). This indicates that prenominally modi- fied expressions may evoke a contrast set with the referent; adults are sensitive to implied contrast information embedded in adjective use and process prenominal modifiers incremen- tally to locate and disambiguate a speaker’s intended referent. However, adults are not always Gricean in their production; although they rarely produce scalar modifiers without a size contrast set present, they frequently over-modify with color terms (Grodner & Sedivy, 2005; Sedivy, 2003). In all, adults are sensitive to the implications of adjective use, but they are not always maximally informative. Children seem to be developing similar skills in their preschool-age years. By kindergarten, children can recognize the informativeness of adjective use in both comprehension and production; children are more likely to use an adjective to uniquely identify a big cup from a small cup than when only a single cup is present (Nadig & Sedivy, 2002), suggest- ing that they are able to consider what level of description is most useful to the perspective of an interlocutor. Preschoolers can also learn to produce unambiguous references for more complex scenes with feedback (Deutsch & Pechmann, 1982). In processing speech, 3-year-olds make use of adjective infor- mation as soon as it becomes available; they correctly look to Pragmatic abilities are not only a component of efficient com- munication; they can also be an important learning mechanism for young children. We discuss four experiments and a corpus analysis to investigate whether children and adults can infer information about a speaker’s knowledge based on the choice of an adjective. In Experiments 1 – 3, we found that adults are sensitive to adjective use as an indicator of intended con- trast dimension (e.g. that people say “red” if an object could have been blue, but “tall” if it could have been short). In Ex- periment 4, we found developmental differences between older and younger 4-year-olds: older children were above chance at selecting the referential dimension of interest, while younger children exhibited some contrast inference but a strong color bias. This suggests that by preschool, children are beginning to make inferences from a speaker’s word choices, but that there are differences between adjective types. We conducted an ex- ploratory corpus analysis to investigate possible causes for this developmental difference. Keywords: Pragmatics; adjectives; language development. Introduction A key feature of human language is its ability to convey in- formation efficiently in context. For adults, the ability to make pragmatic inferences—extrapolations about meaning in context—can dramatically facilitate the exchange of informa- tion between conversational partners. For example, from “I can’t find my left shoe,” we can make the inference that the speaker probably knows where her right shoe is, or else she would have mentioned that both of her shoes were lost. For children, sensitivity to word choice information is instrumen- tal in early word learning; pragmatic inference helps guide both language acquisition and comprehension. In general, recognizing that speakers have chosen to say something in a particular way because of some communicative goal is an integral part of understanding language (H. Clark, 1996). In addition to aiding in the acquisition and comprehension of language, inferences about the pragmatic implications of speakers’ wording decisions might also be an important learn- ing mechanism for children. Following our shoe example fur- ther: Children who learn to infer implied information embed- ded in word choices can incorporate implicit knowledge (we are talking about one specific shoe) and move on to acquire additional information (“where was it last seen?”) rather than spending time repeating and confirming implied details (“only one shoe is lost?”). Using speakers’ word choices to make broader inferences allows children to learn from both what is stated and what are implied alternatives. The ear- lier and faster children can recognize implicit contrasts from word choice, the greater their opportunities to make use of this information.