January 31, 2014

Guest Speaker: Ted Gibson (MIT)

 This afternoon (Jan 31) Ted Gibson (MIT) will present his work entitled "Language for communication: Language as rational inference" -- see abstract below.

WHERE: The talk will take place in *Wilson Hall 524.* Wilson Hall is located at the corner of Huron and Wilcox, across the street from Sid Smith, and the room is in the basement.

WHEN: *Jan 31*, at *3:10pm*.

A reception in the LIN lounge will follow.


Language for communication: Language as rational inference
Ted Gibson, MIT

Perhaps the most obvious hypothesis for the function of human language is for use in communication. Chomsky has famously argued that this is a flawed hypothesis, because of the existence of such phenomena as ambiguity. Furthermore, he argues that the kinds of things that people tend to say are not short and simple, as would be predicted by communication theory. Contrary to Chomsky, my group applies information theory and communication theory from Shannon (1948) in order to attempt to explain the typical usage of language in comprehension and production, together with the structure of languages themselves. First, we show that ambiguity out of context is not only not a problem for an information-theoretic approach to language, it is a feature. Second, we show that language comprehension appears to function as a noisy channel process, in line with communication theory. Given si, the intended sentence, and sp, the perceived sentence we propose that people maximize P(s i | sp ), which is equivalent to maximizing the product of the prior P(si) and the likely noise processes P(si → sp ). We show that several predictions of this way of thinking of language are true: (1) the more noise that is needed to edit from one alternative to another leads to lower likelihood that the alternative will be considered; (2) in the noise process, deletions are more likely than insertions; (3) increasing the noise increases the reliance on the prior (semantics); and (4) increasing the likelihood of implausible events decreases the reliance on the prior. Third, we show that this way of thinking about language leads to a simple re-thinking of the P600 from the ERP literature. The P600 wave was originally proposed to be due to people's sensitivity to syntactic violations, but there have been many instances of problematic data in the literature for this interpretation. We show that the P600 can best be interpreted as sensitivity to an edit in the signal, in order to make it more easily interpretable. Finally, we discuss how thinking of language as communication can explain aspects of the origin of word order. Some recent evidence suggests that subject-object-verb (SOV) may be the default word order for human language. For example, SOV is the preferred word order in a task where participants gesture event meanings (Goldin-Meadow et al. 2008). Critically, SOV gesture production occurs not only for speakers of SOV languages, but also for speakers of SVO languages, such as English, Chinese, Spanish (Goldin-Meadow et al. 2008) and Italian (Langus & Nespor, 2010). The gesture-production task therefore plausibly reflects default word order independent of native language. However, this leaves open the question of why there are so many SVO languages (41.2% of languages; Dryer, 2005). We propose that the high percentage of SVO languages cross-linguistically is due to communication pressures over a noisy channel. We provide several gesture experiments consistent with this hypothesis, and we speculate how a noisy channel approach might explain several typical word order patterns that occur in the world's languages.

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