LingLang Lunch (10/31/2012): Peter Graff (MIT)

Communicative Efficiency in the Lexicon

Some of the earliest as well as some of the most recent work on the role of communicative efficiency in natural language examined the patterning of word-length in the lexicon (Zipf 1949; Piantadosi et al. 2011). Frequent and predictable words tend to be phonologically shorter, while their infrequent and unpredictable counterparts tend to be longer, thus relativizing the articulatory effort invested by the speaker to the probability of her being misunderstood. In this talk, I show that it is not only word-length but also the actual phonological composition of words that facilitates the successful communication of intended messages. I show that the English lexicon is probabilistically organized such that the number of words that rely exclusively on a given contrast for distinctness follows from that contrast’s perceptibility (cf. Miller and Nicely 1955) beyond what is expected from the occurrence frequencies of the contrasting sounds. For example, there are more minimal pairs like pop:shop, which rely on the highly perceptible /p/:/ʃ/ opposition in the English lexicon than expected from the frequencies of /p/ and /ʃ/. Conversely, there are fewer minimal pairs like fought:thought, which rely on the confusable /f/:/θ/ contrast, than expected from the frequencies of /f/ and /θ/. Redundancy in the phonological code is thus not randomly distributed, but exists to supplement imperceptible distinctions between meaningful linguistic units as needed. I also show that English is not unique in this respect: across 60 languages, the perceptibility of a given contrast predicts the extent to which words in the lexicon rely on that contrast for distinctness. I argue that these patterns arise from the fact that speakers choose among words in ways that accommodate anticipated mistransmission (Mahowald et al. to appear) and present computational evidence in favor of the hypothesis that the global optimization of the phonological lexicon could have arisen from the aggregate effects of such word choices over the course of a language’s history (cf. Martin 2007).