Similar information rates across languages, despite divergent speech rates

Spanish may seem to be spoken at a higher speed than Vietnamese, but that doesn’t make it any more “efficient”. Researchers affiliated with the CNRS and Université Lumière Lyon 2 (Dynamique du Langage laboratory) have shown that human languages are equally effective at transmitting information, even if the speeds at which they are spoken differ. To come to this conclusion, they compared recordings in 17 languages1 of 15 short texts describing daily situations, read out loud by 10 native speakers per language. For each of the languages, they measured speech rate, in number of syllables per second, and the average information density of the syllables uttered. (The more easily the utterance of a particular syllable may be predicted from the preceding one, the less information the former is deemed to provide.) The researchers found that higher speech rates are matched by lower information densities—as in Spanish—and slower speech rates with higher information densities—as is often the case with tonal Asian languages like Chinese and Vietnamese. In the end, by multiplying speech rate by information density, all languages, no matter how different, may be shown to convey information at a rate of roughly 39 bits per second.2 This suggests a potentially optimal rate of language processing by the human brain. The findings appear in Science Advances (4 September 2019).

• 1Basque, Cantonese, Catalan, English, Finnish, French, German, Hungarian, Italian, Japanese, Korean, Mandarin, Serbian, Spanish, Thai, Turkish, and Vietnamese.
• 2To simplify, an information density of 1 bit corresponds to guessing which of 2 (= 2^1) possible syllables will be the next, while a 2-bit information density is equivalent to guessing between 4 (= 2^2) possible syllables. The 17 languages studied have information densities ranging from 5 (i.e. choice of 2^5 = 32 possible syllables) to 8 (2^8 = 256 syllables) bits per syllable. For any of these languages, if we multiply information density by speech rate (syllables per second), which also varies, we obtain nearly the same information rate: about 39 bits per second.