Human speech tends to deliver the same amount of information per second regardless of the language being spoken, a major international study suggests. Native speakers adapt their average speed of speech according to the information density of their language, according to Christophe Coupé and colleagues.
It has long been observed that some languages sound quicker than others. The researchers, who were drawn from universities in France, New Zealand, Hong Kong and South Korea, thought this might be related to how efficient different languages are at delivering information.
The study compared seventeen languages, from nine different European and Asiatic language families. There was substantial variation on several measures: Japanese, for example, uses only a few hundred syllables, compared to the almost 7,000 used in English.
The speaking rate was measured in syllables per second and recorded for each speaker. The researchers chose to use read-aloud texts to control what was being so that they could make valid comparisons between the speakers.
Ten native-speakers of each language were each given a set of fifteen texts. They were asked to familiarise themselves with the text before reading them aloud so they could speak as naturally as possible.
The study found that the speaking rate varied from four syllables to nine depending on the language. Some languages sound faster because they are delivering syllables at twice the rate of others.
For each language, an estimate of information density was then calculated. The study used large written corpora to work out how much information was being communicated as bits per syllable. This builds on research finding that the ability to process syllables is central to speaking and listening skills.
Information density also varied by language: Basque, for example delivers around five bits of information per syllable, while Vietnamese delivers eight.
By multiplying the speaking rate by the information density, researchers were able to arrive at the ‘information rate’ – the number of bits of information being delivered per second. Despite the variation in speaking rate and information density, the information rate was relatively constant, at an average of 39 bits per second.
Across all languages, women tended to speak more slowly and consequently deliver less information. The authors suggest this may reflect the influence of biological constraints of the kind that also cause the average women’s voice to be higher in pitch – but it is also possible that pervasive cultural gender differences play a role.
Despite these sex differences, the overall information rate, however, appears to be stable across the wide range of languages studied, suggesting that speakers adapt their speaking rate to deliver information at a preferred rate for both speaker and listener – not too fast and not too slow.
Speaking too quickly is hard work for the speaker and increases the cognitive strain on the listener – which is why teachers like myself often have to learn to speak more slowly.
Speaking too slowly leads to slower turn-taking in conversation, where the average turn takes just two seconds. It also requires the speaker to keep more information in their working memory – a problem familiar to anyone who has gotten half-way through a sentence only to forget what it was they were talking about.
The solution is for speakers of languages that deliver more information per second to speak more slowly – and those delivering less information per second to speak more quickly. So, for example, Turkish speakers may sound faster than Vietnamese speakers, or slower than Spanish-speakers, but the rate of information received is pretty much the same.
- Coupé, C., Oh, Y. M., Dediu, D. and Pellegrino, F. (2019) ‘Different languages, similar encoding efficiency: comparable information rates across the human communicative niche’, Science Advances 5: eaaw2594.