Longer eye blinks lead to shorter answers

Adults blink approximately 13,500 times a day – much more often than necessary to wet their eyes. People also blink more when they are having a conversation than when they are reading or just looking at something. Why do people blink during face-to-face communication? There is evidence that eye blinking – like nodding – is an important social cue, providing speakers with visual feedback. In an earlier study, Paul Hömke and his colleagues found that people do not just blink randomly during a conversation. For his PhD research, Hömke studied a large collection of natural conversations between Dutch speakers. He noticed that blinks tend to occur in typical ‘feedback slots’

Also, longer blinks often co-occurred with nods, and seemed to signal ‘message received’. To test whether speakers really perceive listeners’ blinks as meaningful feedback signals, the researchers decided to study eye blinking experimentally. Are speakers sensitive to the duration of listeners’ blinks in face-to-face communication? If speakers interpret longer blinks as a sign that their message is understood, they might shorten their answer to a question.

The scientists used a novel approach based on virtual reality. A group of 35 volunteers was asked to talk to different avatars, who acted as a ‘virtual listeners’. People answered questions such as 'How was your weekend, what did you do?' After each answer, the avatar would respond verbally ('Oh, how interesting').

Three avatars were created, each providing the speaker with different types of nonverbal feedback while listening to the answers to these questions. One avatar would not respond at all during listening. The other two avatars responded with nods, accompanied by ‘short’ (208 ms) or ‘long’ (607 ms) blinks. The avatar’s responses were controlled by a person who could see and hear the participant (via a video-camera link), but who could not see the avatar. This person (who was blind to the experimental manipulations) was instructed to press a button whenever it felt appropriate to signal understanding. In this way, the avatar’s behaviour mimicked the way blinks naturally occur in conversation. Would people pick up on the subtle millisecond difference in blink duration, and change their answers accordingly?

On average, participants’ answers were about 3 seconds shorter when the avatar responded with a nod and a long blink. When there was no response or just a nod and a short blink, participants provided relatively longer answers. “Our findings show that one of the subtlest of human movements—eye blinking—appears to have a surprising effect on the coordination of everyday human interaction”, says Hömke. Blinking may function as a “move on” signal of understanding, signalling “I’ve received enough information for current purposes”.

According to the authors, the effect of eye blinking on communication is even more striking when you consider that speakers were completely unaware of it. When asked after the experiment, only about half of the participants noticed that the avatars blinked, and crucially, none of the participants noticed any variation in blink behaviour.

'This study underlines the multimodal as well as the interactive nature of human language use', says Judith Holler. 'Importantly, it very much defeats the idea that addressees are passive receivers. Addressee behaviour, even in the form of very subtle visual signals, can have a profound effect on speaker’s language production.' Speaking in interaction is thus not a unilateral process but a joint activity involving active contributions from both speaker and listener.

Publication

Paul Hömke, Judith Holler & Stephen C. Levinson (2018). Eye blinks are perceived as communicative signals in human face-to-face interaction. PLoS ONE 13 (12):e0208030. https://doi.org/10.1371/journal.pone.0208030.