Monday, October 21, 2013

Entrainment in human conversational turn-taking

Margaret Wilson has a guest post at Language Log that's questioning a recent article arguing that marmoset vocal interactions have a similar style of turn-taking. In the course of that argument she gives the following brief summary of the literature on human conversational turn-taking, which strongly implies that people are entrained to one another's rhythms:
When humans take turns, there is a cyclic structure to the extremely short gaps between speakers' utterances (Sacks, Schegloff, & Jefferson, 1974; Wilson & Wilson, 2005; Wilson & Zimmerman, 1986). A between-turn gap of, say, 200 milliseconds is more likely to be broken by the second speaker at certain regular intervals (say, odd multiples of 50 ms) than during the "troughs" between those intervals. That is, short silences are not of arbitrary length, but reflect a cyclic passing back and forth of who has the "right" to speak next (Wilson & Zimmerman, 1986). The troughs represent moments when the right to speak has shifted back to the original speaker, hence the second speaker inhibits speech during those fractions of a second. And this is happening at the order of tens of milliseconds. This "structured silence" can only be explained by extremely tight coupling — entrainment — of some oscillatory mechanism in the brains of the two speakers. (For further research on this framework, see O'Dell, Neiminen & Lennes, 2012; Stivers et al., 2009).

Addendum (10.22.2015): It's worth mentioning the pioneering work of psychiatrist William Condon. who was publishing on interpersonal synchronization as long ago as 1963. He published an article in Science (183: 99) in 1974: Neonate movement is synchronized with adult speech. Integrated participation and language acquisition. I don't have that paper in front of me at the moment, but I know that in one experiment he filmed neonates (less than an hour old) while adults were talking too them and discovered that their body movements where synchronized to the speech rhythms. He also made observations where autistics failed to synchronize normally with others.

David Hays brought Condon's work to my attention back in the 1970s, saying he thought it was of fundamental importance. Since it was Hays telling me this, I read Condon carefully. But I didn't really get it back then. Now I do.

The conceptual problem seems to be that this is about how a physical mechanism works, that of the mind-brain. It's got rhythms and when it engages in a certain kind of communication, those rhythms have to be synched among participants. But there's a lot of thinking that's latched on to superficial information speak, where information isn't physical, it's something else. But sending a signal through a phone line IS physical, and information theory arose around that problem.

Getting back to Condon and autism. Autism has figured centrally in thinking about so-called Theory of Mind (ToM). ToM has also been linked to gaze following. Could there be a causal link between gaze following and synchronization?

Some years ago in an essay review of Mithin's The Singing Neaderthal, I speculated as follows:
Let us push the argument a step further. For the last decade or so there has been considerable interest in the notion that people acquire a so-called theory of mind (TOM) early in maturation and that this TOM is critical to interpersonal interaction (see e.g. Baron-Cohen 1995). Gaze following is one behavior implicated in TOM. Humans beyond a relatively early age will follow the direction of one another's gaze. I would like to suggest that we notice gaze direction in people with whom we synchronize, but not otherwise.

Think about the perceptual requirements of noticing and tracking gaze direction. Even at conversational distance, another person’s eyes are small in relation to the whole visual scene; thus the visual cues for gaze direction will also be small. Further, people in conversation are likely to be in constant relative motion with respect to one another. The motions may not be large – head turns and gestures, trunk motion – but they will be compounded by the fact that one’s eyes are in constant saccadic motion. Synchronization would eliminate one component of relative motion between people and therefore simplify the process of picking up the minute cues signalling gaze direction. But if one cannot properly synchronize with others, then those cues will be more difficult to notice and track. Thus the capacity for interpersonal synchrony may be a prerequisite for the proper functioning of TOM circuitry.

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