In Brief

Within minutes, two people walking hand-in-hand along the beach will automatically move their hands and legs in perfect harmony. For years, researchers believed mimicry was behind those reflexive movements. But according to a study in the February Journal of Experimental Psychology: Human Perception and Performance (Vol. 31, No. 1), processes known as the coupled oscillator dynamic works to unconsciously create interlimb coordination between people.

The finding counters previous interpersonal coordination research that failed to distinguish synchrony from mimicry.

"Synchrony is more of a dynamic phenomenon than mimicry," says lead research Richard Schmidt, PhD, of the College of the Holy Cross. "Synchrony unfolds in time, while mimicry is a response to a stimulus."

The coupled oscillator dynamic was discovered in the 17th century when scientist Christian Huygens placed two pendulum clocks on a wall. Although the clocks initially beat out of phase, within minutes they beat in sync due to the wall's vibrations acting as mediating force.

While the synchronization of clocks and other such inanimate objects occurs because of a force linkage, the synchronization of living beings, such as the couple on the beach, is due to self-organizing processes across a verbal or visual informational linkage, Schmidt and his team find.

To reach that finding, Schmidt and his colleagues had 36 college students form 18 pairs. The participants sat across from each other, performed a dyadic picture discrimination task and swung a pendulum in their right hands at their own tempo. They were told this was a distraction task.

To find whether verbal or visual information induces synchrony of wrist movements, the researchers tested three conditions: A visual condition that had participants silently swing pendulums; a visual/verbal condition that had participants swing pendulums while conversing and looking at projected cartoon faces positioned on each other's pendulums; and a verbal condition that had participants converse without looking at each others' pendulums.

The researchers found that wrist-movement synchrony was only created with a visual exchange. The researchers believe that the circular flow of visual information created by the coupled oscillator dynamic spurs the interpersonal coordination.

"To synchronize the rhythms of the pendulums, vision provides sufficient information. However, verbal communication does not," Schmidt says. "And in tasks that test postural synchrony, the roles are reversed. The question remains, 'What causes the intimacy between synchronous wrist movements and vision but not conversation?'"

In the future, Schmidt and his colleagues aim to expand upon the differences of mimicry and synchrony while testing the effects of synchrony during various other behaviors, such as people changing their postures.

The line of research--by profiling healthy synchrony--could hold implications for better understanding why interpersonal synchrony breaks down, such as in autism and other such pathology, says Schmidt.