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Two People on Task Better Than One

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May 31, 2006 | by Megan Fellman

EVANSTON, Ill. --- Having another person help you with a simple physical task often seems to be more trouble than it's worth. However, researchers at Northwestern University have found that in some cases, pairs perform better than individuals even when each individual thinks the other is a hindrance.

The findings, published in the May 2006 issue of Psychological Science, shed new light on haptic communication, which relates to the sense of touch and motion. The research team included psychologists, neuroscientists and robotics researchers who were interested in this form of communication. (Haptics comes from the Greek word “haptiko.”)

“Many other kinds of pair interactions have been heavily studied, including facial expression, gesture, spoken language and visually observing each other's actions,” said Michael Peshkin, professor of mechanical engineering and an author on the paper. “We wanted to determine if pairs could coordinate effectively through a haptic channel of communication, which has been little studied.” Kyle Reed, a graduate student of Peshkin's, was lead author of the study.

Their experiment was designed to be as simple as possible, yet to isolate haptic interactions from other kinds of interactions. In the experiment two individuals grasped opposite ends of a rigid two-handled crank. A marker was attached to the crank. The participants were asked to move the marker toward a target as quickly as possible whenever a target appeared. Each participant had to deal with the other's actions, as experienced solely through the shared forces and motions of the crank. A curtain kept them from seeing each other, and they were asked not to talk.

Thirty undergraduates participated in the experiment in the mechanical engineering department's Laboratory for Intelligent Mechanical Systems, and many said they thought the other person interfered with them. However, despite the perceived difficulty of coordination, most pairs performed significantly faster than individuals doing the same task. Not only were pairs faster than individuals, most pairs quickly developed a cooperative strategy, such that one participant primarily accelerated the crank when the target appeared, while the other brought it to rest accurately when the marker reached the target. Most participants were unaware that they had adopted a cooperative strategy.

The researchers speculate that a capacity for haptic communication is a basic human ability used in everyday tasks such as cooperatively moving a table or exchanging a drinking glass, in helping someone learn a manual skill, or in assisting a patient's motions in therapy after a stroke.

In addition to Peshkin and Reed, authors on the paper include Mitra J. Hartmann, assistant professor of biomedical engineering and of mechanical engineering; Marcia Grabowecky, adjunct lecturer in the department of psychology; and James Patton, research assistant professor of physical medicine and rehabilitation, all from Northwestern; and Peter M. Vishton, from the College of William and Mary.

Topics: Research