  Group decisions can outperform the choices of the best individual group
members. Previous research suggested that optimal group decisions require
individuals to communicate explicitly (e.g., verbally) their confidence levels.
Our study addresses the untested hypothesis that implicit communication using a
sensorimotor channel -- haptic coupling -- may afford optimal group decisions,
too. We report that haptically coupled dyads solve a perceptual discrimination
task more accurately than their best individual members; and five times faster
than dyads using explicit communication. Furthermore, our computational
analyses indicate that the haptic channel affords implicit confidence sharing.
We found that dyads take leadership over the choice and communicate their
confidence in it by modulating both the timing and the force of their
movements. Our findings may pave the way to negotiation technologies using fast
sensorimotor communication to solve problems in groups.
