Free manipulation facilitates bimanual integration in a haptic pliers' size discrimination task

Humans can accurately distinguish the shape of objects through haptic interaction. In the present study, we investigated the haptic perception of the size of large pliers held with both hands. An haptic size discrimination task was conducted in three experimental conditions: (1) a free bimanual condition where the pliers were free to move in the fronto-parallel plane; (2) a bimanual constrained condition where the position of the rotation axis was fixed; and (3) a one-hand condition with the position of the rotation axis fixed. The first objective was to find out whether the perception of the pliers' size is affected by the constraint on the pliers' rotation axis. The second objective was to investigate the integration of bimanual information in this task. We found that the discrimination threshold was lower in the free condition than in the bimanual constrained condition. This finding indicates that bimanual physical interaction in the free condition can facilitate bimanual integration during haptic exploration. We propose that bimanual physical interaction could facilitate the construction of a mental representation of the pliers' size from the sensory cues that are collected by the two hands during haptic exploration.

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