Somatosensory anticipation of curvature in a haptic virtual environment

The human visuomotor system uses predictive mechanisms to allow the eye or hand to efficiently follow a moving target. The long-term goal of the present study is to determine whether the somatosensory system has similar capabilities. Subjects used the right arm to move the index fingertip inside of virtual tubes shaped as large elliptical objects positioned in the frontal plane. The virtual ellipses had three different aspect ratios and two different tilts, and some had flattened portions inserted in one of three regions. Each of the 24 virtual shapes was presented only once to each subject, but the subject explored each one by moving in five consecutive laps. Performance was more improved over the laps when subjects were allowed to stay in constant contact with the walls of the tube, rather than attempting to stay off the walls. However, even with this continuous haptic feedback, subjects could not precisely anticipate the timing of an upcoming flattened region. Thus, similar to recent results for visually-guided eye movements, it appears that it is difficult for the haptic guidance system to time the anticipation of an upcoming event.