Learning dynamic balancing in the roll plane with and without gravitational cues.
We determined the relative contributions of gravity-dependent positional cues and motion cues to the learning of roll balance control. We hypothesized that gravity-dependent otolith and somatosensory shear forces related to body orientation would yield better initial performance, more rapid learning, and better retention. Blindfolded subjects rode in a device programmed to roll with inverted pendulum dynamics in a vertical (UPRIGHT) or horizontal plane (SUPINE), and used a joystick to align themselves with the direction of balance. Each subject completed five blocks of four 100 s long trials on two consecutive days in one of four groups (n = 10 per group): Group 1, UPRIGHT balancing both days; Group 2, SUPINE both days; Group 3, UPRIGHT then SUPINE; and Group 4, SUPINE then UPRIGHT. On Day 1, UPRIGHT subjects showed better initial performance and greater improvement in performance than SUPINE subjects, who showed improvements only in having fewer deviations exceeding ±60 deg from the direction of balance. Subjects tested UPRIGHT on both days showed full retention of learning across days and additional Day 2 learning, but subjects tested SUPINE on both days showed partial retention of their marginal learning from Day 1 and little improvement on Day 2. Subjects tested SUPINE on Day 2 after being tested UPRIGHT on Day 1 showed no better performance than subjects tested SUPINE on Day 1. By contrast, there was transfer from SUPINE on Day 1 to UPRIGHT on Day 2. We conclude that absence of gravitationally dependent otolith and somatosensory cues degrades balance performance.