American Physiological Society, Journal of Neurophysiology, 2(93), p. 1055-1068, 2005
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We studied how subjects learn to deal with two conflicting sensory environments as a function of the probability of each environment and the temporal distance between repeated events. Subjects were asked to intercept a visual target moving downward on a screen with randomized laws of motion. We compared five protocols that differed in the probability of constant speed (0 g) targets and accelerated (1 g) targets. Probability ranged from 9 to 100%, and the time interval between consecutive repetitions of the same target ranged from about 1 to 20 min. We found that subjects systematically timed their responses consistent with the assumption of gravity effects, for both 1 and 0 g trials. With training, subjects rapidly adapted to 0 g targets by shifting the time of motor activation. Surprisingly, the adaptation rate was independent of both the probability of 0 g targets and their temporal distance. Very few 0 g trials sporadically interspersed as catch trials during immersive practice with 1 g trials were sufficient for learning and consolidation in long-term memory, as verified by retesting after 24 h. We argue that the memory store for adapted states of the internal gravity model is triggered by individual events and can be sustained for prolonged periods of time separating sporadic repetitions. This form of event-related learning could depend on multiple-stage memory, with exponential rise and decay in the initial stages followed by a sample-and-hold module.