Nibbles: during acquisition (d1-8), performance increased, except in the initially low uncertainty group for the distal lever. Between days 8-24, nibbling slightly decreased in the initially high uncertainty group and slightly increased in the initially low uncertainty group, but a significant group difference was maintained for the PS and distal levers on day 24. Speed: during acquisition (d1-8), speed increased, except in the initially low uncertainty group for the PE and distal levers. Between days 8-24, speed slightly decreased in the initially high uncertainty group (but strongly with respect to the PS lever, p = 0.001) and slightly increased in the initially low uncertainty group. No group difference was shown on day 24. Legends: * p < 0.05, ** p < 0.01, *** p < 0.001.