Unexpected downshifts in reward magnitude induce variation in human behavior.

We investigated how changes in outcome magnitude affect behavioral variation in human volunteers. Our participants entered strings of characters using a computer keyboard, receiving feedback (gaining a number of points) for any string at least ten characters long. During a "surprise" phase in which the number of points awarded was changed, participants only increased their behavioral variability when the reward value was downshifted to a lower amount, and only when such a shift was novel. Upshifts in reward did not have a systematic effect on variability.

Effects of practice on variability, effects of variability on transfer.

Five experiments examined how practice early in skill acquisition affected variability and accuracy during skill retention (Experiments 1-5) and skill transfer (Experiments 3, 4, 5). Lag constraints required that each path from apex to base of a computer-generated pyramid display differ from some number (the lag) of immediately prior paths. Location constraints specified end points at which paths must exit the pyramid. In all experiments, an early optimal period for acquiring a variability level was identified. Both low and high levels of variability were sustained during retention; high levels facilitated transfer. The results suggest that (a) early practice that requires high variability sensitizes learners to changes in condition and (b) such perception-performance links facilitate transfer by activating appropriate alternative strategies/schema or initiating their construction.

Constraints have different concurrent effects and aftereffects on variability.

Three experiments showed that constraints imposed early in learning have different effects on variability when they are in effect and after they are removed. Task constraints, which determine how something can be done, limited the number of possible responses in a computer game. Variability constraints, which specify how differently something must be done, required that each response differ from some number of prior responses. Less restrictive constraints (Experiments 1 and 2) produced higher variability during the constraints. More restrictive constraints (Experiments 2 and 3) led to higher variability after the constraints were relaxed. The authors discuss how these differences reflect strategies acquired during the constraints (default rules) and modified in closely related ways (exception rules) afterward.