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Professional athletes involved in sports that require the execution of fine motor skills must practice for a consider- able length of time before competing in an event. Why is such practice necessary? Is it merely to warm-up the muscles, tendons, and ligaments, or does the athlete's sensorimotor network need to be constantly recalibrated? In this article, the authors present a point of view in which the human sensorimotor system is charac- terized by: (a) a high noise level and (b) a high learning rate at the synaptic level (which, because of the noise, does not equate to a high learning rate at the behavioral level). They argue that many heuristics of human skill learning, including the need for a prolonged period of warm-up in experts, follow from these assumptions.

In the present work the effect of two task variables on transfer were studied: shape of the track-circular or triangular; and target speed-constant or variable. One or both of these variables was changed on transfer. Experimental conditions were (a) 10 preshift and 10 post-shift trials, and (b) 20 single-trial alternations of two tasks. 22 groups of 12 Ss each were tested. Condition (a) showed positive transfer with single variable change and zero or negative transfer with simultaneous change in two variables, and condition (b) annulled all transfer effects. Results are discussed in terms of commonality between tasks and receptor and perceptual anticipation.

80 Ss performed a horizontal adduction movement of the arm attempting to approximate a velocity of 6 or 10 ft/sec with or without a 2-lb. weight in the hand, and Ss were randomly divided into 4 equal subgroups based upon the possible velocity-weight combinations. Ss were blindfolded and received only verbal cues as to the direction of error. After 60 trials on the initial task, each group was divided into 4 subgroups, based upon the original velocity-weight combinations, and performed 60 transfer trials. The two groups approximating the faster velocity were significantly more accurate on the initial task while weight had no effect on accuracy. Negative transfer occurred from the faster movement to the slower, more difficult movement.

The principal defect in the Osgood (1949) transfer surface is the treatment of negative transfer. This may be corrected, although no surface can incorporate all the relevant transfer variables. The explanation and the scoring of negative transfer are discussed, with an emphasis on problems of skills learning. The conclusions reached are represented in the design of a new transfer surface.

Cognitive factors in motor behavior were defined as verbal and imagery mediators for a discrete, sequential motor task. The question was asked whether these mediators become nonfunctional with extended practice. Non-motor interference training was given in inappropriate verbal and imagery mediation. If cognitive factors in the motor task involve verbal an/or imagery dimensions, and they dominate early in learning, then the non motor interference training should produce relatively large negative transfer effects in the motor performance early in learning and little or no such effects late in learning. The results did not conform to expectation; small negative transfer effects were found both early and late in learning. The discussion considered several possible reason for the outcome: the motor task was dominated by visual and proprioception factors rather than cognitive ones, the method of delivering knowledge of results may have minimized cognitive factors, or the hypothesis is wrong.