Characteristics of target-reaching in cats. III. Lifting and protraction with an obstacle in the movement path and after its removal.

Three cats were trained to perform target-reaching to a horizontal tube with food placed at shoulder level, and the kinematic characteristics of the movements were investigated by recording the trajectory of the wrist. From the very onset of training, a vertical obstacle was placed in front of the cats. The obstacle forced the animals to perform movements with an initial phase dominated by limb-lifting to position the wrist above the obstacle, followed by a second phase of protraction towards the tube; in the sagittal plane, the movement paths were segmented with an upwards convexity. After a training period of 1 year (about 7000 movements), the obstacle was removed. All cats then quickly (within a few trials) changed the trajectory so that the main part of protraction now occurred in parallel with limb-lifting during the first half of the movement. The initial slope of the sagittal movement path became less steep and the upwards convexity less pronounced. Such trajectories, which predominated for several experiments after removal of the obstacle, were only slightly different from those observed in control cats not trained with an obstacle. The results are discussed in relation to a previously proposed hypothesis of motor "imprinting" during extensive training in a particular experimental paradigm.