Characteristics of target-reaching in cats

Abstract

Trajectory formation of unrestrained forelimb target-reaching was investigated in relation to the effect of a change in target location. Sagittal displacement of the target (6 cm in each direction) gave a selective change of velocity in the x direction (protraction) with an increase or decrease at larger and shorter distances, respectively. In the case of a double-peaked x velocity profile, the change was mainly with respect to the first major component. The shape of the y (sideways) and of the z (lifting) velocity profiles were both almost unchanged, but the onset of the movement in the z direction changed with the x distance. Vertical displacement (4 cm up or 5 cm down) gave increased velocity in the z direction (lifting) when the target was above the normal mid-position and decreased velocity when the target was lower. The velocity was changed with constant rate of rise, so that the rise time increased when the target was elevated and shortened when the target was lowered (pulse width control policy). The change in the z velocity was not selective. In cats with a double-peaked x velocity profile, the second component decreased when the target was elevated and increased when it was lowered. With excessive lowering of the target (14 cm down), the first x velocity component was very much reduced in amplitude so that protraction depended mainly on the second x velocity component. In the cat with a unimodal x velocity profile, a second component appeared in the x and net velocity profiles when the target was excessively lowered. The velocity profile in the y direction changed when the target was lowered so that the horizontal movement path became straighter. Sideways displacement (10–13 cm) produced adduction/abduction, with only moderate changes in x and z velocity profiles. The results are discussed with reference to the angular movements in the elbow and shoulder.