CHARACTERISTICS OF TARGET-REACHING IN CATS .2. REACHING TO TARGETS ATDIFFERENT LOCATIONS

Trajectory formation of unrestrained forelimb target-reaching was inve stigated in relation to the effect of a change in target location. Sag ittal displacement of the target (6 cm in each direction) gave a selec tive change of velocity in the x direction (protraction) with an incre ase 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) a nd of the z (lifting) velocity profiles were both almost unchanged, bu t the onset of the movement in the z direction changed with the x dist ance. Vertical displacement (4 cm up or 5 cm down) gave increased velo city in the z direction (lifting) when the target was above the normal mid-position and decreased velocity when the target was lower. The ve locity was changed with constant rate of rise, so that the rise time i ncreased when the target was elevated and shortened when the target wa s lowered (pulse width control policy). The change in the z velocity w as 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 dow n), 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 ap peared in the x and net velocity profiles when the target was excessiv ely lowered. The velocity profile in the y direction changed when the target was lowered so that the horizontal movement path became straigh ter. Sideways displacement (10-13 cm) produced adduction/abduction, wi th only moderate changes in x and z velocity profiles. The results are discussed with reference to the angular movements in the elbow and sh oulder.