VARIATION OF ISOMETRIC RESPONSE FORCE IN THE RAT

Hungry, unrestrained rats (N = 7) were rewarded for pressing a respons e beam in excess of 11 different force requirements. Changes in peak f orce production as a function of peak force requirement were examined by analyses of the first four moments of distributions of peak respons e forces: constant error, the within-subject standard deviation, skewn ess, and kurtosis. Results were similar to those previously obtained w ith human subjects: Constant error was positive at low and negative at high force requirements, the within-subject standard deviation increa sed as a negatively accelerating function of force requirement, and sk ewness and kurtosis were positive at low force requirements and decrea sed to negative values at the highest increments. Additional analyses of response kinetics indicated that rats, like humans, meet increasing force requirements by altering the rate of rise of force. The perform ance similarities suggest that common processes are engaged by the hum an and rat motor control systems to solve the problem of generating fo rces that are appropriate to the prevailing environmental constraints.