Combining movement kinematics, efficiency functions, and Brinley plots to study age-related slowing of sensorimotor...

Measurement of changes in human information-processing capacities underlying slowing of sensorimotor processes is an important challenge for aging research. Methods exist to estimate the magnitude of slowing and variability coefficients, but attempts to apply them in motor tasks have been scarce. In the present experiment we combined movement kinematic analysis, efficiency functions and Brinley plot to assess age-related slowing and variability of sensorimotor processes in a discrete Fitts' aiming task.

(1) Quantifying slowing and variability for the different sensorimotor processes involved in aiming movements, and (2) determining whether changes occurred continuously over time by comparing different age groups.

29 participants (24-90 years) divided into four age groups were tested. Target size manipulation resulted in three levels of difficulty. Total movement time, durations of the first and secondary movement phases and related variability were analyzed. Fitts and Brinley regression functions were calculated on the basis of the different movement variables.

Only older participants were slower than the three younger age groups. For this group, age-difficulty effect was observed for total movement times, but analyses showed that only the secondary movement phase slowed multiplicatively. Additive and proportional increases in variability were also observed in older participants for the first and secondary movement phases, respectively. For the secondary movement phase, estimated slowing coefficients were comparable to those reported in cognitive literature. In addition, Brinley analyses showed that variability increased more than movement time in the secondary movement phase.

Combination of the different methods of analysis allowed a precise assessment of the locus of slowing and variability of sensorimotor processes in the different movement phases. Results showed that significant changes in both slowing and variability of the different processes occurred late in life. Our findings also suggest that slowing could result from age-induced increase in noise produced by the neural system. Finally, the present results raise the question of whether age-related slowing and increase in variability observed in both cognitive and sensorimotor domains share common causes in the central nervous system.