Aging of sensorimotor processes: a systematic study in Fitts' task.

Though age-related decrease in information-processing capacities is hypothesized to be a prominent cause of behavioral slowing, it has been scarcely systematically studied in goal-directed motor tasks. The present study investigated how the decrease in information processing affects the sensorimotor processes underlying the control of a discrete Fitts' task. The index of difficulty (ID) of the task was manipulated using changes in either target distance (D) or target width (W). In each manipulation, movement (MTs), acceleration (ATs) and deceleration times (DTs) of young and older participants were compared across eight ID levels. They were analyzed with efficiency functions, state traces and Brinley plots. Our results showed that older participants were always slower. However, in both age groups, MTs were longer in D manipulation, which resulted from a slowing of both ATs and DTs, while W manipulation affected mainly DTs. In D manipulation, equivalent age-related slowing ratios were observed for AT and DT (1.3). In W manipulation, ATs of older participants were additively slower than those of young participants. Conversely, DTs presented a multiplicative slowing ratio of 1.3. These findings showed that ID manipulations differentially loaded information processing in the nervous system and that age-related slowing of multisensory control processes was independent of the manipulated dimension. Nevertheless, ID manipulations revealed different age-related adaptations to task constraints, suggesting that D and W manipulations are complementary means to assess age-related slowing of the processes involved in target-directed rapid-aiming tasks, with D scaling being more specific to capture the slowing of force-impulse control.

Combining movement kinematics, efficiency functions, and Brinley plots to study age-related slowing of sensorimotor processes: insights from Fitts' task.

BACKGROUND: 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. OBJECTIVES: (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. METHODS: 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. RESULTS: 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. DISCUSSION: 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.

Aging and changes in complexity in the neurobehavioral system.

The issue of complexity is more and more present in numerous domains of biological research, including aging research. In the present paper, based on a selective review of literature, we propose both a conceptual and a methodological framework to address age-related changes in functional complexity of the neurobehavioral system, presumably resulting from modifications of the coupling between cognitive and sensorimotor processes. In particular, after reviewing pioneering and more recent studies on aging and complexity in the neuromusculoskeletal system, we explore the possibility that an age-induced increase in the coupling between cognitive and sensorimotor domains could be captured by a stronger covariation of high-order variables, common to both cognitive and sensorimotor functioning. Our main assumption is that these variables could behave as neurobehavioral markers of aging in the neuromusculoskeletal system. The present approach markedly differs from other traditional approaches, which focused on process-specific variable correlates of chronological age, domain-by-domain, and task-by-task. It provides a coherent conceptual framework, a terminology, and a method for studying age-related coupling of cognitive and sensorimotor processes with the use of complexity and nonlinear dynamical systems theories.