THE EFFECTS OF AGING ON DISCRETE AND CONTINUOUS MOTOR COORDINATION A. S. Bangert 1, C. M. Walsh 2,3, A. E. Boonin 1,4, E. Anderson 4, D. J. Goble 4, P. A. Reuter-Lorenz 1,2, R. D. Seidler 1,2,3,4 1 Department of Psychology, 2 Neuroscience Program, 3 Institute of Gerontology, 4 Division of Kinesiology, University of Michigan Introduction  Bimanual coordination for continuous motor tasks (e.g. circling, Figure 1) and for discrete, repetitive tasks (e.g., repetitive finger tapping) may rely on separate timing mechanisms.  Performance of callosotomy patients implicates subcortical coordination of discrete, repetitive movements and cortical/callosal coordination of continuous movements (Ivry & Hazeltine, 1999; Kennerley et al., 2002).  Temporal consistency on unimanual and bimanual discrete and continuous tasks is correlated within, but not between, task types (e.g., Roberston et al. 1999; Zelaznik et al., 2000; 2002). This provides additional support for task-dependent coordination mechanisms.  Older adults show impairments in continuous bimanual coordination (Swinnen et al., 1998). Is the same true for discrete repetitive bimanual tasks, or does age differentially affect cortical versus subcortical substrates of motor control? Methods  17 older (M = ± 3.79 years) and 17 younger (M = ± 1.13 years) right-handed adults participated in tasks administered over 2 testing sessions.  Discrete Repetitive Tapping: Tapped with index fingers in time to visually-presented targets Responses made on a button box situated under each hand 3 Speeds (ITI = 800 ms, 1000 ms, 1200 ms) 5 Conditions Right Hand Only Left Hand Only Simultaneous (0 ms lag between hands) Right leads Left (180 ms lag between hands) Left leads Right (180 ms lag between hands) Dependent Variables All Conditions = Within-Hand Standard Deviation Bimanual Conditions = Between-Hand Standard Deviation  Continuous Circle Drawing: 2 Speeds - Preferred & Maximum rate 4 Conditions – See Figure 1 Dependent Variable = Average Absolute Time Lag Between Hands Acknowledgements This work was supported by NIA AG18286 (PARL), UM OAIC and OVPR (RDS) grants. References  Ivry, R. B. & Hazeltine, E. (1999). Human Movement Science, 18,  Kennerley et al. (2002). Nature Neuroscience, 5,  Robertson et al. (1999). Journal of Experimental Psychology: Human Perception and Performance, 25,  Swinnen et al. (1998). Cognitive Neuropsychology, 15,  Zelaznik et al. (2000). Journal of Motor Behavior, 32(2),  Zelaznik et al. (2002). Journal of Experimental Psychology: Human Perception and Performance, 28, L is CCW, R is CW L is CW, R is CCW Mirror -Symmetric Both Hands CCW Both Hands CW Parallel Figure 1. A schematic of the 4 bimanual circling conditions. Predictions  If aging globally affects motor control and its subcortical and cortical substrates, then for older adults; Temporal consistency between hands for both discrete and continuous tasks should suffer over all levels of task complexity. All performance measures should correlate positively.  If aging has differential effects: Older adults’ performance should dissociate on the two tasks. Complex Conditions Discussion  It is important to note that while older adults’ performance did not dissociate on the two types of motor tasks, there was also no evidence for global declines with age.  Though minimal on easier tasks, age differences appeared with increasing temporal and spatial coordination demands.  Positive intertask correlations for hard tasks in older adults suggest increased reliance on common resources when dealing with increasing difficulty on otherwise diverse motor tasks.  Intermanual synchrony appears harder to maintain at slower speeds for all participants, especially older adults.  Motor slowing with aging may, therefore, be a source of compromised intermanual temporal synchrony.  Surprisingly, older adults appear to use the same strategy as younger adults for complex tapping (lead finger more variable than following finger). However, greater difficulty with intermanual synchrony in these tasks suggests they implement the strategy less effectively.  In summary, age-equivalent intermanual synchrony for circling (normalized data) and simultaneous tapping, as well as the preserved benefit for simultaneous relative to unimanual tapping argue against global declines in cortical and subcortical coordination mechanisms with age. Results – Task Correlations: Does Aging Lead to Increased Reliance on Common Resources? Figure 3. Circling results when lag normalized by circling speed. This analysis corrected for slower circling evidenced by older adults. Parallel circling is harder for both groups, p <.001 No Age differences in circling performance. Results – Circle Drawing: Does Aging Lead to Impairment on Continuous Bimanual Tasks? Figure 2. Circling results. Parallel circling is harder for both groups, p <.001 No significant age differences, but a trend towards worse performance in older adults, p = 0.12 Older adults’ tendency toward slower circling (an average of 50 ms slower) prompted us to normalize the lag measure by circling speed to avoid inflated estimates of lag between hands for this group. Figure 4. Bimanual Tapping Results. Results – Tapping: Does Aging Lead to Impairment on Discrete Repetitive Bimanual Tasks? Simultaneous less variable than complex, p <.001 Older adults more variable in complex tasks, p <.001 Figure 6. Tapping Results: Within-Hand Performance. Each point was derived from collapsing data across the right and left hands. Follow and Lead refer to finger position in the complex (180 ms lag) tap conditions. Both age groups show an advantage when tapping in the simultaneous versus the single hand only condition, p <.01 For both age groups, the follow hand during complex tapping was as consistent as either hand during simultaneous tapping. Thus, there is an advantage for the follow hand in the complex conditions. The lead hand in complex tapping was more variable than either hand during simultaneous tapping for both groups, p < Results – Tapping: Does Aging Lead to Impairment on Discrete Repetitive Bimanual Tasks? Figure 5. Bimanual Tapping Results x Tapping Speed. Results for complex tapping were collapsed across both lag conditions. Both groups are more variable at slower speeds, p <.001 Effect of speed is more apparent in complex conditions, p <.001, and in older adults, p <.05 Older adults were more variable than young adults, p <.01 Ability to maintain consistency of tapping within each hand was dependent on tapping condition for both groups, p <.001 No significant intertask correlations between easy conditions for older adults, countering the idea of global declines in the bimanual coordination mechanisms subserving these tasks. Older adults had higher overall positive intertask correlations than younger adults, especially for hard tasks. Tap Simultaneous Tap Complex Circle Symmetric Table 2. Correlations Between Tasks for Older Adults Tap Circle Circle Complex Symmetric Parallel.588*** **.377*.357* *Trend at.05 < p <.10 (one-tailed) **Significant at the p <.05 level (one-tailed) ***Significant at the p <.01 level (one-tailed) Tap Simultaneous Tap Complex Circle Symmetric Table 1. Correlations Between Tasks for Younger Adults Tap Circle Circle Complex Symmetric Parallel Results – Tapping: Do Older Adults Show ‘Two Hands Better than One’ Effect? Specific Findings For the Bimanual Conditions