Age and Cognitive Stress Influences Motor Skill Acquisition, Consolidation, and Dual-Task Effect in Humans

Abstract

This study examined motor skill learning using a weight-bearing and cognitive-motor dual-task that incorporated unexpected perturbations and measurements of cognitive function. Forty young and 24 older adults performed a single-limb weight bearing task with novel speed, resistance, and cognitive dual task conditions to assess motor skill acquisition, retention and transfer. Subjects performed a cognitive dual task: summing letters in one color/orientation (simple) or two colors/orientations (complex). Increased cognitive load diminished the rate of skill acquisition, decreased transfer to new conditions, and increased error rate during an unexpected perturbation; however, young adults had a dual-task benefit from cognitive load. Executive function predicted 80% of the variability in dual-task performance. Although initial learning of a weight-bearing cognitive-motor dual-task was poor, longer term goals of improved dual-task effect and retention emerged.

Keywords: Dual-task; aging; executive function; perturbation.

Figure 1. Experimental setup.

Top left: schematic of the standing frame, monitor, and rack and pinion knee resistance / force measurement system. Top right: representative example of user generated line (dashed) and target line (solid line) of the five-cycle sinusoid task. Bottom right: nine speed × resistance combinations of the testing paradigm. Training is performed under condition 1 (medium speed and medium resistance.

Figure 2. Experimental Design.

Testing conditions presented for four training groups on three different days (Day 1, Day 2, and Day 3). Testing flow begins at the top of each column (Day 1), continuing to the bottom of the same column (Day 3). Each group (CT1, CT2, DT1, DT2) contains 10 younger adults and 6 older adults.

Figure 3. Skill Acquisition and Retention Full Trial Analysis.

Twenty training trials on day 1, and 5 training trials 48 hours later were performed without distraction (closed circle: Control), a simple cognitive task (open circle: Dual-Task 1), and a complex cognitive task (open triangle: Dual-Task 2). Mean and standard deviation of the absolute value of trial mean (A,B), and Coherence (C,D) is presented. # = Older adults in the dual-task 2 group experienced greater error and lower coherence compared to all other groups on day 1, and in both younger and older adults on day 2. & = Older adults with higher error or lower coherence from younger adult for similar training group (p<0.05).

Figure 4. Transfer of Learning: Full Trial Variables.

Trial Error (A,B) and Coherence (C,D) for younger (A,C) and older (B,D) adults, performing only the motor task (control, closed circle), and simultaneous motor, and simple (open circle) and complex (open triangle) cognitive tasks. The left side depicts each individual combination and the right side depicts the mean of three trials of each resistance and velocity. * = younger controls perform differently than dual-task groups. ^ = condition of resistance or velocity is significatly different from the others. # = older dual-task 2 group different from other older groups. #* = indicates dual-task 2 group only different from the control group.

Figure 5. Transfer of Learning: Non-Volitional Feedback Variables.

Knee flexion rate (A,B) and error rate (C,D) 50-200 ms following an unexpected force perturbation for younger (A,C) and older (B,D) adults, performing only the motor task (control, closed circle), and simultaneous motor, and simple (open circle) and complex (open triangle) cognitive tasks. The left side depicts each individual combination and the right side depicts the mean of three trials of each resistance and velocity. ^ = condition of resistance or velocity is significatly different from the others. ^* = condition different from each condition with the same symbol. #* = dual-task 2 group only different from the control group. & = all older adult groups different from the younger adult groups.

Figure 6. Dual-Task Cost: Day 2.

Younger (A,C) and Older (B,D) adults performed both a single motor (closed symbol) and dual cognitive-motor (open symbol) tasks. Presented is the difference in motor performance between single and dual-task conditions at each resistance and velocity. ##** = dual-task groups different from control groups. ** = CT2 group different from all other groups. *** = both CT2 and CT1 different and different from dual-task groups. ^* = different from other conditions with the same symbol.

Figure 7. Dual-Task Cost: Day 3.

Young (A,C) and Older (B,D) adults performed both a single motor (closed symbol) and dual cognitive-motor (open symbol) tasks. Presented is the difference in motor performance between single and dual-task conditions at each resistance and velocity. ##** = dual-task groups different from control groups. #* = CT1 and DT1 different from CT2 and DT2. * = CT1 different from DT2. ^* = different from other conditions with the same symbol.