1. Two Hemispheres are Better Than One for
Motor Learning
Kalpish M. Shah, Samantha L. Stevenson, Nathan R. Vassey, Alexandra V. Court
& Robert M. Kohl
Department of Kinesiology & Health Sciences, The College of William and Mary
Williamsburg, Virginia, USA
MOTOR LEARNING EXPLANATIONS
Motor learning research has been largely associated with the
cognitive perspective. Varied practice schedules/conditions have
been administered to infer different cognitive processes (e.g.,
elaboration and memory reconstruction) in order to determine their
relative impact on motor memory. Collectively, it has been
demonstrated that practicing simple responses in a repetitive
schedule benefited motor learning less then practicing simple
responses in a more random schedule. Also, the controlling of
simple, repetitive responses activates the contralateral hemisphere
while controlling simple repetitive responses in a more random
fashion activates both hemispheres. Hence, it is difficult to
determine if motor learning effects are best explained by cognitive
constructs or by network adaptation associated with hemispheric
interaction. The purpose these experiments was to determine the
impact of inter-hemispheric interaction on motor learning
independent of changing practice conditions associated with
underlying cognitive constructs.
EXPERIMENT I
Participants’ alternated simple hand and foot taps to control the
direction of a vertical accelerating curser to trace a dynamic vertical
sine wave target. During acquisition practice, half of the participants
employed ipsilateral (i.e. contralateral hemispheric activity)
alternating hand and foot tapping, and half employed bilateral (i.e.
contralateral/ipsilateral hemispheric activity) to control the curser.
After a 24 hr interval, half of the participants that had ipsilateral
acquisition practice were given a retention test on the bilateral
condition, and half were given a retention test on the ipsilateral
condition. Likewise, half of the participants that had bilateral
acquisition practice were given a retention test on the bilateral
condition, and half were given a retention test on the ipsilateral
condition (i.e., spit-plot design). Based on transfer of specificity, it is
predicted that each practice group will perform best on their
respective retention test.
Methods
Participants: Twenty-four undergraduate students.
Apparatus: See Figure 1.
Procedure: See the introduction to Experiment 1 and Figure 2 that
describe and illustrate the split-plot design used in this study. There
were thirty 15 s trials with 15 s intervals during acquisition
performance. After a 24 hr retention interval, participants had a three
trial retention test on either ipsillateral or bilateral tapping
performance (see Figure 2).
Figure 2. The illustration depicts a split plot design with
counterbalancing of laterality for acquisition conditions (left) and
retention tests (right).
Results and Discussion
Acquisition: Collapsed (by every 3 trials) averaged data is presented
in Figure 4 (left). Separate 2 x 10 ANOVA [Laterality (ipsilateral,
bilateral) x Trial (1-10, repeated)] revealed an interaction on all
dependent variables indicating that bilateral and ipsilateral
acquisition groups improve their performance differently across trial
blocks.
Retention: Collapsed (by 3 trials) averaged data is presented in
Figure 3 (right). Separate 2 x 2 ANOVA [Acquisition Practice
(ipsilateral, bilateral) x Retention Test (ipsilateral, bilateral)]
revealed an interaction for all dependent variables. The follow-up
analyses indicated that the bilateral acquisition group performed
better on the ipsilateral retention test compared to the performance
of the ipsilateral group on the bilateral retention test. However, more
acquisition tap production by the bilateral group compared to the
ipsilateral group (see Figure 4 top, left) may account for this pattern.
Experiment 2 tested this explanation.
EXPERIMENT II
The procedure for Experiment 1 was identical to Experiment 2 with the
exception that the amount of ipsilateral acquisition practice was doubled
compared to the amount of bilateral acquisition practice.
Methods
Participants: Twenty-four undergraduate students.
Apparatus: See Figure 1.
Procedure:The procedure was identical to Experiment 1 except the ipsilateral
acquisition group had an additional 30 acquisition trials on the day prior the
original acquisition practice conditions as described in the pervious. In brief,
ipsilateral group = Day 1 practice + Day 2 practice vs bilateral group = Day 2
practice only. Day 3, ipsilateral and bilateral retention tests.
Results and Discussion
Acquisition day 1: Collapsed (by every 3 trials) averaged data is presented in
Figure 5 (far left). A separate ANOVA on trials (1-10) indicated an increased
number of taps, increased rhythmicity, and decreased RMSE for the
ipsilateral group.
Acquisition day 2:Collapsed (by every 3 trials) averaged data is presented in
Figure 5 (center left). Separate 2 x 10 ANOVA [Laterality (ipsilateral,
bilateral) x Trial (1-10, repeated)] revealed an interaction on all dependent
variables indicating that bilateral and ipsilateral acquisition groups improved
their pefromance differently across trial blocks.
Retention day 3: Collapsed (by 3 trials) averaged data is presented in Figure
5 (right). Separate 2 x 2 ANOVA [Acquisition Practice (ipsilateral, bilateral)
x Retention Test (ipsilateral, bilateral)] revealed an interaction for all
dependent variables. The follow-up analyses indicated that the bilateral
acquisition group had a greater positive impact on the ipsilateral retention
test compared to the positive impact of the ipsilateral acquisition group had
on the bilateral retention test.
EXPERIMENT III
The purpose of Experiment 3 was to determine if the pattern results from
Experiments 1 and 2 would be replicated under conditions of four practice
days (30 trial each day) and a 48 hr retention interval.
Methods
Participants: Twenty-four undergraduate students.
Apparatus: See Figure 1.
Procedure:The same split plot design was utilized. There were four days of
acquisition practice. Each day of practice was identical to Experiment 1.
After a 48 hr retention interval there were retention tests that matched
Experiments 1 and 2 (see Figure 5).
Figure 5. The illustration depicts a split plot design for acquisition conditions
(left) and counterbalancing retention tests (right).
Results and Discussion
Acquisition days (1-4), Collapsed (by day, 30 trials) averaged data is
presented in Figure 6 (left). Separate 2 x 10 ANOVA [Laterality (ipsilateral,
bilateral) x Day (1-4, repeated)] revealed a main effect of Laterality
indicating increased number of taps, increased rhythmicity, and decreased
RMSE for both groups with the bilateral groups performing better.
Retention day 5: Collapsed (by 3 trials) averaged data is presented in Figure
6 (right). Separate 2 x 2 ANOVA [Acquisition Practice (ipsilateral, bilateral)
x Retention Test (ipsilateral, bilateral)] revealed an interaction for all
dependent variables. The follow-up analyses indicated that the bilateral
acquisition group had a greater positive impact on the ipsilateral retention
test compared to the positive impact of the ipsilateral acquisition group had
bilateral retention test.
GENERAL DISCUSSION
Collectively, all three experiments provide strong evidence that inter-
hemispheric interaction had a positive impact on motor learning adaptation
independent of any change in practice conditions associated with differing
underlying cognitive processes/constructs. This is an important
demonstration because practice conditions associated with underlying
cognitive processes that promote motor learning also have greater inter-
hemispheric interaction. The present data and explanation advocates the need
for inter-hemispheric adaptation as the common bases for motor learning and
calls into question the need of cognitive explanations (memory
reconstruction, elaboration) to explain motor learning effects.
Figure 1. The same Pew type Task was used in all 3 experiments. The cursor on the screen
accelerated vertically (38.6 cm/s2). Participant’s attempted to keep the curser on the dynamic
center target (1.5 cycles of a sine wave, 0.1 Hz, with an amplitude of 1.25 cm), by controlling its
direction. Hand tap directed the curser down and a foot tap directed the curse up. An ipsilateral
condition left and a bilateral condition right.
Figure 3. Laterality (ipsilateral, bilateral) conditions across acquisition trial blocks (left) and
Laterality (ipsilateral, bilateral) of retention tests for acquisition laterality conditions (right).
Mean number of key presses (top), rhythmicity (middle), and RMSE (bottom).
Figure 4. Laterality (ipsilateral, bilateral) conditions across acquisition trial blocks (far left and left)
and Laterality (ipsilateral, bilateral) of retention tests for acquisition laterality conditions (right). Mean
number of key presses (top), rhythmicity (middle), and RMSE (bottom).
Figure 6. Laterality (ipsilateral, bilateral) conditions across acquisition days (left) and
Laterality (ipsilateral, bilateral) of retention tests for acquisition laterality conditions
(right).Mean number of key presses (top), rhythmicity (middle), and RMSE (bottom).