1. Inter-hemispheric Interaction is the Bases
for the Goldilocks Principle of Motor Learning:
A Postulate
Alexandra V. Court, Samantha L. Stevenson, Kalpish M. Shah, Nathan R. Vassey
& Robert M. Kohl
Department of Kinesiology & Health Sciences, The College of William and Mary
Williamsburg, Virginia, USA
The term GLP originated in
planetary science and represents a
“just right” distance from the sun
to sustain life.
Goldilocks Principle
According to this principle, if methods of practice are too simple or
challenging for the learner’s skill level, motor learning will be
minimized. The relationship between the skill level of the learner and the
difficulty of practice must be “just right” in order to maximize the
learning process. While the GLP is well established in our culture for
teaching and learning applied skills, from a theoretical perspective it is
more problematic to identify the critical underlying phenomena that are
amenable to tests of disproof.
The GLP as Described by Guadagnoli and Lee
Guadagnoli and Lee may have been the first to formalize a description of
the GLP for motor learning. Cultural mores stipulate that practicing to
obtain some level of competency at simple activities should proceed the
practice of more difficult variations of the same activity. G&L
congruently proposed that it is critical for all learners, from novices to
experts, to practice activities that require the “just right challenge” for
optimal motor learning. Such a “challenge” would be determined by a
certain (unspecified) moderate level of performance efficiency during
practice, and this represents the optimal processing capacity to maximize
motor learning. However, from this point of view, any pattern of results
from any motor learning experiment could be explained away by the “just
right- not just right” challenge or elaboration, memory reconstruction,
knowledge of results guidance, or cognitive effort. Hence it eliminates the
possibility of a test of disproof.
Testable Propositions
Section 1. Research demonstrating the “reversal effect” and motor
memory sleep consolidation represent manifestations of the same
phenomena.
Practice, subsequent rest, and their interactions are arguably the most
fundamental ingredients that contribute to motor memory consolidation.
One often demonstrated pattern in motor learning experiments is referred
to here as the “reversal-effect.” In the most straightforward case, the
reversal-effect describes a pattern of two practice groups in which one
group performs with less error than another group during acquisition
practice, but after a delayed-retention interval (e.g., 24 or 48 hours) the
two groups’ relative retention standings reverse. The group, that practiced
simple, repetitive responses with 100% feedback (KR), performed with
less error during acquisition performance but with more error during
delayed-retention performance when compared to a group that had
acquisition practice with responses that were more variable or random or
had partial KR withdraw (see Figure 1, top). This implies that different
practice methods interact differently with delayed retention for motor
memory consolidation.
Also, there have been many experimental demonstrations showing that
after acquisition practice, the group that had sleep during the delayed-
retention interval typically performed with less error on the retention test
when compared to the group that had no sleep during the retention
interval (see Figure 1, bottom panel). This implies that sleep after
acquisition practice contributes to motor memory consolidation.
While both experimental paradigms employed acquisition practice, a
delayed retention interval, and a retention test, researchers in these two
areas have clearly focused on different aspects of their experiments.
Researchers who have demonstrated the reversal-effect largely focused
on the composition of acquisition practice, whereas researchers who
investigated sleep as an independent variable largely focused on the
composition of the retention interval, but both represent the same motor
learning phenomena.
Testable Proposition 1: Repetitive practice of simple responses during
acquisition are not consolidated into motor memories as a function of
sleep. However, sleep consolidates motor memory when acquisition
practice response demands are sufficiently increased.
Figure 1. Illistration of the commonality for the pattern of results of
motor “reversal effect” research (top) and motor sleep consolidation
research (bottom).
Section 2. Hemispheric Lateralization during motor control.
It has been consistently demonstrated that as response complexity
increases, brain activity increases and becomes more lateralized. In
fact, multiple experiments utilizing brain scans have revealed that the
control of simple repetitive responses were associated with the
activation of the contralateral hemisphere only. Whereas, when
simple responses became more randomized, variable, or had
increased demands, both hemispheres were activated. These findings
have been attributed to decreased network activation necessary to
direct and organize the neuro-motor system in the execution of
simple, repetitive responses. In contrast, each hemisphere is thought
to control different or unique response features which are integrated
to perform more complex responses, thus increasing inter-
hemispheric interaction.
Testable Proposition 2: Less inter-hemispheric interaction is
required to control simple repetitive responses. Likewise, greater
inter-hemispheric interaction is required to control responses with
increased cognitive demands.
Section 3. Combining Testable propositions 1 and 2 into Testable
proposition 3
Testable Proposition 3: Sleep will not consolidate acquisition
practice into motor memory unless such acquisition practice has
sufficient inter-hemispheric interaction.
Section 4. Response Demands and Inter-hemispheric limitations.
Comparing dual arm and leg control under different conditions
provides a venue to examine the limitations of response demands.
When arms and legs were coupled by continuously moving in the
same direction, their performance was more stable and efficient than
when arms and legs were decoupled by continuously moving in
different directions. This pattern of unstable motor control was much
greater during ipsilateral decoupling. Brain scans have revealed that
arm and leg coupling and decoupling networks were very similar,
apart from decoupling producing greater activation in both
supplementary motor areas (SMA). One possible implication from
this research was that arm and leg decoupling surpassed the capacity
of inter-hemispheric communication between SMAs and related
networks that regulate effector and response selection, exceeding
their capacity as well, producing unstable motor control. The bottle
neck would be expected to be greater when the response demands
were asymmetrical across limbs/hemispheres (ipsilateteral control).
Testable Proposition 4: When response demands are exceedingly
high, the capacity limitations of inter-hemispheric communication
are surpassed, thereby bottle necking hemispheric communication
and associated motor execution networks and producing inefficient
motor control.
The Postulate
Arguably, some form of the GLP acts as the foundation for all higher order
motor learning situations in the animal kingdom. When learning a new motor
skill, the learner must have some level of efficiency of more elementary
activities before being exposed to more complex activities. When some level
of efficiency has been obtained, the process is progressively repeated. We
propose that hemispheric communication is the basis of the GLP. If practice
does not elicit sufficient inter-hemispheric interaction, motor control
performance will be efficient, but motor learning will be attenuated. That is,
practice needs to be sufficiently difficult/complex so as to require hemispheric
interaction for subsequent motor memory consolidation during sleep.
As part of the consolidation process, brain networks are actually manifested to
expand inter-hemispheric communication routes resulting in improved motor
control efficiency. This can be maximized with practice utilizing multiple
limbs. However, all hemispheric communication routes have a limited
capacity. If this capacity is exceeded during practice, inter-hemispheric
communication would be overwhelmed and have a negative impact on the
consolidation process. In summary, inter-hemispheric communication (which
can be measured independent of skill level of the learner) needs to be “just
right” to maximize motor learning (expanding inter-hemispheric
communication routes).
Based on the GLP, animals learn to, for example, hunt, climb trees, and forage
for food. Likewise, based on this principle humans learn to, for example,
perform surgery, play a musical instrument, recover the skill of buttoning a
coat after a brain lesion, as well as learn to shoot a basketball or hit a baseball.
We have provided a testable postulate (i.e. lowest common denominator for
motor learning) to explain the GLP.
Testable Proposition 5: Practice with multiple limbs will increase inter-
hemispheric communication routes (during sleep) thereby increasing
motor efficiency.
Section 5. Practice with bilateral limbs benefits motor control efficacy.
There is some indirect evidence to indicate that substantial limb coupling and
decoupling practice attenuated and/or eliminated unstable behavior as well as
modified the structural routes responsible for inter-hemispheric
communication. It has been shown that concert pianists, who started training
when developmental myelination was optimal (at the mean age of 5.8 years),
had a substantial increase in myelinaiton of fiber tracts of the corpus callosum.
It has also been shown that long time experience in playing a musical
instrument resulted in superior bimanual coordination and faster unilateral and
bilateral RTs. Similarly, musical training with children has been related to
benefits associated with coordinating fine motor skills as well as long-term
visuospatial, verbal and mathematical functions. Such benefits have been
attributed to substantial practice that includes the decoupling of multiple limbs
under varied conditions. This is an important supposition given the necessity
for inter-hemispheric communication to efficiently process motor tasks and
problems, especially as tasks and problems increase in complexity (GLP).
Recommendations for Practice
Based on the inter-hemispheric postulate of the GLP, we propose that the main purpose of practice should be
directed toward building a better brain. In other words, motor practice should enrich inter-hemispheric
commination for network growth, which in turn, would enhance skill development. Hence, all optimal
practice methods should consider the mantra “two hemispheres are better than one for motor learning.”
Figure 2. Proposed brain activation for simple (left) and complex responses (right).
Figure 3. Proposed brain activation for complex responses (left) and extreme complex
responses (right).
Figure 4. Proposed brain activation before (left) and after (right) considerable bilateral multi-limb
practice