Biomedical Engineering Reference
In-Depth Information
than the previous one. A fractal pattern of dynamic variability can be generated to
mimic those observed in healthy human gait. Instructing a patient to synchronize to a
fractal metronome might induce desired patterns of dynamic variability in their gait
cycle, enhancing adaptive functional mobility.
Evidence that participants can synchronize to a noisy visual metronome was first
observed in finger tapping [
53
]. A flashing square on a computer screen prescribed
the inter-tap intervals for the participant. The long-range correlations of the visual
metronome intervals (indexed by DFA) were manipulated between conditions, and
the participants' inter-tap intervals were shown to exhibit the same long-range cor-
relations as the visual metronome. This provided evidence that the structure of vari-
ability of a movement task could be manipulated by altering the dynamic properties
of a visual stimulus.
We recently extended this methodology to the gait domain to determine whether
similar shifts in gait dynamics could be elicited in a desired direction [
47
]. Participants
synchronized their steps to a flashing square on a computer screen while walking on
a treadmill. The visual metronome generated intervals with a variety of long-range
temporal correlations (indexed by DFA), yielding either a more “fractal” metronome
(with a more correlated pink noise structure) or a more “random” metronome (with
a more decorrelated white noise structure). The stochastic variability in participants'
stride-to-stride intervals correspondingly shifted in the prescribed direction, from a
normal pink noise pattern toward a more fractal pattern or a more random pattern,
respectively. This result provides a proof-of-concept for the efficacy of using noisy
visual metronomes to manipulate the nonlinear dynamics of the gait cycle. The
exciting possibility is that this effect might be harnessed clinically to enhance adaptive
gait and functional mobility.
It should be noted that visual stimuli can be presented continuously as well as dis-
cretely. A discrete visual stimulus (i.e., a classic visual metronome) only prescribes
the time when an event should occur (e.g., a heel-strike during locomotion). A con-
tinuous visual stimulus, on the other hand, provides information that anticipates and
specifies the timing of the upcoming event (e.g., motion of the foot and/or limb lead-
ing to and including a heel-strike). While a discrete stimulus has been shown to be
useful, a continuous stimulus might enable a participant to more precisely synchro-
nize to irregular events. VR has the potential to present novel classes of stimuli, such
as virtual humans and avatars
8
that provide continuous information. It is therefore
possible to imagine a number of ways that continuous information about the desired
gait pattern could be presented to a patient. For example, footprints could appear
discretely on the ground plane in a virtual environment, providing visual informa-
tion about the timing leading up to heel-strike (see Fig.
15.2
a). A stick figure could
8
Adistinctionmust bemade about the origin of the continuous information. If a computer algorithm
drives the character in virtual reality, then it is presenting continuous information about walking
biomechanics that is non-biological and is termed a virtual human. Alternatively, the character can
be driven by the actual motion of a human in either real-time or via a recording, which is deemed
biological motion and termed an avatar. Current literature has not made a distinction about which
type of motion is optimal for a gait synchronization task.
