Journal
Articles
Tremblay S, Houle G, Ostry DJ (2008) Specificity of speech motor learning. J Neurosci 28:2426-2434.
Abstract PDF
The idea that the brain controls movement using a neural
representation of limb dynamics has been a dominant hypothesis in
motor control research for well over a decade. Speech
movements offer an unusual opportunity to test this proposal by
means of an examination of transfer of learning between utterances
that are to varying degrees matched on kinematics. If speech
learning results in a generalizable
dynamics representation, then, at the least, learning should
transfer when similar movements are embedded in phonetically
distinct utterances. We tested this idea using three different pairs
of training and transfer utterances that substantially overlap kinematically. We find that, with these stimuli,
speech learning is highly contextually sensitive and fails to
transfer even to utterances that involve very similar movements.
Speech learning appears to be extremely local, and the specificity
of learning is incompatible with the idea that speech control
involves a generalized dynamics representation.
Lametti DR, Houle G, Ostry DJ (2007) Control of movement variability and the regulation of limb impedance J Neurophysiol 98:3516-3524.
Abstract
PDF
Humans routinely make movements to targets that have different accuracy
requirements in different directions. Examples extend from everyday
occurrences such as grasping the handle of a coffee cup to the more
refined instance of a surgeon positioning a scalpel. The attainment
of accuracy in situations such as these might be related to the
nervous system's capacity to regulate the limb's resistance to
displacement, or impedance. To test this idea, subjects made
movements from random starting locations to targets that had
shape-dependent accuracy requirements. We used a robotic device to
assess both limb impedance and patterns of movement variability just
as the subject reached the target. We show that impedance increases
in directions where required accuracy is high. Independent of target
shape, patterns of limb stiffness are seen
to predict spatial patterns of movement variability. The nervous
system is thus seen to modulate limb impedance in entirely
predictable environments to aid in the attainment of reaching
accuracy
Shiller DM, Houle G, Ostry DJ (2005) Voluntary control of human
jaw stiffness J Neurophysiol 94:2207-2217
Abstract
PDF
Recent studies of human arm movement have suggested that the control
of stiffness may be important both for maintaining stability and for achieving
differences in movement accuracy. In the present study, we have examined
the voluntary control of postural stiffness in 3D in the human jaw. The
goal is to address the possible role of stiffness control in both stabilizing
the jaw and in achieving the differential precision requirements of speech
sounds. We previously showed that patterns of kinematic variability in
speech are systematically related to the stiffness of the jaw. If the
nervous system uses stiffness control as a means to regulate kinematic
variation in speech, it should also be possible to show that subjects
can voluntarily modify jaw stiffness. Using a robotic device, a series
of force pulses was applied to the jaw to elicit changes in stiffness
to resist displacement. Three orthogonal directions and three magnitudes
of forces were tested. In all conditions, subjects increased the magnitude
of jaw stiffness to resist the effects of the applied forces. Apart from
the horizontal direction, greater increases in stiffness were observed
when larger forces were applied. Moreover, subjects differentially increased
jaw stiffness along a vertical axis to counteract disturbances in this
direction. The observed changes in the magnitude of stiffness in different
directions suggest an ability to control the pattern of stiffness of the
jaw. The results are interpreted as evidence that jaw stiffness can be
adjusted voluntarily, and thus may play a role in stabilizing the jaw
and in controlling movement variation in the orofacial system.
Conference
presentations / published abstracts
Lametti DR, Houle G, Ostry DJ. The central nervous system regulates limb impedance based on target shape. Presented at the 36th Annual Meeting of the Society for Neuroscience, Atlanta, GA, 2006.
Tiede MK, Guenther FH, Perkell JS, Zandipour M, Houle G, Ostry DJ (2004) Perturbation and
compensation in speech acoustics using a jaw-coupled robot. J Acoust Soc Am 116:2631.