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Dynamics
and Adaptation in the
Vestibular and Oculomotor Systems |
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My research is along two
main lines:
vestibular adaptation, including adaptation to space flight, and
mathematical analysis and modeling of predictive and reflexive eye
movements. All of these projects have as their general aim the
understanding
of sensory processing for motor control, with an emphasis on adaptive
capabilities
and mathematical modeling. The laboratory (which is part of Dr.
David
Zee's laboratory) is also associated with the vestibular clinic of the
Johns Hopkins Hospital.
Other topics in which I am interested are signal processing, control of saccade trajectories, and human spatial orientation. Our research is supported by grants from the NIH, and in the past from NSF and NASA through the National Space Biomedical Research Institute (NSBRI). |
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1. We are studying the properties and adaptive abilities of the human vestibulo-ocular reflexes, both angular (AVOR) and translational (TVOR). The AVOR (TVOR) is a vestibular reflex that drives the eyes so as to compensate for head rotation (translation), and thereby maintain stable vision. We stimulate the AVOR with a rotating chair, and the LVOR using a human linear acceleration sled (see photo), and drive adaptation by presenting moving visual scenes that conflict with the motion transduced by the vestibular system. We test the limits of the adaptive capability and model it mathematically, and explore such issues as the most effective error signals and scheduling of adaptation. |
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2. In addition to the large whole-body sled pictured above, we have developed a smaller "head-sled" with which we can translate the head with brief high-acceleration (0.5 g) steps. These motions are more similar to the natural head movements encountered in daily life than those we can apply with the larger sled. Stefano Ramat and David Zee have characterized many properties of the normal response to this stimulus. We are now using this device to adapt the TVOR and test for transfer of adaptation to the AVOR, to smooth pursuit, and to motion in the fore-aft direction. |
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3. In a closely-related project, we study the ability of human subjects to acquire two different adaptive responses at the same time, and to switch between them based on a context cue. These experiments involve adaptation of saccade amplitude (rapid eye movements made to visual targets) or adaptation of the TVOR. Some property of the response is adaptively altered in one way (e.g., gain increase) with, for example, the head in one orientation, and altered in another way (e.g., decrease) with the head in a different orientation. After adaptation, the particular response that is invoked becomes dependent on the instantaneous head orientation. We are exploring the rate of acquisition and the limits of this adaptive capability, and recently extended the work to the use of gravity as a context cue, with implications for space flight. (Click the photo on the left for details on these experiments, conducted during "weightless" aircraft flight. |
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4. Using
techniques from
nonlinear dynamics ("chaos theory") and stochastic processes (fractal
Brownian motion), we study the ability of humans to generate predictive
eye movements - that is, eye movements that anticipate a visual
stimulus in terms of timing and location. |
| 5. We have been studying the relationship between adaptability and variability in human eye movements, with the aim of predicting adaptive capabilities in different sensorimotor tasks. A related aim is to find strategies for enhancing the adaptation process. This work has implications for physical rehabilitation, in which some knowledge of the ability of a patient to adapt to a specific problem might be used to tailor rehabilitation exercises to favor those areas that are more susceptible to adaptive alteration. | |
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6. We have begun
the development of a new method for measuring eye movements, based
on the widely-used scleral search coil technique, in which an annular
contact lens with a small coil of wire is placed on the eye, and its
orientation
determined from the magnitude of the current induced in the coil by
external
magnetic fields. (With Dale Roberts)
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