Primary Investigators
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Gary Paige, M.D., Ph.D.
Department Chairman, |
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William E. O'Neill, Ph.D.
Associate Professor, |
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Scott H. Seidman, Ph.D.
Assistant Professor, |
Laboratory Overview
The Big Picture
An essential goal of the nervous system is to maintain our orientation relative to the outside world. This is crucial even for simple activities such as walking and reaching for objects. To perform these tasks, we must accurately identify our position with respect to our surroundings, distinguish our own movements from those of others, and control our movements through a complex world. Spatial orientation is maintained by the nervous system and its sensory inputs: vision and audition provide information about external objects, proprioception conveys the configuration of the body and its parts, and vestibular inputs register head orientation and motion. These sensory inputs are integrated and processed to generate specific behaviors that support natural activities. Examples include coordinated eye and/or head movements that help us fixate or track targets of interest, others that control posture and gait, and those that control hand movements in order to acquire and manipulate objects. How these crucial and ubiquitous functions work, how they maintain proper coordination and concordance, and how they break down with disease or aging constitute important and persistent concerns. A further interest is how specific sensorimotor functions can be manipulated adaptively in ways that might lead to the development of effective interventions. Such interventions are essential to the process of improving rehabilitation following disease or surgery, and might be exploited to ameliorate the deteriorations of aging.
Technical Capabilities of the Laboritories
Sled-Rotator Laboratories
The central feature of our multisensory motion control laboratory is its ability to move subjects in angular, linear, and combined fashion along with visual and/or auditory targets. The centerpiece is a unique and flexible human motion stimulator capable of producing angular and linear acceleration profiles in the earth-horizontal plane, either in isolation or in combination. It consists of three independently controlled axes configured as a linear sled sandwiched between two rotational axes (see photo).
The topmost "chair axis" holds a seat with a head-holder/bite bar to fix the head securely to the superstructure. This axis operates under position or velocity control at up to 360°/s (300°/s 2 peak acceleration). A projector/galvo system above the head controls the appearance and motion of a laser spot in front of the subject, serving as a fixation or tracking target. The chair superstructure is mounted on a carriage riding on linear bearings and driven by a lead-screw system, thereby maximizing frequency response and safety at the expense of some noise and vibration relative to other designs. This "linear axis" permits up to 1.1 m of translation with peak accelerations of up to 0.5 G and at frequencies up to 5 Hz, with the subject oriented over a full 360° horizontal range. The entire sled and chair are in turn centered on a "base axis" that can be rotated at up to 200°/s (700°/s 2 peak acceleration) at frequencies up to 5 Hz.
Something is displaced eccentrically on the sled, thereby producing combinations of rotational and translational accelerations, with the head in different orientations. More unusual paradigms are also possible. One example is counter-rotation of the base and chair with the chair off-center. This generates a rotating linear force that resembles "off-vertical axis rotation," but without actually rotating the head. Another option, and an extremely valuable one, is the ability to translate subjects dynamically while spinning the sled at constant velocity. After an initial acceleration of the base axis to constant angular velocity, the canal signal dies away leaving the subject unaware of rotation. Motion of the sled then provides a flexible linear world where sled translation adds with centrifugal force to generate large linear accelerations (e.g. 0.4G) at low frequencies (e.g. 0.01 Hz, or even DC for fixed eccentricity). This, combined with simple linear oscillations on the stationary sled (for high frequencies) allows us to probe broadband interactions between tilt and translation perceptions and behaviors, all driven by otolith inputs in isolation.
A unique version of the sled-rotator specifically designed for use in small primates shares essential design features with its human counterpart. However, the topmost chair axis is mounted earth-horizontally. The chair can be fixed in any horizontal position over a full 360 deg range, and then rotated around the earth horizontal axis, producing head pitch, roll, or anything in between. This chair axis is mounted to a sled (linear axis), which is in turn centered over the base axis. The major advantage of this device is its ability to generate angular, linear, or combined motion with the head in any orientation in 3-D space. A new addition is a vertically oriented sled that allows us to generate linear motion parallel to gravity, and therefore in the presence of a 1g force along any head orientation. Responses to motion stimuli are recorded in the form of eye movements and, in humans, perceptions of motion and orientation. Human eye movements are typically recorded using the ELMAR binocular eye tracker (shown in photo), a state-of-the-art digital camera-based system. Coil and IR-based systems are also available for special circumstances. Perceptions of motion and orientation are registered using a variety of joystick devices.
Human Spatial Localization Laboratory
A new laboratory has been developed that allows us to generate smooth motion of auditory and/or visual targets or discreet locations across a large region of external space (140° horizontally and 60° vertically). This is accomplished by a novel dual-axis robotic arm carrying a speaker-LED target assembly (see photo). The system greatly facilitates our goal of quantifying multi-sensory processing of spatial localization and motion. To measure target localization, we developed a pointing task that utilizes a laser LED on a dual-axis dial to manually aim its beam at a screen immediately in front of the target region (not shown in photo), serving at once to hide the target source and to project the laser "pointer." Alternatively, an "ocular pointing" method combines eye and head tracking to perform a similar role, but now with vestibular and neck sensory modalities included.
In the sled-rotator lab, other methods are used to focus on multi-sensory motion processing. We have designed a speaker-LED target assembly that mounts eccentrically on the sled/rotator at eye level to study auditory-visual-vestibular interactions. This provides a novel experimental opportunity to study ocular responses to smooth motion of auditory (in darkness) and/or visual targets along with vestibular signals.