Turn and Reach Platform (T&R)

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The Turn and Reach Platform is our central apparatus for studying sensorimotor control and adaptation of active torso rotation, arm movement and combinations thereof. The experimental platform includes a motorized rotating platform, a work surface with an array of targets, an OptotrakTM 3-D (Northern Digital, Inc.) motion analysis system (for recording arm and body motion), data acquisition computers and a safety harness and railing.

The base of the device is a 1-m diameter platform on which the subject stands, which rotates around a vertical axis on a .5-m diameter roller bearing. The platform on which the subject stands can be locked in place or driven directly from below by a direct drive motor and servo controller.

A height-adjustable, horizontal work surface is attached to the platform. The work surface is a 1-m radius hemi- disc, with a 30-cm radius central cut-out. The subject can stand in the cut-out with the surface wrapping around them. Visual and auditory targets can be arranged on the surface for turning and reaching tasks.

Subjects wear a safety harness attached to an overhead pivot and are made aware of the safety railing, neither of which interferes with mobility.

Reaching and platform movements are monitored by an OptotrakTM motion analysis system. OptotrakTM tracks active infrared light-emitting diodes with three CCD cameras rigidly mounted on a single sensor. This sensor is pre-calibrated at the factory so no length calibration procedure is required when it is moved to a new experiment. Our system has two sensor units, providing coverage of the full extent of turning and reaching movements without loss of line of sight to the tracked markers and with minimal set up time.

A custom Labview application acquires data from the OptotrakTM in real time (4-ms delay) and stores the data as well as performs movement-contingent dynamic control of peripheral devices, such as driving the platform motor or a visual display. The application includes a flexible interface for designing experimental sequences.