NDI Polaris Provides Position Data for Neurological Research Study
This case study details the use of the NDI Polaris system in providing position data on hand motion. The position data was required for research regarding the relationship of neural activity to voluntary reaching movements.
The Challenge
The monkey sits in front of a monitor and is trained to reach for an image that appears on the screen.
The monkey's reaction time is measured; they are trained to reach quickly or slowly,
depending on the colour of the image. Details of the task are shown in Figure 1. The researcher's challenge was to track and collect position data on eye movement and hand motion.
Eye movement was tracked using an infra-red tracker, but tracking hand motion presented additional challenges.
Monkeys take a long time to train and the more comfortable they are, the better they will perform. If wires were attached to the hand, using a magnetic or active system, it would be one more thing the monkey would have to get used to. In addition, it is probable that the monkey would detach or destroy a wired system and metal in the recording room would interfere with the performance of an electro-magnetic system. A fibre optic solution was tried, but, in this application, could not provide the required high degree of endpoint precision.
A solution was needed that was both ergonomically acceptable and provided the required accuracy.
The Solution
The researchers identified the NDI Polaris system, shown in Figure 2, as being able to provide the accuracy, reliability and ergonomics that they required.
The Polaris Position Sensor was mounted such that it was looking down onto the monkey's finger. Adjacent reflective surfaces were covered in matte black material to prevent spurious reflections.
A passive marker was attached to the monkey's finger and the NDI Polaris system was operated in the wireless passive mode, using the 3D reporting of a single passive marker functionality. The wireless mode provided a key advantage over other systems, removing the need to attach wires to the monkey's hand.
The ability of the NDI Polaris system to provide accurate and reliable three
dimensional tracking allowed:
- Near instantaneous feedback during training
- More extensive offline analyses than could be provided by other wireless systems
Acknowledgement
NDI would like to acknowledge the assistance given by Dr. Mark Churchland, Dr. Krishna Shenoy and Gopal Santhanam in the production of this case study, based on their work at Stanford University, CA.
