TIKL: Development of a Wearable Vibrotactile Feedback Suit for Improved Human Motor Learning (Lieberman 2007)

Summary:
The TIKL system is proposed as an additional channel for learning motor skills, providing low-latency feedback through a vibrotactile feedback suit. The Vicon tracking system uses twelve high speed infrared cameras which record positions of markers so that the 3d position of the markers can be reconstructed and joint angles can be calculated. Differences in joint angle between the teacher and learner are communicated to the learner through timed tactile pulses that utilize the sensory saltation effect. Corrective rotation can be communicated by a sequence of pulses around actuators that are attached in a ring around the arm.
An experiment was run to test how users' ability to learn motor tasks was affected by the tactile feedback provided by TIKL. Using deviations in joint angle as the metric for error, forty subjects' reactions during training sequences were measured. Real-time errors were reduced by up to 27% and learning was improved by up to 23%. Subjects reported no significant loss of comfort due to the wearable system.

Discussion:
One downside of the TIKL system is its reliance on the expensive and bulky Vicon system. Currently, only angle errors are used in determining feedback signal strength, which may not be the best measurement of task fulfillment. Other measures of error such as end effector position probably describe error better for some tasks. The problem of correcting end effector position alone can be hard since there would be multiple joint positions that could result in the same end position.
The users participating in the study were told to mimic joint angles as opposed to another metric. The error reporting assumes that people easily grasp the concept of mimicking angles and remembered to follow only that metric throughout the study. I don't think people naturally mimic only joint angles and that some error was probably introduced due to using only joint angle as the error metric. In regard to the results section, I thought polling users seems like a somewhat subjective way to measure qualities of the system. A more quantitative study could have been designed.