Learning not to feel: reshaping the resolution of tactile perception

Abstract

We asked whether biased feedback during training could cause human subjects to lose perceptual acuity in a vibrotactile frequency discrimination task. Prior to training, we determined each subject's vibration frequency discrimination capacity on one fingertip, the Just Noticeable Difference (JND). Subjects then received 850 trials in which they performed a same/different judgment on two vibrations presented to that fingertip. They gained points whenever their judgment matched the computer-generated feedback on that trial. Feedback, however, was biased: the probability per trial of “same” feedback was drawn from a normal distribution with standard deviation twice as wide as the subject's JND. After training, the JND was significantly widened: stimulus pairs previously perceived as different were now perceived as the same. The widening of the JND extended to the untrained hand, indicating that the decrease in resolution originated in non-topographic brain regions. In sum, the acuity of subjects' sensory-perceptual systems shifted in order to match the feedback received during training.

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“…Finally, the assumptions used here, of a 7% JND, were based on existing work. However, studies have also found that providing feedback, training, and frequency changes can have an impact on JND 30 . Additionally, visual feedback has also been shown to impact user JND 50 .…”

“…Hands and fingers are extremely sensitive to the sense of touch, and it has been found that intentional training can improve surgeon skills 24 – 26 . A JND of [5, 10]% change has been observed during [2, 10] N loads between fingers or in elbow extension, but can vary based on finger, training, and frequency 27 – 30 . Work on haptic devices has found higher JNDs, including 23 ± 13% and 34 ± 24% detectable changes for force and torque on the ranges of [0.4,8.8] N and [20,410] N mm, respectively 31 .…”