Roll tilt self-motion direction discrimination: First evidence for perceptual learning

Perceptual learning, the ability to improve the sensitivity of sensory perception through training, has been shown to exist in all sensory modalities but the vestibular system. Previous studies have failed to demonstrate an improvement of passive self-motion thresholds in the dark for yaw rotation and y-translation, but subjects improved for the same motions in the light (Hartmann et al., 2013). The goal of the present study was to investigate whether vestibular perceptual learning in the dark would occur when there is a simultaneous otolith and semicircular canal input, as is the case with roll tilt motion stimuli. Blindfolded subjects (N = 10) trained a direction discrimination task with 0.2 Hz roll tilt motion stimuli for 6 days, for a total of 1800 trials. Before and after training, motion thresholds were measured for the trained motion (0.2 Hz roll tilt) and for three transfer conditions (1 Hz roll tilt, 0.2 Hz pitch, 0.2 Hz y-translation). Performance before and after training was analyzed using a Bayesian hierarchical logistic regression. We found that sensitivity was increased after training in the 0.2 Hz roll tilt condition (trained motion) and in the 1 Hz roll tilt condition (Transfer condition 1), but not in the other motion conditions. This is the first demonstration of perceptual learning of passive self-motion direction discrimination in the dark using low frequency roll tilt motion stimuli. Surprisingly, we found that a control group with no training within this 6 day period also improved in the 1 Hz roll tilt condition but not in any other motion condition. It is possible that high frequency roll tilt motion (1 Hz) leads to faster learning and does not require extensive training, which requires further study to evaluate. The results have potential therapeutic consequence as higher 0.2 Hz roll tilt thresholds have been associated with worse performance in balance tests that may increase morbidity (Karmali et al., 2017, Bermúdez Rey et al., 2016)