Improved tactile acuity following perceptual learning generalises to untrained fingers

Abstract

The body is represented in a somatotopic framework such that adjacent body parts are represented next to each other in the brain. We utilised the organisation of the somatosensory cortex to study the generalisation pattern of tactile perceptual learning. Perceptual learning refers to the process of long-lasting improvement in the performance of a perceptual task following persistent sensory exposure. In order to test if perceptual learning generalises to neighbouring brain/body areas, 12 participants were trained on a tactile discrimination task on one fingertip (using tactile oriented gratings) over the course of four days. Thresholds for tactile acuity were estimated prior to, and following, the training for the ‘trained’ finger and three additional fingers: ‘adjacent’, ‘homologous’ (the same finger as trained but on the opposite hand) and ‘other’ (which was neither adjacent nor homologous to the trained finger). Identical threshold estimating with no training was also carried out for a control group. Following training, tactile thresholds were improved (as compared to the control group). Importantly, improved performance was not exclusive for the trained finger; it generalised to the adjacent and homologous fingers, but not the other finger. We found that perceptual learning indeed generalises in a way that can be predicted by the topography of the somatosensory cortex, suggesting that sensory experience is not necessary for perceptual learning. These findings may be translated to rehabilitation procedures that train the partially-deprived cortex using similar principles of perceptual learning generalisation, such as following amputation or blindness in adults.