Specificity and flexibility in sensory substitution: learning to grasp with vibration on one or two fingers

Sensory substitution gloves (SSGs) are gloves that provide stimulation to the hand based on information such as the distance to objects in the environment. In recent years, it has been shown that SSGs enable users to interact with objects in the environment, including the grasping of objects. Important for the current study, different configurations of SSGs have been tested, and performance with SSGs has been shown to improve with practice. This led to the main question of our study: Does practice with one configuration of an SSG transfer to another configuration? The SSG that we used had actuators on the index finger and thumb that could vibrate when a finger pointed in the direction of a target. The vibration was more intense if the finger was closer to the object. Two modes of functioning were used: with vibration only on the index finger or with vibration on both fingers. In the reported experiment, 58 participants were divided into two groups that practiced a reaching and grasping task using the SSG either in the one-finger or two-finger mode. Before and after practice, both groups were tested in both conditions. Although average performance was better with two fingers than with one, substantial improvements were observed in both conditions, indicating a large amount of bidirectional transfer. These results are consistent with the interpretation that training with one or two fingers are different ways to improve the same functional system.