Abstract
Purpose: :
Sensory substitution refers to use of an alternate afferent sensory channel to communicate with the central nervous system when the original end-organ is sufficiently damaged to preclude its use or repair. The BrainPort (Wicab, Inc.) uses a spectacle frame mounted video camera coupled to an intra-oral tongue display as a paired substitute for the eye. The electro-tactile stimulation produced by an electrode array placed on the tongue allows users to interpret objects in their ambient surroundings. We assessed whether the use of the device influenced a subjects’ ability to navigate a standardized obstacle course.
Methods: :
Twenty human subjects (n= 16 blind and n=4 control, sighted and blindfolded) ages 22 to 75 years were provided approximately 20 hours of training each on the BrainPort. The camera on the current prototype has a field of view of 73 degrees and uses a tongue stimulation array one-inch square containing 400 electrodes. Blind subjects had light perception or worse vision. We used a modified Tangent Screen with 5cm objects, 2x2m screen at 1 m, and a validated 40-foot obstacle course to administer baseline and post-training tests. The primary outcome measure for the obstacle course was the percentage of the preferred walking speed (PPWS) achieved (ratio of time to walk 40 feet unobstructed divided by the time to navigate the course with the BrainPort).
Results: :
We found that our subjects manifested an average of 58.6 degrees of "visual field," with 60.1 degrees in the horizontal meridian and 57 degrees in the vertical meridian with the device. There was no significant difference between blind and control subjects or with increased use over 6 weeks. Compared to baseline, all subjects paradoxically slowed down after training with the BrainPort (PPWS 3.92 vs 1.90% P=0.001) because, per video review, they were now searching for objects in their paths. With additional experience through the course, the subjects’ speed increased, approaching their time through the unobstructed course (PPWS 1.94 vs 1.90%)
Conclusions: :
Electrical stimulation of the tongue via signals sent from a spectacle-mounted video camera results in a sensation akin to vision, and enables a perception of one’s surroundings that can be useful. The extent of visual field is sufficiently large to enable navigation with obstacle avoidance. As transducers become sophisticated with denser electrode arrays, the utility of this device will likely be enhanced. Furthermore, such a device may be beneficial in screening subjects for retinal chip implants.
Keywords: perception • space and scene perception • retina