Abstract
Purpose: :
For those who are blind, the BrainPort® Vision Device enables perception of visual information using the tongue as a substitute for the eye. Users form a spatial reference with just a few hours of training, mapping cutaneous information on the tongue to their environment. In order to evaluate the potential visual "acuity" of the developing BrainPort Vision system, we designed an experiment to determine spatial discrimination on the tongue using electro-cutaneous stimulation.
Methods: :
Sixteen sighted subjects (10 men; 6 women) participated, ranging in age from 18-39 years old (mean 24.5yrs). Subjects were recruited from the Madison, WI area. All subjects gave informed consent with a study protocol approved by the New England IRB. A linear electro-cutaneous stimulation array was specially fabricated with 10 electrodes (tactors) 169 micrometers (µ) diameter spaced 254µ apart. Half of the trials contained only one stimulating tactor, while the other half contained two firing tactors of a fixed condition distance: 254µ, 580µ, 762µ, 1016µ and 1261µ center-to-center distance. Subjects were instructed to press one button if they felt one stimulus and another button if they felt two stimuli. They were encouraged to use the tip of their tongue and to move and/or explore the stimulation with any part of the tongue in order to respond maximally. There was no response time limit allowing subjects to explore the stimulus with any part of the tongue they felt gave them the best information.
Results: :
Data points were translated into a d-prime score for each spacing condition and subject. Threshold discrimination was a priori defined as a d-prime score greater than 1. As a group, performance exceeded d-prime>1 when tactors were spaced 762µ. A one way ANOVA revealed a significant main effect for tactor spacing (F(4,60)=4.466, p<.005). As the tactor spacing increased, performance improved. Twelve percent of tested subjects scored above threshold individually in the most closely spaced 254µ condition. While the group average threshold is 762µ, there are individuals who have better than average discrimination abilities. This may suggest that an individual’s actual limit may be better than 254µ spacing.
Conclusions: :
These results suggest that without extensive training, average spatial perception on the tongue is 762µ or better. This allows us to optimize the size and spacing of tactors coupled with appropriate optics when designing our prosthetic vision substitution system to report comparative visual acuity measures.
Keywords: plasticity • visual acuity • perception