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Contents Introduction Vision Hearing Mobility & Balance Other Applications

Seeing or balancing with your tongue, cochlear implants, digital and tactile hearing aids, infrared goggles are all classifiable as Alternative Sensory Technology, aka Sensory Substitution Technology—technology designed to furnish the brain with new sensory information through attachments to nerves or sensory organs. This article briefly addresses a few landmarks in alternative sensory research and how such technology is made possible by cross-modal processing in the brain, and why in some cases, the brain by adapting to damaged senses, may make alternative input through other senses necessary to restore function.

Neuroplasticity, as identified by Paul Bach-y-Rita and other leading researchers, shows that the brain can work around damaged parts by developing new channels in closely related areas. The damaged part of the brain itself is rarely restored at all, even if normal function is regained. Neuroplasticity only began to be intensively studied in connection with the effects of sensory damage or deprivation in the 1970s. Then, the major challenge was to provide input that could bypass the damage, and to map the brain areas that were involved in sensory processing. The results of this research would lead to the first generations of cochlear implants.

Testing Bach-y-Rita's Brain Port device

In 1969, Bach-y-Rita succeeded in substituting tactile sensation for vision in the congenitally blind by using a camera on wheels and a chair with 400 solenoids in the back to give tactile information on what the camera saw. His blind subjects learned to recognize objects and even reacted when objects rushed too close. Even as late as 2004, reviewers were writing that this experiment restored sight to the blind and proved the brain was plastic enough to develop an entirely new sensory system (Bach-y-Rita). This is easily disproven. One, this method utilized existing sensory systems–the sense of touch–in individuals already adapted to using touch to glean environmental information. All this experiment proved is that visuospatial information nor-mally known through one sense can be understood through another sense if given consistent stimuli. This groundbreaking work has since been refined and a new human-machine interface was developed around 2000 that allows blind people to see by the tongue. Acuity without training is 20/830, and doubled after 9 hours of training. This is still far from normal vision, but still helpful for navigation. Ten years later, though, it is still in the research stage (Sampaio).

On the other hand, echolocation, as in "echo-mobility," is being widely used by the blind as it requires no machinery, simply training the hearing and voice. Scientist Ken Warwick used ultrasound fed through an electronic implant to see using sound. He was able to discern movement of small objects and distances with it (Warwick). None of those methods replace vision, but they do allow the blind to navigate new terrain, sometimes facilitating the ability to play sports and rollerblade.

Ben Underwood is a blind American teen who uses echolocation to move around avoiding obstacles

A simple, but often overlooked, example of one sense compensating for another would be lip-reading. Because many sounds look alike on the lips, lip-reading alone without sufficient auditory input does not provide enough information to comprehend speech, which is why various lip-reading aids such as cued speech were invented. Most lip readers depend on various strategies to improve their comprehension and bluff their way through a conversation, but no lip reader can ever fully understand a speaker without the use of sufficient hearing. However, provide a simple tool to express auditory input as visual input–such as closed captioning or cued speech–and comprehension jumps significantly without involving hearing at all. Still, they must first know how to read or memorize hand signals to glean language through them. Likewise, blind people can be trained to echo-locate, but do not learn all the nuances instantly.

So, how could blind subjects who were never exposed to any technology like Bach-y-Rita's chairs or tongue interface have learned how to "see" using them quickly? The secret may be in how the brain adapts to blindness by creating a different form of vision using information from all remaining senses.

Blind people routinely solve problems of location and movement through their remaining senses. While this should not be confused with full vision, it does give us increased insight into how cross-modal processing and neuroplasticity may complement each other.

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