Most of us think we can see only with our eyes. But, the development of some recent prosthetic devices may prove otherwise. Take, for example, the vOICe system developed by Peter Meijer. This device uses a video camera mounted on a pair of sunglasses to film the landscape. The pixelated picture is then converted into sounds that are delivered to the wearer via headphones. Brighter objects sound louder, and objects higher up in the visual field are heard as pitches of higher frequency. With practice, individuals, even those who have been blind since birth, can use vOICe to locate objects. They discover how the soundscape of the object varies as they move; they experience a sense of perspective and a feeling of space and openness. In other words, their sensations seem very vision-like.

"Seeing" with vOICe is very reminiscent of the sensory substitution devices that the late Paul Bach-y-Rita developed in the 1960's. They are based on a fascinating premise. We think of the brain as modular, that is, there are specific areas of the brain devoted to sight, others devoted to hearing, and so on. But maybe our brain is simply looking for information and will use the best information out there to create a perception. Vision provides excellent spatial resolution, and the "visual" parts of the brain may be devoted to this skill. But, if vision is lost, can another sense provide this information and feed it to the visual parts of the brain?

Scientists used the vOICe system to ask this question. There is a brain region called the lateral-occipital-tactile-visual area (LOtv) that is activated when we analyze the shape of objects either by sight or touch. This area is not normally activated by sound presumably because sound is not normally useful in analyzing the 3D shape of objects. In this study, both sighted and blind individuals were trained to use vOICe alone to identify the shape of objects. Then their brain were imaged as they performed this task. Under these conditions, sound from the vOICe system could activate the LOtv. Perhaps, connections from the auditory areas of the brain to the LOtv have always been present but are very weak or ineffective under most conditions. When the individuals in this study learned to use vOICe, when auditory input became useful in accomplishing the task, these connections were retuned.

Common knowledge tells us that when one sensory system is damaged or lost, other sensory modalities may step up to take its place. Thus, many blind individuals use their hearing in ways that sighted people do not. Devices such as vOICe expand upon these capacities and reveal an untapped potential of the human brain.

About the Author

Susan Barry by Rosalie Winard

Susan R. Barry, Ph.D., is a professor of neurobiology in the Department of Biological Sciences at Mount Holyoke College and the author of Fixing My Gaze (June, 2009).

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