Sensory Substitution - Physiology of Sensory Substitution

Physiology of Sensory Substitution

When a person becomes blind or deaf they generally do not lose the ability to hear or see, they simply lose their ability to transmit the sensory signals from the periphery (retina for visions and cochlea for hearing) to brain. Since the vision processing pathways are still intact, a person who has lost the ability to retrieve data from the retina can still see subjective images by using data gathered from other sensory modalities such as touch or audition.

In a regular visual system, the data collected by the retina is converted into an electrical stimulus in the optic nerve and relayed to the brain, which re-creates the image and perceives it. Because it is the brain that is responsible for the final perception, sensory substitution is possible. During sensory substitution an intact sensory modality relays information to the visual perception areas of the brain so that the person can perceive to see. With sensory substitution, information gained from one sensory modality can reach brain structures physiologically related to other sensory modalities. Touch-to-visual sensory substitution transfers information from touch receptors to the visual cortex for interpretation and perception. For example, through fMRI, we can determine which parts of the brain are activated during sensory perception. In blind persons, we can see that while they are only receiving tactile information, their visual cortex is also activated as they perceive to see objects. We can also have touch to touch sensory substitution where information from touch receptors of one region can be used to perceive touch in another region. For example, in one experiment by Bach-y-Rita, he was able to restore the touch perception in a patient who lost peripheral sensation from leprosy.