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<unk>  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<unk>  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,<unk>  is possible. During<unk>  an intact<unk>  modality relays information to the visual perception areas of the brain so that the person can perceive sight. With<unk> , information gained from one<unk>  modality can reach brain structures physiologically related to other<unk>  modalities. Touch-to-visual<unk>  transfers information from touch receptors to the visual cortex for interpretation and perception. For example, through fMRI, one can determine which parts of the brain are activated during<unk>  perception. In blind persons, it is seen that while they are only receiving tactile information, their visual cortex is also activated as they perceive sight objects. Touch-to-touch<unk>  is also possible, wherein information from touch receptors of one region of the body can be used to perceive touch in another region. For example, in one experiment by Bach-y-Rita, touch perception was able to be restored in a patient who lost peripheral sensation due to leprosy. Technological support In order to achieve<unk>  and stimulate the brain without intact<unk>  organs to relay the information, machines can be used to do the signal transduction, rather than the<unk>  organs. This brain–machine interface collects external signals and transforms them into electrical signals for the brain to interpret. Generally, a camera or a microphone is used to collect visual or auditory stimuli that are used to replace lost sight and hearing, respectively. The visual or auditory data collected from the<unk>  is transformed into tactile stimuli that are then relayed to the brain for visual and auditory perception. Crucially, this transformation sustains the<unk> motor contingency inherent to the respective<unk>  modality. This and all types of<unk>  are only possible due to Neuroplasticity. Brain plasticity Brain plasticity refers to the brain's ability to adapt to a changing environment, for instance to the absence or deterioration of a sense. It is conceivable that cortical remapping or reorganization in response to the loss of one sense may be an evolutionary mechanism that allows people to adapt and compensate by using other senses better. Brain imaging studies have shown that upon visual impairments and blindness (especially in the first 12–16 years of life) the visual cortices undergo a huge functional reorganization such that they are activated by other<unk>  modalities. Such cross-modal plasticity was also found through functional imaging of congenitally blind patients which showed a cross-modal recruitment of the occipital cortex during perceptual tasks such as Braille reading, tactile perception, tactual object recognition, sound localization, and sound discrimination. This may suggest that blind people can use their occipital lobe, generally used for vision, to perceive objects through the use of other<unk>  modalities. This cross modal plasticity may explain the often described tendency of blind people to show enhanced ability in the other senses. Perception versus sensing While considering the physiological aspects of<unk> , it is essential to distinguish between sensing and perceiving. The general question posed by this differentiation is: Are blind people seeing or perceiving to see by putting together different<unk>  data? While sensation comes in one modality – visual, auditory, tactile etc. – perception due to<unk>  is not one modality but a result of cross-modal interactions. It is therefore concluded that while<unk>  for vision induces visual-like perception in sighted individuals, it induces auditory or tactile perception in blind individuals. In short, blind people perceive to see through touch and audition with<unk> . Through experiments with a Tactile-visual<unk>  (TVSS) device developed by Bach-y-Rita subjects described the perceptual experience of the TVSS as particularly visual, such that objects were perceived as if located in the external space and not on the back or skin. Further studies using the TVSS showed that such perceptual changes were only possible when the participants could actively explore their environment with the TVSS. These results have been underpinned by many other studies testing different<unk>  systems with blind subjects such as vision-to-tactile<unk> , vision-to-auditory<unk>  and vision-to-vestibular<unk>  Such results are also reported in sighted subjects, when blindfolded and deliver further support for the<unk> motor contingency theory.
Sensory substitution
Haptic communication
Decompensation
Body substance isolation
Pruning
Central tolerance
Derealization
Postural restoration