Artificial vision and artificial audition

Devices to provide substitute for visual or hearing sensation have been developed in recent years. However, compared to a marked improvement in artificial audition such as cochlear implant, devices for artificial vision such as retinal implant, optic nerve implant and cortical implant have not developed to the level of daily use for the blind. The poor outcome of artificial vision appears mainly due to the limited number of electrodes in the prosthesis compared to a huge number of receptive cells for vision, but is also partly due to the difference between speech and visual images in the process required of their recognition. Auditory language mediated through voice can be recognized by mere pulse signals without formant information to characterize vowel sounds, and formation of cortical networks during the speech acquisition period appears to compensate for limited auditory information through the cochlear implant. However, visual information should include not only letters or characters for communication, but every environmental images for daily life. Hybridized retinal prosthesis to overcome the limited number of electrodes will be developed. In the near future, exchange of information between the ophthalmological and otological fields will become more important to improve these artificial devices for vision and audition.