Author(s): A B Anani, K Ikeda, L M Krner
Afferent electrical nerve stimulation is an approach showing many promises with regard to sensory feedback for powered prostheses. It is well tolerated, can transmit fairly high amounts of information, and has several characteristics making it superior to electrocutaneous and vibrotactile devices when applied to prostheses. The feedback information is transferred in modulated form either by means of the current pulse amplitude (a.m.) or by the current pulse frequency (f.m.) A.M. stimulation should be applied in such a way that it gives rise to characteristic changes in the distribution of paresthesias with changing current. Used in this way it is not dependent upon minor changes in electrode position, it is easy to learn and gives high rates of information, even in untrained subjects. The number of channels that can be used in each nerve is, however, limited because of the large amount of axons necessary to achieve the spatial spread. F.M. stimulation is more difficult to learn than a.m. but gives the same rate of information transfer when used in trained individuals. Like a.m. it is not dependent upon minor changes in electrode position, but a smaller number of axons is needed to achieve discrimination. Thus several channels can be used in each nerve. Both with a.m. and f.m. stimulation a trained subject can discriminate five or six discrete levels with a rate of correct recognition of more than 75%, the amount of transmitted information being about 1·8 bits per symbol.