Communication assistive method using sympathetic skin response

Persons with seriously disabled speech organs and motor function have difficulty in speaking and communicating through hand gestures. Communication aids have been developed based on AAC (Augmentative and Alternative Communication) concept, and are being used to assist in the transmission of the user’s intention. However, the disabled person must have residual motor function to operate most of these aids. If the disabled person has few motor functions, such communication aids can hardly be used; also, if the disabled person has a progressive disease, it is necessary to constantly adjust the communication aid to the level of residual motor function. To overcome this problem, a device that does not depend on residual motor function must be developed. Recently, a study on BCI (Brain Computer Interface) was carried out, which used electroencephalograms as a communication aid that does not depend on residual motor function (Friedrich et al., 2009). The electroencephalogram switch MCTOS (Technos Japan Co., Ltd.) has already been put to practical use. However, MCTOS must recall exciting and frustrating when the user switches it on. Therefore, MCTOS is hard to operate and to have the feeling that it was switched on purposefully (Nakabayashi et al., 2003). A possible solution to this problem is to use SSR (Sympathetic Skin Response), which can be measured non-invasively and is independent of residual motor function. SSR, which is a biomedical signal that reflects the activity of the sympathetic nervous system, is affected by both cognitive thinking and decision-making (Ito et al., 1996). We hypothesized that the SSR response could be used as a switch in a communication aid which can convey the user’s wish to see a character or a picture displayed on a personal computer. In addition, the advantage of SSR is that measurements can be made easily, unlike with the electroencephalogram, and it is not necessary to think about something else (mental arithmetic, exciting and frustrating) irrelevant to the operation of switching on the communication aid; thus, intuitive operation is possible (Fig.1). It has been reported that disabled persons with SCI (Spinal Cord Injury) and ALS (Amyotrophic Lateral Sclerosis) show amplitude reduction and extension of the SSR latency period. In addition, the absence of SSR response has been confirmed in several patients. However, there are few reports on completely absent SSR (Masur et al., 1995, Oey et al., 2002, Nicotra et al., 2002). On the other 8