Alternative communication systems for people with severe motor disabilities: a survey <s> Switch-based control device <s> We suggest a communication method for severely disabled persons, who have lost both mobility and speech, and their family using Morse code derived by Masseter muscle EMG. We developed a portable system that comprises EMG amplifier, A/D conversion, text-to-speech module, remote control module and serial communication to the host system. After training, the patient can make speech by composing Morse code by moving his/her chin. Calibration and remote control mode is supported. It also supports the adaptive encoding method for fatigue. <s> BIB001 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Switch-based control device <s> A synthetic voice aid for speech disabled people is presented in this work. The system is based on the Morse code, given through four keys. A PIC was used to detect and decode Morse code as well as to make the translation to ASCII code. The data processing was performed by an MC68HC11 microcontroller. Voice was generated by a V8600 commercial synthesizer. The aid includes a liquid crystal display for text exhibition, that serves as a feedback reference. The display was mounted on a structure strategically located to avoid interference with the frontal visual field. <s> BIB002 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Switch-based control device <s> Determining conscious processing in unresponsive patients relies on subjective behavioural assessment. Using data from hand electromyography, the authors studied the occurrence of subthreshold muscle activity in response to verbal command, as an objective indicator of awareness in 10 disorders of consciousness patients. One out of eight vegetative state patients and both minimally conscious patients (n = 2) demonstrated an increased electromyography signal specifically linked to command. These findings suggest electromyography could be used to assess awareness objectively in pathologies of consciousness. <s> BIB003
In situations like the locked-in syndrome, the patient will present control of eyes and cognitive tasks. Therefore, an easy way to communicate is by answering to "yes/no" questions. This approach provides an output channel of communication with low transfer information rate, low interactivity and the care provider must have the necessary skills to formulate the right questions. Patients that are still able to carry out residual movements with one of the limbs, or to move their head, may use a pressure device. The same principle can be applied to EMG signals where the pressure action can be replaced by muscle contraction. Electromyography has already been considered as a way of assessment for patients with disorders of consciousness, indicating its use as a channel of communication BIB003 . Using computational solutions, one can generate binary signals, with '1' being associated to muscle activity and '0' otherwise. One approach consists in composing messages with some kind of code -e.g. the Morse code. Even if it is an unnatural mode of communication, the procedure might turn out to be extremely valuable for persons with severe motor impairments. Any biosignal which can be interpreted as a two-state information source is a potential candidate to use such code. From the Morse-based code the user can control devices and communicate in several ways, depending on the strategy adopted. Studies using other sources than the EMG signal have shown that applying the Morse code BIB002  can be a good option for AAC. As using the Morse code is not natural task in terms of language and that keeping a typing rate is difficulty for the persons with disabilities, modified forms of the code may be adopted BIB002 . Park et al BIB001 developed a system where the user moves his chin so the signal acquired from the Massetter muscle is transformed into "dot" or "dashes" symbols depending on the duration of the contraction. The sequence is decoded into characters that in turn feed a voice synthesizer. This study includes a method for fatigue adaptation, an important concern when using EMG. The major caveat was that people are not capable of chew-and-pause fast, so the transfer information rate was low, although not reported in numbers. The binary signal can also be used to operate a scanning device, e.g. a virtual keyboard and some more complex interfaces. The Impulse™ [19] system -one of the few AAC commercial solutions based on the EMG signal -uses this approach in a wireless solution to offer computer access with a specific scanning interface. When comparing the scanning and the code-based approaches, we can observe that both are based in simple signal processing techniques. The difference lies in the cognitive effort required from the user: the scanning approach transfers the complexity of the message generation process to the system interface whereas, with code-based devices, the user has to learn the sequence of symbols necessary to compose each character or command.