Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> Humans can learn to control the amplitude of electroencephalographic (EEG) activity in specific frequency bands over sensorimotor cortex and use it to move a cursor to a target on a computer screen. EEG-based communication could provide a new augmentative communication channel for individuals with motor disabilities. In the present system, each dimension of cursor movement is controlled by a linear equation. While the intercept in the equation is continually updated, it does not perfectly eliminate the impact of spontaneous variations in EEG amplitude. This imperfection reduces the accuracy of cursor movement. The authors evaluated a response verification (RV) procedure in which each outcome is determined by two opposite trials (e.g., one top-target trial and one bottom-target trial). Success, or failure, on both is required for a definitive outcome. The RV procedure reduces errors due to imperfection in intercept selection. Accuracy for opposite-trial pairs exceeds that predicted from the accuracies of individual trials, and greatly exceeds that for same-trial pairs. The RV procedure should be particularly valuable when the first trial has >2 possible targets, because the second trial need only confirm or deny the outcome of the first, and it should be applicable to nonlinear as well as to linear algorithms. <s> BIB001 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> This study describes the motivation and the design considerations of an economical head-operated computer mouse. In addition, it focuses on the invention of a head-operated computer mouse that employs two tilt sensors placed in the headset to determine head position and to function as simple head-operated computer mouse. One tilt sensor detects the lateral head-motion to drive the left/right displacement of the mouse. The other one detects the head's vertical motion to move up and down with respect to the displacement of the mouse. A touch switch device was designed to contact gently with operator's cheek. Operator may puff his cheek to trigger the device to perform single click, double clicks, and drag commands. This system was invented to assist people with disabilities to live an independent professional life. <s> BIB002 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> The information transfer rate, given in bits per trial, is used as an evaluation measurement in a brain-computer interface (BCI). Three subjects performed four motor-imagery (left hand, right hand, foot, and tongue) and one mental-calculation task. Classification of the EEG patterns is based on band power estimates and hidden Markov models. We propose a method that combines the EEG patterns based on separability into subsets of two, three, four, and five mental tasks. The information transfer rates of the BCI systems comprised of these subsets are reported. The achieved information transfer rates vary from 0.42 to 0.81 bits per trial and reveal that the upper limit of different mental tasks for a BCI system is three. In each subject, different combinations of three tasks resulted in the best performance. <s> BIB003 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> The "Camera Mouse" system has been developed to provide computer access for people with severe disabilities. The system tracks the computer user's movements with a video camera and translates them into the movements of the mouse pointer on the screen. Body features such as the tip of the user's nose or finger can be tracked. The visual tracking algorithm is based on cropping an online template of the tracked feature from the current image frame and testing where this template correlates in the subsequent frame. The location of the highest correlation is interpreted as the new location of the feature in the subsequent frame. Various body features are examined for tracking robustness and user convenience. A group of 20 people without disabilities tested the Camera Mouse and quickly learned how to use it to spell out messages or play games. Twelve people with severe cerebral palsy or traumatic brain injury have tried the system, nine of whom have shown success. They interacted with their environment by spelling out messages and exploring the Internet. <s> BIB004 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> Abstract Interaction with machines is mediated by human–machine interfaces (HMIs). Brain–machine interfaces (BMIs) are a particular class of HMIs and have so far been studied as a communication means for people who have little or no voluntary control of muscle activity. In this context, low-performing interfaces can be considered as prosthetic applications. On the other hand, for able-bodied users, a BMI would only be practical if conceived as an augmenting interface. In this paper, a method is introduced for pointing out effective combinations of interfaces and devices for creating real-world applications. First, devices for domotics, rehabilitation and assistive robotics, and their requirements, in terms of throughput and latency, are described. Second, HMIs are classified and their performance described, still in terms of throughput and latency. Then device requirements are matched with performance of available interfaces. Simple rehabilitation and domotics devices can be easily controlled by means of BMI technology. Prosthetic hands and wheelchairs are suitable applications but do not attain optimal interactivity. Regarding humanoid robotics, the head and the trunk can be controlled by means of BMIs, while other parts require too much throughput. Robotic arms, which have been controlled by means of cortical invasive interfaces in animal studies, could be the next frontier for non-invasive BMIs. Combining smart controllers with BMIs could improve interactivity and boost BMI applications. <s> BIB005 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> We have developed a noninvasive, unobtrusive magnetic wireless tongue-computer interface, called "Tongue Drive," to provide people with severe disabilities with flexible and effective computer access and environment control. A small permanent magnet secured on the tongue by implantation, piercing, or tissue adhesives, is utilized as a tracer to track the tongue movements. The magnetic field variations inside and around the mouth due to the tongue movements are detected by a pair of three-axial linear magneto-inductive sensor modules mounted bilaterally on a headset near the user's cheeks. After being wirelessly transmitted to a portable computer, the sensor output signals are processed by a differential field cancellation algorithm to eliminate the external magnetic field interference, and translated into user control commands, which could then be used to access a desktop computer, maneuver a powered wheelchair, or control other devices in the user's environment. The system has been successfully tested on six able-bodied subjects for computer access by defining six individual commands to resemble mouse functions. Results show that the Tongue Drive system response time for 87% correctly completed commands is 0.8 s, which yields to an information transfer rate of approximately 130 b/min. <s> BIB006 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> This study undertakes a simulation and validation experiment to provide guidelines regarding pointing device usage for quadriplegic individuals assisted by a newly developed integrated pointing device apparatus (IPDA). The simulation experiment involving 30 normal subjects whose upper limb movement was restricted by splints. Another 15 subjects with high level cervical spinal cord injury (SCI) were recruited for the validation study. All normal subjects employed six control modes for target-acquisition and drag-and-drop tasks using an IPDA to integrate common pointing devices. A previously designed software was used to evaluate the operational efficiency (OE), expressed as "able performance" (%AP), of the subjects. The experimental results indicated that the OE of normal subjects for controlling the pointing devices were dominated first by using the unilateral hand (69-100 %AP), then by using the wrist/hand (65-73 %AP), and finally by using either bilateral body parts or the combination of limb and chin (45-53 %AP). The OE for operating an orientation-rotated mouse using the dominant wrist/hand via IPDA in both tasks was equivalent to that for operating a trackball using the dominant hand. The experimental results obtained by subjects with SCI also demonstrated similar findings, although the OEs in each control mode were lower than in normal subjects. Results of this study provide valuable guidelines for selecting and integrating common pointing devices using IPDA for quadriplegic individuals. The priority for selecting which body part should control the pointing devices was as follows: unilateral hands, unilateral wrist/hands, and either bilateral body parts or a limb and chin/head/neck in combination. <s> BIB007 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Measurements of performance without interaction model <s> Abstract For many years people have speculated that electroencephalographic activity or other electrophysiological measures of brain function might provide a new non-muscular channel for sending messages and commands to the external world – a brain–computer interface (BCI). Over the past 15 years, productive BCI research programs have arisen. Encouraged by new understanding of brain function, by the advent of powerful low-cost computer equipment, and by growing recognition of the needs and potentials of people with disabilities, these programs concentrate on developing new augmentative communication and control technology for those with severe neuromuscular disorders, such as amyotrophic lateral sclerosis, brainstem stroke, and spinal cord injury. The immediate goal is to provide these users, who may be completely paralyzed, or ‘locked in’, with basic communication capabilities so that they can express their wishes to caregivers or even operate word processing programs or neuroprostheses. Present-day BCIs determine the intent of the user from a variety of different electrophysiological signals. These signals include slow cortical potentials, P300 potentials, and mu or beta rhythms recorded from the scalp, and cortical neuronal activity recorded by implanted electrodes. They are translated in real-time into commands that operate a computer display or other device. Successful operation requires that the user encode commands in these signals and that the BCI derive the commands from the signals. Thus, the user and the BCI system need to adapt to each other both initially and continually so as to ensure stable performance. Current BCIs have maximum information transfer rates up to 10–25 bits/min. This limited capacity can be valuable for people whose severe disabilities prevent them from using conventional augmentative communication methods. At the same time, many possible applications of BCI technology, such as neuroprosthesis control, may require higher information transfer rates. Future progress will depend on: recognition that BCI research and development is an interdisciplinary problem, involving neurobiology, psychology, engineering, mathematics, and computer science; identification of those signals, whether evoked potentials, spontaneous rhythms, or neuronal firing rates, that users are best able to control independent of activity in conventional motor output pathways; development of training methods for helping users to gain and maintain that control; delineation of the best algorithms for translating these signals into device commands; attention to the identification and elimination of artifacts such as electromyographic and electro-oculographic activity; adoption of precise and objective procedures for evaluating BCI performance; recognition of the need for long-term as well as short-term assessment of BCI performance; identification of appropriate BCI applications and appropriate matching of applications and users; and attention to factors that affect user acceptance of augmentative technology, including ease of use, cosmesis, and provision of those communication and control capacities that are most important to the user. Development of BCI technology will also benefit from greater emphasis on peer-reviewed research publications and avoidance of the hyperbolic and often misleading media attention that tends to generate unrealistic expectations in the public and skepticism in other researchers. With adequate recognition and effective engagement of all these issues, BCI systems could eventually provide an important new communication and control option for those with motor disabilities and might also give those without disabilities a supplementary control channel or a control channel useful in special circumstances. <s> BIB008
A measurement of performance may be deduced of an experimentation concerning a panel of users with disability, generally compared with a pilot panel made up of people without disability. The question which arises here is the choice of the criteria of performance. Thus to evaluate a tilt sensor intended to emulate a mouse, Chen chooses to measure the accuracy of the pointing, this in a binary way (selections successful or not), as well as the time of realization of the task BIB002 . These two same parameters, action time and missed selections, are also adopted by Junker et al. for the evaluation of Cyberlink, a human-machine interface using simultaneously EMG and EEG signals  . In BIB007 the authors developed a pointing device (IPDA: Integrated Pointed Device Aparatus) intended for people with tetraplegia, which assigns the pointing and clicking functions of a mouse to different devices and different body parts. The criterion selected to measure its performance, named OE (Operational Efficiency), is defined like the reverse of the task completion time. In some situations, it is possible to relate a level of motor deficit with the most suitable input sensors. Thus, for people with high-level spinal cord injuries, Bates listed the plausible interface sensors according to the level of the injury classically denoted as Cn, n numbering the cervical branch  . For example, an eye tracker device or tongue controlled switches would be candidates for being used for a C1 spinal cord injury level. A chin joystick or shoulders switches could be selected from C3 to C5 whereas the use of EMG signals could be recommended from C1 to C8 by choosing the most suitable muscles. In  the authors assess the ergonomics of an alternative mouse based on EMG signals collected on the Frontal, Masseter and Trapezius muscles. The objective is, at the same time, to evaluate the ergonomics of the EMG interface and to carry out a comparison between these muscular zones as control inputs. The measurement of performance uses questionnaires and some ergonomic criteria defined for a pointing task: time to reach a target from the previous one, numbers of mouse clicks before reaching a target and number of clicks on the wrong button. Criteria of selection errors and movement times are also used by Chin et al. to evaluate a pointing task in order to compare an EMG interface and an eye-gaze tracking interface  . The information theory initially developed for signals transmission in telecommunication  is often used to evaluate the human-machine or machine-human transmission channel. It is in particular the case in the field of brain-computer interfaces. The recognition of control information in EEG signals being disturbed with errors, we can define an "Information Transfer Rate" (ITR) by analogy with the capacity of a noisy transmission channel BIB001 BIB003 . If each item target among N has the same probability p of being selected without error, we are in the case of a symmetrical channel with N symbols whose capacity is given by: This in particular makes it possible to choose, p being given, an optimal number N of targets to be proposed to the user, i.e. which maximizes C BIB001 . If we multiply this parameter by the number of commands per second μ, we obtain the bandwidth (or "throughput") TP of a given interface BIB005 : Tonet et al. associate to the "throughput" a second parameter, the "latency", defined as the time between the moment when a command is initiated and the moment when its effects start. They thus link the performance of a control interface to the needs of the assistive device BIB005 . The "Information Transfer Rate" can also be applied to human-machine interfaces based on switch sensors. Thus Huo et al. uses it as criterion of performance for the evaluation of a wireless magneto-inductive sensor controlled by the tongue BIB006 . The tests relate to a mouse emulation task and show an ITR of 130, superior to that of the BCI interface described by Wolpaw BIB008 and also to those of other tongue-computer interfaces. Let us finally note that quantitative performance criteria are not always convenient during an evaluation on a panel of people with disability. Thus Betke and al. measure a completion time to compare a task of text selection on a virtual keyboard using a mouse and then a "camera mouse" (device allowing to carry out a visual tracking of a body feature), this on a panel of people without disability BIB004 . On the other hand, for their experiments on users with disability, they are satisfied with qualitative data.