Claude Veraart and Richard Cavonius
Disabled people frequently have difficulty when interacting with their environment, the severity of which depends on the relationship between the type of disability and the nature of the activity. For example, in cases of sensory impairments, blind persons experience problems in reading, writing, face recognition, or obstacle detection, whereas deaf people have trouble with sound detection, verbal communications, etc. Those suffering motor impairments, lost limbs, or spinal cord injuries encounter problems in locomotion, prehension, etc. Traditionally, each of these specific problems has been dealt with by means of aids designed specifically for the circumstances. Examples of such dedicated solutions are the Braille alphabet, guidance cane, and talking books for blind users; text telephone and amplifiers for the deaf and hearing impaired persons; ortheses and prostheses, and wheelchairs, for those with motor difficulties.
Industrial development has fostered the constant introduction of new devices such as vehicles, communication systems, computers, and the like. Unfortunately, although these may be useful for non-impaired people, they may deepen the exclusion of disabled persons from everyday life. Although many adaptations of technological developments have been made to allow disabled persons to use these new systems, these usually require a considerable development time, because they are made only after a system is introduced, and systems are seldom designed to accommodate such adaptations. Moreover, these adaptations usually address only a specific problem: how to allow people with a certain disability to utilize a particular system. As an example, a computer keyboard for blind people is thoroughly different from one for quadriplegic users. Further, the entire process of developing adaptations for disabled users is undermined by the continual advance of technology: each time a new system is introduced, a new difficulty is apt to be created for disabled users, who then have to wait for a subsequent adaptation of the new system before being able to use it. Modern technology is particularly insidious in that new systems may both be incompatible with, and make obsolete, their predecessors: for example, the introduction of PC computers, with their extensive use of windows and icons, made obsolete overnight all adaptations that had been developed for CP/M systems.
These problems provide a powerful incentive for the development of equipment-independent aids for disabled users. Such systems, if they could be implemented, might provide disabled users with supplementary means to improve their ability to interact with the environment and with technological developments: ideally not just with current, but with future technology, and thus provide the user with more independence in everyday life. The purpose of this chapter is to introduce a general theoretical background for such equipment-independent aids and to point out some of the ways in which they differ from dedicated solutions; to provide some examples of existing systems; and to point out some of the problems that developers of such systems face. It should be emphasized that this field is still at a very early stage of development, and that problems far outnumber solutions.
While equipment-independent solutions are possible for both sensory and motor disabilities, to save space only sensory loss will be considered, since problems in using telecommunications systems are more commonly due to sensory impairment. However, the reader can see that analogous methods can be used to analyse cases of motor impairment.
Equipment-specific Solutions for Users with Sensory Impairment
Because aids traditionally have been equipment-specific, this approach will be considered first. A generalized machine is shown in the upper half of Figure 4-35 and its human operator in the lower half. A machine will typically have some input devices (the communications sensors in the figure) with which the user acts upon it: in a telecommunications systems these might well be keys. In addition, it is apt to have machine sensors that receive information from the outside world - a heating system might have a thermostat; while a telecommunications system might receive signals from a network. In addition it will generally have displays (communication actuators) that tell the user something about its internal state, and machine actuators that affect the external world. All these are linked by a central controller, which in telecommunication systems is increasingly a dedicated computer.
The user, in the lower half of Figure 4-35, receives information about the state of the machine through one or more sensory systems (think of how many senses one uses when driving a car!) and issues commands to the machine through one or more effector systems. A part of these motor commands is fed back to the user and can be compared with the desired response as a check on how appropriate the action is. (In the case of the non-impaired user it is assumed that the feedback signal is shown as going to another sensory system, but in principle it could go to the same system as the information about the machine's activity.)
In order to allow it to be general, this example is purely qualitative, but it should be apparent that it could be quantified by adding operating characteristics to the various modules, making it a useful model of the real machine-user system. Examples of such system-analytic solutions can be found in Klause (1981).
In order to interact with a machine, disabled users also need information about the effectiveness of their actions on the machine, and about machine activity. In the case of users with sensory impairment, this information is usually provided to them through their intact sensory modalities, such as the auditory or tactile sense in case of blindness. Two specific interfaces are needed to provide this information: a sensory-motor feedback interface, and a machine-activity feedback interface. These interfaces are dedicated to the specific circumstance, depending on the kind of sensory impairment and the type of machine. For example, if a computer terminal is to be accessible to a blind user, the sensory-motor feedback interface might take the form of Braille embossing on the keyboard, or an auditory echo of the depressed characters. The machine-activity feedback interface might deliver an alphanumeric response, using either ephemeral Braille or synthetic speech (Flanagan, 1982).
Non-specific Methods to Enable Disabled Users to Interact with Systems
In contrast with dedicated solutions that allow persons with a given disability to interact with a specific system, efforts to provide them with all-purpose interfaces are even more challenging. If they are to be equipment-independent, such non-specific interfaces must be able to address a number of different circumstances. Ideally, non-specific interfaces should allow their users to deal with unforeseen interactions, such as may be encountered in everyday situations, or with new technological develop-ments, so that a single interface would be sufficient to solve a wide range of problems. It might be either non-invasive, or partially implanted.
In case of sensory impairments, the ideal single interface should detect all of the needed information relevant to the user's lost sensations, both information about the user's environment and sensory interactions arising from the user's motor activity. A non-invasive interface, or sensory substitution prosthesis, would work as follows (Bach-y-Rita, 1972; Veraart and Wanet, 1985): information related to the impaired sensory function has to be acquired using an artificial system, and then translated to a form accessible to a user's intact sensory channel. As proposed by Veraart (1989), an optimized sensory substitution prosthesis should consist of a model of the impaired sensory system, coupled to an inverse model of the substituting sensory system. As illustrated in the upper part of Figure 4-36, this single interface allows the user to interact with various forms of environmental stimuli related to their impaired sensory channel. For example, in case of blindness, acquisition of graphic information (printed matter, handwriting, drawings, etc.) through the tactile system is possible using the Optacon (Bliss, 1969). Systems for obstacle detection using ultrasonic echolocation (Kay, 1974; Ciselet et al., 1982), or sound emission (Brabyn, 1982) have also been developed. More versatile, but still experimental, examples of sensory substitution prostheses are the TVSS which translates visual information into tactile stimulation (Bach-y-Rita et al., 1969), or new systems that translate visual information into complex sounds (Capelle et al., 1992; see also Meijer, 1992).
An implantable sensory prosthesis should acquire information related to the user's impaired sensory system, including sensory-motor interactions, and translate it into electrical signals acting upon intact parts of the user's impaired sensory channel (Figure 4-36, lower part). An optimal invasive (i.e. surgically implanted) sensory prosthesis should incorporate a model of the portion of the impaired sensory system that is peripheral to the level of the remaining functional part of this system to which the electrical stimulation is provided (Veraart, 1989). For example, in case of deafness, cochlear implants (Figure 4-37) can detect and process sounds and speech using an external device, and send coded signals to the implant, stimulating the cochlea, using transcutaneous transmission (Loeb et al., 1983).
The most common cause of neural auditory loss is damage to the cochlea, the part of the inner ear in which sound energy is converted to neural activity. In auditory prostheses, one or more electrodes are placed in the cochlea and the neural structures are directly stimulated with a series of electrical pulses that are derived by various algorithms from the acoustic signal. Much of the current research in this area is concerned with the development and testing of these algorithms.
Early attempts to simulate visual perception by electrical stimulation of the primary visual cortex were made in the mid 1960s, and resulted in the perception of star-like points of light called phosphenes (Brindley and Lewin, 1968). After a quarter-century of inactivity, stimulation with intracortical electrodes has again been reported (Schmidt, et al., 1992) and several groups are attempting to stimulate the retinal ganglion cells (the cell bodies of the optic nerve neurons) with electrodes designed to be inserted intraocularly between the retina and the vitreous body (Mann, et al., 1994; Rizzo, et al., 1994). However, it should be emphasized that these are still early efforts, and that fully functional prostheses cannot be expected in the near future.
Methods designed to help disabled persons in interacting with their environment, including tele-communications or teleinformation facilities, have until now been chiefly dedicated to specific purposes. Nevertheless, there is now a trend toward developing non-dedicated communication means for disabled users. Even if, in a specific application, a dedicated system may give better results than a non-specific sensory or motor prosthesis, the latter solution will eventually be helpful in many additional circumstances. The condition that must be met in the design of such non-specific systems is to make them versatile enough to provide their users with multiple means of communication.
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