Alternative communication systems for people with severe motor disabilities: a survey <s> Direct communication <s> Abstract The analytical methods of information theory are applied to the data obtained in certain choice-reaction-time experiments. Two types of experiment were performed: (a) a conventional choice-reaction experiment, with various numbers of alternatives up to ten, and with a negligible proportion of errors, and (b) a ten-choice experiment in which the subjects deliberately reduced their reaction time by allowing themselves various proportions of errors. The principal finding is that the rate of gain of information is, on the average, constant with respect to time, within the duration of one perceptual-motor act, and has a value of the order of five “bits” per second. The distribution of reaction times among the ten stimuli in the second experiment is shown to be related to the objective uncertainty as to which response will be given to each stimulus. The distribution of reaction times among the responses is also related to the same uncertainty. This is further evidence that information is intimately con... <s> BIB001 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Direct communication <s> Information theory has recently been employed to specify more precisely than has hitherto been possible man's capacity in certain sensory, perceptual, and perceptual-motor functions (5, 10, 13, 15, 17, 18). The experiments reported in the present paper extend the theory to the human motor system. The applicability of only the basic concepts, amount of information, noise, channel capacity, and rate of information transmission, will be examined at this time. General familiarity with these concepts as formulated by recent writers (4, 11,20, 22) is assumed. Strictly speaking, we cannot study man's motor system at the behavioral level in isolation from its associated sensory mechanisms. We can only analyze the behavior of the entire receptor-neural-effector system. However, by asking 51 to make rapid and uniform responses that have been highly overlearned, and by holding all relevant stimulus conditions constant with the exception of those resulting from 5"s own movements, we can create an experimental situation in which it is reasonable to assume that performance is limited primarily by the capacity of the motor system. The motor system in the present case is defined as including the visual and proprioceptive feedback loops that permit S to monitor his own activity. The information capacity of the motor system is specified by its ability to produce consistently one class of movement from among several alternative movement classes. The greater the number of alternative classes, the greater is the information capacity of a particular type of response. Since measurable aspects of motor responses, such as their force, direction, and amplitude, are continuous variables, their information capacity is limited only by the amount of statistical variability, or noise, that is characteristic of repeated efforts to produce the same response. The information capacity of the motor Editor's Note. This article is a reprint of an original work published in 1954 in the Journal of Experimental Psychology, 47, 381391. <s> BIB002 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Direct communication <s> Contents: Preface. An Applied Information-Processing Psychology. Part I: Science Base. The Human Information-Processor. Part II: Text-Editing. System and User Variability. An Exercise in Task Analysis. The GOMS Model of Manuscript Editing. Extensions of the GOMS Analysis. Models of Devices for Text Selection. Part III: Engineering Models. The Keystroke-Level Model. The Unit-Task Level of Analysis. Part IV: Extensions and Generalizations. An Exploration into Circuit Design. Cognitive Skill. Applying Psychology to Design Reprise. <s> BIB003 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Direct communication <s> This study analyzes user performance of text entry tasks with word prediction by applying modeling techniques developed in the field of human-computer interaction. Fourteen subjects transcribed text with and without a word prediction feature for seven test sessions. Eight subjects were able-bodied and used mouthstick typing, while six subjects bad high-level spinal cord injuries and used their usual method of keyboard access. Use of word prediction decreased text generation rate for the spinal cord injured subjects and only modestly enhanced it for the able-bodied subjects. This suggests that the cognitive cost of using word prediction had a major impact on the performance of these subjects. Performance was analyzed in more detail by deriving subjects' times for keypress and list search actions during word prediction use. All subjects had slower keypress times during word prediction use as compared to letters-only typing, and spinal cord injured subjects had much slower list search times than able-bodied subjects. These parameter values were used in a two-parameter model to simulate subjects' word entry times during word prediction use, with an average model error of 16%. These simulation results are an encouraging first step toward demonstrating the ability of analytical models to represent user performance with word prediction. > <s> BIB004 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Direct communication <s> For children who depend on devices to communicate, the rate of communication is a primary determinant of success. For children with motor impairments, the rate of communication may be limited by inability to contact buttons or cells rapidly or accurately. It is, therefore, essential to know how to adjust the device interface in order to maximize each child's rate of communication. The optimal rate of communication is determined by the channel capacity, which is the maximum value of the information rate for all possible keyboard button or cell layouts for the communication device. We construct a mathematical model for the information rate based on the relationship between movement time and the number of buttons per screen, the size of the buttons, and the length of a sequence of buttons that must be pressed to communicate each word in the vocabulary. We measure the parameters of the model using a custom-programmed touchscreen interface in 10 children with disorders of arm movement due to cerebral palsy who use a DynaVox communication device. We measure the same parameters in 20 healthy control subjects. We show that the model approximates the measured information rate and that the information rate is lower in children with motor impairments compared with control subjects. The theory predicts that for each child there is a combination of button size and number that maximizes the predicted information rate and thereby achieves communication at the optimal channel capacity. Programming communication devices with each child's predicted optimal parameters improved the communication rate in five of the ten children, compared with programming by professionals. Therefore, measurement of information rate may provide an assessment of the effect of motor disorders on success in assisted communication. Optimization of the information rate may be useful for programming assisted communication devices. <s> BIB005
As regards modelling in the field of assistive technology the majority of the studies reported in the literature aim at adapting to people with disabilities a model initially defined for people without disability. Koester and Levine, for example, modelled the user performance for a text entry task with words prediction using a direct control of the keyboard with a headstick BIB004 . To the usual parameter "Keystroke Saving" (the number of keystrokes saved thanks to the words prediction), which reflects only the motor component of the user activity, the authors substitute a cognitive component with a two parameters model, "Keypress Time" and "List Search Time" derived from the KLM model (Keystroke Level Model) BIB003 . The experiments carried out starting from this model enable them to conclude that the time saved thanks to the keystroke saving is partly compensated by the time wasted to scan for the adequate word in the proposed list. Sanger and Henderson model the human-machine interaction in the case of an assistive communication device made up of a touch screen BIB005 . The objective is to optimize the communication rate (IR) according to the number b of items simultaneously on the screen, of the size w of the icons and of the average number m of items to select to reach a vocabulary element. They define IR for that by: The entropy, according to the information theory, is the average value of -p(x).log 2 p (x), x being a vocabulary element and p(x) its probability to be selected. TT(w, b, m) is the time necessary to select one item. It is divided in an action time MT, and a time RT for the choice of the item. RT may be given by the Hicks' law which depends on the logarithm of the number b of possible choices BIB001 . The authors prefer here to use a linear law to take account of the imperfect knowledge of the interface by the users. The action time MT is modelled classically by the Fitts' law BIB002 , frequently used in the analysis of pointing devices.