Alternative communication systems for people with severe motor disabilities: a survey <s> Scanning systems <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> BIB001 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Scanning systems <s> Abstract Keyboard ‘bypass’ techniques allow physically disabled people, otherwise unable to use conventional means of text composition, to do so. Ability to compose text is extremely important to the disabled, offering potential for non-speech communication, computer access, creative writing, etc. Consequently, these techniques have received a good deal of attention and many diverse systems have evolved. They all suffer, however, from the drawback of inherently slow input, quite apart from any disability on the part of the user. For this reason, text composition rate (or communication rate) is the major figure of merit. Since many diverse systems and approaches exist, quantitative methods of comparison are required to guide prescription and development of such aids. Only recently have attempts to produce models which predict communication rate been made. This paper extends the earlier model of Rosen and Gooenough-Trepagnier to encompass scanning-input systems. Scanning input is of considerable interest since it can be used by very severely disabled people. The model developed is applied to the comparison of two very different systems: row-column scanning and the ‘scanning Microwriter’. According to the model, row-scanning is very much faster than the scanning Microwriter when a letter-frequency arrangement of the character selections is used. The relation of the model to classical information theory, treating the disabled user as an information source, is also explored. <s> BIB002 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Scanning systems <s> The standard QWERTY keyboard is the principal text entry device for word processing and computer-based communications. For many motor-impaired individuals, and in particular those without intelligible speech, the low text entry rates they can typically achieve is a major problem. For some, the QWERTY design is completely inappropriate. Alternative designs that can appreciably increase these rates would greatly enhance their ability to communicate. This paper considers and compares several approaches to the design of text entry devices for motor-impaired users. A general method for customising (i e, optimising) these designs is employed, and consideration is given to designs requiring significantly fewer input switches than the 26 or more keys required by QWERTY. Use is made of language statistics in the design procedure, and the increased availability of inexpensive, powerful computers is directly exploited. <s> BIB003 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Scanning systems <s> This paper considers the differences between users with motion-impairments and able-bodied users when they interact with computers and the implications for user models. Most interface design and usability assessment practices are based on explicit or implicit models of user behaviour. This paper studies the applicability of an existing interface design user model to motion-impaired users for the relatively straightforward task of button activation. A discussion of the empirical results is provided and the paper concludes that there are significant differences between the behaviour of motion-impaired users and the accepted modelling theory. <s> BIB004 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Scanning systems <s> Virtual scanning keyboards are commonly used augmentative communication aids by persons with severe speech and motion impairments. Designers of virtual scanning keyboards face problems in evaluating alternate designs and hence in choosing the better design among alternatives. Automatic evaluation of designs will be helpful to designers in making the appropriate design choice. In this paper, we present performance models for virtual scanning keyboards that can be used for automatic evaluation. The proposed models address the limitations present in the reported work on similar models. We compared the model predictions with results from user trials and established the validity of the proposed models. <s> BIB005 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Scanning systems <s> For some people with motor disabilities and speech disorders, the only way to communicate and to have some control over their environment is through the use of a controlled scanning system operated by a single switch. The main problem with these systems is that the communication process tends to be exceedingly slow, since the system must scan through the available choices one at a time until the desired message is reached. One way of raising the speed of message selection is to optimize the elementary scanning delay in real time so that it allows the user to make selections as quickly as possible without making too many errors. With this objective in mind, this article presents a method for optimizing the scanning delay, which is based on an analysis of the data recorded in “log files” while applying the EDiTH system [Digital Teleaction Environment for People with Disabilities]. This analysis makes it possible to develop a human-machine interaction model specific to the study, and then to establish an adaptive algorithm for the calculation of the scanning delay. The results obtained with imposed scenarios and then in ecological situations provides a confirmation that our algorithms are effective in dynamically adapting a scan speed. The main advantage offered by the procedure proposed is that it works on timing information alone and thus does not require any knowledge of the scanning device itself. This allows it to work with any scanning device. <s> BIB006
The scanning systems controlled by adapted switches, only method usable for many people with severe disability, generate an intrinsically slow communication (about 1 to 2 words per minute). It is thus necessary to optimize the communication rate and this in a personalized way in order to adapt to the great diversity of the physical and cognitive capacities of the users concerned. The parameters which we can adjust for this purpose are summarized by the model initially defined by Rosen and Goodenough-Trepagnier giving the average time T necessary to select a word  BIB003 : Where C is the linguistic cost (the average number of language units per word), function of the selected language (alphabetical, phonemes, etc). L is the average number of actions to select a language unit and t is the average time per action. This model initially developed for direct communication devices has been extended to the scanning systems by Damper BIB002 . The product L.t is then a function of the type of scanning, of the geometrical structure of the matrix of items and of the elementary scanning delay. This study does the assumption that, after each selection of item, the scan starts again at the beginning of the matrix. Bhattacharya then extends the model to scannings starting from the selected item BIB005 . In addition to the probability of selection of each item k i , it is necessary in this case to use that of the digraphs (k i , k j ). Moreover, if we want that the performances calculated with the ideal models correspond to those measured in practice, it is necessary to take account of the selection errors which can be numerous with users with severe disabilities. In  it is proposed a users errors modelling by classifying them in two categories: timing errors (the user actuates the sensor too late) and selection errors (the user selects a wrong element (block, row or item)). In the models evoked above, the user performance is reflected by the elementary scanning delay T scan . This time is adjusted in an empirical way in the commercialized systems or in an adaptive way in some studies BIB006  . The action on a switch following a visual stimulus (change of color or appearance of an item) may be modelled using the MHP model (Model Human Processor) initially developed by Card, Moran and Newell for computer tasks of low cognitive level (reaction to stimuli) BIB001 . It requires a time T act = T p + T c + T m where T p , T c and T m are respectively the elementary perception, cognition and motor times. This model is used in  for the design of a simulator aiming at assessing the assistive communication devices. It is also the case in BIB005 but by adding an additional cognitive time following the study reported in BIB004 . Keates et al. indeed tested the applicability of the MHP model on a panel of people with disabilities for a simple task: the activation of an adapted switch in reaction to a visual stimulus. They noted, on the one hand, motor times on average higher than those measured on people without disability, and, on the other hand, the presence of an additional cognitive time compared to the theory, corresponding to the decision of releasing the sensor. In  it is also noted for the use of a scanning communication device that some persons with disabilities do not conform to the MHP model due to motor disorders (persons with cerebral palsy) or cognitive disorders (persons with cranial trauma). Finally, in BIB006 , it is proposed an improvement of the MHP model applied to scanning communication devices, the "three-zone behaviour model", which takes into account the fact that, very often, the user, accustomed to the scanning rate, starts to react before the visual stimulus appears.