Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> Computer head controls provide an alternative means of computer access for people with disabilities. However, a person?s ability to use head controls may be reduced if his or her disability involves neck movement limitations. In this study, 15 subjects without disabilities and 10 subjects with disabilities received neck range of motion evaluations and performed computer exercises using head controls. Regression analysis was used to determine the relationship between neck range of motion and performance on computer exercises. Reduced neck range of motion was found to be correlated with reduced functional range for moving the cursor across the screen, and reduced accuracy and speed in icon selection. Fitts' Law-type models were fit to the data, indicating higher Fitts' law slopes for subjects with disabilities compared to subjects without disabilities. Results also indicate that vertical cursor movements are faster than horizontal or diagonal movements. <s> BIB001 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> In view of the difficulties in evaluating computer pointing devices across different tasks within dynamic and complex systems, new performance measures are needed. This paper proposes seven new accuracy measures to elicit (sometimes subtle) differences among devices in precision pointing tasks. The measures are target re-entry, task axis crossing, movement direction change, orthogonal direction change, movement variability, movement error, and movement offset. Unlike movement time, error rate, and throughput, which are based on a single measurement per trial, the new measures capture aspects of movement behaviour during a trial. The theoretical basis and computational techniques for the measures are described, with examples given. An evaluation with four pointing devices was conducted to validate the measures. A causal relationship to pointing device efficiency (viz. throughput) was found, as was an ability to discriminate among devices in situations where differences did not otherwise appear. Implications for pointing device research are discussed. <s> BIB002 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> Head-operated computer controls provide an alternative means of computer access for people with disabilities who are unable to use a standard mouse. However, a person's disability may limit his or her neck movements as well as upper extremity movements. Software was developed which automatically adjusts the interface sensitivity to the needs of a particular user. This adaptive software was evaluated in two stages. First, 16 novice head-control users with spinal-cord injury or multiple sclerosis used head controls with and without the adaptive software. The adaptive software was associated with increased speed in standardized icon selection exercises (p<0.05). A small increase in accuracy was also observed. In addition, five current head-control users evaluated the software in a real-world setting. One of these five subjects perceived an improvement in comparison to his current head-control system. <s> BIB003 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> In rehabilitation medicine, it is necessary for medical staff members to recommend the suitable computer input device for each patient with a spinal cord injury. This paper describes a measurement and evaluation system to determine the computer input ability of patients with tetraplegia. The authors will define a measurement procedure, a set of objective parameters, and a graphical representation of the parameters. They measure the position locus of the mouse cursor when a patient operates a computer using a computer input device. Using the representation, the medical staff can evaluate the patient's computer input ability and understand the characteristics of the patient's computer operation <s> BIB004 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> Fitts' Law is commonly found to apply to motor tasks involving precise aiming movements. Children with cerebral palsy (CP) have severe difficulties in such tasks and it is unknown whether they obey Fitts' Law despite their motor difficulties. If Fitts' Law still does apply to these children, this would indicate that this law is extremely robust and that even performance of children with damaged central nervous systems can adhere to it. The integrity of motor control processes in spastic CP is usually tested in complex motor tasks, making it difficult to determine whether poor performance is due to a motor output deficit or to problems related to cognitive processes since both affect movement precision. In the present study a simple task was designed to evaluate Fitts' Law. Tapping movements were evaluated in 22 children with congenital spastic hemiplegia (CSH) and 22 typically developing children. Targets (2.5 and 5 cm in width) were placed at distances of 10 and 20 cm from each other in order to provide Indices of Difficulty (ID) of 2-4 bits. Using this Fitts' aiming task, prolonged reaction and movement time (MT) were found in the affected hand under all conditions in children with CSH as compared to controls. Like in the control group, MT in children with CSH was related to ID. The intercept 'a', corresponding to the time required to realize a tapping movement, was higher in the affected hand of the children in the CSH group. Although, the slope b (which reflects the sensitivity of the motor system to a change in difficulty of the task) and the reciprocal of slope (that represents the cognitive information processing capacity, expressed in bits/s) were similar in both groups. In conclusion, children with CSH obey Fitts' Law despite very obvious limitations in fine motor control. <s> BIB005 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> We investigated the performance of three user interfaces for restoration of cursor control in individuals with tetraplegia: head orientation, electromyography (EMG) from face and neck muscles, and a standard computer mouse (for comparison). Subjects engaged in a 2-D, center-out, Fitts' Law style task and performance was evaluated using several measures. Overall, head orientation commanded motion resembled mouse commanded cursor motion (smooth, accurate movements to all targets), although with somewhat lower performance. EMG commanded movements exhibited a higher average speed, but other performance measures were lower, particularly for diagonal targets. Compared to head orientation, EMG as a cursor command source was less accurate, was more affected by target direction and was more prone to overshoot the target. In particular, EMG commands for diagonal targets were more sequential, moving first in one direction and then the other rather than moving simultaneous in the two directions. While the relative performance of each user interface differs, each has specific advantages depending on the application. <s> BIB006 </s> Alternative communication systems for people with severe motor disabilities: a survey <s> Pointing Tasks <s> A brain–computer interface (BCI) is a communication system that takes recorded brain signals and translates them into real-time actions, in this case movement of a cursor on a computer screen. This work applied Fitts' law to the evaluation of performance on a target acquisition task during sensorimotor rhythm-based BCI training. Fitts' law, which has been used as a predictor of movement time in studies of human movement, was used here to determine the information transfer rate, which was based on target acquisition time and target difficulty. The information transfer rate was used to make comparisons between control modalities and subject groups on the same task. Data were analyzed from eight able-bodied and five motor disabled participants who wore an electrode cap that recorded and translated their electroencephalogram (EEG) signals into computer cursor movements. Direct comparisons were made between able-bodied and disabled subjects, and between EEG and joystick cursor control in able-bodied subjects. Fitts' law aptly described the relationship between movement time and index of difficulty for each task movement direction when evaluated separately and averaged together. This study showed that Fitts' law can be successfully applied to computer cursor movement controlled by neural signals. <s> BIB007
The Fitts' law defines that the response time is given by: Where the constants "a" and "b" are empirically determined and ID is the index of difficulty calculated in terms of the distance (D) between the starting point and the centre of the target and width (W) of the target: Originally designed as a model of human psychomotor behaviour, such law leads to a performance measurement standardized and validated by many researchers, being actually used in the International Standard ISO 9241, Part 9: "Requirements for non-keyboard input devices". The performance index is defined by IP = 1/b or, to combine the parameters "a" and "b" in only one metric, IP = ID/MT ("throughput" expressed in bits/s)  . It does not allow however a complete analysis of the pointing movement BIB002 . Thus to evaluate the performances of an EMG-based interface using the neck muscle EMG signals as well as a head orientation sensor, Williams and Kirsch associate the "throughput" parameter of the Fitts' law to other indicators allowing to analyze more precisely the quality of movement BIB006 : initial reaction time, effectiveness of the path (variation between the path carried out and the straight line), overshoot (the number of occurrences of the cursor reaching the target then leaving it before the end of the dwell time), mean velocity and direction ratio (evaluation of the capacity of the subject to move the cursor in diagonal compared to horizontal or vertical movements). Lopresti et al. undertook a study aiming at analyzing if neck movement limitations imply a reduction of performance during the use of a head control sensor BIB001 . They note in particular that, for a pointing task with this interface, their panel of people without disability satisfied to the Fitts' law contrary to the group of 10 people with disabilities (6 with multiple sclerosis, 3 with sustained cervical, 1 with spinal stenosis). They are then brought to model the performance of these people by more precisely analyzing the movement according to 3 phases: • the reaction phase where the person perceives the goal and initiates the movement: the subjects with disabilities have average reaction times longer than the subjects without disability; • The ballistic phase corresponding to the fast movement towards the target: the motor difficulties of the subjects with disabilities result in the presence of several peaks in the profile speed whereas we note only one peak for the subjects without disability; • The homing phase where the movement is slowed down and controlled better to position on the target. As in the reaction phase the time passed in this phase by the people with disabilities is longer on average than that passed by the people without disability; To evaluate the performances of an algorithm of adaptive adjustment of head movement sensors sensitivity, these same authors measure three parameters: the accuracy (proportion of icons selected successfully during their experiments on a pointing task), the "throughput" ID/MT and the overshoot (relationship between the distance covered after having exceeded the target and the distance to the target) BIB003 . In a similar way Tanimoto et al. present an analysis software of the pointing movement which draws the trajectory of the cursor on the screen BIB004 . For people with tetraplegia they note that this trajectory does not follow a " Fitts' configuration» but is punctuated with stopping periods. Then they characterize it by parameters like the time in the stopping period before the click or the times during the moving and positioning phases, quite similar in their definitions to the ballistic and homing phases described above, as well as the distances covered, the velocities and the stopping times during these two phases. The Fitts' law, usually used to analyze and evaluate the performances of the pointing tasks, is not verified for some persons with disabilities. Thus Gump et al., after an experimentation relating to 8 subjects with cerebral palsy, conclude that for a majority of these subjects the movement time MT is better represented by a ballistic law (function of the square root of the distance to the target) that by the Fitts' law  . The authors explain this by the oculomotor difficulties of the subjects. These conclusions are however partly contradicted in BIB005 . Here, for the same type of subjects as previously, the authors choose to carry out their experiments on a very simple manual pointing task to be free from cognitive problems which might affect the movement accuracy. This time the Fitts' law is checked in spite of the significant motor difficulties of the subjects. Felton et al. BIB007 successfully used the Fitts' to the evaluation of performance on a target acquisition task during sensorimotor rhythm-based BCI training. The participants in the study were both disable and able bodied volunteers but with the inclusion criteria of consistent target acquisition task accuracy exceeding 80%, justified by the fact that the Fitts' law emphasizes time over accuracy. However, a few researches may find that the accuracy should be taken in account in the general evaluation of pointing tasks systems, especially in the case of BCI systems that may present great performance variation within the same session. Gajos et al. describe a Supple++ software which generates user interfaces automatically adapted to the motor capacities of the person  . Observing that the Fitts' law is not always checked for people with disabilities, they propose to model the pointing task in a personalized way. They try for that, for each user, the possible combinations of 7 parameters: a constant term, the index of difficulty ID = log 2 (1 + D/W) of the Fitts' law (with D the distance to be crossed and W the width of the target), log 2 (W), log 2 (D), W, 1/W and D.