A new integrated system to assess the amount of information of pointing devices for motor-disabled person

Symbiosis of Human and Artifact Y. Anzai, K. Ogawa and H. Mori (Editors) © 1995 Elsevier Science B.V. All rights reserved.

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A n e w integrated s y s t e m to assess the a m o u n t of i n f o r m a t i o n of pointing devices for m o t o r - d i s a b l e d person Toshiyasu Yamamoto ('), Tetsuya Yamashina (':, Jyunichi ohshima ('~, and Masafumi Ide c"~ ('~Rehabilitation R&D Department, Toyama Prefectural Koshi Rehabilitation Hospital, 36, Shimo-Iino, Toyama, 931, Japan c,~Spinal Injuries Center, Labor Walfare Corporation, 550-4, Ikisu, Iizuka, 820, Japan This paper describes a new system to quantitatively assess the interface control of the input/output devices for the motor-disabled person. A integrated system has been developed, simultaneously to measure for the interface devices and the kinematics of upper extremity. Kinematic analysis is preliminarily introduced to explain a relation between the motor task and its compensatory movement. From a viewpoint of information theory, the amount of information is discussed to describe an quantitative transmitted measure in a specified task. 1. INTRODUCTION Recently though some of the interface devices has been developed for the disabled and the elderly, they are practically selected and served without any quantitative assessment at work place and at home. It is important to consider and estimate a training condition for the residual functions at the stage of rehabilitation program, and the activities of daily livings through the whole environmental process. The final object of this study is to discuss with a method to assess the amount of information of the redisual functions, and to make fit with the amount of information for handling the input/output interface of the electronic devices in the indoor work places, etc. It will be necessary to assess the physically residual functions to control some of the devices: keyboard, joystick, mouse/track ball, push/touch switch, pressure switch, respiratory switch, joint angular switch, voice recognition switch, etc. Here w e introduce a new integrated system to measure the kinematc data for the interface devices, and the upper extremities. And it will be preliminarily discussed about some of the analytical results of the execution errors in pointing the targets, to assess the man-machine interface, sepecially in the computer system. 2. INTERFACE SYSTEM AND TI-IE AMOUNT OF INFORMATION As a measure to express the fitness for the interface system of command control, the following three kinds of indices are introduced, analogous to information theory; (1) A part of funding for this study is provided by Japan Foundation for Aging and Health, supproted by the Ministry of Health and Walfare.

738 multiple access channel(channels), (2) information density(bits/sec), (3) information capacity(bits). Multiple access channel is defined as the number of information access, used for command control. Information density was introduced by Fitts[1]. The amount of information of human motor system is discribed as the variables of \\ x analog measure of successive responses. It is infered as the mean information transmission rate. In 1980, Sakkits defined information capacity as the resolution of angular motion of the Fig.1 The body coordinates system by the joint[2]. This attractive approach has electromagnetic position sensors in pointing a been also applied widely, because it can target, with touch point sensor in the space be explained with no connection with coordinates(O-XYZ) difference in the physical measures. Thougu these methods are based on the error analysis of a motor task, it also 3 dim RS232C Personal can lend insight into the principles, positoin sensoi which the movement of the upper computer extremities is organized and controlled. Some of the researchers has studied to Input/output I experimentarily understand the invariant Personal properties according to the kinematic representation of a motor task in pointing, ~A/D] computer etc. It was often useful to describe a characteristic mechanism of the ip li sensorimotor transformation[3]. In this preliminary study, we have eximined the usefulness of information Fig. 2 The integrated measurement system for theory approach to estimate the human input/output interface of the electronic devices performance in reciprocally and discretely pointing a target. This approach may be able to use a new measure of assessment of the residual functions for a better communication.

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3. THE INTEGRATED MEASURE-MENT SYSTEM First we have developed such an integrated system as shown in Fig. 114]. This is composed of 1) 3 dimensional electro-magnetic positoin sensor(EMPS, POLHEMUS) to sense the motion of the upper extremity, and 2) color LCD (14 inch ) with touch position sensor (TPS). Now this system has been applied for estimating the other devices, as shown in Fig. 2, which has some of the interfaces :mouse, A/D converter, etc. Here the reciprocal and discrete pointings will be experimentally discussed.

739

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Fig. 3 2 dimensional setup of experimental display for reciprocal and discrete motion S=starting point, P(i)=pointing target, W=targel width, L=movement distance between 2 targets. In reciprocal pointing, after holding the hand, the experiment starts on pointing S. P(i) and P(i+l) are shown on the display during a session. In discrete movement, for each trial, after holding the hand, the subject points a target after appearing for 0.5 sec (regulated with the level of motol impairment: 0.5~2.0 sec ). on the 8 directions of randamized position.

The 4 sensorsof EMPS has been fitted on acromion, distal and post. region of humerus, ext. retinaculum, and dorsum manus. The pointing co-ordinates are directly picked up by the touch positoin sensor. In reciprocal pointing, its experimental technique is almost the same as Fitts. Here it is extended into such a 2 dimensional surface as CRT display. In discrete pointing, as an example of thehorizontal direction, the total distance 24.5 cm is divided in 49 sections. W = 0.5, 1.0, 2.0 cmD, and L = 16, 8, 4 cm. The subject was indicated to point a target as fast and accurate as possible, and not to adjust pointing at the end of target. The subjects are 14; normal = 6, SCI = 4, CP = 4. 4. KINEMATICS OF THE UPPER EXTREMITY Here only the results of normal and SCI subjects are shown in Fig. 4. There are few of kinematic motion analysis of the upper extremity, especially on the joint movement of pronation/supination. The normal shows a smooth coordinated motin pattern with the smaller varialbes (s.d.). He mainly controls a motion round the shoulder, and may adjust the joint angles of the wrist, for a precise pointing. The SCI patient is C5 paralysis. His left hand is of a weak flexor, pronator/spinator (PR/SP) of the forearm, which moves with lighter load. The fight hand is severely motorimpaired. His shoulder scarecely gained movement because of difficulty in trunk control. The upper arm has a similar motion as the normal, but a longer and delayed motion in the vicinity of reciprocal pointing. He usually has a large PR/SP of the elbow joint, which has a faster response at the beginning of a pointing motion. This compensatory movement may be related to set a direction, together with extension/flexion of the elbow joint. Lastly we point out that the forearm movement is irregular because of weak muscle force, frequent muscle fatigue, and limited range of motion (ROM), though the variables of the velocity of the hand become larger by adding another session. It may lead to the larger pointing errors. 5. M O V E M E N T TIME AND POINTING E R R O R Here we tested how compensatory movement affects the pointing accuracy at the end of the arm. At first, the displacement and the velocity(and s. d.) of the stylus pen are shown in

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Fig. 4 An example of the motion patterns of the upper extremity in reciprocal pointing The normal and SCI subject put long oponens wrist hand orthosis to lock the wrist joint. Movement distance = 16cm, target width - 1.0cm*, # of sessions = 10, # of reciprocal motion for each session = 25 for the normal, 10 for the SCI patient. Each pattern is shown in the curves of the mean * s.d., FB = forward/backward, LM=lateral/medial, VT-vertical displacement;PR=pronation(+)/spination, AD=abduction/adduction(+), EX = extension(+) /flexion direction

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Fig. 5 Displacement of position and velocity of the hand in a cycle of reciprocal pointing Fig. 5, in which the wrist is free. The displacement is calculated as the distance from the operating hand. The normal shows a smooth curve and a smaller s. d. with a constant speed in pointing a target. On one hand, the SCI has a larger s. d. at the accelerating and decelerating phase. A motion pattern has a tendency of the continuous changes with the muscular force not enough to control a movement precisely (similar to the above). Secondly, the distribution area of pointing (DA) is calculated by estimating the eliptic area, on 2 dimensional normal distribution hypothesis (95% c.i.). A typical movement time (MT) and DA are

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742 shown. In the normal, DA area is less than lcm*, and MT is not well-correlated with the movement distance (L). In the CP, ( quadriplegia, with athetosis), MT has a tendency to decrease with smaller L, but has comparatively larger variances. DA is not correlated with L, and has difference in pointing between the right and left targets, because of difficulty in trunk positioning control. Next, SCI has a remarkable tendency in dependence on a limitted ROM, that is, a large difference of DA between the right and left targets, and a shorter MT with a smaller L. These chracteristics of MT and DA are very useful to estimate one of the main parameters for the characteristic responses of motion control at the end point. 6. INFORMATION ON POINTING RESOLUTION It is useful to test the point resolution for 5 quantitative digital measure of the residual +~C0) function. Here a discrete pointing is used, .__. and its setting is described before. ~ 4 --I-~CC) In Fig. 5, an example of the experimental .....A ..........SCl . results is shown. In the normal, the--= transmitted information is 4, with the eyes ~ 3 CP open, and 3 bits with the eyes closed. The ~.~ CP subject has a similar accuracy with the = 2 normal with the closed. In the case of SCI, it ~ was a little better than CP. I I I I These show that it is possible for the 1 0 10 20 30 40 50 direct pointing motion to apply for Sakkits' s Targets (N) method. For the future work, it may be made use of clarifying the cognitive Fig. 7 Resolution in discrete pointing: spatial-motor process, comparing with data O, C = with the eyes open, and closed obtained under different behabioral manipulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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REFERENCES 1)Fitts, P. M.: The information capacity of the human motor system in controlling the amplitude of movement, J. Exp Psychol, 47, 381-391, 1954 2)Sakkits, B., etal: The information transmitted at final position in visually triggered forearm movements, Biol Cybern, 46, 111-119, 1983 3)Soechting, J. F., Flanders, M.:Sensorimotor Representation for pointing to targets in three-dimensional space, J. Neurophysiol., 62(2), 582-594, 1989 4)T. Yamamoto, Measurement system to assess input control of computer for difficulty in upper extremity, Proc. of 16th Anuual International Conf., IEEE EMBS, Baltimore, 1994