Int. J. Production Economics 60—61 (1999) 235—240

An experimental evaluation of input devices for pointing work

Hiroshi Ichikawa!,*, Manabu Homma!, Mamoru Umemura"

! Department of Management Science, Sanno College, Jiyugaoka, 6-39-15, Todoroki, Setagaya-ku, Tokyo 158-8630, Japan" Department of Industrial Engineering, Science University of Tokyo, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan

Abstract

We have studied the pointing device operation through experiments on pointing time, accuracy, mental work load, andpsychological easiness to operate. As a result, there was a difference in accuracy, pointing time and the mental work loadwith different amounts of movement of the pointing device and amounts of movement of the pointer on the screen. Thecause is that it is difficult to have eye—hand coordination. ( 1999 Elsevier Science B.V. All rights reserved.

Keywords: Pointing device; Mental work load; Operation time; Index of difficulty; Tablet

1. Introduction

As computer input devices, there is a mouse,tablet, track ball, joy-stick and touch screen avail-able, besides a keyboard. These are called pointingdevices and used for selecting menus using graphi-cal user interface (GUI), and for selecting, movingand creating objects in application software. In thecomputer-aided design (CAD) and drawing soft-ware, the operation is made by repeated pointingon the screen using pointing devices. With the in-direct-type pointing device such as a mouse, be-cause of a difference between the actual amount ofdevice movement and that of the pointer on thescreen, it becomes difficult to have eye—handcoordination, which seems to have an effect onoperation efficiency.

*Corresponding author. Tel.: #81 3 3704 4011; fax: #81 33704 7859; e-mail: ichikawa@sun.email.ne.jp.

Many kinds of pointing devices have been de-veloped. Tablet has two types. One is a conven-tional type in which the pointer on the display ismoved by moving a stylus pen on the pad on thedesk (hereinafter referred to as the indirect tablet).The other is a newly developed type in whicha stylus pen directly touches the liquid crystal dis-play for operation (hereinafter referred to as thedirect tablet). The latter is used for entering drawingsoftware as well as is used just as the touch screen.

As for input devices, there are reports on key-board operations [1,2], other pointing device op-erations [3,4], etc. But there are few reports on thedirect tablet [5]. Also a few reports have studied theoperation from the viewpoint of mental work load.

In this paper, we studied the pointing deviceoperation through experiments, from the viewpointof pointing time, accuracy, mental work load, andpsychological easiness to operate. As pointing devi-ces, the mouse and the above-mentioned two typesof tablets were used.

0925-5273/99/$ - see front matter ( 1999 Elsevier Science B.V. All rights reserved.PII: S 0 9 2 5 - 5 2 7 3 ( 9 8 ) 0 0 1 6 2 - 5

2. Methods

2.1. Experiment

Subjects are four women’s junior college studentsranging from 19 to 20 in age. The equipment usedin the experiment is a personal computer (UNISYSCWD 5001-ZE) and a display (10.4 in liquid crystaldisplay with 800 horizontal and 600 vertical pixels).The pointing devices used are;

(1) mouse: UNISYS PWM-1-1-PS2,(2) the indirect tablet: WACOM ART PAD II,(3) the direct tablet: WACOM PL-300.As the targets point, square figures were dis-

played on the screen. They were positioned at ran-dom on the screen making pairs, each of which ison the upper and lower part on the screen witha constant space between them. The procedure was:after pointing was made in the order of lower,upper and lower, a new target to point was dis-played on a new position. Fig. 1 shows the figurespointed. The distances between the upper andlower targets were 3 and 6 cm, and the side lengthsof the squares (target size) were 0.5 and 1 cm. Thepointing condition was to point d3s0.5, d3s1, d6s0.5,and d6s1 (where condition d3s0.5 represents thedistance between the targets is 3 cm and the sidelength of the target is 0.5 cm). The experiment wasmade at random and each pointing condition wasrepeated 100 times.

Fig. 1. Experimental screen.

2.2. Measured items

The pointing time is the time between pointing toone target and pointing to the next target. Theerror rate is the number of failings made by eachsubject in pointing all targets against all the point-ing numbers shown in percentage. The Heart Rate(HR) was measured by Heart Rate Memory (TAKEISCIENTIFIC INSTRUMENT CO., LTD). Theanalysis was made using HR Ratio (%). The HRRatio is the average HR during the operationdivided by the average HR during complete rest(10 min). The psychological easiness to operate wasevaluated by three grades (3: good, 2: average, 1:bad) on these five items:

(1) easiness to point (Point),(2) easiness to move (Move),(3) load to wrist, elbow, arm and shoulders

(Physical),(4) load to eyes (Eye),(5) total easiness to operate (Total).

3. Results

3.1. Pointing time

The relation between the pointing devices andthe operation time is shown in Fig. 2. The pointingtime is an average value of the time obtained fromall the pointing conditions and the subjects. Theaverage pointing times of the mouse, the directtablet and the indirect tablet were 972 , 645 and

Fig. 2. Relation between pointing time and devices.

236 H. Ichikawa et al. /Int. J. Production Economics 60–61 (1999) 235–240

Fig. 3. Relation between pointing time and pointing conditions.

954 ms, respectively. The time required by the di-rect tablet had a tendency to be shorter than theothers. There was a significant difference betweenthe direct tablet and the others (P(0.01). Therelation between each pointing condition and thepointing time is shown in Fig. 3. The pointing timeis an average value required by all devices andsubjects. The condition d3s1 required the shortesttime, 695 ms, and the d6s0.5 required the longesttime, 1029 ms (P(0.01 significant difference). Thisresult indicates that the longer the distance betweenthe targets and the smaller the size of targets, thelonger the pointing time.

3.2. Pointing accuracy

Fig. 4 shows the relation between the pointingcondition and the error rate. The error rate is an

Fig. 4. Relation between error rate and pointing conditions.

Fig. 5. Relation between HR ratio and pointing conditions.

average value made by all the subjects. The errorrate is low in the pointing condition d3s1 and d6s1when the direct tablet was used (P(0.01 signifi-cant difference). In conditions d3s0.5 and d6s0.5, inwhich the mouse was used, the error rate was high(P(0.01 significant difference). There was a ten-dency that when the target size was small, themouse’s error rate was high, and when the targetsize was large, the direct tablet’s error rate was low.

3.3. Heart rate (HR)

The relation between the HR Ratio and the point-ing condition is shown for each device in Fig. 5. Inall the pointing conditions, the HR Ratio was highfor the indirect tablet. For the direct tablet, the HRRatio was low under conditions where target dis-tances were long. Mouse did not show any largevariation even when the conditions were changed.

3.4. Psychological evaluation

Fig. 6 shows the evaluation results obtained fromquestionnaires. The mouse is highly evaluated inpointing easiness and the load to the wrist, elbow,arm and shoulder. The indirect tablet is poorly evalu-ated in pointing easiness and total easiness to operate.

3.5. Index of difficulty (ID)

Fig. 3 shows the tendency that the pointing timeis longer as the target size is smaller and longer as

H. Ichikawa et al. /Int. J. Production Economics 60–61 (1999) 235–240 237

Fig. 6. Relation between evaluation and item of questionnaires.

Table 1Relation between pointing condition and ID

Pointing conditions ID

d3s0.5 3.585d3s1 2.585d6s0.5 4.585d6s1 3.585

the distance is larger. Fitts’ index of difficulty (ID) isused as an index showing the difficulty of workusing the target size and distance as parameters[6—8]. The Fitts’ law defines the following relationbetween the ID and pointing time:

Pointing time"a*ID#b,

where ID"log2(2D/S), a and b are constants, D is

distance, and S is target size. Table 1 lists the ex-periment conditions in this study and the corre-sponding IDs.

Fig. 7 shows the relationship between the ID andthe pointing time for each device. The horizontalaxis reads the ID and the vertical axis reads thepointing time for every three types of the mouse,indirect tablet, and direct tablet. The square of R is0.081 with the mouse, 0.305 with the direct tablet,and 0.231 with the indirect tablet. The direct tabletshows the closest correlation between the ID andpointing time, and the mouse shows the least cor-relation between them.

Fig. 8 shows the relationships between the IDand pointing time for each subject under the testusing the direct tablet that shows the closest rela-

Fig. 7. Relation between pointing time and ID (each device).

tionships between the ID and pointing time. Sub-jects under this test, except subject C, show veryclose correlations between the ID and pointingtime.

The ID values turn out the same under the ex-periment conditions d3s0.5 and d6s1. This can tellthat both have the same difficulty. Table 2 lists the

238 H. Ichikawa et al. /Int. J. Production Economics 60–61 (1999) 235–240

Fig. 8. Relation between pointing time and ID in case of direct tablet (each subject).

Table 2Mean and SD of pointing time (equal ID : 3.585)

Devices Pointing conditions Mean (ms) SD

Mouse d3s0.5 901.68 203.25d6s1 1005.68 271.91

Direct tablet d3s0.5 599.15 185.42d6s1 609.12 106.56

Indirect tablet d3s0.5 842.95 184.72d6s1 847.10 153.98

mean and SD values for individual devices underthese two conditions. The mouse shows that boththe pointing time mean and SD values increase asthe distance becomes longer (P(0.01 significantdifference). The tablet shows almost no change inthe mean values (no significant difference) butshows the tendency that the SD value becomeslarger as the target size is smaller.

4. Discussion

As for the pointing time, the direct tablet isshorter than the mouse and indirect tablet, whichwas a common tendency in each pointing condi-tion. This tendency is supposed to be because in themouse and indirect tablet, the amount of devicemovement is different from that of the pointermovement on the screen, complicated coordinationbetween eyes and a hand is required [9]. On theother hand, it is supposed that in the direct tablet,the spot is directly pointed on the screen just asworking on a sheet of paper with a pen, resulting ina shorter pointing time than the other devices.When arranging pointing times for each pointingcondition in shorter to longer order, it will be d3s1,d3s0.5, d6s1, and d6s0.5. It can be said that thelonger the operation time, the harder the operation.

As for the error rate, the mouse is higher in anypointing condition, especially for d3s0.5 and d6s0.5.This suggests that the mouse is not suitable for

H. Ichikawa et al. /Int. J. Production Economics 60–61 (1999) 235–240 239

pointing operation requiring high accuracy. Thedirect tablet is lower in error rate than the otherdevices in pointing conditions d3s1 and d6s1. It canbe said that the direct tablet exceeds the otherdevices in error rate when high accurate pointing isnot required.

The average HR Ratios for each device are:mouse 102.9%; direct tablet 101.4%; indirect tablet105.1%. The direct tablet ranks lowest, especiallylow in pointing condition d6s0.5 and d6s1 in whichthe moving distance is long. It is supposed that thedirect tablet can be operated just as a pen andpaper, which reduces mental work load as dailymovement.

Although the mouse can hardly be said to bea suitable device from the angle of the operationtime and error rate, it obtained high psychologicalevaluation for all the items. This is supposed to bebecause the subjects working at this time usuallyuse mouse and consequently have more friendlyfeelings toward it.

In terms of the ID, the direct tablet has a closercorrelation than the other devices. This may beexplained by the thinking that the direct tablet,which allows a pen to run directly on the liquidcrystal display, eases visual feedback. Under experi-ment conditions with equal ID values, the directtablet shows larger SD values as the target size issmaller. This is because the tip of the pen hides thetarget. It can be said that the direct tablet is notsuitable for high-precision pointing.

Among the pointing devices taken up this time,the direct tablet can be said as a better device inpointing time and pointing accuracy unless highpointing accuracy is required.

5. Conclusion

We have studied pointing device operationthrough experiments on pointing time, accuracy,mental work load, and psychological easiness tooperate, and found the following matters:

(1) The direct tablet has a tendency to havea shorter pointing time than the other devices.

(2) There is a tendency that when the target size issmall, the mouse’s error rate is high, and when thetarget size is large, the direct tablet’s error rate is low.

(3) From the studied HR Ratio, it is supposedthat the direct tablet can be operated just as a penand paper, which reduces mental work load asdaily movement.

(4) In psychological easiness to operate, themouse obtained high evaluation.

(5) In terms of ID, the direct tablet has a closercorrelation than the other devices.

Our next target is to increase the number ofsubjects and to further study from the other pointof view, such as the easiness to become skilled inoperation.

Acknowledgements

We thank WACOM Co., Ltd. for providing thepointing devices for the experiments.

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