Evaluation of mouse, rate-controlled isometric joystick, step keys, and text keys, for text selection on a CRT

Four devices are ev aluated with respect to how ra pid ly they can be used to sc lccl text on a CRT di splay. The mouse is fo und to be fastest on all counts and also to have the lowest error rales.lt is shown Ihat varia tions in positioning time with the mouse and joystick are accounled ror by Fills's Law. In the case of the mouse. Ihe measured Fins's Law slope oonSlanl is close to that found in other eye-hand tasks leading to the conclusion thai positioning time wi th this device is almost the mini mal achievable_ Positionin~ lime fo r key devices is shown 10 he rropo rlion~l 10 Ihe number of keystrokes which must be Iyped . I. Introduction An important e lement in the design of the man·compute r inte rface is the method of pointing by which the usc r indicates to the computer hi s se lection of some e lement o n the computer display_ This is especiall y imporlant fo r compute r·bascd text-editing where the user may repeatedly usc a pointing device to sc lect the te xt he wi shes to modify or to invoke a command from a menu displayed o n the screen. The choice of pointin g device may have a signifi cant impact on the ease with which the selections can be made, and hence, since pointing typica ll y occurs with hi gh freque ncy, on the success of the entire system. English, Englebart, and Be rman (1967) measured mean pointing times and erro r rates for the mouse, li ghtpen, Grafacon tablet, and posi ti on and rate joysticks. They found the mouse to be the fastest of the devices, but did not in ves ti gate the effect of d ista nce tQ target. They a lso gave no indication or the variabili ty of their measures. Goodwin ( 1975) measured poi nti ng times ro r the lightpen, lightgun, and Saunders 720 step keys. She found the light pen and lightgun equally fa st and much superior to the Saunde rs 720 step keys. Howeve r, she used only o ne target size and did not investiga te distance. In addition, her result s also show large learni ng effects which are confounded with the device comparisons. Both studies were more concerned with the evaluation of devices than with the development of models fr om which performance could be predic ted . In another line of development Fitts and others (Fi tt s 1954, Fitts and Peterson 1964, Fitts and Radford 1966, Knigh t and Dagnal 1967, Welford 1968) developed and tested the relation between di stance, size of ta rget, and hand move ment time. Such a re lation might potentiall y be used to predict pointing times for devices involving continuous hand moveme nts; ho wever this has no t been tesled directl y_ In particular it was not known whether Fitts's Law would hold for targe ts of the shape and charac ter of tex \ strings. The present report ex amines text se lection performance with four devices: the mo use, a rate-controlled isometric j oystick, step keys, and tex t keys. The study differs fr o m the English e ( ,d. a nd Goodwin studies in that distance, target size, and learning are all si multaneously controlled a nd a diffe rent set of devices is measured. Also, unlike those studies, an attempt is made to give a theoreti cal account of the results. In particular, performance o n the continuous move men t d evices is te sted against the predictions of Filts's Law.