IEEE TRANSACTIONS ON HUMAN FACTORS IN ELECTRONICS, VOL. HFE-8, NO. 1, MARCH 1967
`
`5
`
`Display-Selection Techniques for Text Manipulation
`
`WILLIAM K. ENGLISH, MEMBER, IEEE, DOUGLAS C. ENGELBART, MEMBER, IEEE,
`AND MELVYN L. BERMAN
`
`Abstract-Tests and analysis to determiine the best display-
`selection techniques for a computer-aided text-manipulation system
`reveal that the choice does not hinge on the inherent differences in
`target-selection speed and accuracy between the different selection
`devices. Of more importance are such factors as the mix of other
`operations required of the select-operation hand, the ease of getting
`the hand to and gaining control of a given selection device, or the
`fatique effects of its associated'operating posture.
`Besides a light pen, several cursor-controlling devices were
`tested, including a joystick and an SRI-developed device known as
`a "mouse." The study was aimed directly at finding the best display-
`selection means for our own text-manipulation system but generali-
`zations applicable to other types of on-line systems were derived.
`
`1. INTRODUCTION
`This paper describes an experimental study into
`la
`the relative merits of different CRT display-selection
`devices as used within a real-time, computer-display,
`text-manipulation system in use at Stanford Research
`Institute.
`Briefly, we have developed a comprehensive on-
`lal
`line text-manipulation system. We wanted to determine
`the best means by which a user can designate textual
`entities to be used as "operands" in the different
`text-manipulation operations.
`Techniques and devices for display-entity operand
`1a2
`selection represent a major component in any display-
`control scheme, and are readily isolated for purposes
`of comparative testing, once the procedural environment
`in which selection is done has been established.
`laS An important conclusion of our experimentation
`is that this environment has considerable effect upon
`the choice of display-selection means for a given
`display-control system.
`lb Our text-manipulation system is designed for daily
`usage, and our experiments and conclusions stem from
`extensive personal experience as users as well as designers.
`Ibl To emphasize this, we point out that for two
`years we have been using the system for producing
`most of the internal memos-and all of the proposals
`and reports-associated with our research program.
`This paper itself was extracted from one of these
`lb2
`reports-reorganized and modified by use of the system.
`See 1 (ENGLISH 1).
`lbS The format and writing style which represent
`an important experimental component of our research,
`are left in the form with which we work.
`
`Manuscript received December 2, 1966.
`The authors are with the Stanford Research Institute, Menlo
`Park, Calif.
`
`IbSa Statements-be they subheads, phrases, sen-
`tences, or paragraphs-are numbered and presented
`in hierarchical order. These statement numbers are
`one "handle" by which a statement may be grasped
`for any of the operations performed on- or off-line.
`lbSb
`References, which appear in the Bibliography
`at the end of the paper, are shown in the text
`by a mention of their statement numbers "see
`1 (ENGLISH 1)", rather than by the more familiar
`superscript notation.
`lc The tests of the display-selection devices simulated
`the general situation faced by a user of our on-line system
`when he must interpose a screen-selection operation into
`his on-going working operations. See Fig. 1 for a layout
`of the on-line work station.
`
`Fig. 1.
`
`The oii-line system work station showing the CRT display,
`keyboard, pushbuttons, and mouse.
`
`Icl The user has generally been entering information
`on the typewriter-like keyboard.
`/c2 To begin making the screen selection, his right
`hand leaves the keyboard and takes hold of ("accesses,"
`in our terminology) the selection device.
`lcS By moving this device he controls the position on
`the screen of an associated tracking mark (or "bug"),
`placing it over the "target' text entity.
`/c4 He then actuates a pushbutton associated with
`the particular selection device, to tell the computer
`that he is now "pointing at" the target entity.
`1c5 The computer puts a special mark under the
`entity which it determines as having been selected,
`
`SCEA Ex. 1017 Page 1
`
`

`

`6
`
`IEEE TRANSACTIONS ON HUMAN FACTORS IN ELECTRONICS
`
`MARCH
`
`Fig. 2.
`
`Bug-positioning devices from left to right: joystick,
`Grafacon, and mouse.
`
`to give the user an opportunity to see if a correct
`selection has been made.
`ld We designed and conducted our experiments in order
`to learn more about the following characteristics of the
`operand-selecting devices currently available in our on-
`line system:
`ldl The comparative speed with which they could be
`used to select material on the display screen. Two
`kinds of time period were measured:
`"Access time": the time it takes for the user
`ldla
`to move his hand from the keyboard to the operand-
`selecting device.
`"Motion time": the time period beginning with
`ldlb
`the first movement of the bug and ending with the
`"select" action fixing the bug at some particular
`character position.
`1d2 The comparative ease with which an untrained
`user could become reasonably proficient in using the
`various devices.
`ldS The comparative error rates of the various devices.
`2. DESCRIPTION OF THE DEVICES TESTED
`2a The tests included both a light pen and various
`devices to position a cursor (or "bug" as we call it)
`on the CRT screen.
`Operand entities displayed on the screen are
`2a]
`chosen by selecting a character within the operand
`entity (word, line, or statement).
`2a2 The light pen or bug is first located near the
`desired character, then the SELECT switch on the
`device is depressed (or in the case of the knee control
`a special "CA" key on the keyboard is struck).
`Grafacon (see Fig. 2):
`2bl The Grafacon was manufactured by Data Equip-
`ment Company as a graphical input device for curve
`tracing. See 2 (FLETCHER 1). The particular device
`that we tested is no longer marketed under this name.
`
`2b
`
`Fig. 3. Bottom side of mouse, showing mechanical details.
`
`Data Equipment Company now markets the Rand
`Tablet under the name "Grafacon." See 3 (DAVIS 1).
`It consists of an extensible arm connected to a
`2b2
`linear potentiometer, with the housing for the linear
`potentiometer pivoted on an angular potentiometer.
`2b2a The voltage outputs from the Grafacon repre-
`sent polar coordinates about the pivot point, but
`are interpreted by the system exactly as the outputs
`from the "mouse" or joystick, which represent rec-
`tangular coordinates.
`This means that to trace a straight line across
`2b2b
`the screen with the bug, the user must actually move
`his hand in a slight arc.
`2b2c We planned to program polar-to-rectangular
`conversion into our bug-tracking process, but we
`initially coupled the Grafacon "directly" (i.e., with
`this geometric "tracking distortion") to get a general
`feel for its performance. We found no evidence that
`the user was aware of this distortion and never did
`write the conversion routine to eliminate it.
`2b3 A knob on the Grafacon arm is moved about by
`the user, and is depressed to activate the select switch
`(added by SRI) associated with the Grafacon.
`originally obtained was
`2b3a The Grafacon as
`equipped with a pen mounted on the potentiometer
`arm. This was replaced with a knob to better suit
`our purposes.
`2c Joystick (see Fig. 2):
`2c1
`The joystick that we used was manufactured by
`Bowmar Associates (Model X-2438).
`constructed from two potentiometers,
`2c2
`It
`is
`mounted perpendicularly and coupled to a vertical
`stick in such a way that they resolve the motion of the
`stick into two components.
`
`SCEA Ex. 1017 Page 2
`
`

`

`ENGLISH ET AL.: DISPLAY SELECTION FOR TEXT MANIPULATION
`
`7
`
`Fig. 5.
`
`Light pen.
`
`disks in planimeters or in the old-fashioned mechan-
`ical differential analyzers.
`2d4 A travel of about five inches is required for full
`edge-to-edge or top-to-bottom coverage of the CRT
`screen.
`2d5 A switch mounted on the case is used for the
`select function.
`
`2e Knee Control (see Fig. 4):
`2el A preliminary model of a knee control was made
`for this research.
`It consists of two potentiometers and associated
`2e2
`linkage plus a knee lever. The linkage is spring-loaded
`to the right and gravity-loaded downward.
`2eS The user pushes the lever with his knee; a side-
`to-side motion of the knee moves the bug edge-to-edge,
`while the top-to-bottom bug movement is controlled
`by an up-and-down motion of the knee (i.e., a rocking
`motion on the ball of the foot).
`
`2f
`
`Light Pen (see Fig. 5):
`2fl The light pen used was manufactured by Sanders
`Associates of Nashua, New Hampshire (Model EO-CH).
`2f2
`It consists of a hand-held pen coupled to a photo-
`multiplier tube by a fiber optic bundle.
`2f3 The pen is pointed at the desired character on
`the CRT screen with the aid of a projected circle of
`orange light indicating the approximate field of view
`of the lens system.
`2f3a A switch on the pen unit is used for making
`the selection.
`
`3. DESCRIPTION OF THE EXPERIMENTS
`3a The experiments were designed to test the various
`operand-selecting devices under conditions similar to those
`that the user would encounter when actually working
`on-line.
`However, certain features of the live working
`Sal
`conditions were not closely related to the actual effi-
`ciency of the operand-selecting devices, such as
`
`Fig. 4.
`
`Knee control bug-positioning device.
`
`2c2a The original stick was 12 inches long; a 3 inch
`extension to the shaft, housing a switch actuated by
`pressing down on the stick itself, was added by SRI.
`Two modes of operation with the joystick were
`Wc3
`implemented:
`2c6a An "absolute" mode, in which the bug's
`position on the screen corresponds to the position
`of the joystick handle; and
`2cSb A "rate" mode, in which the bug's direction
`of motion is determined by the direction of joystick
`handle deflection, and the bug's rate of motion is
`determined by the amount of joystick deflection.
`2d Mouse (see Fig. 2):
`2dl The "mouse" was developed by SRI in connection
`with this research.
`2d2 It
`is
`constructed from two potentiometers,
`mounted orthogonally, each of which has a wheel
`attached to its shaft (see Fig. 3).
`2d2a The mounting frame for the potentiometers
`is enclosed in a 2 inch X 3 inch X 4 inch wooden case.
`2d3 As the case is moved over a surface (e.g., the
`table surface in front of a display)
`2d3a
`the wheels ride on the surface and turn the
`potentiometer shafts, with a combined sliding and
`tuming action depending upon the relative orientation
`of the motion and the wheel axes,
`2dSb
`to resolve the motion into two orthogonal
`components in much the same manner as do the
`
`SCEA Ex. 1017 Page 3
`
`

`

`S
`
`IEEE TRANSACTIONS ON HUMAN FACTORS IN ELECTRONICS
`
`MARCH
`
`(a) "Character Mlode" operation showing the target
`(Middle X) and bug (plus sign).
`
`(b) "Word Mode" operation. The target is the middle
`five X's.
`
`(e) An incorrect selection is underlined. The configuration
`of X's and the bug remain on the display.
`
`(d) A correct selection. The position of the target is
`indicated by the bug mark and underline.
`
`Targets used to experimentally evaluate the operand-locat-
`Fig. 6.
`ing devices and results of an incorrect and correct selectioll.
`
`Tlle need to cnter literal input from the
`Sala
`keyboard,
`3alb The need to designate commands, and
`3aic The user's indecision in choosing which display-
`ei.tity to select.
`3a2 We tried either to eliminate these features from
`the experimental environmenit, or to fix them in some
`standard way throughout the experiment.
`"targets"
`display-entity
`kinds
`of
`3b Two different
`were presented in the experiments: "word" targets and
`"character" targets. The target patterns presented to
`the subject were configurations of x's rather than actual
`text.
`Sbl A configuration simulating the "character mode"
`operation of the system consisted of ninie x's, in a
`three by three array, with the array as a whole randomly
`placed on the display. The speeific target entity was
`the middle x [see Fig. 6(a)].
`
`3b2 A configuration simulating the "word mode"
`operation of the system consisted of nine groups of
`five x's each, in a three by three "word" array, with
`the array as a whole randomly placed on the display.
`The target entity was any one of the five middle x's
`[i.e., any character in the middle " word"; see Fig. 6(b)].
`3c The subject was given a series of tests with each of
`these two types of target, and was to perform the following
`task sequence:
`3cl When the target appeared on the display screen,
`the subject was to strike the keyboard space-bar with
`his right hand, causing the bug to appear on the
`display. (Requiring that he use his right hand for both
`the space bar and the operand-selecting device made
`the experimental task closer to the actual on-line
`environment, where the user would often have both
`hands at the keyboard before moving to the operand-
`selecting device. It also gave us a way of measuring
`the access times for the various devices.)
`
`SCEA Ex. 1017 Page 4
`
`

`

`9
`1967
`ENGLISH ET AL.: DISPLAY SELECTION FOR TEXT MANIPULATION
`During the second time period, the subject
`3c2 The subject was then to move his hand to the
`3dlf
`proceeded backward through the list of devices,
`bug-positioning device being tested, and use it to
`begining with the last device he had used in the pre-
`guide the bug to the target entity on the display.
`vious time period, then using the next-to-last device,
`3c3 When the bug and the target coincided the subject
`and so on.
`was to "fix" the bug at that location, using the select
`Sdlg Each subject began with a different device
`switch of the bug-positioning device.
`and was presented with devices in a different order.
`3c3a An incorrect selection was signalled by a bell,
`For inexperienced subjects, the experimental pro-
`and the incorrectly selected entity was underlined
`3d2
`in the displayed target pattern [see Fig. 6(c)]; the
`cedure was somewhat different:
`subject was then to relocate the bug and reselect
`3d2a The subject was given an explanation of the
`the target entity.
`experiment, the target patterns, and the way the
`3c3b A correct selection caused the target to dis-
`particular operand-selecting device worked. He was
`appear, and the word "CORRECT" to appear on
`allowed to get the feel of the device, but was not
`6(d)]. About three
`the display screen [see
`Fig.
`given a practice period. He was then presented with
`seconds later, the next target pattern was displayed
`ten sequences of eight target-patterns each, in the
`(in some new randomly-determined position), and
`"character" mode.
`the process was repeated.
`3d2b
`This procedure was followed for each of the
`3c4 When the light pen rather than a bug-positioning
`devices being tested.
`3d2c Each subject began with a different device,
`device was used, the task sequence was much the same:
`after the target appeared, the subject was to strike
`and was given a different order of devices to work
`the keyboard space bar with his right hand, then grasp
`with.
`the light pen and point it at the target entity (with the
`3e The computer was Lised extensively in conducting
`aid of the finder beam). The subject "fixed" his choice
`these experiments: for preseating target patterns, sig-
`by depressing the select switch on the light pen. Correct
`nalling of correct and incorrect selections, determining
`and incorrect selections were signaled in the same way
`the (random) position of the next target pattern, deter-
`as with the bug-positioning devices.
`mining the short time-delays between a correct selection
`and the presentation of the next target, etc. In addition,
`There were two groups of subjects: eight "experi-
`3d
`for each presentation-selection event, the computer re-
`enced" subjects who were already somewhat familiar
`corded the following information on magnetic tape for
`with the on-line system, and three "inexperienced"
`later analysis:
`subjects who had never before used either the system or
`the particular devices being tested. The experienced group
`3e1
`The position of the bug (in relation to the target
`were given experiments to test the devices after a reason-
`entity) was recorded each 10 milliseconds.
`able amount of practice. The inexperienced group were
`3e2 The times the subject hit the space bar, and the
`tested to see how quickly and how well they learned to
`times he made either a correct or an incorrect entity
`use the devices without previous practice.
`selection, were recorded and appropriately tagged to
`aid in identifying these significant points in the late
`For the experienced subjects, the entire testing
`3d1
`data analysis.
`procedure, which was broken into two time periods,
`proceeded as follows:
`3f The length of the experimental runs; the rest periods
`allowed between runs; the order in which the various de-
`3dla The subject was given a brief explanation of
`vices were tested; and the modes of operation ("character"
`the experiment and the target patterns.
`or "word" targets) were controlled by the person con-
`3dlb He was then given his first device and allowed
`ducting the experiments.
`to practice.with it for about two minutes.
`3dlc Next he was tested using this first device,
`4. DESCRIPTION OF THE DATA ANALYSIS
`in both the "word" mode and the "character" mode
`4a The analysis software was designed to allow flexibility
`of selection. Thirty-two targets of each type were
`in studying individual performance curves and results.
`presented.
`This software provided operator commands for scanning
`3dld After a two-minute rest period, the subject
`the recorded data on the magnetic tape, selectively
`was given his second device and allowed to practice
`printing out results, producing CRT-displayed curves
`with it for about two minutes. He was then tested
`of each subject's performance, and calculating certain
`with this device-again, with 32 targets of each type.
`averages over a block of tests.
`This same sequence of rest, practice, and
`3dle
`4a1
`testing was carried out for each of the devices being
`Tape-handling operations,
`controlled by com-
`mands from the on-line keyboard, facilitate searching
`tested. This constituted the first time period of the
`through the data recorded on the magnetic tapes.
`experiment.
`
`SCEA Ex. 1017 Page 5
`
`

`

`10
`
`IEEE TRANSACTIONS ON HUMAN FACTORS IN ELECTRONICS
`
`MARCH
`
`(a)
`
`Fig. 7.
`
`Analysis curves of the experiments.
`
`(b)
`
`These commands allowed one to scan forward or
`(or, an
`backward by one 32-target block of tests
`8-target block, in the records for inexperienced subjects);
`and, within that block, to scan forward or backward
`one target (i.e. one presentation-selection event) at
`a time.
`4a2 For each target-fix, the CRT could display a
`graph showing the bug's distance from its target
`entity as a function of time. This was displayed as two
`curves (see Fig. 7), one showing variation with time of
`horizontal distance, and the other of vertical distance.
`The time-count was begun when the target appeared
`on the display. Vertical lines on the curves mark the
`time at which the space bar was struck and the time
`at which the target was correctly selected. Incorrect
`selections are shown as x's on the curve.
`Figure 7 presents two examples of these
`4a2a
`curves. Figure 7(a) shows a typical performance
`curve for the Grafacon; Fig. 7(b) shows an example
`of joystick performance in which the subject made
`several errors before selecting the correct target
`entity.
`4a2b When viewed on-line on the CRT display,
`the scale of these curves can be changed by keyboard-
`entered commands that independently change either
`the distance or the time scale. This time scale change
`feature was included because of the radical variations
`in the times, among various devices and various
`subjects. The distance scale change allows detailed
`examination of performance when the bug is near the
`target.
`4aSb When studying a given target-fix event, the
`experimenter can, if he wishes, initiate output (to
`the on-line typewriter) of performance data: the
`time at which the space bar was struck, the time at
`which the bug movement began, the time at which
`the target was correctly selected, and the number
`of errors (incorrect selections) made. This software
`also computed and printed out the following incre-
`mental times: the access time (from the time the
`space bar was struck until the time the bug movement
`
`began, measuring how long it took the subject to
`move his hand from the keyboard to the device);
`the motion time (from the time the bug began moving
`until the time the target was correctly selected);
`and total time (from the time the space bar was struck
`until the time the target was correctly selected-i.e.,
`the sum of access time plus motion time).
`Finally, there is another command which causes
`4a4
`the computer to search through a 32-target block of
`target fixes and compute (for output to the on-line
`typewriter) the average incremental times, and total
`number of errors, for that block.
`could be
`distance-vs.-time
`4b The CRT curves of
`scanned with the on-line system, in order to determine
`where the subjects spent most of their time; how much
`time they spent in actually selecting the target entity
`after the bug was already positioned correctly; whether
`the errors seemed more predominant in one direction
`than in another (horizontally or vertically); and other
`such detailed information relating to individual per-
`formances.
`4c The numerical averages computed with the help of
`the rest of the analysis software were collected and
`summarized as experimental results, presented in the
`following description.
`
`5. EXPERIMENTAL RESULTS
`5a Summary data: Figs. 8 through 10 contain the bar
`charts comparing the various operand-selecting devices
`with respect to the time required for a correct selection.
`Figures 8 and 9 are taken from the results of
`5a1
`the eight experienced subjects, some of whom were
`very familiar with the on-line system and had used the
`devices often. Figure 8(a) shows the average total
`time (for all experienced subjects) required for a correct
`selection of the "character" target, with no penalty
`for errors; Figure 8(b) shows the results of the same
`tests with a 30 percent penalty for errors. Figure 9(a)
`and 9(b), respectively, show the same for the "word"
`target.
`
`SCEA Ex. 1017 Page 6
`
`

`

`1967
`
`ENGLISH ET AL.: DISPLAY SELECTION FOR TEXT MANIPULATION
`
`3 rn
`
`JOYSTICK
`(ABSOLUTE)
`
`3
`
`11
`
`JOYSTICK
`(ABSOLUTE)
`
`LIGHT
`
`GRAFACON
`P..................
`I...............
`
`PEN
`
`MOUSE
`
`cnla2C
`o
`
`0c
`
`a,I
`
`0
`
`0
`
`GRAFACON
`
`LIGHT
`PEN
`
`MOUSE
`
`U) 2l0
`(AI
`
`LLJ
`
`H
`
`0
`
`(a)
`
`(b) 30% PENALTY FOR ERRORS
`NO PENALTY FOR ERRORS
`Comparison of the operand-locating devices for "experi-
`Fig. 8.
`enced" subjects, "Character Mode" operations.
`
`3
`
`JOYSTICK
`GRAFACON (ABSOLUTE)
`
`GEN
`
`MOUSE
`
`U)
`
`0,
`
`H.!
`
`C02o~~~~~~~~~~~~~~~~c
`U)I
`
`JOYSTICK
`GRAFACON (ABSOLUTE)
`-
`:
`k
`
`LIGHT
`PEN
`
`MOUSE
`
`((a)
`
`(b) 30% PENALTY FOR ERRORS
`NO PENALTY FOR ERRORS
`Comparison of the operand-locating devices for "experi-
`Fig. 9.
`enced" subjects, "Word Mode" operation.
`
`0
`
`JOYSTICK
`(RATE)
`
`JOYSTICK
`(RATE)
`
`6
`
`5
`
`4
`
`13
`
`2
`
`-
`
`0
`
`(b) 30% PENALTY FOR ERRORS
`Xa ) NO PENALTY FOR ERRORS
`Comparison of the operand-locating devices for "inex-
`Fig. 10.
`perienced" subjects, "Character Mode" operation.
`
`3
`
`12C
`0
`
`I
`
`H-
`
`o
`
`6
`
`5
`
`4.
`
`c 1
`
`3w
`
`2
`
`0
`
`SCEA Ex. 1017 Page 7
`
`

`

`12
`
`IEEE TRANSACTIONS ON HUMAN FACTORS IN ELECTRONICS
`
`NIANCH
`
`LIGHT
`PEN
`
`JOYSTICK
`(ABSOLUTE)
`-_
`
`GRAFACON
`
`0.3 r-
`
`0.2 F-
`
`0.1
`
`O L
`
`w
`
`0 c
`
`r
`11
`
`JOYSTICK
`(ABSOLUTE)
`
`GRAFACON
`
`w
`
`rff0
`w
`
`0.3,
`
`0.2 1-
`
`0.1 [-
`
`MOUSE
`
`0 I...
`
`(a)
`
`CHARACTER MODE
`
`(b) "WORD MODE OPERATION
`OPERATION
`Error rates for "experienced" stibjects.
`Fig. 11.
`
`0.3
`
`Lb 0.2 _
`
`KNEE
`JOYSTICK
`CONTROL (ABSOLUTE)
`
`JOYSTICK
`(RATE)
`
`LIGHT
`PEN
`
`0.1
`
`0
`Fig.
`
`~~~~~~~~~~~~~~..
`
`.
`
`.
`
`..........
`
`12.
`
`Error rate
`
`for "inexperienced"
`Mode" operation.
`
`subjects,
`
`"Character
`
`5ala The 30 percent error penalty is an approximate
`figure arrived at by the following argument: if a
`user wished to correct an incorrectly selected operand,
`he would need to strike the "Command Delete"
`key with his other hand before re-attempting a
`correct operand selection. This would take about
`as long as the time required to strike the space bar
`when the target first appeared. From the experiments
`we found that the time required to strike the space
`bar accounted for about 30 of the total time. Thus
`we computed the time for the error-penalty graphs
`by multiplying the subject's error rate on that device
`by 30 percent of his average time, and adding that
`figure to the total time.
`Figure 10 shows the results from the tests of
`5a2
`subjects who had had no previous experience with the
`devices. Figure 10(a) imposes no penalty for errors.
`Figure 10(b) imposes a 30 percent penalty for errors,
`as explained above.
`Figures 11 and 12 compare the error rates for
`5a3
`the various devices. Figure 11 shows the results for
`the "character" and "word" tests, as performed by
`experienced subjects
`(using four different operand-
`locating devices); Figure 12(a) shows the results of the
`
`"character" tests for inexperienced subjects (using six
`different operand-locating devices).
`
`5b
`These results indicate that for the more experienced
`subjects the mouse was both faster and more accurate
`than any other device-including the light pen. Inex-
`perienced subjects, however, tended to perform better
`with both the light pen and the knee control than with
`the mouse.
`
`5b1 As mentioned above, the knee control was not
`developed soon enough to include it in the tests for
`the experienced subjects (where we included only devices
`that had been available for some time, in order to
`avoid bias). We did, however, perform a few individual
`check tests with experienced subjects, using the knee
`control; in these tests the knee control appeared both
`slower and less accurate than the light pen and mouse.
`Inexperienced subjects found the knee control
`5b2
`was the fastest device. Undoubtedly the main reason
`for this was that the knee control, unlike all the others,
`has no access time. (If the access time is subtracted from
`the total times measured for the other devices, the
`knee control no longer show up so favorably.)
`Inexperienced subjects also found the light pen
`5b5
`
`SCEA Ex. 1017 Page 8
`
`

`

`13
`1967
`ENGLISH ET AL.: DISPLAY SELECTION FOR TEXT MANIPULATION
`that for some tests the intensity of the displayed
`faster than the mouse. A reason for this may be that
`targets was too high, making it easy for the pen to
`the light pen exploits one's inherent tendency to select
`pick up light from an adjoining character. This
`something by straightforwardly "pointing" at it rather
`difficulty could be overcome, and the overall per-
`than by guiding a bug across a screen toward it from
`formance of the light pen improved, if computer
`a remote control. This means that an inexperienced
`feedback were provided, to indicate to the subject
`subject can become reasonably proficient in using a
`which character the pen was actually detecting.
`light pen with relatively little practice.
`5b4 The joystick proved to be both the slowest and
`5d We initially expected to find that the starting
`the least accurate of the devices we tested, in both
`distance between the bug and its target entity on the
`modes of its operation ("absolute" and "rate"), and
`face of the display would significantly affect the motion
`among both the experienced and inexperienced subjects.
`time required for selecting the target.
`It is interesting to note, however, that both the
`5b5
`5d1
`However, the results compiled and plotted -to
`joystick and the Grafacon showed up more favorably
`test this hypothesis did not show any significant
`(relative to the other devices) when used to select
`correlation.
`word entities rather than character entities. These two
`5d2 An examination of the CRT-displayed perform-
`devices seem to perform better where fine control is
`ance curves suggests that this may be because the time
`less critical; they can move into range quickly at the
`to move the bug close to the target is relatively small
`grosser level.
`compared to the average access time, and to the average
`5c There were some obvious defects in the particular
`time required for selecting the target after the bug has
`devices tested. For this reason, and because of the very
`been moved close to it.
`limited nature of the tests, we should be careful not to
`apply these results to the class of device used, but only
`Examination of the CRT-displayed curves (distance
`5e
`to the particular examples that were tested.
`from target as a function of time) allows several other
`observations as well:
`5c1
`Both the Grafacon and joystick suffer from a
`lack of independence in the actions required to actuate
`5e4
`In using the Grafacon and the joystick (rate
`the select switch and to move the bug. By contrast,
`mode), the subjects tended to overshoot the target,
`the mouse is moved by an action of the entire hand,
`losing a significant amount of time in changing the
`while the switch is easily operated by one finger and
`bug's direction and bringing it back into position for
`does not tend to cause bug motion.
`a select action.
`5c2 With the joystick the scale factor between bug
`While our experiments did not provide a measure
`5e2
`motion and device motion was about 4:1 for a normal
`of access time for the light pen, we found (from ob-
`finger position on the stick; for the mouse and Grafacon,
`serving the subjects) that a good deal of time was
`the scale was about 2:1. This may have contributed
`consumed in reaching from the keyboard to grasp the
`to the lack of fine control (and high error rate) for
`light pen.
`the joystick.
`5e3 Though the knee control showed up well in its
`5c3 The rate mode with the joystick is very poor,
`performance as compared with the other devices, an
`partly because of the software implementation.
`examination of its CRT-displayed curves shows that
`its operation is relatively unsmooth; the bug tends
`5c3a We used a nonlinear relationship between
`to move erratically, and it appears to be difficult to
`deflection and rate of bug motion (approximating a
`move the bug vertically on the display.
`square law), and left too much dead space around
`the center position of the stick. This made large bug
`gained by asking the
`5f Our other source of "data"
`motions very easy, but too much stick motion was
`subjects how they liked the various devices-reveals that
`involved in changing directions.
`the light pen, while operating in a natural way, does tend
`In the experiments one reason for the very
`5c3b
`to be fatiguing; and that the mouse-though it requires
`high error rate in this mode is that the subjects
`some practice-seems to be a satisfying device to use
`tried to "catch" the target on the way past, to avoid
`(accurate, and non-fatiguing).
`changing direction.
`6. CONCLUSIONS
`5c4 The light pen may have showed up poorly for
`6a Some specific conclusions about the relative merits of
`several reasons.
`the devices.
`5c4a The mounting was somewhat clumsy and the
`6al
`The operand-selecting devices that showed up
`subject had to reposition the pen on this mounting
`after each target selection, returning to the keyboard
`well in our tests were the mouse; the knee control;
`and the light pen. These three were generally both
`in time for the next target presentation. This tended
`faster and more accurate than the other devices tested.
`to cause hurried motions, and may have resulted in
`Inexperienced subjects did not perform quite as
`many of the incorrect selections made.
`6a2
`well with the mouse as with the light pen and knee
`5c4b A second reason for the higher error rate is
`
`SCEA Ex. 1017 Page 9
`
`

`

`14
`
`6b
`
`IEEE TRANSACTIONS ON HUMAN FACTORS IN ELECTRONICS
`control, but experienced subjects found the mouse the
`Then it must be seen which basic-device approach can
`"best" of the devices tested, and both groups of subjects
`best provide this.
`found that it was satisfying to use and caused little
`Comparative comments of a general sort can
`6b5
`fatigue.
`follow these observations:
`6a3 The select switches on both the Grafacon and
`For the light pen, there is enough less freedom
`6b5a
`joystick tended to move the bug and cause an incorrect
`to vary the above-listed design factors (than there
`fix. These two devices could probably be improved by
`is for the other devices) that its probability of being
`redesigning their select switch mechanisms.
`the best candidate diminishes appreciably.
`6a4 Although the knee control was only primitively
`6b5b Any final, significant differences between best
`developed at the time it was tested, it ranked high in
`designs for joy stick, Grafacon, and mouse are
`both speed and accuracy, and seems very promising. It
`not descernible now.
`offers the major advantage that it leaves both hands
`6b5c The fact that a no-hands bug-control device
`free to work at the keyboard.
`can allow both hands to remain on the keyboard
`6a5 The major advantage of the light pen appeared
`is an important factor in its consideration