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LC 90 .... - _ ............ Technical RepotFigrMovements in Transcription Typing_ 4/79 -. 3/80

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Typing Analysis of MovementControl of Movement Models of MovementMotor Movefent '

20. ABISTRACT (Continue an faors* aide It n*4ee047 And fdoniIf 6Y block umlbor)

-- High speed films and key press latencies of a skilled typist show thatfinger movements usually overlap in time. The starting time of thesemovements is highly variable, even when comparing Identical sentences.Often mvemens toward keys were initiated out of the order in which theletters were eventually typed. These results conflict with current modelsof rapid, well-learned motor movements.-

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fingermovemetsus all koerlpi-im.Tesarig&meo hs

Finger Movements In Transcription Typing

Donald R. Gentner

Jonathan Grudin

Blean Conway

DTICS ELECTE

JUN 2 5 8WD

B

* CENTER FOR HUMAN INFORMATION PROCESSINGLA JOLLA, CALIFORNIA 92093

UNIVERSITY OF CALIFORNIA, SAN DIEGO

This research was supported by the Advanced Research Projects Agency and the Office of Naval Research, Personnel and TrainingResearch Programs and was monitored by ONR under Contract NO0014-79-C-0323, NR 15 7-437, under terms of ARPA Order No. 376 ZThe views and conclusions contained in this document are those of the authors and should not be interpreted as necesmrily representingthe offlcial polis, either expressed or Implied, of the Advanced Research Projects Agency, of the Office of Naval Research, or theUnited States Government.Approved for public release; distribution unlimited. Reproduction in whole or part is permitted for any purpose of the United StatesGovernment.

.K

Gentner, Grudin,Conway Finger Movements

May 7, 1980 1

Abstract

Skilled transcription typing is normally thought to involve highly

routinized, sequential movements. However, high-speed films show that a

typist's finger movements usually overlapped in time, and the starting

times of these movements were highly variable, even when comparing

identical sentences. Movements toward keys were often initiated out of

the order in which the letters were eventually typed. These results

conflict with current models of rapid, well learned motor movements and

suggest instead a multi-level control of movement utilizing feedback or

prediction.

ACCESSION for

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UNANNOUNCED 0jUSTIFICATION

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Gentner,Grudin,Conway Finger Movements

May 7, 1980 2

Rapid, precise, malleable motor activity as demonstrated in speech

and manual tasks is an important human charaoteristic. The task of typ-

ing, becaune it is an extremely rapid skill ta good office typist will

average seven or eight keystrokes per seoond) and has a well defined

output, has been the subject of speculation and some investigation

(Lashley, 1959; Shaffer, 1973; Sternberg, Monsell, Knoll & Wright,

1973). Typing has typically been thought of as a sequential, automatic

process. Models of the motor output generally involve a series of motor

commands, often one for each letter, which are placed in a buffer and

then sequentially executed. The actual finger movement is assumed to be

ballistic with no feedback control once the movement is initiated.

Accordingly, studies of typing have been almost exclusively based on

records of the keys pressed and the Inter-keypress latencies (Sternberg

et al., 19t8; Shaffer, 1976).

A proper test of the ballistic sequential model requires a more

detailed examination of the typing process. In order to study how

skilled motor movements are programmed and controlled, we filmed a tran-

scription typist and analyzed the finger movements in the resulting

motion picture. The data reported here are based on a high-speed (100

frames per second) film of an expert typist. The typist transcribed

English sentences on the typewriter-like keyboard of a computer terminal

at appraximately 90 words/minute. For each such keystroke, we deter-

mined the time at which the finger started a smooth movement toward the

key. During the filming, the keypresses and inter-keypress latencies

were recorded by computer . 1

Gentner,Grudin,Conway Finger MovementsMay 7, 198C0 3

We found that 965 of the finger movements were nitiated before the

previous key was pressed. The mean time for a complete finger movement

was 261 asec, while the mean inter-.keypress latency was 124 mseo. Thus

two or three fingers are often in motion simultaneously.

Insert Figure 1 about here

These data are expanded in Figure 1 which shows the distribution of

the starting and ending times of finger movements, both measured rela-

tive to the time when the previous key was pressed. This figure shows

that the starting times of finger movements are more variable than their

ending times (the keypresses). The starting times have a standard devi-

ation or 103 msec, while the ending times have a standard deviation of

26 msec.

Insert Figure 2 about here

Figare 2 illustrates this result, showing the timing of keystrokes

for two ords from a pair of repeated sentences. Figure 2 also shows

two oases where the keystrokes are initiated in an order different from

the finaL keypresses. Overall, 21% of the movements were initiated out

of order (although the movements always ended with keypresses in the

correct arder). There were several cases where the finger movements

were initiated out of order by 150 msec or more. Movements were ini-

tiated out of order for sequences of letters occurring both within hands

(24% of the time) and across hands (13% of the time). One case, shown

in the top portion of Figure 2, extended over two words: In typing the

0

.)

End

-00 Start I

LCD

E" , .- r-

-800 -00 -400 -200 0 200

Time (msec)

Figure 1. The distribution of starting and ending times of keys-

trokes, measured relative to the time of the previous keypress. Most

keystrokes overlap, with the seoond finger movement starting before the

keypress at the end of the previous movement. The starting times of

movements show muoh more variability than the ending times.

II I I I-

-- .--,a

_epaoe

--- p

= spape

-p.p

- e

_ , I , I I , i , I ! ,

0 200 400 O0 800 1000 1200

Time (msec)

Figure 2. Relative timing of keystrokes for the phrase "... an

epic ..." on repeated typing of the same sentence. The left ends of the

horizontal lines represent the initiation time of the keystrokes, and

the right ends of the lines represent the time of the keypresses. Ini-

tiation times were not measured for the letter A and the spape bar; this

is indicated by the dashed lines to the left of the keypress times.

Note that successive keypresses are more regularly timed than the

corresponding initiations. In two cases, although the keys were pressed

in the proper order, the keystrokes are initiated out of order: in the

first sentence the e keystroke was initiated before that of n in the

previous word; in the second sentence the keystrokes for the word X

were initiated in the order q,, , a, o.

" , L --- - . .. .... .

Gentner, Grudin, Conway Finger MovementsMay 7, 1980 4

sequence a SgIq, the movement to type the j was initiated before the

movement to type the Dq.

These data raise two questions: 1) What is responsible for the

large variation in movement times? 2) How are the movements controlled

so that the inter-keypress latencies are much more regular than the

starting times of the movements?

We found that the movement times were partly determined by the

length of time that the corresponding hand and finger had been free.

Depending on the sequence of letters being typed, a given hand may be

free for varying times before it presses a key, and we found that the

longer the hand was free the earlier the keystrokes were initiated.

This is undoubtedly related to the common observation that sequences of

letters which alternate between the hands are typed faster than

sequences which are typed with a single hand. However, we found that

finger movements within one hand can also overlap. In 51% of the cases

where successive keys were typed by two fingers on the same hand, the

second keystroke was initiated while the first keystroke was still in

progress. Early initiation of the second keystroke was positively

correlated with the length of time that finger had been free. The

analyzed film included two repeated sentences. Comparison of these sen-

tences demonstrated that the particular letter or pattern of letters

being typed accounts for only part of the variation in movement times.

The movement times to type a given letter in identical contexts had a

correlation coefficient of 0.60; that is, only about 35% of the variance

f is related to the letter being typed and the sentence context. The por-t

Gentner, Grudin, Conway Finger MovementsMay 7, 1980 5

tion of the variance associated with the letter being typed and its con-

text can be traced almost entirely to the length of time that the

corresponding finger and hand have been free.

The remaining variance in movement time (65%) indicates that the

automated finger movements in touch typing are not entirely stereotyped

or preprogrammed; the movement appears to be controlled during its exe-

cution. Just as we observed with the overall data, the variation in

movement times on repeated typing is due primarily to variation in

starting times. Measured relative to the previous keypress, the median

difference in starting times was 58 mueo, while the the median differ-

ence in ending times (the inter-keypress latency) was 10 msec. Figure

2, which shows the timing for repeated typing of the phrase, an, eLq,

illustrates this finding by contrasting the Irregularity of the initia-

tions of finger movements with the regularity of the keypresses.

Overall, comparing corresponding letters in the repeated sentences, ear-

lier starting times for a movement were not correlated with shorter

Inter-keypress latencies (r = 0.05). An analysis of corresponding keysh

strokes in the repeated sentences showed that there can be significant

variation in the flnger's position at the start of the keystroke. In

particular, keystrokes which start with the finger closer to the target

key are initiated later than keystrokes starting farther away.

There is precedent for the notion that highly skilled sequential

movements can overlap. An analogous phenomenon is well known in phonol-

ogy, where the artioulatory movements required for a sequence of

phonemes often overlap in time (Perkell, 1969). The great variability

t1I

Gentner, Grudin,Conway Finger MovementsMay 7, 1980 6

in initial finger position, initiation and movement times, and the

existence of frequent initiations out of order, however, present diffi-

culties for existing models which call for sequential keystroke initia-

tion. Models which view the output process in typing as the execution

of a series of motor programs, one for each letter, cannot account for

these observations. Our results indicate that the motor program must be

considerably more general, perhaps specifying only the key to be

pressed, the finger, and its sequential relation to the other keypresses

(Saltzman, 1979). Thus at this level the program appears quite

abstract.

The actual initiption and timing of the movement and control of its

trajectory might then be determined by a lower level of processing which

takes into account the position of the fingers and the other competing

activities. These processes controlling finger movement presumably

utilize detailed information about the location and activities of the

fingers. Sensory information and proprioceptive feedback from the mus-

cles controlling the fingers could play a role. Neural impulses take

about 70 msec to travel from muscle sensors through the cerebellum and

back to the finger (Bizzi, 1979), an appreciable fraction of the move-

ment times. Other control mechanisms are possible, however: For

instance, control could be based on central monitoring of motor com-

mands, rather than feedback from the fingers.

Regardless of the specific interface between the high-level program

and the sequence of muscle movements, the picture of typing which

emerges is very different from that of a stereotyped, ballistic move-

ment.

Gentner, Grudin, Conway Finger MovementsMay 7, 1980 7

References

Bizzi, E. Personal communication, June, 1979.

Lashley, K. S. The problem of serial order in behavior. In L. A. Jef-

fress (Ed.), Cerebral m a m behavior. New York: Wiley, 1951.

Perkell, J. Phygiology2 pec routg: flesults gA= g lcai

A quantitative ceneradiographio study. Cambridge, Mass.: MIT

Press, 1969.

Saltzman, E. Levels of sensorimotor representation. J 2[

M.th MA.icl Psygogav, 1979, ?&, 91-163.

Shaffer, L. H. Latency mechanisms in transcription. In S. Kornblum

(Ed.), At i APerformancf I. New York: Acedemic Press, 1973.

Shaffer, L. H. Intention and Performance. Pavaholofical Review, 1976,

.U, 375-393.

Sternberg, S., Monsell, S., Knoll, R. L., and Wright, C. E. The latency

and duration of rapid movement sequences: Comparisons of speech and

typewriting. In G. E. Stelmach (Ed.), Imaion 2roceis inJ&

gr n n learning. New York: Academic Press, 1978.

I+

'A/

- -t

Gentner ,Grudin,Conway Finger Movements

May 7, 1980 8

Footnotes

This research was supported by the Office of Naval Research, Per-

sonnel and Training Research Programs and the Advanced Research Projects

Agency, and was monitored by ONR under Contract N00014-79-C-0323, NR

157-437, under terms of ARPA Order No. 3767. We thank Dedre Gentner and

Donald Norman for valuable comments on the manuscript.

1. The film which we have analyzed in detail covers 310 keystrokes

(abuut 40 seconds of typing). Because we were primarily interested in

the possibility of overlapping keystrokes, this analysis does not in-

clude keystrokes where successive keys are typed by the same finger,

since the finger movements are necessarily sequential; in addition, the

initiation of a movement toward a home row key is ambiguous, as it may

simply be a return of the finger to a home position. Thus, we restrict-

ed our analysis of the film to the 147 keystrokes to letters on the

upper or lower rows of the keyboard where the previous keystroke was not

made by the same finger. Other films of the same typist and video tapes

of other typists show results similar to those reported here, but they

have not been analyzed quantitatively.

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