How We Type: Movement Strategies and Performance inEveryday Typing
Anna Maria Feit
Daryl Weir
Antti Oulasvirta
Aalto University, Helsinki, Finland

Figure 1. Four users showing different typing behaviours involving different numbers of fingers and movement strategies. This paper reports typing
rates, gaze and movement strategies for everyday typists, including both professionally trained and self-taught typists. We explain how untrained typists
are able to type at very high rates, which were previously attributed only to the touch typing system that enforces the use of all 10 fingers.

ABSTRACTThis paper revisits the present understanding of typing, which
originates mostly from studies of trained typists using the tenfinger touch typing system. Our goal is to characterise themajority of present-day users who are untrained and employ
diverse, self-taught techniques. In a transcription task, we
compare self-taught typists and those that took a touch typing
course. We report several differences in performance, gaze
deployment and movement strategies. The most surprisingfinding is that self-taught typists can achieve performancelevels comparable with touch typists, even when using fewer
fingers. Motion capture data exposes 3 predictors of highperformance: 1) unambiguous mapping (a letter is consistently
pressed by the same finger), 2) active preparation of upcoming
keystrokes, and 3) minimal global hand motion. We releasean extensive dataset on everyday typing behavior.
ACM Classification Keywords

H.5.m. Information Interfaces and Presentation (e.g. HCI):
Miscellaneous
Author Keywords

Text entry; typing performance; touch typing; movement
strategies; motion capture data
INTRODUCTION

This paper revisits present-day understanding of one of themost prevalent activities in computer use: typing. We are concerned that the current understanding mostly originates froman era when typing was much more homogenous than today.
Permission to make digital or hard copies of all or part of this work for personal orclassroom use is granted without fee provided that copies are not made or distributedfor profit or commercial advantage and that copies bear this notice and the full citationon the first page. Copyrights for components of this work owned by others than ACM
must be honored. Abstracting with credit is permitted. To copy otherwise, or republish,
to post on servers or to redistribute to lists, requires prior specific permission and/or afee. Request permissions from Permissions@acm.org.
CHI’16, May 07-12, 2016, San Jose, CA, USA©2016 ACM. ISBN 978-1-4503-3362-7/16/05...$15.00
DOI: http://dx.doi.org/10.1145/2858036.2858233

Studies were carried out with trained typists (e.g., [2, 4, 6,
8, 23, 27, 29]) mostly operating typewriters. The participants
were often professionally employed typists, skilled in typing
with 10 fingers and able to consistently perform at rates ofover 80 words per minute (wpm) [8, 22, 24].
We are seeking to shed new light on the everyday typing techniques, employed by a majority of users, that do not fall within
the touch typing system. Touch typing originates from the
1890s and is the technique taught in typing classes. Columnwise, each key is assigned to one finger. Each finger has ahome position in the middle row to which it returns after pressing a key. Finger travel movements are small, which decreases
inter-key intervals. Touch typists practice these movements
to enter text without having to look at the keyboard. While
the system can be learned rather quickly, it requires deliberate
training of hundreds of hours [26, 35] to reach performance
rates reported in literature. As a result, billions of computer
users today are not skilled in touch typing.
The present study characterises the movement and performance of present-day computer users, hereinafter called everyday typists. A recent study of typing performance in undergraduate students [17] showed average rates of only 33
net wpm, far removed from the figures reported in older studies. Also, modern keyboards are flatter, and their keys have ashorter travel distance than typewriters. The characteristics ofthe typed text vary widely: from the formal language of essays
and reports, to the abbreviations used in chat programs andsocial networks, or different languages entirely. Moreover, thekeyboard is used for many more tasks, such as gaming and programming. Such factors may give raise to typing techniques
driven by other objectives. Thus, while we know much about
the keystroke performance and cognitive aspects of trained
typists, we know barely anything about the everyday typist
who may use anything between “two finger hunt-and-peck”
and touch typing. Figure 1 shows four examples of variable
techniques employed by participants in our study.

We study transcription typing using modern motion tracking
technology. This addresses the challenge that finger articulations in typing are very rapid and complex by nature. Several
fingers are moving simultaneously with inter-key intervals
on the order of a few hundred milliseconds. When asked toreport their strategies, users are usually unable to adequately
describe them. “It just happens.” Motion tracking technology
is able to record exact movements at very high rates and wasrecently used to analyze similar high performance tasks, suchas the movement dynamics in piano playing [10, 19]. We
obtain millimeter-accuracy 3D positions of hands and fingers
at and between each key press. In this way we can explain
differences in typing rates by reference to motor behaviour.
We report on a study with 30 everyday typists, selected tospan a wide range of typing performance (from 34 to 79 wpm)
and age (from 20 to 55 years), as well as two languages. We
describe first observations on performance and movement
characteristics. In this paper, we concentrate on motor aspects
related to performance, as well as on visual attention and gaze
deployment.
Surprisingly, we find that regardless of the number of fingers
involved, an everyday typist may achieve entry rates over 70
wpm. Even some participants using only 1 or 2 fingers per
hand can achieve a level of performance normally attributed totouch typists. This contradicts the common belief that everyday techniques are inferior and exhibit slow or disorganised
movement strategies. In fact, our analysis revealed only few
differences between trained touch typists and those without
formal training, including the amount of time spent looking
at the keyboard and the average number of fingers used. As
expected, the largest difference was in the typing techniqueitself. By using hierarchical clustering on the finger-to-key
mappings, we find 4 clusters for the left and 6 clusters for theright hand that characterise the typing techniques that people
use. They range from easy one finger input with the index or
middle finger, to multi-finger techniques, such as touch typing.
Each cluster shows a broad range of input rates, ranging fromless than 50 to over 70 wpm.
A closer analysis of motion data allowed us to conclude thateveryday typing techniques can be fast if motor behaviour isorganised in a particular way. We identified three predictors
for high performance: 1) unambiguous finger-to-key mapping,such that a letter is consistently pressed by the same finger;2) preparation of upcoming keystrokes; and 3) reduced global
hand motion.
These findings encourage more studies to refine our understanding of typing. The results may be useful for optimisationof keyboard layouts, adaptive and personalised assistive input,
and the design of input methods that leverage the expertiseof users. We note that the fastest typists in our study weretypically not touch typists. Analyzing the commonalities intheir movement strategies could potentially devise a typing
technique superior to the touch typing system.
The HOW-WE-TYPE dataset will be made publicly available
to support further research on this important topic.

RELATED WORK: STUDIES OF TYPINGFor nearly a century, researchers have made efforts to understand cognitive and motor aspects of typing. However,
the achieved understanding is based on professionally trained
touch typists. We briefly review these main findings and summarise key points for comparison in our study. We then discussa few more recent studies looking at other typing techniquesoh physical keyboards and multitouch devices.
Phenomena of Touch Typing

Until the introduction of personal computers, expertise in text
entry implied being a professionally trained touch typist. Studies by Salthouse [23], Gentner [7, 8, 9] and Shaffer [27, 28]from the 1970s and 80s were conducted exclusively with professionally trained touch typists, or typists in different stagesof touch typing courses. Almost all were female. As touch typists, their finger-to-key mappings were clearly defined. Thus,
recording the interval between two key presses was enough tocharacterise the typing behavior and make conclusions about
performances of hands and fingers. Inter-key intervals andtyping speeds were analyzed either by video recordings, timekeepers or computational logs. Studies were performed on
typewriters, both electrical and mechanical, or computer keyboards of this era.
The findings accumulated over numerous studies during thistime are reviewed for example in [24] and [34]. Table 1 summarizes phenomena and results particularly related to performance and motor behavior. Where possible we reference exact
numbers for each measure. We note that the table omits many
known phenomena related to cognitive and perceptual processes, such as the eye-hand span or effect of reduced preview.
In this study, we focus on the observable aspects of motor
control and performance. Moreover, we expand the analysis
by motion capture data which is necessary to understand nontouch typists. We look at factors such as global hand motion,
anticipatory movement and the finger-to-key mapping, which
we found to be predictive of high entry rates.
Theories and Models

One goal of prior research has been to explain the cognitive
processes that organise and schedule the perceptual and motor
aspects of typing — from parsing the text to performing thecorresponding keystrokes. Given a to-be-typed letter sequence,these models try to predict the times between two key presses
based on the hand and fingers used for typing, as given by thetouch typing system.
The Central Control Model from 1980 [30] suggests that theinter-key intervals (IKI) are a result of word-specific time
patterns stored centrally and generated in parallel. The simulation model of Rumelhart and Norman from 1982 [22] assumes
that the finger movements are controlled by hierarchically organised motor programs, which are executed based on theiractivation value. The execution of one program may lead tothe increase or decrease of the activation value of another.
The simulation reproduces a number of phenomena, such as
the benefit of hand alternation and different patterns of errors.
The Typist model, proposed in 1996 [15], is built within theframework of the Model Human Processor [3]. It covers 19

Phenomenon or Measure

M

SD

Ref

Background Factors: Studies were usually conducted with [5, 13,professionally trained and employed typists.
23, 29]Participants touch typing (%) 100 0
Weekly amount of typing (h)1119Performance: Average inter-key interval (IKI) is a fraction of
typical choice-reaction times (e.g. 560 ms). The typing rate isslowed for random letter sequences.
9.7

as the professionally trained touch typists studied by Salthouse.
They made more mistakes and required more visual guidance.
However, average inter-key intervals within words were as low
as 170 ms, despite the lack of deliberate training.

[23]
[23]

Words per minute75

IKI easy prose (ms)

140 –

[29]

[13]

IKI random strings (ms)

326 –

[29]

Hand- and finger alternation: Letter pairs (bigrams) typed [24]by fingers of different hands is 30–60 ms faster than those
typed by the same hand.
Bigrams typed by:Hand alternation (%)

48

–

[5]

- IKI (ms)155 43[23]

Finger alternation (%)

34

–

[25]

- IKI (ms)

194 45[23]

Same finger (%)

4.6

–

[5]

- IKI (ms)223 41[23]

Letter repetition (%)

n/a–- IKI (ms)176 26[23]
Table 1. Well established phenomena and their corresponding measures
based on prior studies of professional touch typists. Exact values are
selected from the referenced papers and may vary in other studies.

phenomena of transcription typing, most of them reviewed
by Salthouse [24]. The more recent Queuing Network Modelfrom 2008 [34] is based on the Queuing Network Model Human Processor [18] which combines mathematical queuing
networks and symbolic models of cognition. These simulation models aim to explain the typing phenomena listed by
Salthouse and others, with varying levels of success. To ourknowledge, the only mathematical model was proposed in1980 [14]. Based on the typing data of a single professional
typist, they proposed a linear model that predicted the interkey interval as a function of different characteristics of thefingers used to press the keys, such as hand alternation, finger
and row transition, as well as the frequency of the letter pair.
To make these models applicable to today’s computer users,
we need to extend them to cover self-taught typing techniques.
This paper makes a first step towards collecting the necessary
data and reports first observations.
Studies of Everyday Typing
Physical keyboards

We could identify only two prior studies investigating nontouch typists entering text on physical keyboards. A study
from 2007 [17] reported on the performance of 60 undergraduate students of different typing background. Average input
performance was 33 net words per minute (“net wpm” is computed by subtracting 5 characters for each mistake). They
found that performance correlates with self-reported deliberate typing practice, where highest entry speed was seen forparticipants who took a typing course. A study from 2008 [12]assessed the performance of 32 female students not trained intyping. They found that self-taught typists were not as efficientMultitouch devices

More extensive studies of everyday typing were done on touchscreen devices. A recent study compared typing performanceon a regular keyboard and tabletop surface [31]. On average,
performance was found to be about 60 wpm on a physical, and
30 wpm on the soft keyboard [31]. Input strategies were only
observed manually by the experimenter. For typing on thetabletop, they fall into three categories: Hunt-and-Peck, FullUse, and Hybrid. They reported that all participants employed
Full-Use on the physical keyboard. However, it is unclear if
this corresponds to the touch typing system. Input strategies,
grips and hand postures were also studied for 1–2 finger input
on smartphones to develop better models of touch locations,
support auto-correction, and adapt the keyboard to users’ behavior [1, 11, 20, 36]. However, this form of input is very
different and much more limited than typing on a physicalkeyboard with global hand motion and 10 end-effectors.
METHOD

We collected typing data in a transcription task with 3 typesof materials: easy sentences, random letter strings, and a mixof both. A phrase was presented on the display and should
be entered as participants would usually do. We allowed
correcting errors to make the task more realistic. Thirty typists
participated in the study, spanning a wide range of typing
performances, ages, as well as two languages. In addition
to key press data, we collected motion capture data of thehands, tracking the position of each finger at and between
the keystrokes. Moreover, we capture the switch of attention
between the keyboard and screen with eye-tracking glasses.
An overview of the setup is given in Figure 2.
Participants

We recruited 30 participants (17 female) ranging in age from
20–55, with a mean of 31. Three participants were left handed.
Our participant pool had either Finnish or English as theirmother tongue or most commonly used language for typing.
In order to observe the over-trained movements used in everyday typing we let participants choose the language they werefamiliar with (18 Finnish / 12 English). The keyboard was
the same for both languages (QWERTY layout with special
characters, see Figures 7, 8). Their performance, measured
based on the collected data, ranged from 34–79 wpm. All
participants reported to have permanent access to a computer
either at work or at home. Their self-reported computer experience varied between 6 and 35 years. Participants wererewarded with a movie ticket worth 10e.
Experimental Design

The experiment followed a within-subject design with one
independent variable: stimulus type, with three levels: easy
sentences with commonly used word (sentences), random
letter strings (random), and a mix of both (mix). Their order
was randomised throughout.

Materials

For the sentences condition, 50 easy and memorable sentenceswere chosen from the Enron Mobile Email Dataset [32]. They
were translated into Finnish by a native speaker, instructed touse simple, everyday language. For the random condition we
randomly sampled 50 6-letter strings from a uniform distribution over the alphabet. In the mix condition the random string
was added as an extra word in the middle of the sentence. The
stimuli were presented in random order.
Apparatus

The setup consisted of three parts: motion capture, text entry, and eye tracking, all shown in Figure 2. In addition werecorded a reference video of the participants’ hands.
Motion capture: The experiment was performed in a motion
capture laboratory with no visual or auditory distraction during
the task. The position and motion of the fingers was tracked
with a motion capture system by Optitrack consisting of 8
cameras, recording at 240 fps. We placed 26 adhesive markers
on anatomical landmarks of each hand.
Keyboard logging: The typing software (implemented in
Python) showed one stimulus at a time on the display. Performance feedback was given at the end of each condition. The
physical keyboard had a Finnish layout, similar to QWERTY(see Figure 7, 8). All keypresses were logged.
Eye tracking: We used eye tracking glasses by SMI (ETG1.8), recording at 30 Hz, to capture the switch of attention
between keyboard and display. 3-point calibration was used
to calibrate the glasses. Tracking quality varied dependingon participants’ expertise and typing style and was infeasible
with some corrective glasses. In one case data could not
be recorded due to technical issues. However, eye tracking
glasses were worn in all cases to ensure the same conditions
for each participant.
Procedure

Participants were informed that the purpose of the study was
to investigate the hand and finger movements of computer
users during text entry. Throughout the experiment they were
instructed to type as they would normally do, without paying
special attention to speed or accuracy, and to correct errors
upon notice by using the backspace key. Errors that were notdetected within 1-3 characters could be left uncorrected. Participants could choose the stimulus language between Finnish
and English. After attaching the markers, participants wereasked to sit comfortably and adjust the position of the keyboard on the table to their liking. They were given a practicetext to familiarise with the keyboard and were then explained
the three conditions. They were asked to first read through astimulus, memorise it and then transcribe it. Between the conditions, participants were asked if they wanted to take a break.
After the study participants filled a questionnaire asking about
demographic factors, their computer experience, their typing
skill, and the tasks they perform with the keyboard.

Figure 2. Experimental setup: The typing process of 30 participants wascaptured using a motion capture system and eye tracking glasses. In
addition, keypress timings were logged and a reference video recorded.

DATA ANALYSISOur analysis covers well-known typing phenomena discussed
in Table 1, as well as more advanced measures that require theanalysis of motion capture data, which were not considered inprevious work. Unless otherwise stated, measures were computed per participant as an average over all phrases typed in
the sentences condition. To identify statistical trends holding
for both languages, we only considered those letters and letter
pairs common to both languages and gave equal weight toeach letter, where relevant.
Preprocessing

The goal of the preprocessing was to extend the motion capture
and typing logs with the information of which finger executedeach keypress. We performed four steps:
1. Cleaning and smoothing: The built-in functionalities of OptiTrack’s Motive:Body [21] software were used to fill short
gaps (up to 10 frames) and smooth the data (fluctuations inthe signal up to 10 Hz). From the typing log, we excluded
outliers more than 2 SD from the mean inter-key interval.
On average this was 4.4 % of the data (maximum 5.9 %).
2. Offline labeling of markers: To match the point cloudrecorded by the motion capture system with the joints of thefingers we used a nearest neighbor approach after manuallylabeling the first frame, supported by heuristics based on
the underlying hand skeleton.
3. Transformation to keyboard coordinate system: To enable comparison between participants, we transformed all
tracked position data to the keyboard coordinate system,
where the Escape key had position (0, 0, 0).
4. Identify executing fingers: Given the pressed key, as wellas the time and frame at which the key was pressed, theexecuting finger was identified as the marker that had theshortest distance to the key at the given frame.
To validate these steps, we randomly sampled one sentence
per participant and manually identified the executing fingers.
On average, one sentence had 23.2 keypresses and the identification was correct for 98.4 % of them.

Non-touch typist
Touch typist

Words per minute

80
70

Sentences
Random

60
50
40
30
20
10
0

5

10

15
20
Participants

25

30

Performance loss, random(%)

90

70
60
50
40
30
Touch typists

2030

Non-touch typists

40
50
60
70
Words per minute, sentences

80

Figure 3. Left: Participants’ performance ranged from 34 to 79 wpm and did not significantly differ between touch- and non-touch typists. Right: The
percentage loss in performance when typing random strings was found to be smaller for typists of high skill, trained or untrained.

Typing Performance

We compute the following measure of typing performance forthe random and sentences condition:
Words per minute (wpm): based on the raw typing log, without
exclusion of outliers. For each sentence we find the time
between the first and last keypresses and divide it by the lengthof the final input given in number of words (any 5 characters).
Inter-key interval (IKI): in milliseconds, average interval
between all keystrokes in the preprocessed data, includingpresses of modifier keys and error correction.
Uncorrected error rate (%): the Damerau-Levenshtein edit
distance between the stimulus and entered text and dividing itby the larger number of characters.

Percentage and average IKI of letter pairs (bigrams) typed by:
1. Hand alternation: fingers of different hands,
2. Finger alternation: different fingers of the same hand,
3. Same finger: typing different letters with the same finger,
4. Letter repetition: pressing the same key twice.
Entropy of the finger-to-key mapping: the finger-to-key mapping describes which finger a participant uses to press eachkey. The entropy tells how consistently a key is pressed withthe same finger. For each key k, given a frequency distribution
over the 10 fingers we compute the entropy as:
Hk = −∑

p f log2 (p f )(1)

f ∈Fingers

Keyboard efficiency: the ratio of number of characters in the
input and number of keystrokes. Characterises the accuracy
during the typing process. A value close to 0 corresponds to alarge number of corrected errors.

where p f is the probability that finger f presses key k. The average entropy of a finger-to-key mapping is then computed assum over the entropies of each key weighted by the frequencyof the corresponding letter. The touch typing system has 0
entropy, as each key is pressed by only one finger.

In addition we compute the percentage difference in WPM
between the two conditions, which further characterises thetyping skill of participants.

Global movement: of each hand, computed at each keypress
as the average of the standard deviations of the x-, y- and zcoordinates of the two markers on the back of the hand.

Eye Gaze

Due to varying tracking quality, analysis was done manuallybased on the video recordings of the eye tracking glasses.
Gaze shifts: the average number of gaze shifts from the monitor to the keyboard during a sentence.
Visual attention: ratio between the time spent looking at the
keyboard and the time a sentence was displayed. Between 0
and 1, where 0 means no time spent looking at the keyboard.
Motion Analysis

In the following analysis we only consider the letters common
to both the Finnish and English sentences and exclude control
keys, space, and punctuation.
Number of keys: operated by each finger and hand.
Keys per finger: the avg. number of keys mapped to eachfinger.

Distance to the next key: the average distance of the executing finger to its target at the time of the preceding keypress.
Measures the preparation of upcoming keystrokes by moving
a finger to to its target during the execution of a preceding
keypress.
RESULTS

We collected 93, 294 keypresses over the three conditions, and36, 955 in the sentences condition. Results of all statisticaltests are summarised in Table 2. It compares participants
trained in the touch typing system (hereinafter called touchtypists) and those that never took a typing course (non-touchtypists) in several dependent variables. The classification was
based on the self-reports of participants. Statistical significance was tested at the 5% level using the the Mann-Whitney
signed rank test, as required by the data, which are not normally distributed and have different cell sizes. Where the distribution of the data allowed, we performed a 2-way ANOVA
with language and touch/non-touch as factors. However, it
showed no effect on any metric, except the reported hours ofweekly typing. Detailed results per participant are provided in
the HOW-WE-TYPE dataset.
Background Factors

Based on the survey, 43% of participants learned and used
the touch typing system. The average amount of touch typing
experience was 17 years (SD = 9.7). The mean age of touchtypists and non-touch typists was not significantly different.
More background factors are shown in Table 2
Performance

Surprisingly, we did not find a significant difference in input
performance between touch typists and non-touch typists. Average entry rate and IKI were found to be 57.8 WPM and176.39 ms for touch typists, and 58.93 WPM and 168.91 ms
for non-touch typists. The performance in wpm of each participant is shown in Figure 3. Touch typists and non-touch typists
had statistically similar uncorrected error rates — measuring
errors remaining in the final input — of 0.76 % and 0.47 % forrespectively. Both groups typed with high efficiency, making
few mistakes and requiring few keystrokes to correct them.
The common understanding in the literature was that touchtypists could type faster and operate with higher accuracy.
However, the presented findings show that touch typists andnon-touch typists have comparable speed and efficiency intranscribing sentences.
Effect of random strings

When typing random letter sequences entry rate dropped on
average by ∼50% compared to the sentences condition. Thechange was similar across both groups, with no significant difference between their performances in the random condition.
The average uncorrected error rate was 0.98 % for touch typists and 0.72 % for non-touch typists, a significant difference.
One participant was excluded from this analysis, as the error
rate in the random condition was 11%.
Figure 3 shows how the loss of performance changes as typing
skill increases. The faster typists can type random material
faster, not only in absolute terms but also as a percentage of
their typing speed. This can be explained with the findingsof Salthouse [23]. He states that high performance text entry cannot only be attributed to well practiced motor patterns
corresponding to larger units of language, such as words orphrases. Instead he finds that skilled typists show more consistency in their inter-key interval when typing the same letter
repeatedly in the same context. This consistency may still beobserved in the random condition.

MeasureBackground
Reported strategy (%)
Years touch typing
AgeComp. experience (y)Weekly typing (h)Performance
WPM- Random
Avg. IKI (ms)- Random (ms)Error rate (%)- Random (%)
Efficiency
Eye gaze
Gaze shift
Visual attention
Motion Analysis#Fingers used
- Left hand
- Right handKeys per finger- pres. by both hands
Hand alternation (%)- IKI (ms)Finger alternation (%)- IKI (ms)Same finger (%)- IKI (ms)Letter repetition (%)- IKI (ms)Hand alt. benefit (ms)Entropy
Global mov. left (cm)Global mov. right (cm)Dist. to next key (cm)

M

Touch
SD

43.33
16.96
33.00
21.69
47.15

–
9.66
9.15
7.73
20.63

Non-Touch
M
SD
56.66
–
28.82
16.38
44.56

–
–
7.59
3.95
18.39

M.-W. Stat.
Up––◦ 75 0.07◦ 64 0.053◦ 98 0.44
57.83 15.25 58.93 10.82 ◦ 103
0.38
27.43
8.73
27.02
8.46 ◦ 96
0.28
176.39 44.31 168.91 33.22 ◦ 103
0.38
382.31 122.56 399.36 133.70 ◦ 100
0.34
0.76
0.62
0.47
0.42 ◦ 82
0.13
0.98
0.86
0.72
1.08 • 60
0.02
0.88
0.03
0.89
0.04 ◦ 100
0.34
0.92
0.99
1.20
0.94 • 96
0.03
0.20
0.27
0.41
0.33 • 85 <0.01
8.54
1.08
6.24
0.94 • 16 <0.01
4.46
0.63
3.47
0.70 • 37 <0.01
4.08
0.73
2.76
0.73 • 23 <0.01
3.64
0.74
5.65
1.51 • 16
<0.01
1.15
1.17
4.41
2.35 • 24 <0.01
46.50
0.61
48.26
2.35 • 50 <0.01
150.64 31.78 141.28 32.53 ◦ 90
0.2
35.94
6.08
26.42 10.76 • 44 <0.01
161.61 31.66 161.10 41.38 ◦ 99
0.32
11.05
5.88
18.67
9.87 • 50 <0.01
194.90 26.60 202.75 34.24 ◦ 98
0.31
6.71
0.10
6.68
0.12 ◦ 91
0.2
159.30 25.36 145.16 12.59 ◦ 72
0.06
16.96 15.83 28.72 23.48 ◦ 82
0.12
0.26
0.18
0.38
0.20 • 71
0.047
0.02
0.06
0.01
0.01 ◦ 110
0.50
1.05
0.80
0.81
0.38 ◦ 104
0.40
1.94
0.41
2.41
0.59 • 60
0.02• : Significant difference ◦ : No significant difference

Table 2. Overview of results, comparing touch- and non-touch typists.
Statistical significance is tested at the 5% level using the Mann-Whitney
signed rank test and reported in the last two columns.

typists. For visual attention the correlation was 0.69 for touchtypists and 0.53 for non-touch typists.
Although touch typing is not necessarily faster, it allows maintaining visual attention on the display. Often self-taught typists, even fast ones with unambiguous mappings, are morereliant on visual attention to the keyboard. However, the trendlines in Figure 4 indicate that IKI of touch typists increases
more rapidly as visual attention increases, whereas non-touchtypists can maintain high performance under gaze switches.

Eye Gaze

Motion Analysis
Hand and finger usage

The analysis of eye gaze found that non-touch typists spent asignificantly higher amount of time looking at the keyboard,as shown in Figure 4. The average number of gaze switcheswithin a sentence was 0.92 for touch typists and 1.2 for nontouch typists, a significant difference. The ratio of time spentlooking at the keyboard was 0.2 for touch typists and 0.41 fornon-touch typists, also a significant difference. We found acorrelation between the average IKI and eye gaze, as shownin the right plots of Figure 4. Correlation between IKI andgaze switch was 0.81 for touch typists and 0.32 for non-touch

Somewhat unsurprisingly, touch typists use more fingers than
non-touch typists (8.5 vs. 6.2). As a consequence, a non-touchtypists needs to operate more keys per finger than touch-typists(3.6 vs. 5.6). Touch typists have a clear separation between
left and right hand, whereas for non-touch typists there are
more keys that fingers of both hands operate. All participants
used significantly more fingers of the left than of the righthand. In the Section Clustering of Movement Strategies wereport on the differences of hand- and finger usage in moredetail by clustering the finger-to-key mappings.

1.2
1.0

0.6
0.8
0.6

0.4

0.4
0.2
0.2
0.0

280
260

Visual attention
Inter-key Interval (ms)Number of gaze shifts

Non-touch typists
Touch typists
0.8

240
220

280
Non-touch
Corr.: 0.32
Touch
Corr.: 0.81

200
180
160
140
120

Gaze shift

Visual attention

0.0

100

Non-touch
Corr.: 0.53
Touch
Corr.: 0.69

260Inter-key Interval (ms)

1.0
1.4

240
220
200
180
160
140
120

0

1

2

Gaze shifts to keyboard

3

100

0.0

0.2

0.4

0.6

0.8

1.0

Visual attention on keyboard

Figure 4. Characteristics of eye gaze during text input. Left: Touch typists spent less time looking at the keyboard (visual attention) and required lessgaze shift. Right: Gaze switches and visual attention correlate with the average inter-key interval, increasing as performance gets slower.

Hand and finger alternation

Touch typists enter significantly more bigrams with different
fingers of the same hand, whereas non-touch typists prefer
to use the same finger for successive keystrokes. However,
non-touch typists were found to enter significantly more bigrams by hand alternation and typed them faster than whenusing fingers of the same hand. On average two letters weretyped with an IKI of 141.28 (SD = 32.53) when using handalternation and 170 ms (SD = 34.53) otherwise, a significant
difference of 29 ms (U = 72, p = 0.01). In contrast, touchtypists entered bigrams by hand alternation with an IKI of
150.64 ms (SD = 31.78), and 167.6 ms (SD = 28.61) otherwise, a non-significant difference of 17 ms (U = 55, p = 0.07).
The distributions of bigrams typed by hand alternation, finger
alternation, the same finger, and number of letter repetitions
are shown in Figure 5 along with their average IKI. Corresponding numbers are given in Table 2.
Entropy of the finger-to-key mapping

On average, we found that non-touch typists showed morevariation in their finger-to-key mapping, which means thata certain key was pressed by different fingers in different
contexts. The average entropy for touch-typists was 0.26
versus 0.38 for non-touch typists, a statistically significant
difference. However, across both strategies we found that theentropy correlated with performance, as shown in Figure 6(a).
Preparation of upcoming key presses

We found that on average touch-typists better prepare upcoming keystrokes. The average distance of the executing finger toFinger alt.

Same finger

Letter repet.

200

80
150

60

100

40

50

20
0

Non-touch

Touch

Non-touch

Touch

Inter-key Interval (ms)Number of bigrams (%)

Hand alt.

100

0Figure 5. Distribution and average IKI of bigrams typed by hand andfinger alternation, the same finger, or letter repetition. Touch typists
enter more bigrams by using different fingers of the same hand, whereas
non-touch typists more often use the same finger.

its target at the time of the preceding keystroke was 1.94 cm
for touch typists and 2.41 cm for non-touch typists. The difference is significant. As shown in Figure 6(b), the preparationof keystrokes correlates with the average IKI.
Global movement of the hands

The deviation from home position measures how much thetypist globally moves the full hand to reach a key as opposed
to individually moving a single finger. We found that the righthand moves significantly more than the left hand for both touchtypists and non-touch typists, as shown in Figure 6(c). The
Figure also shows that the global hand motion is a predictor
for the average IKI in both left and right hand, and for bothtouch- and non-touch typists.
Inspection of the reference videos confirmed that both touchand non-touch typists keep their left hand static in relation tosome home position. In contrast, for most people, the righthand does not show such a home position, but instead at theexecution of a keystroke, all fingers are moved towards thetarget. Interestingly, this was also the case for left handed
participants. Only highly skilled typists could also keep astatic home position in the right hand.
CLUSTERING OF MOVEMENT STRATEGIES

To identify similarities among typists, we performed hierarchical clustering on the finger-to-key mappings of each user.
Clustering in this space groups users with similar mappings,
revealing the input strategies used by multiple users. As described above, we found notable differences in behaviour between the left and right hands — the right hand has higher
global movement, while the left hand typically has more active fingers, independent of the handedness of the participant.
Given these differences, we decided to cluster the finger-to-key
mappings for each hand separately to uncover subtle withinhand effects that might be masked in a joint analysis.
Input Data and Clustering Method

For each user, the feature vector consisted of 10 entries per
key, giving the proportion of total presses by each finger. We
performed Hierarchical Clustering [16] since it is powerful,flexible and makes no assumptions about the distribution of
the data. We used a Euclidean distance measure and Ward’s
linkage criterion [33] to create compact clusters with minimum
internal variance.

Non-touchtypists
typists
Non-touchNon-touchtypists
typists Touch
Touch
Touch
typists
typists
300300300

Inter-key interval (ms)Inter-key interval (ms)Inter-key interval (ms)300300300
250250250

250250250

200200200

200200200

300300300
Corr.
0.62
Corr.
Corr.
0.62
0.62
Corr.
0.65
Corr.
Corr.
0.65
0.65

250250250

LeftLeft
hand:
Left
hand:
hand:
Non-touchNon-touchNon-touch
Corr.
0.57
Corr.
Corr.
0.57
0.57
Touch
Touch
Touch
Corr.
0.71
Corr.
Corr.
0.71
0.71

200200200

Right
hand:
Right
Right
hand:
hand:
Non-touchNon-touchNon-touch
150150150
150150150
Corr.
0.71
Corr.
Corr.
0.71
0.71
Corr.
0.62
Corr.
Corr.
0.62
0.62
Touch
Touch
Touch
Corr.
0.37
Corr.
Corr.
0.37
0.37
Corr.
0.68
Corr.
Corr.
0.68
0.68
100100100
100100100
100100100
0.00.0 0.00.20.2 0.20.40.4 0.40.60.6 0.60.80.8 0.81.01.0 1.01.01.0 1.01.51.5 1.52.02.0 2.02.52.5 2.53.03.0 3.03.53.5 3.5 0.00.00.5
0.00.51.0
0.51.01.5
1.01.52.0
1.52.02.5
2.02.53.0
2.53.0 3.0
Entropy
Distance
to next(cm)
SD SDof global
hand
position(cm)
Entropy
Entropy
Distance
Distance
to next
tokey
next
key
key
(cm)
(cm)
SD
of globalof global
hand
hand
position
position(cm)(cm)
150150150(a) Entropy(b) Preparation(c) Global movement

Figure 6. Correlation of inter-key interval with 3 movement characteristics: (a) the entropy of the finger-to-key mapping, (b) the preparation of
upcoming keystrokes, given by the average distance of the executing finger from its target at the time of the preceding keystroke, and (c) the standard
deviation of the global hand position, given for the left and right hand separately.

In order to avoid biasing the clustering towards effects fromthe two-language sample, we consider only keys which appear
in both the English and Finnish stimuli. This leaves a set of
26 keys (including punctuation and the shift keys) for a totalof 260 features in our clustering. Additionally, we do notweight the keys based on their frequency in the data. Thus, theclustering treats all keys equally, even if they were uncommon
in the typed phrases.
We obtained the number of clusters by examining the cluster
dendogram and consulting multiple goodness-of-clustering
metrics: Dunn index, Davies-Bouldin index, CalinskiHarabasz criterion, silhouette score, and gap criterion.

3. Index-dominated two-finger typists: Primary use of index
finger. The middle finger may press keys in the I, O and P
columns, as well as backspace. N = 6.
4. Two-finger typists: Even and spatially strict distribution ofkeys between the index and middle finger. Ring and little
may be used for punctuation, backspace and shift. N = 7.
5. ‘Lapsed’ touch typists: Similar to touch typing, but keys of
the Y and U columns are often typed by middle instead ofindex finger. Little finger only used for shift. N = 5.
6. Touch typists: Finger-to-key mapping broadly matches thetouch typing scheme, with the exception that little finger
may only be used for shift key. N = 7.

Results

Following the described approach, we obtained 6 clusters forthe right hand and 4 for the left.
Left hand

In the left hand, we found the following 4 strategies:
1. Index finger typists: Majority of keys pressed by the index
finger. Middle and ring finger may be used for A, S and E,
as well as the shift key. N = 6.
2. Middle finger typists: Majority of keys pressed by the middle finger. Ring finger may press the A, S, E or Shift key.
N = 2.
3. Offset touch typists: Variant of touch typing without the useof little finger, thus shifted by one column to the left. The
ring finger handles the A key, and the middle finger the S
and E keys. The index finger frequently presses the D key
in addition to the touch typing assignment. N = 7.
4. Touch typists: Finger-to-key mapping closely matches thetouch typing scheme. N = 15.
Right hand

The right hand displayed more variation. The 6 strategies
found by the clustering are as follows:
1. Index finger typists: Majority of keys pressed by the index
finger. N = 2.
2. Middle finger typists: Majority of keys pressed by the middle finger. N = 3.

Observations

There was less variance in strategy in the left hand. Half ofour sample had a left hand mapping close to true touch typing,with a further 7 participants using a 3-finger variant. Notably,
only 13 participants self-reported as touch typists, so someusers have developed similar behaviour independently. By
comparison, only 12 of 30 participants consistently used morethan two fingers for the letter keys on the right hand.
Within the clusters for both hands, there were small variations
in keying behaviour. Even in our touch typing clusters, there
were instances where the wrong finger stroked a key. Of the
13 self-reported touch typists, only 3 had a ‘perfect’ mapping
according to the original system.
Supporting our previous findings, the strategies extracted inthis way are not predictive of performance. Figures 7 and 8
show fast example users for each cluster and the corresponding performance. Our touch typists ranged in performancefrom 34 to 79 wpm, while some users who used only 1 or 2
fingers per hand reached speeds in excess of 70 wpm. Thus, if
performance is the goal it is not necessarily important which
fingers a typist uses, but rather other factors analyzed above,
such as consistent finger-to-key mappings, preparation andglobal hand movement determine the speed. An exception
is the middle-finger clusters — no user in either cluster was
faster than 55 wpm. It is unclear whether these strategies aresuboptimal or our sample was too small to find a fast typist
with this behaviour.

Figure 7. Strategies found by clustering the finger-to-key mappings ofthe left hand. The figure shows a representative user for each cluster
and their average performance. The bar plots show the percentage ofkeys pressed by the left hand and their distribution over the fingers.

DISCUSSION

This paper has presented an in-depth study of the abilities
and idiosyncrasies that characterise everyday typists. Ourparticipants varied in skill, age, experience, and strategies,
deploying anywhere from 5 to 10 fingers. The collected dataset
is a rich description of their behavior, including finger motions
and eye gaze, which to our knowledge have not been looked
at in prior studies of typing with computer keyboards. We
introduced new metrics to describe their motor behavior basedon finger-to-key mapping, global hand motion and preparationof keystrokes.
We have reported the first findings from this dataset, focusingon performance, gaze and movement strategies. Comparing
typists trained in the touch typing system and those without
any formal training, our main findings are:
• The two groups show no difference in input performance,
error rate, or efficiency. Many touch typists are inefficientand many non-touch typists efficient.
• On average, non-touch typists use 6.2 fingers, which issurprisingly close to the 8.5 of touch typists.
• However, even if (some) non-touch typists are fast, thisgroup spends more time looking at the keyboard. In ourdata, non-touch typists used 40 % of their time looking at
the keyboard, whereas touch typists spent only 20 %.
• Touch typists more consistently press a key with the same
finger, showing lower entropy in the finger-to-key mapping.

Figure 8. Strategies found by clustering the finger-to-key mappings ofthe right hand.

• We could not find a hand alternation benefit, as large aspreviously reported for professional typists. Only the nontouch typists entered bigrams significantly faster by alternating hands than using fingers of the same hand
• Non-touch typists are generally worse at preparing upcoming key presses.
• For both groups, the right hand globally moves significantly
more than the left hand.
The most significant discovery is that entering text at highspeed does not require mastery of the touch typing system.
We have not found this reported earlier in the literature. Figures 7 and 8 show various finger-to-key mappings used byparticipants. Users of almost all strategies were able to type at
speeds over 74 wpm. Thus, in contrast to the common belief,
the number of fingers is not an indicator for high performance.
We provide the first explanation for this finding. Our results
identified three factors that are predictive of performance:

(a) Touch typing(b) Non-touch typing

Figure 9. Linear models of performance based on the entropy of thefinger-to-key mapping, movement preparation, and global hand motion.

1. Entropy of the finger-to-key mapping: faster typist press a
key more consistently with the same finger.
2. Motor preparation: moving towards the target key alreadyduring preceding keystrokes increases performance.
3. Global hand motion: slower typists globally move theirhands more, while fast typists keep them static.
These three factors correlate with the average inter-key intervaland Figure 9 shows a linear model combining them. It predicts
typing rates with moderate-to-high fit to our data.
It is somewhat startling to note that efficient keying strategies can emerge in daily use of computers without systematic
practice. None of our non-touch typists admitted deliberately
practicing typing, yet many achieved entry rates over 70 wpm.
By contrast, for touch typists reaching and maintaining a highlevel of performance (over 70 wpm) requires some form ofdeliberate practice [17, 35]. Only 3 of our 30 participants
stated they deliberately practice typing, and all of them weretouch typists. It is interesting to note that while the touchtyping system has the potential to be used at a very high speed,
when properly trained, none of our participants in this group
showed such levels. A self-taught strategy that is consistentin its finger-to-key mapping, and minimises global hand motion, may be easier to acquire and maintain. However, wenote that non-touch typists were uniformly worse in terms ofgaze deployment. They have to look at the keyboard to guidetheir fingers. Thus the self-taught techniques may be worse ininteractive tasks that require attention to the display.
Hand alternation benefit has been one of the most widely
recognised phenomena also for other input methods, but neverstudied with non-professional typists and modern computer
keyboards. Prior research reported benefits of 30–60 ms [24].
In contrast, the difference we found in this study was below
this range and, more surprisingly, not found to be significant for touch typists. One explanation may be that today’s
computer keyboards have different physical properties thantypewriters and keyboards from before the 1990s. The keys
require less force to be pressed, the activation point is higher,
and the rows of the keyboard are at similar height level. This
reduces the travel distance and makes preparation easier froma biomechanical perspective. As a consequence, fingers of thesame hand may be able to prepare upcoming keystrokes aswell as the fingers of the alternate hand, such that the benefit
vanishes. We call on further research to confirm this analysis.

There are many further analyses that could be carried out withthis data. For example, our results focused mostly on data fromproper sentences — there may be other findings of interestin the random or mixed conditions. The motion capture dataalso offers exciting opportunities. For example, preparatory
movements could be investigated in more detail to understandhow optimally and how much in advance non-touch typists
prepare movements. Further analysis could also investigate thedynamics between the use of gaze and movement of hands, inparticular of non-touch typists. Generally, the combination of
motion capture and eye-tracking data provides unique insights
into the eye-hand coordination when typing.
CONCLUSION

This paper has shown that – in contrast to the common belief – everyday computer users employing self-taught typing
techniques can perform at similar speeds to touch typists. Ourinvestigation of this finding suggests that more important than
the number of fingers is the organisation of motor behavior.
Fast non-touch typists have an unambiguous division of labour
among the fingers. This may minimise uncertainty over which
finger presses which key, reducing the need for visual attention and choice. Fast non-touch typists also move their hands
and fingers more actively in preparation for upcoming key
presses. Most intriguingly, they may be able to obtain this motor behavior without engaging in a systematic training regime.
Many of the fastest typists we observed had no formal training
in typing. Instead, their input strategies have evolved withthe various tasks they perform, such as gaming, chatting, or
programming. These observations call for more research torevise our understanding of the motor and perceptual aspectsof everyday typing.
THE HOW-WE-TYPE DATASETThe outcome of our study is a unique dataset characterising
the performance and behaviour of everyday typists. We are
publicly releasing over 150GB of data, which includes:

1. Motion capture data: x-y-z coordinates of 52 markers
recorded at 240 fps.
2. Keypress data: key symbol, press and release time, andinter-key interval for every keypress
3. Eye tracking data: 30 fps eye tracking video annotatedwith gaze points. Derived variables: # of gaze shifts andtime spent looking at keyboard.
4. Performance measures: classical text entry measures —entry rate, average IKI, error rate and keypress efficiency.
5. Motion analysis: motion derived features — finger usage,
hand alternation, entropy of finger-to-key mapping, global
hand movements, preparation of movements.
6. Reference video: video of the hands as they type.
ACKNOWLEDGMENTS

We thank Tino Weinkauf, Olli Savisaari, and Perttu Lähteenlahti for their contribution to this work. The project has received funding from the Academy of Finland project COMPUTED and the European Research Council (ERC) under
the European Union’s Horizon 2020 research and innovation
programme (grant agreement No 637991).

REFERENCES

1. Shiri Azenkot and Shumin Zhai. 2012. Touch behavior
with different postures on soft smartphone keyboards. In
Proceedings of the 14th international conference on
Human-computer interaction with mobile devices andservices. ACM, 251–260.
2. Russell LC Butsch. 1932. Eye movements and theeye-hand span in typewriting. Journal of Educational
Psychology 23, 2 (1932), 104–121.
3. Stuart K Card, Allen Newell, and Thomas P Moran. 1983.
The psychology of human-computer interaction. (1983).
4. John E Coover. 1923. A method of teaching typewriting
based on a psychological analysis of expert typing. In
National Education Association Addresses andProceedings, Vol. 61. 561–567.
5. August Dvorak and others. 1936. Typewriting behavior;
psychology applied to teaching and learning typewriting.
(1936).
6. Paul Fendrick. 1937. Hierarchical skills in typewriting.
Journal of Educational Psychology 28, 8 (1937),
609–620.
7. Donald R. Gentner. 1983. Keystroke Timing inTranscription Typing. In Cognitive Aspects of Skilled
Typewriting, William E. Cooper (Ed.). Springer New
York, 95–120.
8. Donald R Gentner. 1988. Expertise in typewriting. The
Nature of EExpertise (1988), 1–21.
9. Donald R Gentner, Serge Larochelle, and Jonathan
Grudin. 1988. Lexical, sublexical, and peripheral effects
in skilled typewriting. Cognitive Psychology 20, 4 (1988),
524–548.
10. Werner Goebl and Caroline Palmer. 2013. Temporalcontrol and hand movement efficiency in skilled music
performance. PloS one 8, 1 (2013), e50901.
11. Mayank Goel, Alex Jansen, Travis Mandel, Shwetak N
Patel, and Jacob O Wobbrock. 2013. ContextType: using
hand posture information to improve mobile touch screen
text entry. In Proceedings of the SIGCHI conference onhuman factors in computing systems. ACM, 2795–2798.
12. Joachim Grabowski. 2008. The internal structure ofuniversity students’ keyboard skills. Journal of writing
research 1, 1 (2008), 27–52.
13. Jonathan Grudin. 1983. Non-hierarchic specification ofcomponents in transcription typewriting. Acta
psychologica 54, 1 (1983), 249–262.

16. Stephen C Johnson. 1967. Hierarchical clustering
schemes. Psychometrika 32, 3 (1967), 241–254.
17. Nina Keith and K Anders Ericsson. 2007. A deliberate
practice account of typing proficiency in everyday typists.
Journal of Experimental Psychology: Applied 13, 3(2007), 135.
18. Yili Liu, Robert Feyen, and Omer Tsimhoni. 2006.
Queueing Network-Model Human Processor (QN-MHP):
A computational architecture for multitask performancein human-machine systems. ACM Transactions on
Computer-Human Interaction (TOCHI) 13, 1 (2006),
37–70.
19. Cheryl D Metcalf, Thomas A Irvine, Jennifer L Sims,
Yu L Wang, Alvin WY Su, and David O Norris. 2014.
Complex hand dexterity: a review of biomechanicalmethods for measuring musical performance. Frontiers in
psychology 5 (2014).
20. Josip Music̀ and Roderick Murray-Smith. 2015. Nomadic
Input on Mobile Devices: the Influence of Touch Input
Technique and Walking Speed on Performance and Offset
Modeling. Human-Computer Interaction (2015).
21. OptiTrack. 2015. Motive:Body.Production Motion
Capture Software. (2015).
http://www.optitrack.com/products/motive/body/

22. David E Rumelhart and Donald A Norman. 1982.
Simulating a skilled typist: A study of skilled
cognitive-motor performance. Cognitive Science 6, 1
(1982), 1–36.
23. Timothy A Salthouse. 1984. Effects of age and skill intyping. Journal of Experimental Psychology: General
113, 3 (1984), 345–371.
24. Timothy A Salthouse. 1986. Perceptual, cognitive, andmotoric aspects of transcription typing. Psychologicalbulletin 99, 3 (1986), 303–319.
25. Mark A Schmuckler and Elizabeth L Bosman. 1997.
Interkey timing in piano performance and typing.
Canadian Journal of Experimental Psychology 51, 2(1997), 99.
26. Walter Schneider. 1985. Training high-performanceskills: Fallacies and guidelines. Human Factors 27, 3(1985), 285–300.
27. LH Shaffer. 1975. Control processes in typing. The
Quarterly Journal of Experimental Psychology 27, 3(1975), 419–432.
28. LH Shaffer. 1978. Timing in the motor programming oftyping. The Quarterly Journal of Experimental
Psychology 30, 2 (1978), 333–345.

14. Yuzuru Hiraga, Yoshihiko Ono, and others. 1980. An
analysis of the standard English keyboard. In Proceedingsof the 8th Conference on Computational Linguistics.
Association for Computational Linguistics, 242–248.

29. LH Shaffer and J Hardwick. 1968. Typing performance
as a function of text. The Quarterly Journal of
Experimental Psychology 20, 4 (1968), 360–369.

15. Bonnie E John. 1996. TYPIST: A theory of performancein skilled typing. Human-Computer Interaction 11, 4(1996), 321–355.

30. CA Terzuolo and P Viviani. 1980. Determinants andcharacteristics of motor patterns used for typing.
Neuroscience 5, 6 (1980), 1085–1103.

31. Paul D Varcholik, Joseph J LaViola, and Charles E
Hughes. 2012. Establishing a baseline for text entry for a
multi-touch virtual keyboard. International Journal of
Human-Computer Studies 70, 10 (2012), 657–672.
32. Keith Vertanen and Per Ola Kristensson. 2011. A
Versatile Dataset for Text Entry Evaluations Based on
Genuine Mobile Emails. In MobileHCI ’11: Proceedingsof the 13th International Conference on
Human-Computer Interaction with Mobile Devices andServices. 295–298.
33. Joe H Ward Jr. 1963. Hierarchical grouping to optimize
an objective function. Journal of the American statisticalassociation 58, 301 (1963), 236–244.

34. Changxu Wu and Yili Liu. 2008. Queuing networkmodeling of transcription typing. ACM Transactions on
Computer-Human Interaction (TOCHI) 15, 1 (2008), 6.
35. Eldad Yechiam, Ido Erev, Vered Yehene, and DanielGopher. 2003. Melioration and the transition fromtouch-typing training to everyday use. Human Factors:
The Journal of the Human Factors and Ergonomics
Society 45, 4 (2003), 671–684.
36. Ying Yin, Tom Yu Ouyang, Kurt Partridge, and Shumin
Zhai. 2013. Making touchscreen keyboards adaptive tokeys, hand postures, and individuals: a hierarchicalspatial backoff model approach. In Proceedings of the
SIGCHI Conference on Human Factors in Computing
Systems. ACM, 2775–2784.