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Mobile Circular Keyboards

Lawrence Leung, Parham Aarabi

Department of Electrical and Computer Engineering

University of Toronto

Toronto, Ontario, Canada

Abstract—This paper proposes a circular mobile QWERTY

keyboard and analyzes performance on this keyboard compared

to a standard flat keyboard. The Circularly Arced Keyboard

(CAK) layout for single handed operation using the thumb was

found to have a pangram replication time within 1.2 seconds

compared to the regular keypad and a keystroke accuracy within 1.7%.

Keywords—mobile computing; soft keyboard; user interface;

human-machine interface; human-computer interaction

I. INTRODUCTION

Smartphone market penetration continues to increase every year, with current estimates suggesting over 1 billion smart phones in use. Although the interaction space is limited, the touchscreen on smartphones has resulted in a variety of novel user interfaces optimized for the mobile touchscreen. While there has been significant innovation in mobile user interfaces, mobile keyboard designs (especially that used on iOS) still remain a replica of the typewriters of the last century.

For Latin alphabet based languages, the Sholes (QWERTY) keyboard layout is the most readily available, and has been in use since 1873 [22]. There are variations to suit various Latin based languages, but the basic layout does not vary. The QWERTY keyboard, designed to reduce jamming, and limited by mechanical packaging, is really not ideal in the mobile touch-screen era.

The QWERTY keyboard with a rectangular layout is the default method of entering text. However, the mobility of smart phones with touchscreens smaller than eight inches cannot accommodate traditional two-handed touch typing. When operated by a single hand, the thumb becomes the predominant interaction finger, but becomes awkward when attempting to span the far edges of a touchscreen. In the following sections the design philosophy and choice of a soft keyboard layout more suited to one handed operation will be discussed.

II. DESIGN PHILOSOPHY

The well known and remarkably robust Fitts’ law[1] gives a relation between distance traveled to a target, the target width, and the mean time of completion. It indicates that the mean time is proportional to distance and inversely proportional to target width. With respect to mobile devices, distant buttons require more time to interact with, and smaller buttons also require more time for interaction.

Fitts’ law has been rigorously explored both physically and in the context of computers with keyboards and pointing devices [21]. Fitts’ original tapping task is quite applicable to mobile touch UI, more so than the traditional mouse, due to more direct interaction. It should also be noted that unlike mouse-monitor environments, that are considered to have infinite width buttons at the monitor edge, this is not the case with mobile touch devices.

There is a significant body of work exploring different keyboard configurations, both QWERTY and otherwise. However, the majority is based on rectangular layout and with square keys [3][4][5][9][12][15][16][17].

In this paper, we consider a circular keyboard that is better suited to the motion of the thumb for one-handed typing. Guided by Fitts’ law and the position of a thumb above a touch screen, and by considering a given radius as a one dimensional Fitts’ law situation, nearby buttons with smaller widths would be equivalent to further buttons with larger width. If buttons are not allowed to overlap, then circumferential rows of buttons would radiate from the thumb point, with increasing size as the number of rows increases.

III. DESIGN CHOICE

Figure 1 illustrates the more easily accessible areas of a phone held in a portrait orientation by a right-handed user. Based on the mechanical operation of a thumb, which actuates in an arced fashion at the carpometacarpal joint, a matched arced layout for a keyboard would be a good starting point for minimizing mean interaction time. Keeping the focus of the arc near the point of actuation of the thumb would present basically a quarter of a circle on the screen, thus a 90 degree arc with center located at the bottom corner was chosen. This creates a certain squaring of the keyboard area. From this point this layout will be referred to as the Circularly Arced Keyboard (CAK).

The pervasiveness of the QWERTY keyboard has made it a good choice to relatively populate the buttons, in an attempt to shorten learning times. This also should shorten testing times. The three rectangular alphabet rows were mapped to three arced rows, including the “,” and “.” buttons, to match the number of keys in the bottom two rows for simplicity. This presents a certain thinness to keys in the third row. The fourth row at the bottom is allocated for the a single “space” button. The numeric row was not included similar to commercial touch QWERTY keyboards.

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The arc of each key was determined by equally dividing 90 degrees by the number of keys within each row. The height or radial length of each key was determined by equally dividing the full radius of the arc over the four rows. The final result is displayed by Figure 2.

IV. USER TRIALS

A user trial was conducted attempting to gauge the efficacy and potential relevancy of the CAK.

A. Experiment

The experiment was conducted as follows:

A mobile device maintained in the upright portrait orientation, held in the right hand, and operated by the respective thumb.

Two keyboard configurations are presented; the first, a traditional QWERTY keyboard, and the second the CAK. Both

do not have a backspace key in an attempt to capture errors and facilitate evaluation of accuracy. As a test phrase the well known pangram, "the quick brown fox jumps over the lazy dog", was chosen for its alphabet coverage.

Replication of the test phrase via each keyboard configuration was conducted and timed. In general the first keyboard presented to a user was the last keyboard of the previous user in an effort to have the bias due to presentation order, averaged out. For the CAK a practice sessions was conducted prior to a timed session, lasting between 1 to 2 minutes. For the QWERTY keyboard no practice was conducted prior to timing due to general familiarity with the layout.

The results were timed manually, while the result strings were recorded using a memo application, and later synchronized, minimizing processing errors for post processing. The Levenshtein distance between the entered and test string was used to facilitate calculation of accuracy.

The means, standard deviations, and deltas were computed for each keyboard configuration, along with a histogram of errors.

V. RESULTS AND FEEDBACK

A. Results

A sample size 24 users was collected. The results are summarized in Table 1. The mean time to completion of the task was approximately 30 seconds. The difference between the two keyboards was approximately 1 second. The standard deviation in completion time was 7.6 and 10.68 for the CAK and QWERTY keyboard, respectively.

TABLE I. TABLE 1 RESULTS SUMMARY.

The overall accuracy of the task was approximately 95%. The difference in accuracy between the two keyboards was 1.6%. The standard deviation in completion accuracy was 5.3% and 7.25%, for the CAK and QWERTY keyboard, respectively.

The CAK appears to be competitive in both time and accuracy when compared to a QWERTY keyboard, even when faced with minimal training time. The lower CAK mean time variance indicates a common unfamiliarity with the CAK layout, which also explains the slightly lower variance in accuracy, indicating slightly more care is taken with unfamiliar systems.

User trials

summary

Time (seconds) Accuracy

CAK QWERTY CAK QWERTY

mean 30.85 29.7 0.941 0.957

std. dev. 7.6 10.7 0.053 0.073

mean delta 1.1 0.016

std. dev. delta 3.0 0.019

Figure 2. CAK layout.

Figure 1.One handed operation.

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Histograms for key errors arranged in rows are in Figure 1, Figure 2, and Figure 3. It must be noted that errors were not

normalized over frequency of appearance in the test phrase, where “space”, and “o” occur most frequently. Errors at row edge keys, appear lower than non-edge keys, except for the “m”, located in the bottom row, which had higher errors in the CAK layout.

B. Feedback

The feedback received from the user trial is as follows.

intuitive

space button awkward

bottom row keys too thin

gestures for backspace and enter

transparency

key colour

visual feedback

haptic feedback

high area occupancy

Gestures, transparency, key color, visual and haptic

feedback, are all features that can be added to augment the functionality of practically any soft keyboard, but for the purposes of this experiment are not critical to exploring the CAK layout.

With respect to space button position and key sizes; these have ultimate bearing on layout. It was suggested to remove ",", and "." from the bottom row, which should add significant area to the remaining keys in the row. This was foreseen during construction, but left for simplicity. There were very few space errors during the test, when considering its frequency. This could be attributed to its large area. However, given its obscured position along with frequency, a more accessible position should be considered.

VI. CONCLUSIONS

In this paper, the motivation for a single thumb operated mobile touchscreen keyboard layout, based on Fitts’ law, was discussed and designed. The CAK was the result. A user trial was conducted to evaluate the efficacy and relevance.

From the results of the experiment, there is significant competitiveness in single handed CAK usage when compared to a standard rectangular QWERTY keyboard, both in mean time and accuracy. The training time to become functional with the CAK layout was minimal. Given the basic configuration of this first iteration, further optimization can be performed, and should result in increased performance.

The findings in this work can be further confirmed with additional trial data. Also, the creation of a dedicated test application would allow for finer data collection. Longer term trials would provide information about user acceptance or potential concept fatigue.

0

1

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3

4

5

6

7

8

q w e r t y u i o p

CAKQWERTY

Figure 1. Top row errors.

0

1

2

3

4

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a s d f g h j k l

CAKQWERTY

Figure 2. Middle row errors.

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4

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z x c v b n m space

CAKQWERTY

Figure 3. Bottom row errors.

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There is a wealth of change that could be applied to future iterations. Currently, the area required is higher than a standard QWERTY soft keyboard. This can be addressed by optimizing the key dimensions, and perhaps applying a more elliptical arc. Exploration of compliance with available design guidelines similar to ANSI/HFES 200 [6], can lead to commercial release. Finally, adding incremental functionality currently available for keyboards, advanced color scheme, visual preview and feedback, gestures, could potentially bring this layout to commercial competitiveness.

Figure 4. Iteration screenshot.

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