Publication statistics

Pub. period:2003-2008
Pub. count:8
Number of co-authors:5


Number of publications with 3 favourite co-authors:

Keith Vertanen:
Barton A. Smith:
Jason Alexander:



Productive colleagues

Per-Ola Kristensson's 3 most productive colleagues in number of publications:

Andy Cockburn:68
Shumin Zhai:67
Jason Alexander:9

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Per-Ola Kristensson

Has also published under the name of:
"Per Ola Kristensson"


Publications by Per-Ola Kristensson (bibliography)

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Zhai, Shumin and Kristensson, Per-Ola (2008): Interlaced QWERTY: accommodating ease of visual search and input flexibility in shape writing. In: Proceedings of ACM CHI 2008 Conference on Human Factors in Computing Systems April 5-10, 2008. pp. 593-596.

Shape writing is an input technology for touch-screen mobile phones and pen-tablets. To shape write text, the user spells out word patterns by sliding a finger or stylus over a graphical keyboard. The user's trace is then recognized by a pattern recognizer. In this paper we analyze and evaluate various keyboard layouts, including alphabetic, optimized (ATOMIK), QWERTY, and interlaced QWERTY for shape writing. The goodness of a layout for shape writing has two aspects. For users' initial ease of use the letters should be easy to visually locate. For long term use, however, the layout should maximize the imprecision tolerance and writing flexibility for all words. We present empirical studies for the former and mathematical analyses for the latter. Our results led to a new layout, interlaced QWERTY, which offers excellent separation of word shapes, while still maintaining a low visual search time. Many of the findings in our study also apply to traditional soft keyboards tapped with a stylus or one finger.

© All rights reserved Zhai and Kristensson and/or ACM Press

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Vertanen, Keith and Kristensson, Per-Ola (2008): On the benefits of confidence visualization in speech recognition. In: Proceedings of ACM CHI 2008 Conference on Human Factors in Computing Systems April 5-10, 2008. pp. 1497-1500.

In a typical speech dictation interface, the recognizer's best-guess is displayed as normal, unannotated text. This ignores potentially useful information about the recognizer's confidence in its recognition hypothesis. Using a confidence measure (which itself may sometimes be inaccurate), we investigated providing visual feedback about low-confidence portions of the recognition using shaded, red underlining. An evaluation showed, compared to a baseline without underlining, underlining low-confidence areas did not increase user's speed or accuracy in detecting errors. However, we found that when recognition errors were correctly underlined, they were discovered significantly more often than baseline. Conversely, when errors failed to be underlined, they were discovered less often. Our results indicate confidence visualization can be effective -- but only if the confidence measure has high accuracy. Further, since our results show that users tend to trust confidence visualization, designers should be careful in its application if a high accuracy confidence measure is not available.

© All rights reserved Vertanen and Kristensson and/or ACM Press

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Kristensson, Per-Ola and Zhai, Shumin (2007): Command strokes with and without preview: using pen gestures on keyboard for command selection. In: Proceedings of ACM CHI 2007 Conference on Human Factors in Computing Systems 2007. pp. 1137-1146.

This paper presents a new command selection method that provides an alternative to pull-down menus in pen-based mobile interfaces. Its primary advantage is the ability for users to directly select commands from a very large set without the need to traverse menu hierarchies. The proposed method maps the character strings representing the commands onto continuous pen-traces on a stylus keyboard. The user enters a command by stroking part of its character string. We call this method "command strokes." We present the results of three experiments assessing the usefulness of the technique. The first experiment shows that command strokes are 1.6 times faster than the de-facto standard pull-down menus and that users find command strokes more fun to use. The second and third experiments investigate the effect of displaying a visual preview of the currently recognized command while the user is still articulating the command stroke. These experiments show that visual preview does not slow users down and leads to significantly lower error rates and shorter gestures when users enter new unpracticed commands.

© All rights reserved Kristensson and Zhai and/or ACM Press

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Cockburn, Andy, Kristensson, Per-Ola, Alexander, Jason and Zhai, Shumin (2007): Hard lessons: effort-inducing interfaces benefit spatial learning. In: Proceedings of ACM CHI 2007 Conference on Human Factors in Computing Systems 2007. pp. 1571-1580.

Interface designers normally strive for a design that minimises the user's effort. However, when the design's objective is to train users to interact with interfaces that are highly dependent on spatial properties (e.g. keypad layout or gesture shapes) we contend that designers should consider explicitly increasing the mental effort of interaction. To test the hypothesis that effort aids spatial memory, we designed a "frost-brushing" interface that forces the user to mentally retrieve spatial information, or to physically brush away the frost to obtain visual guidance. We report results from two experiments using virtual keypad interfaces -- the first concerns spatial location learning of buttons on the keypad, and the second concerns both location and trajectory learning of gesture shape. The results support our hypothesis, showing that the frost-brushing design improved spatial learning. The participants' subjective responses emphasised the connections between effort, engagement, boredom, frustration, and enjoyment, suggesting that effort requires careful parameterisation to maximise its effectiveness.

© All rights reserved Cockburn et al. and/or ACM Press

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Zhai, Shumin, Kristensson, Per-Ola and Smith, Barton A. (2005): In search of effective text input interfaces for off the desktop computing. In Interacting with Computers, 17 (3) pp. 229-250.

It is generally recognized that today's frontier of HCI research lies beyond the traditional desktop computers whose GUI interfaces were built on the foundation of display -- pointing device -- full keyboard. Many interface challenges arise without such a physical UI foundation. Text writing -- ranging from entering URLs and search queries, filling forms, typing commands, to taking notes and writing emails and chat messages -- is one of the hard problems awaiting for solutions in off-desktop computing. This paper summarizes and synthesizes a research program on this topic at the IBM Almaden Research Center. It analyzes various dimensions that constitute a good text input interface; briefly reviews related literature; discusses the evaluation methodology issues of text input; presents the major ideas and results of two systems, ATOMIK and SHARK; and points out current and future directions in the area from our current vantage point.

© All rights reserved Zhai et al. and/or Elsevier Science

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Kristensson, Per-Ola (2005): Breaking the laws of action in the user interface. In: Proceedings of ACM CHI 2005 Conference on Human Factors in Computing Systems 2005. pp. 1120-1121.

Fitts' law, Steering law and Law of crossing, collectively known as the laws of action, model the speed-accuracy trade-offs in common hci tasks. These laws impose a certain speed ceiling on precise actions in a user interface. My hypothesis is that for some interfaces, the constraints of these laws can be relaxed by using context information of the task. To support this thesis, I present two systems I have developed for pen-based text input on stylus keyboards. These systems break either Fitts' law or the Law of crossing by taking advantage of high-resolution information from the pen, and the fact that words can be seen as patterns traced on the keyboard. Using these systems users can potentially gain higher text entry speed than on a regular stylus keyboard that is limited by the laws of action. I conclude by discussing planned future research, primarily improved visual feedback and empirical evaluation.

© All rights reserved Kristensson and/or ACM Press

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Kristensson, Per-Ola and Zhai, Shumin (2004): SHARK{sup:2}: a large vocabulary shorthand writing system for pen-based computers. In: Proceedings of the 2004 ACM Symposium on User Interface Software and Technology 2004. pp. 43-52.

Zhai and Kristensson (2003) presented a method of speed-writing for pen-based computing which utilizes gesturing on a stylus keyboard for familiar words and tapping for others. In SHARK{sup:2}:, we eliminated the necessity to alternate between the two modes of writing, allowing any word in a large vocabulary (e.g. 10,000-20,000 words) to be entered as a shorthand gesture. This new paradigm supports a gradual and seamless transition from visually guided tracing to recall-based gesturing. Based on the use characteristics and human performance observations, we designed and implemented the architecture, algorithms and interfaces of a high-capacity multi-channel pen-gesture recognition system. The system\'s key components and performance are also reported.

© All rights reserved Kristensson and Zhai and/or ACM Press

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Zhai, Shumin and Kristensson, Per-Ola (2003): Shorthand writing on stylus keyboard. In: Cockton, Gilbert and Korhonen, Panu (eds.) Proceedings of the ACM CHI 2003 Human Factors in Computing Systems Conference April 5-10, 2003, Ft. Lauderdale, Florida, USA. pp. 97-104.

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