I. Scott MacKenzie

Phrase sets for evaluating text entry techniques

In evaluations of text entry methods, participants enter phrases of text using a technique of interest while performance data are collected. This paper describes and publishes (via the internet) a collection of 500 phrases for such evaluations. Utility programs are also provided to compute statistical properties of the phrase set, or any other phrase set. The merits of using a pre-defined phrase set are described as are methodological considerations, such as attaining results that are generalizable and the possible addition of punctuation and other characters.

A comparison of input devices in element pointing and dragging tasks

An experiment is described comparing three devices (a mouse, a trackball, and a stylus with tablet) in the performance of pointing and dragging tasks. During pointing, movement times were shorter and error rates were lower than during dragging. It is shown that Fitts’ law can model both tasks, and that within devices the index of performance is higher when pointing than when dragging. Device differences also appeared. The stylus displayed a higher rate of information pmeessing than the mouse during pointing but not during dragging. The trackball ranked third for both tasks,

The design and evaluation of a high-performance soft keyboard

The design and evaluation of a high performance soft keyboardfor mobile systems are described. Using a model to predict theupper-bound text entry rate for soft keyboards, we designed akeyboard layout with a predicted upper-bound entry rate of 58.2wpm. This is about 35% faster than the predicted rate for a QWERTYlayout. We compared our design (OPTI) with a QWERTY layout in alongitudinal evaluation using five participants and 20 45-minutesessions of text entry. Average entry rates for OPT1 increased from17.0 wpm initially to 44.3 wpm at session 20. The average ratesexceeded those for the QWERTY layout after the 10 session (about 4hours of practice). A regression equation (R = .997) in the form ofthe power-law of learning predicts that our upper-bound predictionwould be reach at about session 50.

Accuracy measures for evaluating computer pointing devices

In view of the difficulties in evaluating computer pointing devices across different tasks within dynamic and complex systems, new performance measures are needed. This paper proposes seven new accuracy measures to elicit (sometimes subtle) differences among devices in precision pointing tasks. The measures are target re-entry, task axis crossing, movement direction change, orthogonal direction change, movement variability, movement error, and movement offset. Unlike movement time, error rate, and throughput, which are based on a single measurement per trial, the new measures capture aspects of movement behaviour during a trial. The theoretical basis and computational techniques for the measures are described, with examples given. An evaluation with four pointing devices was conducted to validate the measures. A causal relationship to pointing device efficiency (viz. throughput) was found, as was an ability to discriminate among devices in situations where differences did not otherwise appear. Implications for pointing device research are discussed.

Metrics for text entry research: an evaluation of MSD and KSPC, and a new unified error metric

We describe and identify shortcomings in two statistics recently introduced to measure accuracy in text entry evaluations: the minimum string distance (MSD) error rate and keystrokes per character (KSPC). To overcome the weaknesses, a new framework for error analysis is developed and demonstrated. It combines the analysis of the presented text, input stream (keystrokes), and transcribed text. New statistics include a unified total error rate, combining two constituent error rates: the corrected error rate (errors committed but corrected) and the not corrected error rate (errors left in the transcribed text). The framework includes other measures including error correction efficiency, participant conscientiousness, utilised bandwidth, and wasted bandwidth. A text entry study demonstrating the new methodology is described.

Testing pointing device performance and user assessment with the ISO 9241, Part 9 standard

The IS0 9241, Part 9 Draft International Standard for testingcomputer pointing devices proposes an evaluation of performance andcomfort. In this paper we evaluate the scientific validity andpracticality of these dimensions for two pointing devices forlaptop computers, a finger-controlled isometric joystick and atouchpad. Using a between-subjects design, evaluation ofperformance using the measure of throughput was done forone-direction and multi-directional pointing and selecting. Resultsshow a significant difference in throughput for themulti-directional task, with the joystick 27% higher; results forthe one-direction task were non-significant. After the experiment,participants rated the device for comfort, including operation,fatigue, and usability. The questionnaire showed no overalldifference in the responses, and a significant statisticaldifference in only the question concerning force required tooperate the device - the joystick requiring slightly more force.The paper concludes with a discussion of problems in implementingthe IS0 standard and recommendations for improvement.

KSPC (Keystrokes per Character) as a Characteristic of Text Entry Techniques

KSPC is the number of keystrokes, on average, to generate each character of text in a given language using a given text entry technique. We systematically describe the calculation of KSPC and provide examples across a variety of text entry techniques. Values for English range from about 10 for methods using only cursor keys and a SELECT key to about 0.5 for word prediction techniques. It is demonstrated that KSPC is useful for a priori analyses, thereby supporting the characterisation and comparison of text entry methods before labour-intensive implementations and evaluations.

Measuring errors in text entry tasks: an application of the Levenshtein string distance statistic

We propose a new technique based on the Levenshtein minimum string distance statistic for measuring error rates in text entry research. The technique obviates the need to artificially constrain subjects to maintain synchronization with the presented text, thus affording a more natural interaction style in the evaluation. Methodological implications are discussed, including the additional need to use keystrokes per characters (KSPC) as a dependent measure to capture the overhead in correcting errors.

Multimodal mouse: A mouse-type device with tactile and force display

A mouse was modified to add tactile and force display. Tactile feedback, or display, was added via a solenoid driving a small pin protruding through a hole in the mouse button. Force feedback was added via an electromagnet and an iron mouse pad. Both enhancements were embedded in the mouse casing, increasing its weight from 103 to 148 g. In a target selection task experiment, the addition of tactile information feedback reduced target selection times slightly, compared to the no additional feedback condition. A more pronounced effect was observed on the clicking time—the time to selection once the cursor entered the target. In this case, we observed a statistically significant speed-up of about 12% in the presence of tactile feedback. The modified mouse was also used in a test of virtual texture. The amplitude and frequency of solenoid pulses were varied according to the movement of the mouse and the underlying virtual texture. Subjects could reliably discriminate between different textures.

Performance differences in the fingers, wrist, and forearm in computer input control

Recent work in computer input control has sought to maximize the use of the fingers in the operation of computer pointing devices. The main rationale is the hypothesis that the muscle groups conmolling the fingers have a higher bandwidth than those controlling other segments of the human upper limb. Evidence which supports this, however, is inconclusive. We conducted an experiment to determine the relative bandwidths of the fingers, wrist, and forearm and found that the fingers do not necessarily outperform the other limb segments. Our results indicate that the bandwidth of the unsupported index finger is approximately 3.0 bits/s while the wrist and forearm have bandwidths of about 4.1 bits/s. We also show that the thumb and index finger working together in a pinch grip have an information processing rate of about 4.5 bits/s. Other factors which influence the relative performance of the different limbs in manipulation tasks are considered.