Fitts’ law 50 years later: applications and contributions from human–computer interaction

Since the advent of graphical user interfaces, electronic information has grown exponentially, whereas the size of screen displays has stayed almost the same. Multiscale interfaces were designed to address this mismatch, allowing users to adjust the scale at which they interact with information objects. The technology has progressed quickly and the theory has lagged behind. Multiscale interfaces pose a stimulating theoretical challenge: reformulating the classic target-acquisition problem from the physical world into an infinitely rescalable electronic world. We address this challenge by extending Fitts’ original pointing paradigm: we introduce the scale variable, thus defining a multiscale pointing paradigm. This article reports on our theoretical and empirical results. We show that target-acquisition performance in a zooming interface must obey Fitts’ law and, more specifically, that target-acquisition time must be proportional to the index of difficulty. Moreover, we complement Fitts’ law by accounting for the effect of view size on pointing performance, showing that performance bandwidth is proportional to view size, up to a ceiling effect. Our first empirical study shows that Fitts’ law does apply to a zoomable interface for indices of difficulty up to and beyond 30 bits, whereas classical Fitts’ law studies have been confined in the 2–10 bit range. Our second study demonstrates a strong interaction between view size and task difficulty for multiscale pointing, and shows a surprisingly low ceiling. We conclude with implications of these findings for the design of multiscale user interfaces.     

Characterizing computer input with Fitts’ law parameters—the information and non-information aspects of pointing

Throughput (TP), also known as index of performance or bandwidth in Fitts’ law tasks, has been a fundamental metric in quantifying input system performance. The operational definition of TP is varied in the literature. In part thanks to the common interpretations of International Standard ISO 9241-9, the “Ergonomic requirements for office work with visual display terminals—Part 9: Requirements for non-keyboard input devices”, the measurements of throughput have increasingly converged onto the average ratio of index of difficulty (ID) and trial completion time (MT), i.e. TP=ID/MT. In lieu of the complete Fitts’ law regression results that can only be represented by both slope (b) and intercept (a) (or MT=a+b ID), TP has been used as the sole performance characteristic of input devices, which is problematic. We show that TP defined as ID/MT is an ill-defined concept that may change its value with the set of ID values used for the same input device and cannot be generalized beyond specific experimental target distances and sizes. The greater the absolute value of a is, the more variable TP (=ID/MT) is. ID/MT only equals a constant 1/b when a=0. We suggest that future studies should use the complete Fitts’ law regression characterized by (a, b) parameters to characterize an input system. a reflects the non-informational aspect and b the informational aspect of input performance. For convenience, 1/b can be named as throughput which, unlike ID/MT, is conceptually a true constant.     

“Beating” Fitts’ law: virtual enhancements for pointing facilitation

We survey recent research into new techniques for artificially facilitating pointing at targets in graphical user interfaces. While pointing in the physical world is governed by Fitts’ law and constrained by physical laws, pointing in the virtual world does not necessarily have to abide by the same constraints, opening the possibility for “beating” Fitts’ law with the aid of the computer by artificially reducing the target distance, increasing the target width, or both. The survey suggests that while the techniques developed to date are promising, particularly when applied to the selection of single isolated targets, many of them do not scale well to the common situation in graphical user interfaces where multiple targets are located in close proximity.     

Speed–accuracy tradeoff in Fitts’ law tasks—on the equivalency of actual and nominal pointing precision

Pointing tasks in human–computer interaction obey certain speed–accuracy tradeoff rules. In general, the more accurate the task to be accomplished, the longer it takes and vice versa. Fitts’ law models the speed–accuracy tradeoff effect in pointing as imposed by the task parameters, through Fitts’ index of difficulty (I_d) based on the ratio of the nominal movement distance and the size of the target. Operating with different speed or accuracy biases, performers may utilize more or less area than the target specifies, introducing another subjective layer of speed–accuracy tradeoff relative to the task specification. A conventional approach to overcome the impact of the subjective layer of speed–accuracy tradeoff is to use the a posteriori “effective” pointing precision W_e in lieu of the nominal target width W. Such an approach has lacked a theoretical or empirical foundation. This study investigates the nature and the relationship of the two layers of speed–accuracy tradeoff by systematically controlling both I_d and the index of target utilization I_u in a set of four experiments. Their results show that the impacts of the two layers of speed–accuracy tradeoff are not fundamentally equivalent. The use of W_e could indeed compensate for the difference in target utilization, but not completely. More logical Fitts’ law parameter estimates can be obtained by the W_e adjustment, although its use also lowers the correlation between pointing time and the index of difficulty. The study also shows the complex interaction effect between I_d and I_u, suggesting that a simple and complete model accommodating both layers of speed–accuracy tradeoff may not exist.     

Towards a standard for pointing device evaluation, perspectives on 27 years of Fitts’ law research in HCI

This paper makes seven recommendations to HCI researchers wishing to construct Fitts’ law models for either movement time prediction, or for the comparison of conditions in an experiment. These seven recommendations support (and in some cases supplement) the methods described in the recent ISO 9241-9 standard on the evaluation of pointing devices. In addition to improving the robustness of Fitts’ law models, these recommendations (if widely employed) will improve the comparability and consistency of forthcoming publications. Arguments to support these recommendations are presented, as are concise reviews of 24 published Fitts’ law models of the mouse, and 9 studies that used the new ISO standard.     

Behind Fitts’ law: kinematic patterns in goal-directed movements

Half a century ago, Paul Fitts first discovered that the time necessary to complete a pointing movement (MT) linearly increases with the amount of information (ID) necessary to specify the target width (W) relative to the distance (D). The so-called Fitts’ law states that , with ID being a logarithmic function of the D/W ratio. With the rising importance of pointing in human–computer interaction, Fitts’ law is nowadays an important tool for the quantitative evaluation of user interface design. We show that changes in ID give rise to systematic changes in the kinematics patterns that determine MT, and provide evidence that the observed patterns result from the interplay between basic oscillatory motion and visual control processes. We also emphasize the generality and abstract nature of Fitts’ robust model of human psychomotor behavior, and suggest that some adaptations in the design of the (computer-mediated) coupling of perception and production of movement might improve the efficiency of the interaction.     

Unobtrusive touch‐free interaction on mobile devices in dirty working environments

In this work, we propose a new mode of interaction using hand gestures captured by the back camera of a mobile device. Using a simple intuitive two‐finger picking gesture, the user can perform mouse click and drag‐and‐drop operations from the back of the device, which provides an unobstructed touch‐free interaction. This method allows users to operate on a tablet and maintain full awareness of the display, which is especially suitable for certain working environments, such as the machine shop, garage, kitchen, gym, or construction site, where people's hands may be dirty, wet, or in gloves. The speed, accuracy, and error rate of this interaction have been evaluated and compared with the typical touch interaction in an empirical study. The results show that, although this method is not, in general, as efficient and accurate as direct touch, participants still consider it an effective and intuitive method of interacting with mobile devices in environments where direct touch is impractical.     

Effects of positioning optimization in an alternative computer workstation for people with and without low back pain

The aim of this study was to measure the impact of positioning optimization on typing performance and user comfort for people with and without low back pain (LBP) in alternative working postures. Participants completed a series of typing tests in each of five randomly ordered alternative working postures ranging from upright to fully supine. Typing accuracy and typing speed were recorded as were subjective measures of overall comfort and body part discomfort. The impact of positioning optimization of the monitor, keyboard, and arm supports was determined by comparing results from an “Optimized” test study protocol (n = 27) with those from a “Non-Optimized” test study protocol (n = 26). The results indicate a significant improvement in user comfort with the optimized positioning, but no significant differences in typing performance between the two test protocols. However, in both tests the slowest typing speeds occurred in the fully reclined and zero gravity working postures. Results of the user comfort scores indicated that for the Non-Optimized test, all alternative working postures were less comfortable than the upright posture. Whereas, in the Optimized test the tilted and reclined postures were comparable to the upright working posture and only the zero gravity posture was viewed as less comfortable.

Relevance to industry

Understanding the importance of position optimization for VDT operators in alternative working postures will provide valuable information toward the development of more comfortable and more accommodating computer workstations.     

Predictive pull-based control of an unmanned manufacturing cell, accounting for robot mobility

In order to remove the cell size limitation and to make cellular manufacturing systems more flexible, a manufacturing cell has been equipped with a mobile robot which moves from machine to machine, much like its human counterpart would do. To further acquire a portion of the attributes (intelligence and adaptability of the human worker) lost in robotizing the traditional manned manufacturing cell, a “limited” knowledge-based cell control algorithm is developed. This algorithm maintains standard pull control logic as its underlying basis while utilizing heuristically, knowledge of the ongoing processes and their current status. In this paper, an analysis of this ‘new’ predictive pull-based controller is presented. The simulation results from the predictive pull-based controller are evaluated and compared with the standard pull control logic, first come first serve and shortest distance. A test-bed of an unmanned manufacturing cell with a self-propelled mobile robot was used for experimental verification. Simulation and experimental results show that the degree of improvements gained in the cell performance over the standard pull control method is dependent on the robot’s mobility velocity and how much part inspection/part rejection is performed within the cell. In conclusion, the predictive pull-based algorithm is relatively simple variation of pull control which has the ability of enhancing the “near optimal” pull cell control performance.     

Musculoskeletal symptoms among mobile hand-held device users and their relationship to device use: A preliminary study in a Canadian university population

The study aims were, in a population of university students, staff, and faculty (n = 140), to: 1) determine the distribution of seven measures of mobile device use; 2) determine the distribution of musculoskeletal symptoms of the upper extremity, upper back and neck; and 3) assess the relationship between device use and symptoms. 137 of 140 participants (98%) reported using a mobile device. Most participants (84%) reported pain in at least one body part. Right hand pain was most common at the base of the thumb. Significant associations found included time spent internet browsing and pain in the base of the right thumb (odds ratio 2.21, 95% confidence interval 1.02–4.78), and total time spent using a mobile device and pain in the right shoulder (2.55, 1.25–5.21) and neck (2.72, 1.24–5.96). Although this research is preliminary, the observed associations, together with the rising use of these devices, raise concern for heavy users.     

基于人工神经网络对sEMG信号的手势动作识别

针对利用表面肌电信号(sEMG)对手势动作的肌电信号的研究较少和sEMG信号处理过于复杂的问题,提出了利用人工神经网络和sEMG信号对人的手势动作进行识别研究,引入了MYO硬件设备对新的手势动作sEMG信号采集.利用MYO从手臂上获取每一个手势动作的sEMG信号,提取信号特征值,作为算法的训练数据和测试数据.采用人工神经网络中的反向传递神经网络算法来进行对4种不同手势动作分类,对应目标手指识别率在90.35%.研究结果可以被用来做临床诊断和生物医学的应用以及用于现代硬件的发展和更现代化的人机交互的发展.     

Push selling—Multicast messages to wireless devices based on the publish/subscribe model

Push technology automates the information delivery process by not requiring users to request for the information they need. Wireless has experienced explosive growth in recent years, and “push” will be the predominant wireless service delivery paradigm of the future. A wide variety of services, alerts and messages, such as promotional content, will be delivered to consumers’ phones or PDA. However, to push information to a wireless device can be a challenge because of the problem of intermittent communication links and resource constraints on wireless devices as well as limited bandwidth. This paper explores an efficient multicasting mechanism that “pushes” pre-specified information to groups of wireless devices. The mechanism operates with limited bandwidth and also overcomes the connectivity problem. Based on the above concept, we have designed and implemented a system to multicast sales information via wireless technology. The system is message-oriented and JMS compliant.     

基于T9的移动终端中文输入系统的设计

探讨了彩屏WCDMA、GPRS/GSM双模移动终端上和PC模拟器上的PDK(Phone Development Kit)控件以及事件-消息机制、文件系统及其安全性的设计等.为了使得T9中文输入法与该双模移动终端系统能够无缝地融合在一起,还创造性地运用了Adapter设计模式以及具有良好安全性的文件系统和内存分配机制.     

Robot navigation in the real world:: Experiments with Manchester’s FortyTwo in unmodified, large environments

Mobile robot navigation under controlled laboratory conditions is, by now, state of the art and reliably achievable. To transfer navigation mechanisms used in such small-scale environments to applications in untreated, large environments, however, is not trivial, and typically requires modifications to the original navigation mechanism: scaling up is hard.In this paper, we discuss the difficulties of mobile robot navigation in general, the various options to achieve navigation in large environments, and experiments with Manchester’s FortyTwo, which investigate how scaling up of navigational competencies can be achieved. We were particularly interested in autonomous mobile robot navigation in unmodified, large and varied environments, without the aid of pre-installed maps or supplied CAD models of the environment. This paper presents a general approach to achieve this.FortyTwo regularly travels the corridors of the Department of Computer Science at Manchester University, using topological maps, landmarks, low level “enabling behaviours” and active exploitation of features of the environment. Experimental results obtained in these environments are given in this paper.     

基于事件框架的移动摘要方法研究

本文提出了一种面向移动终端的文本摘要方法,该方法基于框架思想,将文本摘要生成过程分解为信息抽取和文本生成两个阶段。信息抽取阶段对原文进行词频统计,关键词句分析,并在此基础上利用规则抽取相应信息填充摘要框架。文本生成阶段利用框架编码协议对框架进行解析,并结合相关模板生成文本摘要。     

Development of a mobile robotic system for working in the double-hulled structure of a ship

Shipbuilding processes involve highly dangerous manual welding operations. Welding ship walls inside double-hulled structures presents a particularly hazardous environment for workers. This paper describes the “Rail Runner X” (RRX), a new robotic system that can move autonomously inside the walls of a double-hulled ship and automatically execute the required welding processes. The RRX robotic system is composed of a mobile platform and a welding robot consisting of a 3P3R serial manipulator. The robot is used to weld U-shaped trajectories located between two longitudinal stiffeners. The mobile platform enables traverse movements onto neighboring longitudinal stiffeners. The entire cross section of the robotic system is small enough to be placed inside the double-hulled structure via a conventional access hole from the outside shipyard floor. The overall engineering design process that led to the final robot solution developed is presented in this paper, including kinematic analysis data and experimental results for verifying the autonomous movement and welding performance.     

Visual recognition of pointing gestures for human–robot interaction

In this paper, we present an approach for recognizing pointing gestures in the context of human–robot interaction. In order to obtain input features for gesture recognition, we perform visual tracking of head, hands and head orientation. Given the images provided by a calibrated stereo camera, color and disparity information are integrated into a multi-hypothesis tracking framework in order to find the 3D-positions of the respective body parts. Based on the hands’ motion, an HMM-based classifier is trained to detect pointing gestures. We show experimentally that the gesture recognition performance can be improved significantly by using information about head orientation as an additional feature. Our system aims at applications in the field of human–robot interaction, where it is important to do run-on recognition in real-time, to allow for robot egomotion and not to rely on manual initialization.     

The design of hand gestures for human–computer interaction: Lessons from sign language interpreters

The design and selection of 3D modeled hand gestures for human–computer interaction should follow principles of natural language combined with the need to optimize gesture contrast and recognition. The selection should also consider the discomfort and fatigue associated with distinct hand postures and motions, especially for common commands. Sign language interpreters have extensive and unique experience forming hand gestures and many suffer from hand pain while gesturing. Professional sign language interpreters (N=24) rated discomfort for hand gestures associated with 47 characters and words and 33 hand postures. Clear associations of discomfort with hand postures were identified. In a nominal logistic regression model, high discomfort was associated with gestures requiring a flexed wrist, discordant adjacent fingers, or extended fingers. These and other findings should be considered in the design of hand gestures to optimize the relationship between human cognitive and physical processes and computer gesture recognition systems for human–computer input.     

CAD data visualization on mobile devices using sequential constrained Delaunay triangulation

3D graphic rendering in mobile application programs is becoming increasingly popular with rapid advances in mobile device technology. Current 3D graphic rendering engines for mobile devices do not provide triangulation capabilities for surfaces; therefore, mobile 3D graphic applications have been dealing only with pre-tessellated geometric data. Since triangulation is comparatively expensive in terms of computation, real-time tessellation cannot be easily implemented on mobile devices with limited resources. No research has yet been reported on real-time triangulation on mobile devices.In this paper, we propose a real-time triangulation algorithm for visualization on mobile devices based on sequential constrained Delaunay triangulation. We apply a compact data structure and a sequential triangulation process for visualization of CAD data on mobile devices. In order to achieve a high performance and compact implementation of the triangulation, the nature of the CAD data is fully considered in the computational process. This paper also presents a prototype implementation for a mobile 3D CAD viewer running on a handheld Personal Digital Assistant (PDA).     

Practical multiagent rendezvous through modified circumcenter algorithms

We present a class of modified circumcenter algorithms that allow a group of agents to achieve “practical rendezvous” when they are only able to take noisy measurements of their neighbors. Assuming a uniform detection probability in a disk of radius σ about each neighbor’s true position, we show how initially connected agents converge to a practical stability ball. More precisely, a deterministic analysis allows us to guarantee convergence to such a ball under r-disk graph connectivity in 1D under the condition that r/σ be sufficiently large. A stochastic analysis leads to a similar convergence result in probability, but for any r/σ>1, and under a sequence of switching graphs that contains a connected graph within bounded time intervals. We include several simulations to discuss the performance of the proposed algorithms.