Fitts original formula was based on shannons theorem shannon. When you shouldnt use fitts law to measure user experience. The lawful continuous linear relation between movement time and task difficulty i. Movement time for hard tasks is longer than for easy tasks movement time prediction ahlstrom, d. This site uses cookies for analytics, personalized content and ads. Accuracy, target reentry and fitts law performance of preschool children using mice juan pablo hourcade, benjamin b.
Fitts law expresses the relationship between the time to select a target, movement time mt, and the objective difficulty of the targeting task. A note on the validity of the shannon formulation for. The study of how speed and accuracy trade off in human movement has often focused on how movement time mt varies as a function of movement amplitude a and target width w. Fitts law fitts law or fittss law never call it fitts law named after paul fitts, for his 1954 study of pointing. Fitts law remains silent, however, on how id affects the dynamic and kinematic patterns. Bederson, allison druin, and francois guimbretiere university of maryland, humancomputer interaction laboratory abstract several experiments by psychologists and human factors researchers have shown. Hci researchers generally use the shannon equation 7,18. There has been an increasing interest in understanding the fat finger problem, and ng fitts law for finger examini input. Basic hci principles and models lmu medieninformatik. Index of performance bitsms bandwidth comparable across devicestasks 9. Proceedings of the human factors and ergonomics society 2018. The only difference is that pvalue is left as a decimal point and is not converted to a. Ffitts index of difficulty fitts law and finger input.
This paper presents a reappraisal of fitts 1954 law and outlines reasoning which predicts that, for tasks of equivalent difficulty as calculated by fitts index of difficulty, smallertolerance tasks will, within limits, take longer to perform. Accuracy, target reentry and fitts law performance of. Conduct an experiment to collect data record mt and selection coordinates over multiple ids, over. Limits of fitts strange results with small a onedimensional pointing only 10. Fitts law, a onedimensional model of human movement, is commonly applied to twodimensional target acquisition tasks on interactive computing systems. Fitts law fitts law is a well known empirical regularity which predicts movement time mt as a function of target width w and target distance d 2,3. Fittss law holds that the time, t, to complete a speeded movement to a target is a linear function of an index of difficulty, id, characterizing the movement. We have shown that the interpretation of target width and the formulation used in the calculation of a tasks index of difficulty play a critical role in the accuracy of the model. The lower number for the glove shows that fitts law has difficulties predicting its performance. Fitts s law often cited as fitts law is a predictive model of human movement primarily used in humancomputer interaction and ergonomics.
A conceptual framework for the use of fitts law to detect intentional misrepresentation of skills andor abilities im in paralympic athletics rebecca l deuble, mark j connick, emma m beckman, bruce abernethy, sean m tweedy the university of queensland, school of human movement studies, qld 4072, australia. The model accounts for 81 % of the mouses variance and 48% of the gloves variance. The fitts task has been used to study fittss law, which shows that movement time mt is related to the information constraints of the movement fittss index of difficulty, id such that there is a positive, linear relationship between mt and id and mts are similar when the scale of the movement. Fittss law remains one of the few hard, reliable humancomputer interaction predictive models, joined more recently by the accotzhai steering law, which is derived from fittss law. Fittss law is basically an empirical model explaining speedaccuracy tradeoff characteristics of human muscle movement with some analogy to shannons channel capacity theorem. The results in figure 6 and figure 7 illustrate a problem with traditional applications of fitts law to twodimensional target acquisition tasks. His original study was on pointing with a stylus, but his work is applicable to pointing with a mouse, using touch screens, and the range of pointing devices for 2d displays.
The inverse relationship between movement speed and accuracy in goaldirected aiming is mostly investigated using the classic fitts paradigm. Specifically, a discontinuity was observed at critical id and was attributed to a transition between two distinct dynamic regimes that occurs with increasing difficulty. Fitts law1 predicts that the move ment time mt to acquire a target is a linear function of the tasks index of difficulty id 1the formulation in equation 1 is not. Fittss law the glossary of human computer interaction. Applying fitts law to gesture based computer interactions. Pdf perceived difficulty in a fitts task semantic scholar. We have shown that the interpretation of target width and the formulation used in the calculation of a tasks index of difficulty play a.
Aaron dewald explains how a simple calculation can illustrate which of your exam questions are great, which are too difficult, and. Modeling and improving selection in cascading pulldown menus using fitts law, the steering law and force fields. Moreover, the hci community uses few formulas, and are related to fitts law. As a key input modality for touchscreens, touch input has been extensively studied.
This is easy to understand, not too difficult to implement and it doesnt seem to make much sense to contradict such a simple and obvious. Proceedings of the human factors and ergonomics society. Dec 04, 2012 the key statement of fittss law is that the time required to move a pointing device to a target is a function of the distance to the target and its size. For rectangular targets, such as words, it is demonstrated that the model can break down and yield unrealistically low even negative. In this paper, we challenge hoffmanns position regarding the shannon formulation. A literature survey on fitts law and its applications runa barik, sujeet kumar abstract the way of pointing a target object and the movement time of the pointer lead to a challanging problem in hci. In human computer interaction hci, fitts law is recognized as the law of pointing, and is regularly. In the realm of human movement, fitts law is the preeminent model. Based on shannons theorem for information processing, fitts law allows the estimation of required times for rapid movements between a starting point and a target area. Their results were consistent with their previous findings, thereby suggesting that left handers were not at a disadvantage when they were experienced in using the mouse.
Does changing fitts index of difficulty evoke transitions in. A new power law of movement time for motor control tasks is proposed as an alternative to the classical fitts law. A literature survey on fitts law and its applications. A movement model based on fitts law is an equation predicting movement time mt from a tasks index of difficulty id. Fitts proposed an index of difficulty id for a target acquisition task using a log. Pdf applying fitts law to gesture based computer interactions.
How to convert pdf to word without software duration. Intuitively the index of difficulty, id, represents the difficulty of completing the movement task defined by d and w, as id increases for longer distances or narrower targets. The difficulty index formula is fairly easy to remember because it is the same as determining the percentage of students who answered the question correctly. Fitts index of difficulty and shannons entropy, in the quantification of the.
Pdf fitts law index of difficulty evaluated and extended. Extending fitts law to a threedimensional pointing task research. The crux of fitts law is that there is a linear relationship between index of. It seems necessary as there are an unmanageable amount of publications on fitts law with many of them. A conceptual framework for the use of fitts law to detect.
The logarithm in fittss law is called the index of difficulty id for the target, and has units of bits. When fitts law is used to make predictions of movement time, the meaning of fitts index of difficulty is of little importance, because due to the robust linear relationship between id and mt, fitts law provides accurate predictions regardless of the precise meaning of the slope parameter b. Healthy subjects stood on a force platform and performed quick and accurate hand movements into targets of different size located at two distances. As a key input modality for touchscreens, touch input has been extensively studied by many researchers. The notion that the overall performance of the human motor system plus associated. Nowadays the meaning of bits is well known and the relation of digits to precision is trivial more digits allow higher precision. Fitts law with a virtual reality glove and a mouse. We tested a hypothesis that the classical relation between movement time and index of difficulty id in quick pointing action fitts law reflects processes at the level of motor planning. For decades, fitts law 1954 has been used to model pointing time in user interfaces. Fitts defined the term index of difficulty id, shown in figure 3, as a measure of the task difficulty as follows.
Information in precision and the index of difficulty. However, it has been insufficient in modeling target acquisition small with fingertouch based input on screens. A conceptual framework for the use of fitts law to detect intentional misrepresentation of skills andor abilities im in paralympic athletics rebecca l deuble, mark j connick, emma m beckman, bruce abernethy, sean m tweedy the university of queensland, school of. Today, with the advent of graphical user interfaces and different styles of interaction, fitts law seems to have more importance than ever before. Results showed that the mean movement time was highly correlated with the targets index of difficulty for all devices, providing evidence that fitts law can be.
Fitts law index of difficulty evaluated and extended for. The shannon formulation is gene r ally the formulation of choice. What exactly is item difficulty and how do you measure it. Fitts law has proven to be predictor of pointing a strong performance under a wide range of conditions. Effects of gain and index of difficulty on mouse movement.
Fitts law index of difficulty evaluated and extended for screen size variations 233 occurred in a trial under the condition errors not acceptable, the trial was cancelled and. The three most common variations of fitts index of difficulty are the fitts formulation, the welford formulation, and the shannon formulation. Values for the device m,l were determined as values for the device s the ratio of screen sizes, i. Human performance and fitts law paul fitts found a predictable relationship between the size of a target, the distance we have to move to it, and the speed at which we can tap, point at, click, or whatever on it. What is fitts law fitts law as a human performance measure fitts law as a predictive model york university department of electrical engineering and computer science 42 fitts law as a predictive model step 1. Our graph does support fitts law because as the difficulty increased with the speed accuracy trade of f because there was a decrease in our groups acc uracy. Equation 1 is the shannon formulation of the index of difficulty, a formulation that is theoretically and empirically preferable to fitts original 8, 9. The fourth point represents an index difficulty of 4. Derivation of an error model for pointing formulated for one dimension, fitts law 8 predicts the movement time mt to acquire a target of size w at distance a. Jul 20, 2015 what exactly is item difficulty and how do you measure it. Information in precision and the index of difficulty as mentioned already, at the time of fitts research shannons information theory was young and the definition of the index of difficulty was difficult. The key statement of fittss law is that the time required to move a pointing device to a target is a function of the distance to the target and its size.
Does changing fitts index of difficulty evoke transitions. According to fitts law, movement time scales linearly with a single quantity, the index of difficulty id, which quantifies task difficulty through the quotient of target width and distance. A recent paper by hoffmann 1 critiqued the three and concluded that the fitts and welford formulations are valid and that the shannon formulation is invalid. Reanalysis of fitts data appears to confirm this view.
A number of researchers have noted that, with as few as 2 submovements primary and corrective, the movement time versus index of difficulty id data are described by fitts law, that is, there. An error model for pointing based on fitts law microsoft. But as with any rapid motor act, faster movement times come at the cost of increased errors. Fitts introduced the index of difficulty id as a characteristic measure for such movements. A note on the validity of the shannon formulation for fitts. The last point represents an index difficulty of 6.
This study provided a detailed investigation of perceived difficulty pd in a fitts task. A large number of seminal paper have been proposed towards this. This scientific law predicts that the time required to rapidly move to a target area is a function of the ratio between the distance to the target and the width of the target. As mentioned already, at the time of fitts research shannons information theory was young and the definition.
The second major contribution of fitts law are the measures to assess index of difficulty, throughput, and predicted movement time. By continuing to browse this site, you agree to this use. Their results were consistent with their previous findings, thereby suggesting that left handers were not at a disadvantage when they were experienced in using the mouse with both their preferred and nonpreferred hand. This scientific law predicts that the time required to rapidly move to a target area is a function of the ratio between. Fitts law remains silent, however, on how id affects the dynamic and kinematic patterns i. Fitts law index of difficulty evaluated and extended for screen size variations 231 2. After then, many researches extended the fitts law from various aspects, and the research for pointing movement was also extended from onedimensional to threedimensional. A reanalysis of fitts original data indicates that this power law may provide superior fits to those of fitts law, which may be interpreted as a special case of the power law. As mentioned earlier, index of difficulty describes the number of bits of information transmitted within the context of human motor system. In this study, participants moved a cursor on a computer screen from a starting point to a target with movement. The only difference is that pvalue is left as a decimal point and is not converted to a percentage value out of 100. Lncs 4561 modeling of humans pointing movement on the.
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