movements. ISO 9241-9 for measuring human performance. A recent study showed that you can increase sales conversions on a website by moving the add cart button to the left-hand menu of that site. The debate about its validity and which incarnation of the multiple versions that have been developed continue to drive researchers to learn more about its effectiveness based on particular applications. There is a reason. independent variables, can be explored using Fitts' throughput as a dependent Fitts's law has been extended to two-dimensional tasks in two different ways. Whilst it may seem obvious, user interface design often ignores that the larger a button is the easier it is to click with a pointing device. The range was limited due to the small display and finger input. Fitts' Law has been shown to generalize to a . While such models may indeed be valid, characterizing them Prentice-Hall. calculate We. their non-dominant hand, if desired. adjustment for accuracy is used, the situation is different. responses under different cognitive sets. redundancy, bits, noise, and channels entered the vocabulary of experimental years, and in particular by Card et al. of a target selection task could be quantified using the information metric The user can continue interaction right from their mouse position and don't have to move to a different preset area. The full spectrum of human movement applicable to Fitts' law is broader than doi:10.1016/j.ijhcs.2004.09.001, Bootsma, R. J., Fernandez, L., & Mottet, D. (2004). Data is accumulated in the live plots as long as the test parameters remain unchanged. With Participants 2 Tasks 5 Blocks 3 Amplitudes 2 Widths 20 Trials = Below you can find an interactive Fitts's test. Human-Computer Interaction, 7, 91-139. negative for a selection on the near side. that different researchers using benefit from a standardized methodology. amplitudes (A) were crossed with four target widths (W). Typically, we take the prime pixel as a starting point, until we take the first action. How can MT depend on the number of corrections when there is not enough time to make even a single correction? Let's continue with an for such evaluations, we also detail the calculation of throughput according to validity of these studies is not in question, there is considerable Today, IP is more commonly called throughput (TP). as good as, or sometimes slightly better than, a mouse see MacKenzie et al., To make an encompassing assessment further metrics have to be used (e.g. How does Examples The original investigation (Fitts, 1954) involved four experiment conditions: predicting and Fitts' law as a model for measuring. when ID is greater than about 2 bits (see Figure 17.3) and the general increase in Scope and Application Fitts' law is an effective quantitative method of modeling user performance in rapid, aimed movements, where one appendage (like a hand) starts at rest . In the decades after the first publication (Fitts, 1954), numerous Fitts' law The 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. Copyright terms and licence: CC BY-NC-SA 2.0. For Examples Fitts formulation (Fitts & Peterson, 1964, p. 110). target selection on a mobile phone with a contact-sensitive display. Zhang, X., & MacKenzie, I. S. (2007). time (MT) is the denominator: With ID in bits and MT in seconds, TP has units bits per second While many individual differences will never cease to exist between users, we are united by our shared psychology; the constraints and abilities of the human mind are much the same for all of us. The temporal width is a short duration from the moment the target appears until it disappears. Testing lasted reappraisal of twelve years progress. Participants were asked to select targets as quickly and accurately as Fitts used a paradigm in which the participant tapped alternately between two target plates as quickly as possible. The tasks in Figure 17.1 are commonly called the At its most simple, Fitts Law states that the bigger an object is and the closer it is to us, the easier it will be for us to reach it. (Several interesting yet difficult issues arise in interpreting the slope and Microsoft. This project is licensed under the permissive MIT license, The full source is available on GitHub. dropdown menus) or horizontal (e.g. to input research in HCI. The positon taken in the above paragraph follows from two points. In other words, a condition that target width applied research communities. Although the prospect of a negative ID may seem unlikely, Theres also the factor of distance to consider. Through learning about different aspects of human cognitionand how they relate to interaction designyou will find yourself much better equipped to put yourself in your users shoes, shifting their thoughts to the forefront and keeping a firm hold of them there when designing your next creation. modeling, predicting, and measuring human performance. summed and averaged across participants and trial sequences. Fitts' idea was novel for two reasons: First, it suggested that the difficulty / 20 = 18 with each trial. As Stimulus information as a determinant of reaction time. Usability is not dead: how left navigation menu increased conversions by 34% for an eCommerce website. With the adjustment for accuracy, Fitts's law more truly encompasses the speed-accuracy tradeoff. Sixteen participants were recruited from a wide range for Fitts (There are exceptions. We recomend a modern browser and fast computer to run the interactive tests. (2017) have developed formal models of the processes involved in the speed-accuracy trade-off that extends our understanding of Fitts' principles. MacKenzie, I. S. (2012). The premise for this is twofold: The second point is of ecological concern. are not included in ISO 9241-9. 17.6). At this juncture, it is worth stepping back and considering the big picture: The As the menu starts right on the pixel which the user clicked on, this pixel is referred to as the "magic" or "prime pixel".[24]. (Shannon & Weaver, 1949, pp. With 145,793 graduates, the Interaction Design Foundation is the biggest An Introduction to Information Theory. is useful for demos and to help inform and motivate participants during The example is a subset of a larger user study (see MacKenzie, 2015). the data in Table 17.1, TP = 8.97 bits/s using Eq. 2007), glove input (Calvo, Burnett, Finomore, & Perugini, 2012), and lip input (For consistency, the term throughput is used throughout this chapter.). calculation. The linear equation in Figure 17.2 takes the following general form: The regression coefficients include an intercept a with units Crafting the Experience of User Interface Messages. Similar to space, the distance to the target (i.e., temporal distance Dt) and the width of the target (i.e., temporal width Wt) can be defined for temporal targets as well. It was reported that Fitts' Law mathematically imply a predictive error rate model [ 12 ]. Given the complexity of the log-term for ID, this method is likely to Movements in the 2D information processing is relatively independent of task difficulty. computed using the discrete-error method. to (x2, y2), and select Fitts' law to examine similar phenomena should obtain similar results. version 4.2.2. For predicting, Fitts' law is an 1607 N. Market Street Champaign, IL 61820, Sign up and be the first to know about upcoming deals and new releases. Optimality in human motor performance: Ideal control of rapid aimed equation giving the time to acquire and select a target based on the distance We is computed from the standard deviation in the selection coordinates gathered over a sequence of trials for a particular D-W condition. (Available as free downloads at http://www.yorku.ca/mack/FittsLawSoftware/. In this task, which is now typically known as the Fitts tapping task (see figure 6.1), the widths (W) of each target and the amplitude (A) between the targets were varied in different combinations, and the participant's goal was to alternately tap each target as quickly as possible while making as few errors as possible (missed targets < 5%). For desktop interaction the mouse is well-known to The However, there is some good news. . Small objects that are far from your starting position or related objects that are far away from . Consider Table 17.1. An empirical two reciprocal or serial tapping tasks (1-oz stylus and 1-lb stylus), a disc If you created an object thats 500 pixels wide (to satisfy Fitts Law) but only a couple of pixels high, its pretty clear that a user will struggle to click on that object with any real accuracy. vs. mobile see MacKenzie, 2015). Group Members: Simon Wallner, Otilia Danet, Trine Eilersen, and Jesper Tved. Notably, for each of these input This course will equip you with the knowledge to relate to your users psychologically, thus allowing you to create stand-out products. published body of Fitts' law research that followed.1 There are several Fitts' law is a well-known rule of thumb of experimental psychology discovered by Fitts half a century ago. Mouse values are typically in the proposed by Crossman in 1957 in an unpublished report (cited in Welford, 1968, 1. 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. Such movements typically consist of one large motion component (ballistic movement) followed by fine adjustments to acquire (move over) the target. Lets try something now. and W. For each sequence, MT = 15 / m, where m is the number of stylus taps. 17.10 will yield different values for throughput. law is a model for rapid, aimed movements, and the presence of a nominal yet noise" (Shannon & Weaver, 1949, p. 100). Fitts Law experiment (goal, procedure, formula) GOAL. In HCI, a myriad of factors, or Fitts published summary data for his 1954 experiments, so a re-examination of for movements in any direction or angle. Fitts proposed an index of difficulty (ID) for a target acquisition task using respectively: Fitts referred to the target width as the "permissible (1991)[30] compared radial menu designs. V is Volt. weekly inspiration and design tips in your inbox. In other words, they are instructed to adjust MT so that the errors are acceptably small. That is to say, the equation for Fitts' Law also applied to the single-movement paradigm, which increases our confidence that Fitts' Law is one of the truly fundamental laws of motor behavior. Given a, b, and c, as above, A JavaScript project for calculating Fitts' Law. "[1] Thus. This is in part due to the In Fitts's law, the distance represents signal strength, while target width is noise. Overall the W-model represents the state-of-the-art measurement. implement the methods. of 768 1184 pixels and a pixel density of 320 dpi. The participant taps between two targets of varying width (W) and with varying amplitude between them (A), attempting to move as rapidly as possible while keeping the number of target misses to a minimum. ): we use it to assess the appropriate sizes of interactive elements according to the context of use and highlight potential design usability problems. 17.9 and Eq. with the most deviate point at ID = 1 bit. as improvements to Fitts' law, or even as variations on Fitts' law is, By following Fitts law, standard interface elements such as the right-click pop-up menu or short drop-down menus have had resounding success, minimizing the users travel distance with a mouse in selecting an optionreducing time and increasing productivity. Massachusetts: Morgan Kaufmann. Let's take a closer look at that: Distance, as you might expect, is the distance between the user's starting point and his or her end point (the target). (A possible exception is the stylus. These corresponded to task difficulties from ID = 1.14 bits to ID = 3.17 bits lies in the distinguishing properties of direct input vs. indirect input. 147-148). perform target selection by maintaining the cursor within the target for a p. 381). There are two methods for determining the effective target width, the Figure 6.3 illustrates two other tasks used in Fitts (1954) research. ACM Symposium on Engineering Interactive Computing Systems EICS 2009, For instance, 0.5cm_X_2cm would mean that the ribbons were 0.5cm wide, and 2cm apart. Then, try doing the same with your computer screen and maybe a big building outside your window. In general, Fitts' Law indicates that, as the width of the target (W) or the distance (D) between targets decreases (Fig 1), the movement time (MT) required to acquire that target grows in a linear way. in assistive technologies (pp. In essence, it leads to a generalization the prime pixel, from a web designers point of view, is the one sitting in the middle of the screen (until such a point as an action is taken, whereupon it will shift). Fitts, P. M., & Peterson, J. R. (1964). Also similar was that these single actions were to be done as rapidly as possible while maintaining an acceptable rate of error. Houston, TX 77027. The altered GOMS Spreadsheet If the observed error rate was 4% in the sequence of trials, then We = W. If the error rate was greater than 4%, We > W, and if the error rate was less than 4%, We < W. By using We, a Fitts' law model more closely reflects what users actually did, rather than what they were asked to do. high error rates for smaller targets. useful for summarizing participant responses or building a Fitts' law Journal of Experimental Psychology, 35A, 251-278. measurement. If the standard This chapter provides an overview of Fitts' law. moved and the size of the target. (2014). A movement during a single Fitts's law task can be split into two phases:[10]. And so, the information metaphor techniques on computing systems is an important area of research in related to pointing devices. More Excerpts From Motor Learning and Performance 6th Edition With Web Study Guide Loose Leaf Edition, Foundations of Kinesiology/Exercise and Sport Science, Research Methods, Measurements, and Evaluation, Motor Learning and Performance 6th Edition With Web Study Guide-Loose-Leaf Edition, Injury and Repair of Tendons and Ligaments, Psychological Reactions to Exercise and Athletic Injuries, Treatment and Prevention of Overtraining and Burnout, Quarterback Challenges in Canadian Football, Introduction to Physical Literacy on the Move, Improve shoulder internal rotation range of motion for throwing athletes. in a sequence of trials is differed. An additional feature of the Shannon formulation is that ID cannot be negative. [2014, Sept 1], Chopra, P (2010) Usability is not dead: how left navigation menu increased conversions by 34% for an eCommerce website [2015, Nov 1], Karafillis, A. Wishing to extend their ideas to tasks that are more typical and realistic, Fitts and Peterson (1964) used the same idea and variables as in the reciprocal-tapping task (figure 6.1), but used them with movements in which a single action was required from a starting position to a single target. Finally, it is reasonable to suspect that slower movements are more accurate, at least in part, because there is more time available to detect errors and to make corrections (as discussed in chapter 4), and that MT lengthens when the number of corrections to be made increases. Some of these questions are answered in the next section. The idea was first law research. (FITTSTOUCH is available as a free download including source code. 1c: Movement speed in px/ms over time in ms. fig. bits) will obviously take longer than "easy tasks" (e.g., ID = 1 bit). Data collection for a sequence began on the The metric is Fitts's index of difficulty (ID, in bits): Fitts also proposed an index of performance (IP, in bits per second) as a measure of human performance. horizontal movement to the right, the calculations described next are valid Eq. The information capacity of the human motor system in Proceedings of Graphics Interface 2009, power or theoretical basis. Which ones can you clearly point out? where S is the signal power and N is the noise power ISO 9241, "Ergonomic requirements for office work with visual display terminals International Journal of Human-Computer Studies, 61, 751-789. In 1954, Fitts described the relationship between the target distance, width, and time needed for a target acquisition task. ID in the table is calculated from A and W using Eq. Participants' average touchscreen experience was 22.9 months (SD = 15.8). is analogous to noise is that the distribution is normal with 96% of the hits Fitts called the rate of transmission the index of performance, 100-103). updated to the more generic title "Ergonomics of human-system interaction". In contexts such as gaming, virtual reality, or accessible fig. [27] The model predicts the error rate, the human performance in temporal pointing, as a function of temporal index of difficulty (IDt): Multiple design guidelines for GUIs can be derived from the implications of Fitts's law. data acquisition and statistical software for analysis, but manual measurement Figure 17.6c shows a typical reveal the true distribution of hits. This is as true in application design as it is in web design; its usability so well designed that you could click and find items in your sleep. A pragmatic [17] The Shannon-Entropy results in a different information value than Fitts's law. FITTS' Law Calculator: FITTS' Law Calculator estimates the time for younger and older adults to move a limb to a target. How do all of these experimental tasks converge to define Fitts' Law? View Fitts' Law - Lab Activity.doc from APA 3120 at University of Ottawa. The metric was based on an information analogy, where the distance to the center of the target (D) is like a signal and the tolerance or width of the target (W) is like noise. This is in contrast to Card, English, and Burr (1978) - Human movement is ubiquitous in computing. Fitts's law has been shown to apply under a variety of conditions; with many different limbs (hands, feet,[2] the lower lip,[3] head-mounted sights[4]), manipulanda (input devices),[5] physical environments (including underwater[6]), and user populations (young, old,[7] special educational needs,[8] and drugged participants[9]). theoretical problem. MacKenzie, I. S. (1989). information capacity of the human motor system (Fitts, 1954). See also the equation in Figure 17.7. So what does that mean for our designs? Task bars impede movement through the interface as they require a more time-consuming level of precision than when options are placed on the outer limits of the screen. Extending Fitts's law to two-dimensional tasks. The experiment task was demonstrated to participants, after which Although human behavior. The numerator in The testing device was an LG Nexus 4 touchscreen smartphone running Android OS 1992). adjusted measures (cf. (in "bits/s") as a dependent variable. If only the percentage of errors is known, the method uses a table of Soukoreff, R. W., & MacKenzie, I. S. (2004). underlying Fitts' law assumes that the signal is "perturbed by white thermal The two main performance testing procedures in ISO 9241-9 employ the Fitts' numerous researchers (e.g., Fitts & Radford, 1966; MacKenzie, 1991, p. 84; McArthur, V., Castellucci, S. J., & MacKenzie, I. S. (2009). For each A-W point-to-point movement distance for the trial, as projected on the task axis. Fitts's Rule Number 1: Create Larger Targets The likely most prominent statement derived from Fitts's Law is that the larger a target, the faster it is to acquire. responses, each trial begins at the center of the from target. I is Ampere. Furthermore, occlusion is unavoidable for some The 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. The information capacity of the human motor system in controlling the amplitude of movement. This chapter has provided an overview of Fitts' law in view of current practice This later became known as Fitts's law [Fitts 1954]. An important point is that Fitts' Law describes the tendency for performers to trade speed for accuracy. Massachusetts: Morgan Kaufmann. Fitts' law models the relationship between amplitude, precision, and speed of rapid movements. Therefore, this guideline is called Rule of the infinite edges. In a review of Fitts' All communication with of effective values for target amplitude and target width. It states that the time it takes someone to select an object depends on how far they are from the object and the size of the object. such conditions have actually been reported in the Fitts' law literature (Card Throughput was fairly flat over the five blocks of testing increase (or decrease) in the effective ID, and this tends to lessen the history of HCI (since Card et al., 1978), research on point-select computing Eq. The difference was statistically 1 bit to 7 bits. A formula that was originally proposed by Paul Fitts in 1954. fig. Figure 6.1 Illustration of a participant performing a Fitts tapping task. Experiments using the adjusted or effective target width will typically find a evaluation of video game controllers. Human perception and performance. Understanding Fitts Law (sometimes called Fittss Law) will give you a key to unlock another dimension in designing. stylus-tapping experiment extended as low as 1:1! (Of course, a direct comparison is not possible since mouse input is not MT decreases as movement amplitude increases 4. the principles of Fitts' Law are valid for a variety of body parts used top-level navigation), takes longer than clicking options in pie menus - where choices are arranged in a circle. 411, "Evaluation methods for the design of physical input devices" (ISO, While so tiny I cant see it is clearly not very good, and bigger than that is better there comes a point when increasing the size of an option makes it only a tiny bit more usable. While it may sound disappointing, think about this: it would probably nauseate users if the design of the website were to change immediately every time they touched the mouse. This derived from the W parameter. Experimental Psychology, 4, 11-36. Figure 6.3 Alternative reciprocal-movement tasks used by Fitts (1954): (a) disc-transfer task, (b) pin-transfer task. Upon selection, the highlight With only 3 downs to make 10 yards, the quarterback really has to be a playmaker. Journal of Experimental Psychology, 47, Proceedings of the Human Factors and Ergonomics Society 56th Annual Meeting - Travelling distance is the same for all options in pie menus, unlike linear menus where distance increases the further along or down the list of options the user goes. am i performing this equation wrong? [16] It describes the transmission of information using bandwidth, signal strength and noise. Evaluating eye tracking systems for computer input. The mean throughput was 10.10 bits/s. 71, 475-482. When You Shouldnt Use Fittss Law to Measure User Experience. was 1.33 bits/s, which is just 13.2% of the mean. ), Gaze interaction and applications of eye tracking: Advances It is also common to include an adjustment for accuracy in the calculation. English Deutsch Franais Espaol Portugus Italiano Romn Nederlands Latina Dansk Svenska Norsk Magyar Bahasa Indonesia Trke Suomi Latvian Lithuanian esk . The latter presents a particular challenge when Where details are given, it is clear that throughput Command buttons and any other interactive element in the graphical user interface must be distinguished from other non-interactive elements by size. Natapov, D., Castellucci, S. J., & MacKenzie, I. S. (2009). The terms probability, The relationships between A, W, and MT are plotted in figure 6.2 for one of Fitts' data sets. Like many psychologists in the 1950s, Fitts was motivated to investigate This is not a controlled experiment, and no definitive truths should be derived from it. 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