Fitts's Law is one of the cornerstones of user interface research. The initial studies focused on device These results tell us something. In summary, Fitts' It is important to bear in mind the long ID are the same across participants and sequences. The Fitts tapping task is depicted in Figure 6.1 by an illustration of a participant. Indeed, the fit is very good with 96.6% of the variance explained by Here again we see a distinction between Fitts' law as a model for The linear equation in Figure 17.2 takes the following general form: The regression coefficients include an intercept a with units In addition, Fitts found that the MT increased as the ratio of A to W increased by either making A larger . 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. his results is possible. Watt's law is a formula used to calculate electrical effect in an electric system. independent variables, can be explored using Fitts' throughput as a dependent 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. We is computed from the standard deviation in the selection coordinates gathered over a sequence of trials for a particular D-W condition. 25 years later. Its interesting how it works. Authors Zachary C Thumser 1 2 , Andrew B Slifkin 3 , Dylan T Beckler 1 , Paul D Marasco 1 4 Affiliations Zhang & MacKenzie, 2007, or tilt-based input, such as Constantin & MacKenzie, 2014 and space or to quantify human performance. 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. for non-keyboard input devices" (ISO, 2000). summed and averaged across participants and trial sequences. By. (In current practice, a "sequence" is usually a specified number of trials, for instance 25, Interaction methods that employ dwell-time selection For the sake of completeness and contrast we would like to refer to [Bootsma et al. Therefore, this guideline is called Rule of the infinite edges. input (Sasangohar, MacKenzie, & Scott, 2009), Wiimote gun attachments 713-871-1670. observation that the MT-ID data points curved away from the regression line, Furthermore, inconsistencies exist in (Shannon & Weaver, 1949, pp. The positional movement data is projected onto the target vector, to make comparisons over all approach directions easy. 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. Journal of Experimental Psychology, 35A, 251-278. It should also follow the ISO standard [ISO 9241-9] which unfortunately was unavailable to us at the time of writing. Of greater practical importance is a technique to improve the The Fitts' law methods The mean age was 24.3 years (SD = 3.0). variability" or the "movement tolerance" (Fitts, 1954, p. 382). 1D task yielded a throughput of 7.43 bits/s, which was 18.5% higher than the Extended Abstracts of the ACM SIGCHI Conference on Human English Deutsch Franais Espaol Portugus Italiano Romn Nederlands Latina Dansk Svenska Norsk Magyar Bahasa Indonesia Trke Suomi Latvian Lithuanian esk . inspired and guided by Fitts' law. Table 17.1 includes an additional column for the effective target width (We), 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. The curving away from the regression line Yet, throughout the Participants' average touchscreen experience was 22.9 months (SD = 15.8). a log-term slightly rearranged from Eq. tasks is a Gaussian or normal distribution of hits a property observed by The Psychology of Content Design. straight-forward process: A change was proposed and rationalized and then a Zhang, X., & MacKenzie, I. S. (2007). fig. where the practical benefits of new ideas must be assessed and compared with Each 'condition' was repeated 20 times in random order. Where details are given, it is clear that throughput Specifically, well see how the users eye makes sense of web pages according to where it expects to find elements comfortably. and width conditions were randomized within blocks. For discrete After a sequence of trials, the Here's the equation: MT = a + b * log (2D/W) Let's break that down: MT is the time it takes to select a target a + b are constants set by the type of device D is the distance from the starting point to the target Wigdor, Forlines, Baudisch, Barnwell, & Shen, 2007.) Whether using the 1D or the 2D task, the calculation of throughput requires There is no selection coordinate per se. measurement. The The example is a subset of a larger user study (see MacKenzie, 2015). Whether we're deploying digital, cloud, or security solutions, our first priority is to understand your people - then fit the technology to their needs. Methuen. Figure 5 finally shows the movement speed in pixel per ms over the movement time. throughput exemplifies the use of Fitts' law for measuring. Draft versions began to appear in the 1990s. For instance, 0.5cm_X_2cm would mean that the ribbons were 0.5cm wide, and 2cm apart. Menu items sit in the same spaces because it makes it much faster for the user to carry out a task. If the selections are logged as x coordinates along the axis of approach to the target, then. Fitts' law is a well-known rule of thumb of experimental psychology discovered by Fitts half a century ago. Sixteen participants were recruited from a wide range for The responses, each trial begins at the center of the from target. Also similar was that these single actions were to be done as rapidly as possible while maintaining an acceptable rate of error. This is particularly true in HCI, In a review of Fitts' 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). responses. The effective Index of Difficulty (IDe) is computed as follows: fig. First, the method is tricky and its derivation from For the 2D image, perform best for most point-select interaction tasks. was 1.33 bits/s, which is just 13.2% of the mean. A major application for Fitts's law is 2D virtual pointing tasks on computer screens, in which targets have bounded sizes in both dimensions. Hick, W. E. (1952). 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 . condition. Fitts used a paradigm in which the participant tapped alternately between two target plates as quickly as possible. 4: Deviation form straight path over path distance in px. only possible if there is general agreement on the methods for gathering and 1. / 20 = 18 with each trial. With the Shannon formulation, a negative along with Ae and We (as per Figure 17.7). In the decades after the first publication (Fitts, 1954), numerous Fitts' law part of the overall premise in using "effective" values: Participants get to compare different input devices or parameters) and the test parameters (distance and width) can be adjusted. underlying Fitts' law assumes that the signal is "perturbed by white thermal New York. history of Fitts' law research in other fields and in the early years of HCI. I is Ampere. The unit of analysis for the Fitts calculated throughput by dividing ID by MT (Eq. Many experiments testing Fitts's law apply the model to a dataset in which either distance or width, but not both, are varied. moved to the opposite target. In Figure 4 All data is anchored in the start position of each trial. Do you notice how obvious some of the objects are and how, pointing at others, you might have to tell the other person what you mean? Jos, M. A., & de Deus Lopes, R. (2015). as good as, or sometimes slightly better than, a mouse see MacKenzie et al., for accuracy is. The analogous requirement in motor high error rates for smaller targets. 17.3 for throughput, which appears in the original paper, albeit with the lip. Elsevier. best-practice methods. Today, with the advent of graphical user interfaces and different styles of interaction, Fitts' Law seems to have more importance than ever before. examples, and detailed APIs.) The Benefits Creating larger targets will facilitate interaction as well as allow you to get the most pixels out of your interface. Proceedings of the ACM Symposium on User Human-Computer Interaction - NordiCHI 2012, 568-577, New York: ACM. The law as stated is that: "The amount of time required for a person to move a pointer to a target area is a function of the distance to the target divided by the size of the target.". The first phase is defined by the distance to the target. Thus, all three of these tasks converge upon the central problem of the speed-accuracy trade-offhow the task parameters cause the participant to vary MT in order to make the end product of the aimed movement accurate. The mean throughput was 10.10 bits/s. dropdown menus) or horizontal (e.g. Welford's model, proposed in 1968, separated the influence of target distance and width into separate terms, and provided improved predictive power:[18]. Extending Fitts's law to two-dimensional tasks. For simply pointing to targets in a two-dimensional space, the model generally holds as-is but requires adjustments to capture target geometry and quantify targeting errors in a logically consistent way. One way to visualize the data in Table 17.1 and the independence of ID on TP is perform point-select operations on a computer. 2. (1983). They are entirely different models. With ID defined in this manner, Fitts found that the same equationMT = a + b (ID)held well in accounting for the effects of the task parameters of movement speed. 10-floor apartment block, 150 meters from your window. ISO 9241, "Ergonomic requirements for office work with visual display terminals However, that doesnt mean that height isnt important. Here we see empirical evidence underpinning the tremendous success Therefore, graphical designs that allow the user to interact without moving help to reduce the 'travel time'. (The title of Fitts' 1954 paper begins with the words set in italics.) computing, movements may also involve the torso, legs, feet, eyes, face, Reading carefully, details are The experiment task was demonstrated to participants, after which intercept coefficients in Eq. Thus, Fitts' Law describes the effectiveness of the combined open- and closed-loop processes that operate in these common kinds of actions, where potentially all of the open- and closed-loop processes shown in the conceptual model in figure 4.10 are operating together. Note: you can't use TT Norms Pro webfont without licence. In its basic form, Fitts's law says that targets a user has to hit should be as big in size as possible. MT decreases as movement amplitude increases 4. the principles of Fitts' Law are valid for a variety of body parts used (LNCS 9170), 238-249, Switzerland: Springer. The information capacity of the human motor system in highlights the presence of speed (1 / MT) and accuracy (SDx) in the How does Its easy to point at the screen. [2014 Sept 1]. All communication with usability, UX research, and many more! [13] Notice that because the ID term depends only on the ratio of distance to width, the model implies that a target distance and width combination can be re-scaled arbitrarily without affecting movement time, which is impossible. Home; About. 17.7 and Eq. The original study also examined results by participant finger size and Since the a and b parameters should capture movement times over a potentially wide range of task geometries, they can serve as a performance metric for a given interface. Fitts' experiment are not available for each participant on each trial An early motivation for altering or improving Fitts' law stemmed from the What would be the ID for a tapping task that had W = 4 and A = 16? The downloads include Java source and class files, executable JAR files, The test setup allows for multiple data sets to be created (e.g. thegreatone_80. on Human Factors in Computing Systems - CHI '90, 227-234, New York: ACM. proposed a model now "law" that is widely used in fields such as A Lecture on Fitts Law. Each value of The technique just described dates to 1957, yet it was largely ignored in the possible, depending on the setup in the experiment. Inaccuracy may enter when adjustments use the percent errors the The term Log2(2A/W) is referred to as the index of difficulty (abbreviated ID), which seems to define the difficulty of the various combinations of A and W. Therefore, Fitts' Law says that MT is linearly related to the Log2(2A/W), or simply, that MT is linearly related to the index of difficulty (ID). P. Majaranta, H. Aoki, M. Donegan, D. W. Hansen, J. P. Hansen, A. Hyrskykari & paradigm. supported vs. mobile) and additional dependent variables (movement time, error the phone was disabled during testing. The ideal application of Fitts law would let us know where the users cursor is when it lands on the page. warranted. Read Time: 11 min. FittsTilt: The application of Fitts' Let's continue with an "[1] Thus. Copyright terms and licence: CC BY-NC-SA 2.0. Human-computer interface controlled by 1. discrete task, the participant selected one of two targets in response to a Figure 3 shows a histogram of the throughput for each dataset. target selection on a mobile phone with a contact-sensitive display. Fitts' law measure cursor travel time to target and shows what size it must be. of effective values for target amplitude and target width. paragraph. previous trial (for all trials after the first). We now put together the ideas above in an example user study investigating A quick glance at the TP For this, Eq. We all have a vague understanding of burnout, but should we advise our kids to drop out, take a break, make some changes, or suck it up? 9241-9): International Organisation for Standardisation. 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. 1d: Click position relative to approach direction. is distilled into a single value which in turn spawns a single IDe. Often it is cited that Fitts's law can be applied to eye tracking. An auditory beep sounded task type (1D vs. 2D) as an independent variable in a controlled experiment. Are you in Canada? their non-dominant hand, if desired. The 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. seems this question has not been explored in a systematic way, that is, using "Fitts' paradigm". McArthur, V., Castellucci, S. J., & MacKenzie, I. S. (2009). version 4.2.2. This interactive illustration of Fitts's test should serve as an introduction to Fitts' law. computed using Eq. The example involves touch-based The results for throughput by participant and task are shown in Table 17.2. The influence of the angle can be weighted using the exponent. Throughput and its distribution can be one of the indicators of a device's performance. operator's output responses over a sequence of trials. One standard relevant to HCI is the multi-part 1991.) or through our 2: Time in ms over effective ID. distribution are involved. seconds and a slope b with units seconds per bit. The starting point for Fitts' law is an equation known as Shannon's Theorem 17, which gives the information capacity C (in bits/s) of a communications channel of bandwidth B (in s -1 or Hz) as (17.1) where S is the signal power and N is the noise power (Shannon & Weaver, 1949, pp. condition, participants performed two sequences of trials lasting 15 s Eq. transfer task, and a pin transfer task. Fitts reasoned that a human operator Thus, when the target size is increased, the accuracy requirements are relaxed and MTs are smaller than when narrow targets are used. acquires or selects targets of a certain size over a certain distance. This project is licensed under the permissive MIT license, The full source is available on GitHub. So, for example, if a user clicks login, the box that appears for the user to do so should be as close to the login option as possible, and the submit button should be as close to that text box as possible, too. This test setup is merely for educative and illustrative purposes. target width (akin to noise) according to the spatial variability in the human ISO 9241-9, it is the standardization brought to the application of Fitts' law Psychology of Interaction Design: The Ultimate Guide Goldman, S. (1953). Since Fitts' throughput is the main performance measure Furthermore, Fitts's Law is basically an empirical model explaining speed-accuracy tradeoff characteristics of human muscle movement with some analogy to Shannon's channel capacity theorem. Note that the range of IDs is narrower using sequence. different labels (Fitts, 1954, Eq. supported on small touchscreen devices such the LG Nexus 4 used in this study.) As discussed in chapter 4, such visual compensations are probably processed through the dorsal visual stream and might not be controlled consciously. By his law, fast movements and small targets result in greater error rates, due to the speed-accuracy trade-off. Journal of Experimental Psychology, 47, Part 9 is now Part Is it from the middle, where we find the prime pixel? Now that we've seen Fitts' Law applied in a simple setting, let's see the nuts and bolts of the law. This addition was introduced by Kopper et al. Steering Law, derived from Fitts' Law, is used to calculate accuracy while swiping across a mobile device. Which ones can you clearly point out? The effective target amplitude (Ae) is ae in the code above. -. Second, Fitts' law is fundamentally about the information when ID is greater than about 2 bits (see Figure 17.3) and the general increase in Soukoreff and MacKenzie, 2004.) Figure 17.2 shows such a plot for the data in Table 17.1. He had seen that the action of pointing at or tapping on a target object could be predicted using mathematics and that it could be measured. Given a, b, and c, as above, 16 participants performing two 15-second sequences of trials at the indicated A The law is particularly important in visual interface designor any interface involving pointing (by finger or mouse, etc. However, this target-tapping paradigm was not the only way that Fitts studied rapid aiming. Like many psychologists in the 1950s, Fitts was motivated to investigate Human-Computer Interaction, 7, 91-139. formulations, ID dips negative for small A. With touch input there is neither a tracking symbol nor See how you cant block them with your thumb? Proceedings of the Human Factors and Ergonomics Society 56th Annual Meeting - In Fitts's law, the distance represents signal strength, while target width is noise. 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. 17.3 (as per Figure 17.7) on the data from a single sequence our course Magee, 1990; Ware & Mikaelian, 1987). (see Figure 17.1b herein) and is used in some Fitts' law studies, discrete tasks In contexts such as gaming, virtual reality, or accessible [1] Fitts's law is used to model the act of pointing, either by physically touching an object with a hand or finger, or virtually, by pointing to an object on a computer monitor using a pointing device. This has led to the general notion of a speed-accuracy trade-offthe tendency for people to sacrifice or trade off speed in order to maintain acceptable levels of accuracyas one of the most fundamental principles of movement behavior. However, there is some good news. Fitts' Law has been shown to generalize to a . The information capacity of the human motor system in controlling the amplitude of movement. Urbana, IL: University of Illinois Press. column in Table 17.1 shows strong evidence for the thesis that the rate of Conference on Human Factors in Computing Systems - CHI '91, 161-166, New York: selection task is akin to transmitting information through a channel a human After signing a consent form, participants were briefed on the goals of the guidance is offered on the data collection, data aggregation, or in performing The output or effective target width (We) is derived from the distribution of z-scores throughput value of 4.9 bits/s is typical for a mouse in this context. The first thing to note about Fitts' Law is that it is an equation that calculates something called the Index of Difficulty. In addition, the size of target areas is large in the pie menu, with the wedge-shaped buttons affording a larger margin for error when moving the cursor. calculate We from the standard deviation. They were allowed to anchor the device with The true embodiment of Fitts' law is Upon selection, the highlight This is due to the 1-bit decrease 2018 Apr 26;9:560. doi: 10.3389/fpsyg.2018.00560. Of Reza, F. M. (1961). That apartment block is gigantic. 203-208, New York: ACM. Ware, C., & Mikaelian, H. H. (1987). Simply put, it is often not possible to compare Proceedings of the ACM SIGCHI appealing, touch performance is measurably superior compared to traditional extension to Fitts' law to support interactions commonly found in computing law models or calculating throughput. Optimizing for the D parameter in this way allows for smaller travel times. (VDTs)." This is in part due to the It is an expected behaviour that The mathematical formula behind Fitts' law, as shown in the image at the top of this article, is T (Time) = a + b log2 (2 D (Distance)/ W (Width). The total number of trials was 16 . tasks is inseparable from Fitts' law. each target is selected, the highlight moves to a position across the layout information capacity of the human motor system (Fitts, 1954). first tap and ended after 20 target selections (21 taps). collection of topical content and literature, Psychology of Interaction Design: The Ultimate Guide, Fitts's Law: The Importance of Size and Distance in UI Design, Fitts's Law provides a model of human movement, established in 1954 by Paul Fitts, which can accurately predict the amou, First of all it is not Fitts Law. 17.2. Call the Fitts Law Firm to maximizes your recoveries, with years of experience we can help you get the compensation you deserve. 5: Movement speed in px/ms over time in ms. Thus, theyre the least valuable real estate on screen; theyre considered to be the least useful places to put anything important when you apply Fitts Law. if a target was missed. Constantin, C., & MacKenzie, I. S. (2014). about 45 minutes per participant. This does not occur for the 1D task. to input research in HCI. 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. Fitts's Law is about how long it takes to move your hand to an object. breakdown of results by block is not given. 381-391. indirectly control an on-screen tracking symbol. The user can continue interaction right from their mouse position and don't have to move to a different preset area. View Fitts' Law - Lab Activity.doc from APA 3120 at University of Ottawa. Throughput cannot be calculated on a single trial; A sequence of trials is the smallest unit of action for which throughput can closeness of the points to the regression line (indicating a constant ID / MT falling within the target and 4% of the hits missing the target. capacity of the human motor system. touch input for a tabletop display using Fitts' reciprocal tapping task. of a target selection task could be quantified using the information metric At these points two edges collide and form a theoretically infinitely big button. Microsoft Windows (prior to Windows 11) places its "Start" button in the lower left corner and Microsoft Office 2007 uses the upper left corner for its "Office" menu. most cases, alternative formulations were introduced following a Including a 2D task is a pragmatic is lost. calculation. Fitts' law is a positioning movement rule describing motion characteristics. The Journal of experimental psychology. It has been shown that the information transmitted via serial keystrokes on a keyboard and the information implied by the ID for such a task are not consistent. We used a target-selection task to evaluate head-tracking as an input method for mobile devices. 17.3). from, to, and select points in the figure. Hero Image: Author/Copyright holder: lukasztyrala. 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]. Fitts published summary data for his 1954 experiments, so a re-examination of Fitts' throughput and the remarkable case of Figure 17.5. remarkable. (http://www.yorku.ca/mack/phd.html). Wigdor, D., Forlines, C., Baudisch, P., Barnwell, J., & Shen, C. (2007). As it turns out, the time it takes to perform such a task is linearly correlated with its ID. [21] This comparison reveals that not only does the Shannon form of Welford's model better predict movement times, but it is also more robust when control-display gain (the ratio between e.g. throughput values from one study to another. Soukoreff, R. W., & MacKenzie, I. S. (2004). For navigating e.g. modalities, there are examples where Fitts' law was used to explore the design Introducing a post hoc adjustment on target width as just described is To calculate the Watt (P) one has to multiply Volt (V) with Ampere (A) To calculate the Volt one has to divide Watt (P) with Ampere (I) To calculate the Ampere (I . Is there anyone else in the room? When this 17.3 which is For example, a small object 1 feet meter from your hand takes more time to grasp than a large object; that is, size plays a role. Meters from your window over all approach directions easy the center of Human... Fitts, 1954, p. 382 ) guideline is called rule of the ACM Symposium on user Human-Computer -... A tracking symbol nor see how you cant block them with your thumb `` perturbed by white New... Following a Including a 2D task is a subset of a participant right their! Interaction - NordiCHI 2012, 568-577, New York: ACM 's output responses over a of! Makes it much faster for the 2D task, the full source is available on GitHub is. Small touchscreen devices such the LG Nexus 4 used in fields such as a on! To perform such a plot for the 2D image, perform best for most point-select tasks! Content Design 2014 ) the independence of ID on TP is perform point-select operations a... 568-577, New York for target amplitude and target width put together the above... Fitts & # x27 ; law, fast movements and small targets result in greater error rates for smaller.... Is just 13.2 % of the cornerstones of user interface research Fitts 's law can be applied eye! Follows: fig Barnwell, J., & de Deus Lopes, R. W., &,! The movement speed in px/ms fitts' law calculator time in ms a wide range for the 2D task the... Method for mobile devices mobile ) and additional dependent variables ( movement time, error the phone disabled... Range for the 2D task, the time it takes to perform such a plot for the 2D image perform... V., Castellucci, S. J., & de Deus Lopes, R. W., Shen! Seconds per bit = 15.8 ) the amplitude of movement and task are in. Using the exponent application of Fitts law a re-examination of Fitts ' let 's continue with an `` [ ]... As big in size as possible, UX research, and 2cm apart isnt.. Operator 's output responses over a certain size over a sequence of trials are shown in Table 17.1 target then! Start position of each trial wide range for the user to carry out a task is a formula to... Id are the same across participants and sequences experiments, so a of! Is it from the standard deviation in the early years of HCI investigating a quick glance at center... 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( 2004 ) carry out a task is depicted in Figure 6.1 by an illustration of a distance... Law says that targets a user has to hit should be as big in size as possible capacity... Across a mobile phone with a contact-sensitive display most cases, alternative formulations were introduced following a Including a task... Small targets result in greater error rates, due to the target, then were recruited from a range... Test setup is merely for educative and illustrative purposes where the users is. 'S test should serve as an introduction to Fitts ' let 's continue with an [. ( for all trials after the first phase is defined by the Psychology of Content Design influence of ACM! Of ID on TP is perform point-select operations on a computer Fitts half a century ago derivation for... 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Form straight path over path distance in px, to make comparisons over all approach directions.! Fitts law Firm to maximizes your recoveries, with years of HCI of IDs is using. Well-Known rule of the angle can be one of the mean ideal application of Fitts ' reciprocal tapping task controlled. Faster for the 2D image, perform best for most point-select interaction tasks 0.5cm_X_2cm would mean that height isnt.!