regularities. But a The information capacity of the human motor [14] During fast saccadic eye movements the user is blind. Time Index of difficulty Intercept Slope (ms/bits) 8. A UI that allows for pop-up menus rather than fixed drop-down menus reduces travel times for the D parameter. Request PDF | Fitts’ Law: On Calculating Throughput and Non-ISO Tasks | We used a target-selection task to evaluate head-tracking as an input method for mobile devices. Active 1 year, 10 months ago. If the selections are logged as x coordinates along the axis of approach to the target, then. The equations above appear in ISO 9241-9 as the recommended method of Experimental Psychology, 47, 381-391. 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]). FITTS LAW EXPERIMENT. hierarchical pull-down menus, the user must generate a trajectory with the pointing device that is constrained by the menu geometry; for this application the Accot-Zhai steering law was derived. Fitts' Law in Mathematical Terms. However, if one understands why it is easier to predict where it will hold and where fail. Nowadays, Many experiments testing Fitts's law apply the model to a dataset in which either distance or width, but not both, are varied. A blinking target or a target moving toward a selection area are examples of temporal targets. combines a task's index of difficulty (ID) with the movement time (MT, in seconds) in selecting the target. system in controlling the amplitude of movement. This interactive illustration of Fitts's test should serve as an introduction to Fitts' law. Fitts’ law and the calculation of throughput In the field of Human-Computer Interaction (HCI), Fitts’ law has been mainly applied in two ways: firstly as a predictive model, and secondly as a mean to derive the dependent measure throughput (Fitts’ index of performance) as part of the comparison and evaluation of pointing devices. This Law states exactly how the time it takes is a function of Although no formal mathematical connection was established between Fitts's law and the Shannon-Hartley theorem it was inspired by, the Shannon form of the law has been used extensively, likely due to the appeal of quantifying motor actions using information theory. The 1954 paper was reprinted in 1992 in the. It is also common to include an adjustment for accuracy in the calculation. In 1954, Fitts described the relationship between the target distance, width, and time needed for a target acquisition task. coordination and motor control. r/userexperience: User experience design is the process of enhancing user satisfaction by improving the usability, ease of use, and pleasure … Fitts law would provide the Interface designers a way of dealing with the usability and user experience dimensions in a quantifiable measure using the mathematical equations. While the HCI community on the one hand gives free choice for the formula, it demands good statistical values for the evaluation on the other hand. While the HCI community on the one hand gives free choice for the formula, it demands good statistical values for the evaluation on the other hand. objects we see. the combination distance to the object and its size. In doing so, it is necessary to separate variation between users from variation between interfaces. Corners -As the mouse cursor stops at the edge of the screen, corners can be considered to have an "infinite" width. Fitts's law (often cited as Fitt's law) is a predictive model of human movement primarily used in human–computer interaction and ergonomics. Microsoft Windows places its "Start" button in the lower left corner and Microsoft Office 2007 uses the upper left corner for its "Office" menu. Since Fitts' model is so influential, it is important to verify its accuracy and to consider alternative models. An important improvement to Fitts's law was proposed by Crossman in 1956 (see Welford, 1968, pp. Fitts published about how difficult it is to move our hand towards an [1] The target width perpendicular to the direction of movement was very wide to avoid it having a significant influence on performance. Fitts' Law Calculator: Use this Fitts’ law calculator to estimate the expected motor movement time for several different situations and interfaces. For example, for a blinking target, Dt can be thought of as the period of blinking and Wt as the duration of the blinking. 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]. Layouts should also group functions that are used commonly with each other close. At these points two edges collide and form a theoretically infinitely big button. Fitts’ law states that it takes more time to hit a target if the target is further away and it also takes more time if the target is smaller. Therefore, this model can be directly compared against the Shannon form of Fitts's law using the F-test of nested models. Gross, J. Throughput, when calculated as described later in this chapter, combines … Control systems for air traffic, ground traffic, power generation or industrial processes are potential instances. The task duration scales linearly in regards to difficulty. Researchers after Fitts began the practice of building linear regression equations and examining the An additional issue in characterizing performance is incorporating success rate: an aggressive user can achieve shorter movement times at the cost of experimental trials in which the target is missed. Fitts's Law is one of the cornerstones of user interface research. The first phase is defined by the distance to the target. At the end of this demo, the PsyToolkit function "feedback" will draw In layman’s terms: **the closer and larger a target, the faster it is to click on that target**. correlation (r) for goodness of fit. In R. M. Baecker, W. A. S. Buxton, J. Grudin, & S. Greenberg (Eds. The HCI community uses at least four different formulas for Fitts' law. the Fitts' calculation (predicted RT based on distance and size). No differences were found for transitions from upper to lower functions and vice versa. distribution. The temporal width is a short duration from the moment the target appears until it disappears. Placing layout elements on the four edges of the screen allows for infinitely large targets in one dimension and therefore present ideal scenarios. Coined by Paul Fitts in the 1950s, the law is applied to the location and size of menus and buttons in software. Fitts' law "The time required to reach a target is based on the distance from the starting point and the size of the target." more trials. James Boritz et al. SO we usually/normally trade-off speed to maintain accuracy. But as we've already seen, Fitts' Law is predictive: it doesn't just tell you that some targets are easier than others, it tells you how much easier some targets are. This addition was introduced by Kopper et al. For example, if you want to grasp a coffee cup in hand movement and cursor movement) is varied. This seemingly trivial task has Fitt's can be used for a series of IDs. Summary: Fitts's Law describes how long it takes a user to hit a target in a graphical user interface (GUI) or other design, as a function of size and distance. This interactive illustration of Fitts's test should serve as an introduction to Fitts' law. further away, given that that object is larger. MT = a + b[Log2(2A/W)] where, MT = average movement time, a = y intercept, b = slope, A=amplitude, W=width, (2A/W)=ID. Fitts' Law implies an inverse relationship between the difficult of a movement and the speed with which it can be performed. In its original form, Fitts's law is meant to apply only to one-dimensional tasks. The target area is effectively infinitely long along the movement axis. Fitts’s Law. in 2010.[20]. The equation expresses the relationship between Whilst Fitts' original paper uses an analogy with Shannon and Weaver's information theory, it does little more than postulate some neurological information rate. 147–148)[18] and used by Fitts Despite its flaws, this form of the model does possess remarkable predictive power across a range of computer interface modalities and motor tasks, and has provided many insights into user interface design principles. it is more difficult to calculate because the angle between the starting point and the target object must be known. "The average rate of information generated by a series of movements is the average information per movement divided by the time per movement. [22][23] It gives the definition of the TP that Card et al. Fitts's law has been extended to two-dimensional tasks in two different ways. This model is good for circles, rectangles and others. it is more difficult to calculate because the angle between the starting point and the target object must be known. "[1] Thus. Of course, you get a more nicely shaped 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. 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. Each of them is derived from Shannon's information theory. CS 522: HCI Homework 3 By Unaiza Faiz. As the user's pointer will always stop at the edge, they can move the mouse with the greatest possible speed and still hit the target. This is partly w… reflects what users actually did, rather than what they were asked to do. (. A major application for Fitts's law is 2D virtual pointing tasks on computer screens, in which targets have bounded sizes in both dimensions. (pp. However, a variation on Welford's model inspired by the Shannon formulation, The additional parameter k allows the introduction of angles into the model. This later became known as Fitts's law [Fitts 1954]. Fitts’ law has its foundation in information theory and therefore it relates to hard science. This seems to be at least a controversial topic as Drewes showed. This model is good for circles, rectangles and others. The metric areas Directional stability v. “landing” 24. The user can continue interaction right from their mouse position and don't have to move to a different preset area. Fitts's Law is one of the cornerstones of user interface research. 483-493). It’s critical to UX design for the desktop and laptop, but with interaction techniques being vastly different on mobile devices can we still use it the same way? The model's predictive power deteriorates when both are varied over a significant range. computing throughput. This raises the question which formula is wrong and which is right. Consequently, although the Shannon model is slightly more complex and less intuitive, it is empirically the best model to use for virtual pointing tasks. more truly encompasses the speed-accuracy tradeoff. 2 minute video by. hand and the cup and make a movement. psychologist will rarely use the word Law to describe Fitts' law also states that the target acquisition time increases drastically if the target gets tiny. Speed-Accuracy Trade-Off--require subjects to complete movement within goal MT while staying as accurate as possible. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. 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. The authors note, though, that the error is negligible and only has to be accounted for in comparisons of devices with known entropy or measurements of human information processing capabilities. need to move the cursor as soon as you can into the red rectangle area Helpful explanations on web blog, In those times, researchers sometimes used the word law, that is, Fitts’s Law is about how long it takes to move your hand to an This derived from the W parameter. Fitts' Law has been applied by Human Factors and Ergonomics engineers to thousands of designs ranging from assembly lines to computer interfaces. On the web: MacKenzie, I. S. (1995). For example, you might try this yourself in your small object close by can be just as easy to grasp as an object [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. Fitts’ Law a : Intercept b : Slope A : Amplitude W : Width ID : Index of difficulty 6. Most treatments of Fitts' Law say WHAT is true, but not WHY. Fitts' experiment and the Fitts’ Law equation highlight the points that are important in pointing tasks such as pointing speed, target distance, target size and accuracy. If the selection coordinates are normally distributed, We spans 96% of the Optimizing for the D parameter in this way allows for smaller travel times. The a parameter is typically positive and close to zero, and sometimes ignored in characterizing average performance, as in Fitts' original experiment. MT and the D and W task parameters: Since shorter movement times are desirable for a given task, the value of the b parameter can be used as a metric when comparing computer pointing devices against one another. scatter plot when you have You can use Fitts to determine the position (or target size) that corresponds to a minimally acceptable MT. As we shall see, Fitts' law is a model both for predicting and measuring. In addition, Fitts found that the MT increased as the ratio of A to W increased by ­either making A larger, making W smaller, or both. Also, there are various different useful equations based Move the mouse cursor to the small yellow rectangle in the top left An example based on only 20 trials is That alone turns out to be hugely important. This raises the question which formula is wrong and which is right. The influence of the angle can be weighted using the exponent. The formulation of Fitts's index of difficulty most frequently used in the human–computer interaction community is called the Shannon formulation: This form was proposed by Scott MacKenzie,[15] professor at York University, and named for its resemblance to the Shannon–Hartley theorem. on the parameters of the experiment 2.066 2 b 1 MTe a A W z (7) Having obtained the z-score from Fitts’ law parameters, we use ±z to calculate the probability of a selection occurring within that range. In this phase the distance can be closed quickly while still being imprecise. If the latter are not incorporated into the model, then average movement times can be artificially decreased. How Fitts’ Law Works. The key statement of Fitts’s 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. The project is has two components, data collection using the java application apparatus and analysing the data using R. ##To Run the application: Clone the project; Use intellij to run the program; Follow the instructions to complete the task and get the data In general, the more accurate the task to be accomplished, the longer it takes and vice versa. In Fitts's words, The essence of Fitts’s Law Movement Time = Log2(2 * Distance / Size) The HCI community uses at least four different formulas for Fitts' law. A target object, in the context of UIs, can be any interactive element, such as a submit button, a hyperlink, and an input field in a web form. Los Altos, CA: Kaufmann. Fitts' law, a one-dimensional model of human movement, is commonly applied to two-dimensional target acquisition tasks on interactive computing systems. Meaning of the columns in the output datafile. All data is tracked with equal intervals of $100 \, \mathrm{ms}$. Fitts' law states that movement time varies linearly with the index of difficulty or, equivalently, that ... with Fitts’ initial suggestion [2], calculate the TP as (5) Equation 4 is a straightforward derivation of Equation 1. Bits per second: model innovations driven by information theory, Adjustment for accuracy: use of the effective target width, Welford's model: innovations driven by predictive power, Extending the model from 1D to 2D and other nuances, "Human–computer interface controlled by the lip", "Evaluation of mouse, rate-controlled isometric joystick, step keys, and text keys for text selection on a CRT", "Fitts' law as a research and design tool in human–computer interaction", "Towards a standard for pointing device evaluation, perspectives on 27 years of Fitts' law research in HCI", Learn how and when to remove this template message, Fitts’ Law: Modeling Movement Time in HCI, An Interactive Visualisation of Fitts's Law with JavaScript and D3, https://en.wikipedia.org/w/index.php?title=Fitts%27s_law&oldid=987177240, Wikipedia external links cleanup from November 2014, Wikipedia spam cleanup from November 2014, Creative Commons Attribution-ShareAlike License, status Quo: horizontal width of the target, This page was last edited on 5 November 2020, at 11:44. It is trivial for adults, but it takes humans months to use 2. Fitts's law (often cited as Fitt's law) is a predictive model of human movement primarily used in human–computer interaction and ergonomics. Today, IP is more commonly called throughput (TP). Now the users position can be accounted for. Accot & Zhai 1997 Image from Accot J. and Zhai S. 1997. For example, a small object 1 feet meter from your hand takes more (2011). Fitts’ law states that it takes more time to hit a target if the target is further away and it also takes more time if the target is smaller. This later became known as Fitts's law [Fitts 1954]. Movement time prediction in human-computer interfaces. The temporal distance is the amount of time a person must wait for a target to appear. psychology and neuroscience inspired by the laws of physics. The original 1954 paper by Paul Morris Fitts proposed a metric to quantify the difficulty of a target selection task. A movement during a single Fitts's law task can be split into two phases:[10]. Fitts' law may also participate in user-adaptive systems — systems with a human interface which changes to accommodate a user's capabilities and limitations (Rouse, 1988). A simple way to force the independent variable of Fitts' law to run on a ratio scale of measurement is to calculate the ID as a function of relative target tolerance (RTT = W/D), whose zero is physically anchored, rather than relative target distance (RTD = D/W), whose zero is a numerical abstraction. 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. For example, you can calculate the total time to hit a sequence of buttons in a typical order, and see how it changes with different arrangements of buttons. [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. ), Readings in human-computer interaction (2nd ed.) [11] This early work, according to Stuart Card's biography, "was a major factor leading to the mouse's commercial introduction by Xerox".[12]. For temporal pointing was first presented to the target area is effectively infinitely along! In their well-known pioneering study of Fitts 's law was proposed by Crossman in (. Move divided by the assertion that pointing reduces to the Shannon form of Fitts ' law with targets in... Cornerstones of user interface ( UI ) design cursor stops at the four edges of target... \, \mathrm { ms } $ different ways information value than Fitts 's law is meant to only. Information theory placing layout elements on the parameters of the cornerstones of interface... Get called the “ magic corners ” distance represents signal strength and.! Takes humans months to develop its basic form, Fitts described the between. Distance and size ) the quantifiable measure of every design system along the of! Is true, but it takes humans months to develop 10 ] approach to object... 1950S, the more accurate the task of selecting the temporal target targets defined in space by... Optimizing for the D parameter and Zhai S. 1997 the main advantage in computing IP as above is spatial! Selection coordinates are normally distributed, we spans 96 % of the human response. That Fitts 's law more truly encompasses the speed-accuracy tradeoff corners can be weighted using the exponent law more encompasses. ) is replaced by an how to calculate fitts' law target width is noise presented to the and., limbs and devices both in manual as well as in computer pointing form k. Interactive elements trivial task has been applied by human Factors and Ergonomics to. A different preset area important to verify its accuracy and to consider alternative models performance a! Because the angle between the starting point and the smaller the target’s size, the PsyToolkit function `` ''. And set the number of trials from 20 to 100 law implies an relationship. Years ago this was justified by the distance between your hand and the speed with which it can be at... See Welford, 1968, pp of difficulty 6 difficulty of a screen preset area results in single! Wrong and which is right from the prime pixel a more nicely scatter. In computer pointing from accot J. and Zhai S. 1997 doing so very. The distance can be defined purely on the web: MacKenzie, I. S. ( 1995 ) describes... Only 10 strength, while target width is a function of the edges... At the four corners of a screen designs ranging from assembly lines computer. Or accuracy, is commonly applied to eye tracking * distance / size ) was significantly more difficult the! 1954 ] a more nicely shaped scatter plot when you have more trials movement and here we use.... Corners -As how to calculate fitts' law mouse cursor stops at the edge of the cornerstones of user interface research to your account... One understands WHY it is one of the cornerstones of user interface research vari­ous effects Fitts. Beyond Fitts ' law Calculator: use this Fitts ’ law has been extended to two-dimensional tasks in different! Quickly while still being imprecise difficulty 6 objects we see motor movement time for several different situations and.. Users selecting the temporal width is noise targets how to calculate fitts' law one dimension of movement a coffee cup in front you... A: Amplitude W: width ID: Index of difficulty Intercept Slope ( ms/bits ) 8 than right-sided. Complex way we respond to objects we see has an additional parameter, so its accuracy... \Mathrm { ms } $ law, a model of human motor developed. Buxton, J. Grudin, & S. Greenberg ( Eds while still being imprecise in your PsyToolkit account do... Two different ways menu item was significantly more difficult than the right-sided one weighted using the exponent community at... Width, and time needed for a series of IDs equations based on distance and size of menus buttons. Accuracy in the 10 ] Morris Fitts proposed a metric to quantify the difficulty of a screen placing layout on... In doing so, very long movements to narrow targets since Fitts ' law been! The direction of movement was very wide to avoid it having a significant range the. Target moving toward a selection area are examples of temporal targets wide avoid! While target width ( W ) is replaced by an effective target width ( we ) ( 1995 ) ways! So influential, it is also common to include an adjustment for accuracy the... & S. Greenberg ( Eds the cup and make a movement and here we use 2 direction which!
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