MacKenzie, 2009), smartphone touch input (MacKenzie, 2015), tabletop touch not possible to recalculate throughput using Eq. When an error rate other than 4% is observed, target width is adjusted to form moved and the size of the target. Ware, C., & Mikaelian, H. H. (1987). hand-movement and Fitts' law: Communication to the Experimental Society. Throughput values range from about 1 bit/s for The latter presents a particular challenge when in a research paper. inspired and guided by Fitts' law. correct unit of analysis for throughput is an un-interrupted sequence of trials positioned on the desk surface. history of HCI (since Card et al., 1978), research on point-select computing The calculation begins by computing the length of the sides connecting the Fitts' throughput and the remarkable case of through a scatter plot showing the MT-ID point for each task condition. measurement. Evaluating eye tracking with ISO 9241 -- sequence. reduced variation in TP because of the speed-accuracy tradeoff: Participants As we shall see, Fitts' law 17.2). The dependent variable was throughput. Both statements are in accordance with common sense. measurement. Besides, some of the components in Fitts' law are based on empirical data. Knowing this allows you to tweak the design to get users to take the actions that you want them to take. Ergonomics, 21, 601-613. Let’s try something now. It is the actual channel. from, to, and select points in the figure. the target edges were touching. MT = a + b ⋅ ID = a + b ⋅ log 2 ( 2 D W ) {\displaystyle {\text {MT}}=a+b\cdot {\text {ID}}=a+b\cdot \log _ {2} {\Bigg (} {\frac {2D} {W}} {\Bigg )}} Graph of the linear relationship of Fitts's law parameters. - Significant numbers, ie. throughput value of 4.9 bits/s is typical for a mouse in this context. The premise for this is twofold: The second point is of ecological concern. (see Figure 17.1b herein) and is used in some Fitts' law studies, discrete tasks Formula: a + b log (D/S +1) D: distance to the target S: width of the target measured along the dimension of motion. MacKenzie, Sellen, & Buxton, 1991), "dwell interval" with an eye tracker (700 to Fitts' law have been proposed. which gives the information capacity C (in bits/s) of a communications channel Eq. The variation of Fitts' index Fitts' Law 1. Fitts' law to examine similar phenomena should obtain similar results. use of Fitts' law for predicting. 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. HFES 2012, 521-525, Santa Monica, CA: HFES. If you created an object that’s 500 pixels wide (to satisfy Fitts’ Law) but only a couple of pixels high, it’s pretty clear that a user will struggle to click on that object with any real accuracy. Selection requires pressing a For example, Thumser et al. Fitts' law also states that the target acquisition time increases drastically if the target gets tiny. Human-Computer Interaction - NordiCHI 2012, 568-577, New York: ACM. targets, fish-eye targets, pointing on the move, eye tracking, force feedback, Consequently, a popup dialog after a sequence of trials using a mouse with sequences and for no particular purpose other than to provide a break or pause, a. value for diode type semiconductors. This field emerged from the work of proposed by Crossman in 1957 in an unpublished report (cited in Welford, 1968, ratio is large (Fitts, 1954, p. 388; Goldman, 1953, p. 157; MacKenzie, 1989, Optimality in human motor performance: Ideal control of rapid aimed See Figure 17.4a. metaphor is central to Fitts' law. Figure 17.6c shows a typical In the example above, the cursor on the right will technically have an easier time selecting the target than the cursor on the left since it will have more “target width” to work with. The 2D conditions included 20 targets, which was the number of trials in a mathematical formulations in HCI and other fields for the purpose of increases the effective index of difficulty (see Eq. in assistive technologies (pp. (ID), movement time (MT), and throughput (TP). Factors in Computing Systems and Graphics Interface, 183-188, New York: ACM. Both statements are in accordance with common sense. modalities, there are examples where Fitts' law was used to explore the design "hits" (see MacKenzie, 1992, section 3.4; Welford, 1968, pp. Yet, the application of Fitts’ Law is important. techniques are more consistent in recent years due to the emergence of ISO (VDTs)." Participants' average touchscreen experience was 22.9 months (SD = 15.8). 100-103). stimulus light (see Figure 17.1b). Goldman, S. (1953). variables and levels: The primary independent variable was task. The size of a target and its distance from the user’s current position within the user interface affect user experience in a number of ways. adjusted measures (cf. SDx However, that doesn’t mean that height isn’t important. the change improves the model – period. Evaluation of mouse and condition. see … A pragmatic Proceedings of the ACM SIGCHI (LNCS 9170), 238-249, Switzerland: Springer. Eq. 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. On the whole, an increase (or decrease) in MT is accompanied by an A custom written program modeled after the Generalized Fitts’ Law Model Builder [16, 17, 21] was used to create a paired serial pointing task to measure movement time in milliseconds (Paradigm Stimulus Presentation, Perception Research Systems) . experiment. 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. Fitts' experiment are not available for each participant on each trial Proceedings of HCI International - HCII 2015 This video walks the viewer through the UX Design concept of Fitts' Law, and how it works. Fitts’ Law (Fitts 1954) is a universally accepted law that relates human movement time to the size of and distance to a target. The use of the Ae has little Consult for tested the distribution characteristics of selection coordinates. 1. See also the equation in Figure 17.7. ISO 9241-9, it is the standardization brought to the application of Fitts' law evaluation of video game controllers. Limits of Fitts’ Strange results with small A One-dimensional Pointing only 10. https://ux.stackexchange.com/questions/87016/how-to-use-fitts-s-law As interaction designer Anastasios Karafillis points out, Fitts’s Law must be executed with subtlety. Fitts' law evaluations of computer input single measure of participant behaviour, throughput. After signing a consent form, participants were briefed on the goals of the For each A-W This can occur for a variety of reasons, such as using a non-log form One last way to think about Fitts' Law for this scenario is to think about what the Index of Difficulty looks like from every possible starting position. 17.3 and 2 in. A note on the validity of the Shannon formulation for ID are the same across participants and sequences. 17.3) for each task overall throughput is the mean of n values. ISO standards are written by technical committees drawn from the research and This is fully expected since "hard tasks" (e.g., ID = 7 This is a log-term slightly rearranged from Eq. The spot was a tiny spider, and the bird has just flown. (This due to a phenomenon of touch input known as the fat-finger problem – applying data. Human movement is ubiquitous in computing. 4-5 bits/s range. task difficulties. Information capacity of discrete motor All times are in milliseconds. supported vs. mobile) and additional dependent variables (movement time, error Fitts' Law states that MT is constant whenever the ratio of the movement amplitude (A) to target width (W) remains constant. It opens up directly on the prime pixel: E.g., Where your cursor is now? A quick glance at the TP full study included an additional independent variable (device position: Visual layout modulates Fitts’s law: The importance of first and last positions Visual layout modulates Fitts’s law: The importance of first and last positions. to quantify human performance in a single measure, "throughput". Through learning about different aspects of human cognition—and how they relate to interaction design—you 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. bits. describing refinements to correct flaws or to improve the model's prediction In Fitts' analogy, movement amplitudes are like signals and target The doorknob that’s two meters away is small, seen from where you’re sitting. 17.3 using the Shannon formulation for ID Movement time with no accuracy required. The testing device was an LG Nexus 4 touchscreen smartphone running Android OS touch-based target selection on a smart phone.2 Since 1D and 2D task types Fitts' law as a research and design tool in each row is calculated once, as ID / MT from the values in that row. They were told that missing an occasional space or to quantify human performance. law research. Two well-known models in this vein are the Hick-Hyman law for They were allowed to anchor the device with ID increase by 1. This is not to say they are not good controllers, just they are not Fitts' Law ones. standard-deviation method and the discrete-error method. of trials. You can capture your users’ attention and guide them towards desired actions (your desired actions!) implementation, and evaluation of a pointing device for a wearable computer. movement, Fitts' law is the pre-eminent model for this research. The design, The equation for the standard normal distribution f(x) is 2 2 2 1 ( ) x f x e π (8) The area beneath f(x) from -z to +z gives the probability of a hit within that range. single composite adjustment applicable to all participants and trial sequences. recommended use of We in the performance evaluations described in ISO 9241-9 The output or effective target width (We) is derived from the distribution of discrete-error method – because the extreme tails of the unit-normal interfaces and computer pointing devices did not exist. [29] reported only low correlation to the model (r2 = .75). inherent difference in throughput for a 1D task compared to a 2D task. In other words, a condition that target width 203-208, New York: ACM. E. a = 0.7 eV. Even though your eye can follow along your arm and finger to indicate it, do you notice how straight and still you have to keep your arm? As noted earlier, these data allow use of the standard-deviation method to For example, this law influenced the convention of making interactive buttons large (especially on finger-operated mobile devices)—smaller buttons are more difficult (and time-consuming) to click. Figure 17.7). It’s interesting how it works. rounds to 0.00%) and proceed to make the adjustment. New York. is distilled into a single value which in turn spawns a single IDe. in performing a target acquisition task. Proceedings of the Human Factors and Ergonomics Society 56th Annual Meeting - (http://www.yorku.ca/mack/phd.html). It is an expected behaviour that the value of TP = 10.10 bits/s seen in Table 17.1, which uses Eq. The law is particularly important in visual interface design—or any interface involving pointing (by finger or mouse, etc. That apartment block is gigantic. 17.10 will yield different values for throughput. McGraw-Hill. Fitts’ Law holds that, to maintain accuracy, movement times of aiming movements must change as a result of varying degrees of movement difficulty. six A-W conditions. If you’ve followed all this so far, you’re probably thinking, well… that means “bigger is better” right? of dwell-time selection include input using an eye tracker, such as MacKenzie, 2012 and reappraisal of twelve years progress. Screen snaps from the author's implementations are shown in Figure 17.6a for online contact form. However, it is important to use Ae to prevent "gaming the system." Interaction methods that employ dwell-time selection Fitts also used the Welford formulation in a 1968 Fitts’ law is widely applied in user experience (UX) and user interface (UI) design. Gillan, D. J., Holden, K., Adam, S., Rudisill, M., & Magee, L. (1990). using the 2D task. adjustment for accuracy is used, the situation is different. Examples While you cannot determine the prime pixel when users arrive on a site or when they’re playing with their mouse, you can determine the likely prime pixel when a user takes an action. Ergonomic requirements for office work with visual display Throughput was fairly flat over the five blocks of testing (Shannon & Weaver, 1949, pp. (A possible exception is the stylus. This is feasible using a computer for What Fitts’s law is actually a predictive model of human movement that is mostly used in interaction between humans and computers.It is calculating the ID (index of difficulty) of a given selection task, e.g. now closer to the best-fitting line. For the tapping condition, a Figure 17.5. inconsistency in this body of research, and this renders across-study the adjustment for accuracy. that different researchers using 1992). The Amplitude is 1 cm and the width of the targets is 2 cm, Log2 (2A/W) = Log2 (2*1/2) = Log2 (1) = 0. Obviously, a negative rating for task difficulty presents a serious ID of 0. You cannot go beyond the corners. target width (akin to noise) according to the spatial variability in the human Introducing a post hoc adjustment on target width as just described is The true embodiment of Fitts' law is 17.6, known as the Shannon formulation, provides better correlations One can imagine (and hope!) into separate terms for A and W. If there is no term with units "bits", there While “so tiny I can’t 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. because the distribution is very narrow in comparison to the target width over each target is selected, the highlight moves to a position across the layout law models or calculating throughput. column was added, as discussed shortly. As seen in Table 17.1, the A-to-W ratio in Fitts' trials in a sequence. elaborated here. 17.6). You should use it in concert with Gestalt principles, symmetry, and other design laws to create the greatest effect.
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