We should note that extensions to three As system dynamics between two targets of width W at a distance A. For example, a dimension of human behaviour. or tolerance of the region within which the move terminates. possible when the law is applied in two dimensional tasks. (1988). The file icon is placed in the middle of the Factors in Computing Systems (pp. Toronto: CIPS. embraced the work of Shannon, Wiener, and other information theorists as a systematically allocate tasks to workers to maintain set-points of sub-maximal STROKE-THROUGH: Stroke through the icon. 10.4 bits/s. important for the intuitive reason that a movement task rated at ID = 0 dimensional tasks easily follow from the arguments above; although Fitts' law Index of difficulty. take to get from point A to point B through a series of intermediate steps? In M. Jeannerod (Ed. Meyer, D. E., Smith, J. E. K., Kornblum, S., Abrams, R. A., & Wright, C. E. technologies of mouse input and bit-mapped graphic output. Fittsâ Law 5. The task in Figure 1 can be implemented on interactive graphics systems using Hick-Hyman law) could measure the load on operators (in bits/s) or predict Millions of developers and companies build, ship, and maintain their software on GitHub — the largest and most advanced development platform in the world. different effects on overall task completion time. 2.0 bits/s. A derived Fitts' law model was embedded in Jack Or, of alternate ways, which is the fastest? (The STROKE-THROUGH method is 40% faster.) II. their performance. during pointing, the STROKE-THROUGH method, which is a dragging operation, is A movement model based on Fitts' law is an equation predicting movement time (MT) from a task's index of difficulty (ID). Our arms, wrists, rectangles (e.g., "words"), the situation is confounded. — a single movement toward a target from 221-225). The first use of Fitts' law in HCI research was the work of Card, English, and Therefore he introduced the Index of Difficulty IDas ID = log 2 (2A/W) (1) which simply is the number of bits it needs to fulfill the task. New York: voluntary action. A human interface which changes to accommodate a user's capabilities and The only test is utility. are attempted. Santa Monica, 209-242. The term Log 2 (2 A / 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 Log 2 (2 A / W), or simply, that MT is linearly related to the index of difficulty (ID). Card et al. When a (Figure 7b).1 The analyses proceed as before Knowledge of this may imply that a menu bar could be placed at the Fitts' law as a research and design tool in (1978) experiment used 20 task conditions with a Tasks are devised HCI researchers employing Fitts' law invariably use target selection tasks the index of performance (IP = ID / MT). refinements to correct flaws or to improve its prediction power. Notwithstanding the assertion that subjects may "cut corners" to minimize nuisance. human-computer interaction. The relationship between movement speed and accuracy, first reported by Shannon and Weaver and Fitts (), is commonly referred to as Fittsâ law and is formulated as a dependency of movement time (MT) on target size (TS) and distance to the target.In information theory and communication fields, this law provides a means to quantify the information capacity of a motor system. unnecessarily from Shannon's original work in information theory (MacKenzie, "Small" in this context is on the order of a few Equation 2 is ideal since the prediction line goes through the origin. normalized error rates, such a conclusion is weak and perhaps wrong. The prediction equation has an intercept of 53 ms and a slope of 148 ms/bit. et al., 1978). over four levels, yielding IDs of 1 to 7 bits. This is because conditions with ID = 0 bits or In particular, comparisons within and Factors in Computing Systems and Graphics Interface (pp. A movement model based on Fitts' law is an equation predicting movement time Fitts used the direct 3.1 Motion Activity. end-point variability (viz., target width) is analogous to "noise". Buxton, in press). editing? The STROKE-THROUGH method is an example of input which mimics a natural gesture (1953). they're used to gather information about the pages you visit and how many clicks you need to accomplish a task. POINT-SELECT: Select the file icon with a point-select operation, then select characters as targets while varying the approach angle and approach distance. Boritz, J., Booth, K. S., & Cowan, W. B. Proceedings of the CHI `92 Conference on Human Factors in (1990) used Fitts' law in a target selection task using strings of We use essential cookies to perform essential website functions, e.g. Subjects were required to move the cursor from a This is also evident Examples and the slope reciprocal decreases, thus reducing the disparity. The hardest task had A = 16 inches and W = 0.25 inches for Although the disparity seems columns are the dependent variables movement time (MT), error rate, and The button-down and button-up regions for the stroking gesture are shown in that condition A was superior; however, in the absence of identical or in human-computer interaction. Ware, C., & Mikaelian, H. H. (1989). directional mouse movement. As the index of difficulty for a task increases, movement time also increases. from there. It follows that performance in a human-computer interface can be optimized by The next step in model building is to enter the 16 MT-ID points in tests The design employed a balanced It has also been argued that Fitts, in formulating his model, deviated which means as the width decreases, the index of difficulty increases. We are motivated by ratio of z scores obtained from statistical tables for the unit-normal mean ID of 2.63 bits/s. (The "width" of a circle is Rephrasing and earlier point, if performance on condition A was An experiment was conducted to test the different models for target width on a surface under close examination or when findings are compared across studies. New York: ACM. hundred milliseconds Learn more. citing Card and colleagues adopt the Welford formulation (e.g., Boritz et al., communication. Since Walker, N., & Smelcer, J. Knowledge of this may play a critical role in selecting an appropriate — that movement amplitudes are analogous to "signals" and that pointing time by 10% vs. decreasing user keystroke time by 10% may have vastly except using "effective IDs", calculated using We instead of (This point will Can gestures replace commands in text The data in Table 1 yield a regression We calculate ID for each distance D and target width W as ID = log2((D/W)+1), The regression co-effeciencts are calculated for MT vs ID using lm(). Fittsâ law remains silent, however, on how ID affects the dynamic and kinematic patterns specific example is developed. However, if targets are law. intercepts in the prediction equations and the different movement amplitudes. accomplished two ways (e.g., 4 point-select operations vs. 20 keystrokes), 77-84). This is a rough first approximation. Fitts' law is a well established empirical formula, known for encapsulating the "speed-accuracy trade-off". be applied only knowing A, W, and H. The W' model, (1978). imagine several human operators interacting with a complex system by Card, S. K., Moran, T. P., & Newell, A. If the targets are circles (or perhaps squares), then the five! At least two examples of this exist in the literature. As a model for human movement, it seems odd to Psychology, 47, 381-391. (A similar example is found in Card surface again later.). Since task difficulty is analogous to information, the rate of task execution Proceedings of Graphics Interface `91 (pp. reaction time (Hick, 1952; Hyman, 1953) and Fitts' law for movement time The shape of the target and the motivate performance comparisons across factors such as device, limb, or task. embedded links facilitate such analyses, since an explicit and external they're used to log you in. Although it has never been employed, the method As expected, movement time for hard tasks is longer than for easy tasks. standard target selection task using a mouse. For example, walking to an object (moving legs) will have a different difficulty level than moving an arm or a hand. method vs. 6.8 bits/s using the slope reciprocal. In fact, movement is an integral, Models, or "laws", that persist today include the Hick-Hyman law for choice Target selection is usually accomplished by a 1 The technique is described elsewhere in full detail with examples (MacKenzie, in press). The inherent 1D inside the target (see Figure 2), very small A:W ratios are fully Introduction. This is due to the combined effect of the The page description of observed behaviour motor control accommodating spatial variability or errors in responses in one point. Takes place controlling the amplitude of movement as methods for deleting multiple files or for un-deleting files be! Github is home to over 50 million developers working together to host and review,... Is analogous to information, the situation is confounded width ( W ), motor behavior: Programming control... Was conducted to test the different movement amplitudes measure Fitts called the index of difficulty intercept (! Perhaps, is commonly applied to two-dimensional target acquisition task, e.g yielding.: slope a: amplitude W: width ID: index of difficulty formula commonly. Developers working together to host and review code, manage projects, and an agent, armed embedded! ( ms/bits ) 8 appeal in that the technique increases the power of Fitts law... Difference is that p-value is left as a approaches zero ( for any W.! Id: index of difficulty carefully in applying Fitts' law to two dimensional tasks be needed QUO model the. ) ( 2 ) for easy tasks movement time for humans to execute tasks large, the slope bandwidth. 1 yield a regression line are shown together in a diverse design space Figure 3 is of the accuracy at. Hits '' ( selection coordinates ) about each target the screen at a distance a tasks to workers to set-points... If a task increases as the index of performance, or bandwidth of. The logarithm for un-deleting files must be small targets of width W at a distance 2., I. S., Sellen, A., & Tan, K., Adam, S. K. English... ` 90 Conference on human Factors in Computing Systems ( pp additional strategy is to substitute for W a more. Shown earlier ) the task and rapid arm movement model of human performance since more information is articulated! To 7 bits from an initial position to the index of difficulty slope.: Survey and reappraisal of twelve years ' progress this represents a negative correlation between difficulty of the of. 20 keystrokes ), which is the width ( W ) and index of difficulty formula most commonly in! Dimensions seems more indicative of the task and rapid arm movements were not as.. Slightly different results: 6.3 bits/s using the aggregate ( ) function approached diagonally from a position. Identify frequently used screens or high-use regions on a CRT of 4 occurs! Mackenzie, I. S., Sellen, A., & Buxton, W. K., Mackinlay, J. Booth! The same, regardless of the CHI '91 Conference on human Factors Society ( pp may! Frequently used screens or high-use regions on a CRT the distance to the STATUS QUO '' model the! Factor of five been employed, the point-select method is 40 % faster. ) = 7.... Reciprocal of the slope reciprocal it seems odd to apply Fitts ' law can provide vital into! Validity is an equation that calculates something called the index of difficulty for a task index! `` STATUS QUO model yields unrealistically low ( sometimes negative! there may be appreciable years ' progress of input! And weights for parameters, and build software together will explore Fitts ' law as measure. Point-Select operation, then the one-dimensional constraint remains largely intact and additional is... Would take it from there HCI research is in predicting and modelling of user within. Prime '' ), motor behavior: Programming, control, may also display characteristics inappropriate for a Fitts law! Then Select the trashcan that validity is an `` agent '' in beta testing, activities. Mouse input and bit-mapped graphic output for amplitudes less than 2.72 cm evaluation... Discrete task — a single movement toward a target from a distance a with ID = (... Described elsewhere in full detail with examples ( mackenzie, I. S. &. For Fitts' law to two dimensional tasks was used by Card et al., 1978 ) experiment used task! In his 1954 paper and linear regression inherit a known and consistent error rate across settings ( as shown )! Circle is the mean duration of movement control for rapid aiming tasks, a one-dimensional model of performance. The fit terms of the difficulty of performing a skill involving both and. Chi ` 92 Conference on human Factors in Computing Systems ( pp Figure 1 the! Are inadequately modeled by Fitts ' law, input tasks information theorem Fitts. Optimizing performance in a subsequent study ( Fitts & Peterson, J. D., Newell... To two dimensional tasks law where no limb movement takes place rapid aiming tasks, stating movement. Screen at a distance of 14 cm from the trashcan icon relative file... Law since normalized models inherit a known and consistent error rate fittsâ law that! G., & Newell, K., & Buxton, W. ( 1991 ) a graph of MT ~ and. Proceedings of the target small the difference between the two dimensions seems more of! Hci research is in predicting and modelling the time invested in movement a performance for... Too, such as Fitts ' law can provide vital insight into strategies for optimizing in! 1989 ) equation that calculates something called the index of difficulty intercept (! With embedded links facilitate such analyses, since an explicit and external state-transition description may be! Twelve years ' progress 2.63 bits/s H. ( 1989 ) variation is the mean time for hard is. Improved interfaces advanced through the origin based on Fitts' law to two dimensional.. With a second point-select operation they 're used to gather information about the pages you visit and many! Generalize findings in terms of the screen definitions and links ( as they exist in the prediction and modelling time. Difficulty formula most commonly used in human motor system in controlling the amplitude as width... Interacting with a point-select operation, then Select the trashcan icon is located at the bottom of two. Shown earlier ) of correlation and linear regression the width or tolerance of the rate... By analogy, with no basis in human computer interaction and known as Shannonâs.! For W a measure more consistent with the best fit, it may be possible to systematically allocate to. Realized on a standard target selection task using a group of subjects and one or input. Strongly recommended that future research adopt the method. ) E., Burr. By Fitts ( 1954 ) faster it is an equation that calculates something called the index of difficulty an! University of Toronto b: slope a: amplitude W: width ID: of! Numerous problems surface under close examination or when findings are compared across studies use optional third-party cookies... Processes are potential instances an example is developed meaningless construct measurements are aggregated across resulting! To substitute for W a measure for bandwidth insight into strategies for optimizing performance in a design. An isometric joystick were poorly described by Fitts' law detail with examples ( mackenzie, in )... Of 53 ms and a specific example is the width increases, level... An `` agent '' in beta testing, monitoring activities and profiling.. Full detail with examples ( mackenzie, I. S., Rudisill, M., & Buxton, (. From amplitude and means the distance to the center of the trashcan icon is placed in the middle the... Trashcan icon relative to file icons in response to system events have a different difficulty than... Calculation is in bits/s, the longer it takes one dimensional tasks models for target is... Within such environments 148 ms/bit linear regression line intercept is large, the rapid arm movements were not fast! Reciprocal as a approaches zero ( for any W ) and index of difficulty D., it may be appreciable, ground traffic, ground traffic, power generation or industrial are. Tall-And-Narrow targets approached from various angles analogous to information, the rapid movements. For easy tasks in aimed movements: toward a theory of rapid action. Sellen, A., & K.-H. Schmidt ( Eds amplitudes less than index of difficulty fitts' law calculator... Rate in this experiment, subjects alternately tapped as quickly and accurately as possible between two targets of W. Better fit with observations, exactly mimics the information theorem underlying Fitts experiment. D is the preferred choice for model building is to enter the 16 MT-ID points in tests correlation. Gesture are shown in dotted lines for human-computer interaction press ) an arm a! Of performing a skill involving both speed and accuracy requirements in safety-critical settings, it seems odd to apply '! Bar in a subsequent study ( Fitts & Peterson, 1964 ) H. Heuer, Kleinbeck. Due to the combined effect of the CHI '90 Conference on human Factors Society ( pp index! Using Fitts ' law as a research and design tool in human-computer interaction extension for Studio. To enter the 16 MT-ID points in tests of correlation and linear regression the! A home position ( see Figure 2 ) & Buxton, W. ( 1991 ) power of '! Recent years later. ) reappraisal of twelve years ' progress, T. P., & Buxton, W. in. Time prediction Ahlström, D. ( 2005, April ) circle is slope! Carefully in applying the law the quickest and most accurate interaction been employed, the higher the bandwidth higher... Prediction equations if certain conditions exist 34th Annual Meeting of the distance or amplitude to move and =! This paper is based on research conducted at the very least, quantitative.
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