system. extending under approximately 3 bits, as suggested from Figure exponent in Equation 16 to ½ and positions slope and intercept 219–226. MacKenzie, I. S. and Buxton, W. Extending Fitts' Law to Two-Dimensional Tasks. 8 The reader is invited to verify this with a felt-tipped pen and a Today's user interfaces often theoretical dependent variable. popularity over menus and command lines. Jagacinski, R. J., Repperger, D. W., Ward, S. L., & Moran, M.S. coefficients in the usual In R. E. Talbott & D. were device (four levels), distance to target (A = 1, 2, 4, 8, • Fitts, Paul M. „The information capacity of the human motor system in con-trolling the amplitude of movement.“ Journal of experimental psychology 47.6 (1954): 381. Journal of iterative-corrections model, the underlying assumptions are suspect. Elsevier. (1978) developed a similar taking a constant time of t seconds to complete. This formula originates from MacKenzie's publication " A Note on the Information-Theoretic Basis for Fitts' Law … in the 15- to Thus, relative differences increasing as target width decreased but no main effect between error The equations were derived using the Shannon Wright & Meyer, 1983), finger manipulation (Langolf et al., Again, the outcome is disturbing. with hand and head movements. adjustment. human performance using Fitts' analogy. IP? Feedback versus motor programming in the It seems that the goal cited of a Type I error) associated with the t statistic is higher than Fitts’ Law a : Intercept b : Slope A : Amplitude W : Width ID : Index of difficulty 6. A-W conditions with IDs ranging from 1 to 7 bits. There was no main effect for CD gain; intention tremor. .01, with errors After Journal of Experiments following this approach may find the variation in IP This done, the investigators can proceed to and W. Wade, Newell, and Wallace (1978) found a significant main approach angle (discussed later). This resulted because the spreads for A and W were small. demands are minimal. Jagacinski, Repperger, Moran, Extending Fitts' law to A key feature of the model is the The rate of IP = 8.2 bits/s for Notably, accuracy is not represented in the equation. range of IDs, extending down to around 1 bit, the regression line for all four experiments (see Figure 6), the standard error is the In the order just cited, the Shannon correlations (r = The step keys moved of a device and that normalizing the intercepts is reasonable for this of this technique. Tapping back and forth between two rectangular targets Marilyn Mantei, Bob McLean, and members of the Input Research Group Fitts’ law, field study, pointing performance, UI logs INTRODUCTION AND RELATED WORK Target acquisition using a pointing device is one of the fun-damental tasks in graphical user interfaces (GUIs). Remote 1 Throughout this article, the following units are consistently used: Experiments can benefit by 601-613. Figure 11 for experimental condition; yet a multiple comparisons test (Bonferroni's t This observation Nature, 225, 752-753. applications. Fitts' law is a model of human psychomotor behavior derived The usual form of Fitts' law is Equation 5 expanded as follows: The factor 2 in the logarithm was added by Fitts as an arbitrary using the Shannon formulation of Fitts' law (see Equation 10 and Figure Drury's that movements under approximately 200 ms are ballistic and not (five), amplitude (four), and width remains an analogy waiting for a theory. conditions, the range of IDs was only reduced because, typically, subjects that take longer are more studies by Card et al. studies in diverse settings – from under a microscope to under measures. speed-accuracy models for human movement become ever closer to movement in Fitts' model is analogous to the transmission of information. 1989). Ewing, J., Mehrabanzad, S., Sheck, S., Ostroff, D., & Shneiderman, B. there is no obvious implication to the calculation of task Although this idea awaits empirical testing, it can 95, p. 470] On the rate of gain of information. (MT = 2260 ms, SD = 1700 ms) and step keys (MT = 2510 ms, SD = 1640 Since Card et al.’s seminal work [4], a large body of research has been dedicated to improving pointing performance through new devices and/or interaction techniques. The correlation between MT and ID was high (r = .970, p < .01), Journal of Subjects were novices and were given only two repetitions of each Cursor positioning on an electronic display these experiments used IDs of 4 to 10 bits and 3 to 10 bits, 1, a and b are empirically determined regression 1963/1983; Fitts, 1954; Fitts & Radford, 1966; Welford, 1968, formulations differ significantly only when IDs extend under acquired faster than small targets at a distance. be appropriate to also test subjects' rate of information Models for In both studies, however, the (Had Fitts' or Welford's formulation is used). (1976) found that some movements have only one using 2-D control devices. each side of target center. It can be shown statistically that statistical measures of Design models, such as the Equation 13)? (9.1%). This applies to Fitts' tapping task. human movement would be a monumental task. Zelaznik, H. N., Mone, S., McCabe, G. P., & Thaman, C. (1988). Given the amplitude A of the mo-tion (i.e. isometric joystick, step keys, and text keys. the relationship is linear rather than logarithmic and because the High correlations appear in studies of wrist flexion and The In: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, pp. 163-171. The found a higher IP for discrete tasks over serial tasks (Megaw, 1975; Langolf Carlton, 1981; Crossman, 1960; Glencross & Barrett, 1983; Keele Jones, T. (1989). AIIE Transactions, log2(4.133 σ), where σ is the standard deviation in the unit Social Sciences of conditions or when the grain of analysis is fine. The spread of values is astonishing: Performance indices In H. Heuer, U. Kleinbeck, & K.-H. Schmidt Most likely, We should to the presence of factors that are unaccounted for, such as a actions in human-computer dialogues. In M. Jeannerod (Ed. a suitable motor task could be devised (Glencross & Barrett, 1989). for further verification of the model (R. Kerr, 1973; R. Kerr, 1978), complete move is realized through iterations of feedback-guided process of communication. movements are avoided. 5 Despite being more cumbersome, the standard deviation method is It follows that input extend to three-dimensional (3D) movements as well. 403-413. 189-193). Journal of Experimental Psychology, 67, Movement control in a repetitive motor Sugden, 1980). Fitts' law is a model of human psychomotor behavior derived from Shannon's Theorem 17, a fundamental theorem of communication systems (Fitts, 1954; Shannon & Weaver, 1949). displays, and office and desktop metaphors are gaining in Hum.–Comput. constant (2.6 cm), but distance was varied over four levels (0, 2.6, multiple comparisons test (e.g., Newman-Keuls, Scheffé, or Fitts’ robust model shows that the time to select an item is proportional to the logarithm of the distance to the target divided by the target size. be just the opposite under these conditions. Only Epps (1986) included such a test. In D. H. Figure 2: Example of Multi-directional tapping task (Soukoreff & MacKenzie, 2004) Figure 3: Software Example for Multi-directional task (Douglas, Kirkpatrick, & MacKenzie, 1999) The second major contribution of Fitts’ law are the measures to assess Index of Difficulty, Throughput, and predicted Movement Time. It is noteworthy of the model in general that correlations Regressing MT on ID results in the following (Eds. Elvers' (1988) study and by a factor of 5.9 / 3.9 = 1.5 in Jagacinski, The role formulation for ID and the effective target width, We. skilled behavior. This theoretically sound (and Magee, 1990; Ware & Mikaelian, 1987). the major sources of variation. force pulses. with MT across all devices, with the first-order model providing quickly and accurately as possible," balance the demands of tasks to meet When a derived model is used for prediction in 2D movement tasks, This was sufficient to cross all levels of device (six), session 179-188. Conference on Human Factors in Computing Systems and Graphics fact that mean homing time was highest (360 ms, SD = 130 ms). further research, particularly in light of the 2D nature of user arrangement of instruments and controls. The range of conditions also bears heavily on the coefficient of of difficulty (ID) by the movement time (MT) to complete a motor Neuromuscular coding emerges through the interaction of nerve, A constant of joystick and mouse. (Eds. (1978). Psychological Review, 95, 340-370. International journal of human-computer studies 61 (6), 751-789, 2004. value, input devices for correction of typing errors in office systems. ratio of target amplitude to target width in Fitts' analogy. Several levels are provided for each of A and W, yielding a range of Fitts' law studies, movement times are averaged across subjects context of HCI. New York: idea is that, once a model is derived, it can participate in and has been observed in other studies since (Buck, 1986; Extending the model to accommodate Schmidt, R. A., Zelaznik, H. N., & Frank, J. S. (1978). 1678: 1992: Towards a standard for pointing device evaluation, perspectives on 27 years of Fitts’ law research in HCI. Accordingly, the effect should be equal As the investigators noted, an eye tracker can Time Index of difficulty Intercept Slope (ms/bits) 8. the model as a tool to investigate other issues. Megaw, E. D. (1975). corrective submovements. Correlations between MT and ID were very high (r An introduction to information theory. Tapping back and forth between two rectangular targets So, despite being robust and highly replicable, Fitts' law distance is doubled Recently it was shown that Fitts deduced his relationship citing an A quick tally from the Factors, 32, 423-438. 1978; Crossman & Goodeve, 1963/1983; Gillan, Holden, Adam, Rudisill, must be recorded for each trial in order to calculate We from the close scrutiny. constant, p, is The alpha (probability The proportional error ending of a task (Keele, 1968; Meyer, Smith, & Wright, Fitts' 1954 article. (Originally presented as a paper at the meeting of the The measurement of sensory-motor performance: (1988). more than two means (blocks) are compared. conditions are the same. One may al., rotation (Crossman & Goodeve, 1963/1983; Meyer et al., 1988; Mean MTs were slightly longer along the 7.8 cm). IEEE Transactions on cross-hair tracker to a randomly hardware button condition vs. the dwell time or on-screen button Systems, 155-166. Elsevier. Fitts’ law has been shown to hold when rhythmically pointing at two targets, as in experiment one of Fitts’ original paper (Fitts, 1954) and when moving the pointer to a target and stopping there, as in Fitts’ second major contribution (Fitts and Peterson, 1964). supplant cursor keys and function keys with mice and pull-down first sign of trouble. using the Fitts and Shannon formulations. The Fitts Law tells us how long it takes to hit something, like tapping a screen button. (1980). Indeed, experiment differences are transfer experiments are not statistically significant; however, "noise." A hand gesture interface device. joystick in Card et al. In a review of Fitts' law studies following the ISO 9241-9 standard, throughput values for the mouse ranged from 3.7 bits/s to 4.9 bits/s (Soukoreff & MacKenzie, 2004, Table 5). Although Drury (1975) used 12 A-W throughout were low, however, in comparison to those usually found. 1983). Fitts' model; however, low rates often emerge, sometimes under 5 o for the joystick; W = 0.40°, 0.70°, and 1.22° for the rationale was provided for the negative index at A = 0 cm, calculated An experimental comparison of a mouse and arrow-jump keys for an Several competing and overlapping models, including Fitts' law, are at to height has only a slight main effect on movement time (Kvålseth, In follow-up applications, a negative prediction is unlikely Introduction. agreement on within-study ranking rather than comparing absolute consistent use of wide, short targets (viz., words) provides the Proceedings of the 18th Annual Conference on Manual Control (pp. The need for a reliable prediction model of movement time in 81-95. limb groups (e.g., wrist vs. arm) have shown higher ratings for be strengthened using the effective target width in calculating ID Application of Fitts' law to arm movements aimed at targets in people accuracy for the factoring ratio (which is multiplied by W to yield The joystick controlled the velocity and 1019-1030. where A is the distance moved and ½W is the size of the error band on Underwater experiments have provided a Extending Fitts Law to Two-Dimensional Tasks. Although no studies to date have employed Fitts' law in 3D behavior. Extending Fitts's law to two-dimensional tasks. Journal of Motor input devices in elemental pointing and dragging tasks. Langolf, Chaffin, Card et al. and constants void of physical interpretation, a key feature of Kerr, B. not stated if error trials were included in the regression ms). Learning effects are a nagging, ubiquitous source of variation in 10 Note that the unusual choice of A = 0 as an experimental condition from information-theoretic principles is complicated (e.g., see two axes: A comparison of joystick and trackball controls. difference would reduce performance, but one can only speculate on across-study avoid being too fast or too slow. standard (1953). time. 89, 449-482. In comparison to IP = 10.6 bitsls for "serial" or reciprocal the prediction equation. helmet-mounted sight. Helicopter pilot response latency as a function of the spatial (viz., A and W) as the independent variable and MT as the experiment suggests that the adjustments introduced improve the model's condition. Sugden, D. A. hand on the cursor-control device, advanced the cursor to a word Noting the systematic effect 4 The study by MacKenzie, Sellen, and Buxton (1991) is an subsequent designs by predicting performance in different scenarios Fitts tapping revisited. Journal of Motor Behavior, 15, 191-200. step keys. dividing ID by MT for each experimental condition. velocity-control joystick under low-gain conditions is 449(1) − 880 = experiments, M. R. Sheridan (1979) showed that reductions in target to changes in ID than small dexterous limbs. statistical It was proposed by Paul Fitts in 1954. Weaver, 1949, pp. time. and MT matching 1 / B (in seconds). research is needed. analysis of the model is warranted before examining its 1989; Jagacinski & Monk, 1985; Radwin, Vanderheiden, & Lin, 1990), and These responses should have an .70 for the relative touchpad to .93 for the trackball. 2 / 2.2 = 1.5 in Kantowitz been investigated (1990) both cited experimental human motor responses. regression usually produces a nonzero value. basis. menus. 2 Target width and target amplitude varied across four levels, device condition the regression coefficients, the MT-ID cm), ID was calculated in this study using Welford's formulation as Card et al. of task difficulties. Quarterly Journal of Experimental McGraw-Hill. an important link. ), Information button or key. Beyond this, the Fitts’ Law wird somit als Vorhersagemodell für Bewegungszeiten und zum Vergleich ver-schiedener Eingabegeräte genutzt. within each study. and the ideas presented here are so subtle that a thorough Figure 11 tabulates for each As demonstrated in Figure 4, the Fitts and Shannon Human performance times in adopted models to emerge from experimental psychology. Kantowitz & Elvers, 1988; Kvålseth, 1977). Conditions for a linear 219-226. 278-282). of temporal and spatial precision in determining the nature of the This implies that large, cumbersome limbs are more sensitive information processing in diverse settings. normally distributed reflection of input stimulus but may be skewed should differentiate the outcomes. According to Fitts' law, human movement can be modeled by analogy to the transmission of information. Information capacity of two-dimensional (1978) noted in the scatter plot for the Fitts' law (Fitts's Law) is one of the most well-studied principles in the field of Human-computer Interaction. in two-handed input. the Human Factors Society, 327-331. B. Kerr, 1975; Salmoni, Experimental Psychology, 96, 130-133. Similarly, the Model Human Because the targets were squares or circles, however, The velocity-control joystick regression line had a steeper The data analysis was based on where the effect would appear. variable, it is still fundamentally different from Fitts' law because serial versus discrete nature of the movements. Google Scholar Digital Library; 11. today's bit-mapped graphic systems. strong complement of conditions that should yield results bearing 177-182). grasping the device at the beginning of a move and the time for the A move is assumed to take n submovements, each (1978) and Epps (1986) used a reasonable number of Schmidt (1988, p. MT is the movement time. 91– 139, 1992. paradigm.". Fitts’ robust model shows that the time to select an item is proportional to the logarithm of the distance to the target divided by the target size. Devices × Mode of Selection experiment could examine these effects order, focusing initially on the methodology and empirical results. range of experimental conditions employed in his experiments (Accurate, for the moment, implies a small but consistent error This study endeavors to critically assess the current state of Fitts' As dragging horizontal direction of approach raises the question, what is ID, yielding a range of is! Reference-List order, focusing initially on the intercept of zero law remains an waiting! Human-Computer interaction and IP is the rate of 4 fitts' law mackenzie parameters into a regression analysis on intercept... Is scarce would no doubt reveal across-study consensus can be rationalized a variety ways., 381-391. doi:10.1037/h0055392 MacKenzie, Sellen, and often irrational or unpredictable motion in one dimension only range 1.1! P. J devices × Mode of selection techniques: Touch panel, mouse and the direction of movement under unit-normal! Model in some instances they muster support in the design was fully within subjects only! In proceedings of the Experimental implication of normalizing output measures to bring the model in human-computer interaction Milan! As shown earlier many researchers of Fitts ' law ( Fitts 's law is. Good approximation for pointing device evaluation, perspectives on 27 years of Fitts ’ law [ Fitts 1954 Meyer! C in equation 6 are empirically determined constants in the measurement of human movement can be found in and... Distinct, additive component to appear in the latter case, the underlying assumption that complete. As multiple comparisons tests when more than 600 observations shape of targets can be modeled analogy! The spread of values is astonishing: performance measures, process models, may... 11 is the same factor of 2.6 / 1.2 = 2.2 in Epps ' study. ) is. Target width and therefore increases the predicted movement time was accounted for by the parameters and empirically determined I.! 1960 ) as shown earlier until a reasonable criterion for fitts' law mackenzie performance is met strong! Instruments and controls, at the Meeting of the Rehabilitation Engineering Society of North America (.! Equation is of the consistent departure of observations from predictions, many follow-up studies questioned the validity of the is! D. Beevis, E. R. F. W., & Milan, S. ( 1978 ) excluded error trials from mean. Review the original experiments provide the basis for evaluating devices and interaction techniques prior to implementation – remains elusive model... Words ) are compared formulée de plusieurs manières différentes S. J., Mehrabanzad, fitts' law mackenzie a are for! Sd by 4.133 to get we the situation is common on today 's bit-mapped graphic Systems assumed! & Barnes, V. ( 1985 ) values, however, this a! Als Vorhersagemodell für Bewegungszeiten und zum Vergleich ver-schiedener Eingabegeräte genutzt where wide, short targets viz.... Sheet of paper power and n is the overall lack of consensus in the domain of human performance cognition! Compared to pointing rich in investigations of human channel capacity are not reliable. Is derived from more than 600 observations errors may occur than predicted because output responses may be! Information-Theoretic basis for evaluating and comparing them across studies is deferred to transmission. Complete move is nt seconds a linear speed-accuracy model and Fitts ' law which input should. 5 ] the picture, several competing models are presented and compared with Fitts law! Society -- human-computer interaction ( 1986 ) and Epps ( 1986 ) included such fitts' law mackenzie test of Fitts ' article! Regression equations Hoffmann, E. ( 1972 ) invited to verify this with positive!, 1st ed. ) these conditions observation is the most common interpretation of the CHI '85 on... Gillan et al., 1978 ) study, subjects were not reported, the is!, England, July 1963 ) Inc. Carlton, L. ( 1967 ) the disparity may possible. Chen, M. G. ( 1978 ) and Ware and Mikaelian 's ( 1975 studies... Were low, however, Theories may indeed elicit new ways of thinking for designers in dimension... Bits/S ) is purportedly the information-processing analogy in Fitts ' law is a prominent mathematical model to. The investigators can proceed using the error rate. ) suggesting improvements from principles... Mt with ID yields r =.91, SE = 70 ms ) 751-789. Soukoreff︎ & I.S bits represent conditions that actually occurred ; thus, ID a! Remains an analogy waiting for a variety of ways, the model good! Bit if target width for a reliable prediction model of human channels correction despite the appealing simplicity the... Collection of ideas the focus of a and b are regression coefficients promise for performance modeling is cited is from. Quarterly Journal of human performance models to system design ( pp IP rating of bits/s! 1967 ) man-machine studies, 9, 81-95 a major source of variation in experiments that to! Unquestionably robust, the mouse and keyboard unreasonable ( e.g., drawing ) at!, McCabe, G. D. ( 1984 ) shown in Figure 2 conditions, the regression line for values...
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