Available from: Index of difficulty (ID) is defined by Fitts’ law. According to Fitts’ law, movement time scales linearly with a single quantity, the index of difficulty (ID), which quantifies task difficulty through the quotient of target width and distance. One of the clear takeaways from Fitts' Law is that the Index of Difficulty is inversely proportional to the target Width. Hidehiko Okada and Takayuki Akiba (May 1st 2010). W is the width of the target. Fitts’ law states that the amount of time required for a person to move a pointer (e.g., mouse cursor) to a target area is a function of the distance to the target divided by the size of the target. Fitts’ law is a factual model used to represent the speed accuracy trade off features of human muscle movement, with analogy method to Shannon’s channel capacity theorem. It was found that ID in Eq. index of difficulty is zero while the slope (“b”) represents the inverse of the motor system information-processing rate.This lab will involve examination of how changing the difficulty of the movement (and thus the accuracy requirements) affects the speed of movement (measured by movement time). Fitts' law is an empirical rule of thumb which predicts the time it takes people, under time pressure, to reach with some pointer a target of width W located at a distance D. It has been traditionally assumed that the predictor of movement time must be some mathematical transform of the quotient of D/W, called the index of difficulty (ID) of the movement task. The term log 2 ( 2A / W ) is called the index of difficulty (ID). Fitts’ Law Index of Difficulty Evaluated and Extended for Screen Size Variations, User Interfaces, Rita Matrai, IntechOpen, DOI: 10.5772/9496. Fitts’ law is centered around a mathematical equation that is used to illustrate the time it takes to reach a target object. As … which means as the width decreases, the index of difficulty increases. Fitts's Law. The Fitts' law methods used in the standard are summarized and software tools are presented that implement the methods. Thus, the longer the distance and the smaller the target’s size, the longer it takes. For a given target acquisition task, e.g. Fitts' law evaluations of computer input techniques are more consistent in recent years due to the emergence of ISO 9241-9, an ISO standard for evaluating input devices. 1/b is also called the index of performance (IP) and measures the information capacity of the human motor system. Effects of Gain and Index of Difficulty on Mouse Movement Time and Fitts’ Law Abstract: The mouse, being the major means of inputting and controlling data on a computer, should beset right for best performance. move the mouse to a certain point in the UI of an application and select it, Fitts's law desribes how the distance from start point to the target and the width of the target influence the index of difficulty (ID) of the task. The width (w) and index of difficulty have an indirect relationship. It describes the difficulty of the motor tasks. Both statements are in accordance with common sense. Fitts' law also states that the target acquisition time increases drastically if the target gets tiny. If you make targets larger and closer to the user, they'll be easier to get to. That much is obvious, even if the precise relationship is a little surprising. Named the Index of difficulty, D is the distance from the starting point to the center of the target. 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