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Modeling Human–System Interaction by Thomas B. Sheridan

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8 IMPLEMENTING AND EVALUATING THE ACTION

TIME TO MAKE A SELECTION

Hick (1952) proposed a model, based on Shannon’s (1949) information measure H (see Chapter 5, Section Information Communication), for the time T it takes to choose which of several alternative movements, i, to make. The choice is based on the information in an immediately displayed signal calling for that move and the assumption that the move time itself is brief and constant,

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where Hchoice is information in bits, pi is the probability of signal i, Tchoice is the time required to choose, and α and β are scaling constants dependent on task conditions. α includes at minimum the base reaction time for making the slightest hand movement in response to a visual stimulus.

TIME TO MAKE AN ACCURATE MOVEMENT

Fitts (1954) also used the information measure for his model, in this case of the time required for making a discrete arm movement to a bounded location or target,

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where (see Figure 8.1) Hmove is information in bits (sometimes also called index of difficulty), A is the distance moved, B is the tolerance to within which the move must be made (for Fitts’ experiment a tap between two lines), T is the task completion time, and α and β are again scaling constants, different for different conditions. ...

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