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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,

where *H*_{choice} is information in bits, *p*_{i} is the probability of signal *i*, *T*_{choice} 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.

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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,

where (see Figure 8.1) *H*_{move} 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. ...