PERFORMANCE TIME AS EFFECTED BY CHOICE UNCERTAINTY AND INDEX OF DIFFICULTY.

Applications of Index of Difficulty (I. D. ) developed by Fitts are well documented in the literature. The effect of Choice Uncertainty (H) on 'reach' type of elements has also been investigated as well. The unit of measurement used for H and I. D. is the same i. e. bit. There are many instances where a worker is required to perform a task involving I. D. and H. To Study the effect of I. D. and H on performance time in a Combined Manual and Decision Task involving 'move' and 'positioning' a set of experiments was conducted. Twenty subjects, ten male and ten female, were tested. Each subject performed under six I. D. levels and four H levels. To avoid confusion I. D. was measured in IBITS. (I. D. equals log//2 2A/W IBITS) I. D. and H were found to significant variables effecting performance time. Sex of the subjects was not found to be a significant variable. A linear prediction model for estimating performance time for tasks involving I. D. and H i. e. move and positioning has been developed.