Speed, Accuracy and Power of Attention in Prolonged Work Tasks

In prolonged work tasks subjects are required to engage in simple, repetitive activities, such as letter cancellation, detecting differences in simple shapes, adding three digits, and so on. Performance is recorded as a series of reaction times. In overlearned prolonged work tasks, reaction times usually show an increase at the beginning of the test and, after some time, reach a stationary state. According to each of the inhibition models developed thusfar, the expectation of the reaction time T in the stationary state is as follows: E(T) = A + (a1/a0)A, where A corresponds to the real total working time, a1 corresponds to the rate of inhibition increase during working intervals and a0 corresponds to the rate of inhibition decrease during distraction intervals. The concepts "speed of work" and "power of attention" (Spearman, 1927, page 88) are defined in terms of the parameters of the inhibition process. "Speed of work" is defined as the inverse of A (or the logarithm of A) and "power of attention" as the inverse of a, (or the logarithm of a), where a = a1/a0. These new measures were used in the analysis of two experiments, which were originally conducted by van Breukelen and Jansen. In the experiment by van Breukelen the subjects were instructed to work more quickly and in the experiment by Jansen to work more accurately. The instruction to work faster was indeed followed, but at the cost of accuracy. A decrease was found in the parameter A and an increase in the number of errors. The instruction to work more accurately, however, did not primarily result in a decrease of the number of errors, as was to be expected, !but in a decrease of the parameter a, indicating an increase in the power of attention. Obviously, rather then working more accurately, the subjects reverted to paying more attention to the task. The results are in complete agreement with Thurstone's hypothesis that motivatition may have an effect on the speed-accuracy trade-off. However, in addition to speed and accuracy, power of attention must also be taken into account.