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,
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.