Mr. Endsley et Db. Kaber, Level of automation effects on performance, situation awareness and workload in a dynamic control task, ERGONOMICS, 42(3), 1999, pp. 462-492
Various levels of automation (LOA) designating the degree of human operator
and computer control were explored within the context of a dynamic control
task as a means of improving overall human/machine performance. Automated
systems have traditionally been explored as binary function allocations; ei
ther the human or the machine is assigned to a given task. More recently, i
ntermediary levels of automation have been discussed as a means of maintain
ing operator involvement in system performance, leading to improvements in
situation awareness and reductions in out-of-the-loop performance problems.
A LOA taxonomy applicable to a wide range of psychomotor and cognitive tas
ks is presented here. The taxonomy comprises various schemes of generic con
trol system function allocations. The functions allocated to a human operat
or and/or computer included monitoring displays, generating processing opti
ons, selecting an 'optimal' option and implementing that option. The impact
of the LOA taxonomy was assessed within a dynamic and complex cognitive co
ntrol task by measuring its effect on human/system performance, situation a
wareness and workload. Thirty subjects performed simulation trials involvin
g various levels of automation. Several automation failures occurred and ou
t-of-the-loop performance decrements were assessed. Results suggest that, i
n terms of performance, human operators benefit most from automation of the
implementation portion of the task, but only under normal operating condit
ions; in contrast, removal of the, operator from task implementation is det
rimental to performance recovery if the automated system fails. Joint human
/system option generation significantly degraded performance in comparison
to human or automated option generation alone. Lower operator workload and
higher situation a awareness were observed under automation of the decision
making portion of the task (i.e. selection of options), although human/sys
tem performance was only slightly improved. The implications of these findi
ngs for the design of automated systems are discussed.