Page 27 - Innovations in Intelligent Machines

Predicting Operator Capacity for Supervisory Control of Multiple UAVs 15
3.1 Wait Times

Modeling interaction and neglect times are critical for understanding human
workload in terms of overall management capacity. However, there remains
an additional critical variable that must be considered when modeling human
control of multiple robots, regardless of whether they are on the ground or in
the air, and that is the concept of Wait Time (WT). In HSC tasks, humans
are serial processors in that they can only solve a single complex task at a time
[3, 4], and while they can rapidly switch between cognitive tasks, any sequence
of tasks requiring complex cognition will form a queue and consequently wait
times will build. Wait time occurs when a vehicle is operating in a degraded
state and requires human intervention in order to achieve an acceptable level
of performance. In the context of a system of multiple vehicles or robots, wait
times are significant in that as they increase, the actual number of vehicles that
can be effectively controlled decreases, with potential negative consequences
on overall mission success.
Equation 2 provides a formal definition of wait time. It categorizes total
system wait time as the sum of the interaction wait times, which are the
portions of IT that occur while a vehicle is operating in a degraded state
(WTI), wait times that result from queues due to near-simultaneous arrival of
problems (WTQ), plus wait times due to operator loss of situation awareness
(WTSA). An example of WTI is the time that an unmanned ground vehicle
(UGV) idly waits while a human replans a new route. WTQ occurs when a
second UGV sits idle, and WTSA accumulates when the operator doesn’t even
realize a UGV is waiting. In (2), X equals the number of times an operator
interacts with a vehicle while the vehicle is in a degraded state, Y indicates the
number of interaction queues that build, and Z indicates the number of time
periods in which a loss of situation awareness causes a wait time. Figure 2
further illustrates the relationship of wait times to interaction and neglect
times.
Increased wait times, as defined above, will reduce operator capacity, and
Equation 3 demonstrates one possible way to capture this relationship. Since

Robot 1
Robot 1 IT
WTQ 1 IT`
Robot 2 Robot 2
WTQ IT`` WTSA IT```
2 Robot 3
Robot 3

IT+NT IT+NT
(a) (b)

Fig. 2. Queuing wait times (a) versus situational awareness wait times (b)