Task Analysis Workload Methodology (TAWL)

The Task Analysis Workload (TAWL) Methodology is a task load approach to workload assessment developed within the context of military operations (specifically the US Army Light Helicopter Experimental Program – LHX). The method places primary emphasis on workload assessments based on construction of descriptions of the task or set of tasks to be performed which can take either a descriptive or prescriptive form. TAWL is a partially time- based analysis technique insofar as timing data can be incorporated into the

The TAWL approach has dominated US army workload evaluations since the late 1980s. According to Mitchell (2000), present tools originate from two TAWL software based tools developed in the early 1990s. MAN-SEVAL (Manpower System Evaluation Tool) was a workload assessment module incorporated into a suite of human performance assessment tools known as Hardware Versus Manpower III (HARDMAN III) work package (cf: Allender et al, 1997). CrewCut (Little et al, 1993) provided more complex evaluations of workload and was developed to model dynamic relationships between workload and task performance.

MAN-SEVAL

System designers used the MAN-SEVAL module to predict likely workload demands for military systems in an early design stage. Assessments were achieved using VACP modelling techniques in which workload is characterised in terms of the demand placed upon the visual, auditory, cognitive, psychomotor components of human cognition. VACP modelling is a practical implementation of multiple resource theoretic models discussed in Section 3. In the first phase of a MAN-SEVAL assessment a task analysis is constructed and areas requiring dual task performance are singled out for special attention. Each sub-task is then categorised according to the VACP model and rated using the values shown in Figure 15 below. Workload metrics can be computed in the range 1 to 7 (with 7 representing full resource deployment) using one of several schemes dependent upon the issue being considered at a particular time.

CREWCUT

CrewCut is a tool used to compare operating team workload resulting from the particular design of crew workstations. The application allows designers to consider how an operating team might react to different task demands using a default set of workload management strategies incorporated into the software tool. The relationship between task demands and team performance with respect to workload is explored in the method using discrete event simulation, which are encoded using a task network simulation language (e.g., Hart and Wickens, 1990).

CrewCut assumes that the evaluation of workload management allows designers to account for the fact that people adopt coping strategies to deal with workload demand. At the start of assessment, a threshold value is set to denote the point at which task demand is considered excessive (See Figure 8 Section 2.1). The CrewCut assessment module provides six workload management strategies for dealing with overload conditions and these are summarised in Figure 22.

Task Descriptors WL Rating Visually Unaided Tasks (naked eye)

Visually register or detect object 3.0

Visually discriminate or detect visual difference 5.0 Discrete visually inspection or check in static conditions 3.0

Visually locate or align 4.0

Visually track or follow target (maintain orientation) 4.4

Read 5.0

Scan or search monitor for multiple possible conditions 6.0 Visually Aided Tasks (with NVGs)

Visually register or detect object 5.0

Visually discriminate or detect visual difference 7.0 Discrete visually inspection or check in static conditions 5.0

Visually locate or align 5.0

Visually track or follow target (maintain orientation) 5.4 Scan or search monitor for multiple possible conditions 7.0 Auditory

Detect or register sound 1.0

Orientate to sound (general orientation or attention) 2.0 Orientate to sound (selective orientation or attention) 4.2 Verify auditory feedback (detect occurrence of anticipated sound) 4.3 Interpret semantic content of message (simple) 3.0 Interpret semantic content of message (complex) 6.0 Detect auditory difference between similar sounds 6.6 Interpret sound patterns (e.g., pulse rates, etc) 7.0

Speech (Simple) 2.0

Speech (Complex) 4.0

Cognitive

Automatic processing (simple association) 1.0

Selection between alternatives 1.2

Sign or signal recognition 3.7

Evaluation or judgement (single aspect) 4.6

Encoding or decoding recall 5.3

Evaluation or judgement 6.8

Estimation, calculation, conversion 6.8

Rehearsal 5.0 Psychomotor Discrete actuation 2.2 Continuous adjustive 2.6 Manipulative 4.6 Discrete adjustment 5.5 Symbolic production 6.5

Serial discrete manipulation 7.0

Strategy Description

1 No effect: All tasks are performed, regardless of workload values. This is the default strategy.

2 Do not begin next task: The start of the following task is deferred or cancelled by the operating team. This strategy is known as “task shedding”.

3 Perform tasks sequentially: Time sharing between tasks can occur when the operating team perform task elements sequentially.

4 Interrupt task performance: Interrupt performance of ongoing task in favour of later – but more pressing need – of subsequent task or tasks. Restart performance of interrupted task when workload falls to acceptable value

5 Reallocate next task to contingency operator: If a spare operator exists then performance of certain tasks can be reallocated to spare person. On occasions the contingency operator can be an automated system (e.g., engagement of autopilot).

6 Reallocate task: Reallocate ongoing task to contingency operator or automated system.

Figure 23 Predefined Workload Management Strategies for CrewCut

In addition to the default strategies, system designers can also create their own strategies for the operator to use. These are created by combining pre- defined system variables and arithmetic and logical operators into “if-then- else” statements. The variables used by designers to establish the workload management strategy are: P: Task priority (a value between 1 and 5), H: Highest priority for any concurrent ongoing task set, T: Total workload for the operator after commencement of the next task, and S: The operators workload threshold value. An example of a defined strategy might be:

If P > H, then 3, else 4.

Where 3 and 4 are the predefined strategies shown in Figure 23 above.

CrewCut output is used to optimise work flows in (usually) partially automated work systems. When potential problems with workload are predicted by the modelling activity, designers have the opportunity to revise job-designs and information flows, to allow effective management of foreseeable workload problems. Sometimes workload can be managed by making revisions to the design of the workstation. Sometimes, task demand can be managed by changing procedure, and on other occasions, when other means fail, by increasing manning levels.

IMPRINT and WinCrew

The latest releases of MAN-SEVAL and CrewCut are presently available as options in the US Army improved performance research integration tool

(IMPRINT)4. MAN-SEVAL has been retained in this suite of tools to provide quick and ready data of use in the early system design phase of military systems development. CrewCut has been retained as an advanced workload analysis model intended for use during the detailed engineering design phase. The CrewCut module is also available as a stand-alone commercially available application now called WinCrew.