Mental Workload

What is Mental Workload?

• Why measure it?– Performance limits– Predict top performance

• Tasks– Cognitive/perceptual– multiple

What kind of tasks have High mental workload?

High• Air traffic control• Pilot• Military command & control• Nuclear power plant operator• anesthesiologist

N/A• Computer programmer• College professor• Mathematician• Technical writer

Key Elements for High mental workload tasks

• Stimulus driven not self paced• Large fluctuations in demand• Multiple simultaneous tasks• High stress/High consequence

Workload & Arousal

Yerkes-Dobson law

Low arousal Low performance

Moderate arousal High performance

Over arousal Low performance

Basic approaches to measuring mental workload

• Analytic – Task difficulty– Number of simultaneous tasks

• Task performance– Primary task– Secondary task

• Physiological (arousal/effort)• Subjective assessment

Analytic Models

• Tracking models predict based on systems dynamics

• Queuing models predict on the basis of task co-occurrence

• SAINT / microSAINT best developed queuing models

Resources/Attention

• Some limited capacity– Unitary: task always depletes common pool by

a constant amount– Multiple: task depletes pools of resources to

varying degrees– Mixed: cost of sharing even for highly

dissimilar resources

Simplified HIP Model

Unconscious/Automatic Processes

Working Memory

Long

Term

Memory

AttentionS

E

N

S

O

R

Y

S

T

O

R

E

Physiological Measures• heart rate: sinus arrhythmia• blood pressure• respiratory rate variability• tidal volume • ventilation • galvanic skin response• evoked response amplitude• evoked response latency

• evoked response latency• electroencehpalogram,• spectral components• time domain, • flicker fusion frequency• pupil diameter• electromyograms• electrooculograms

Subjective Workload Measures

• Cooper-Harris – Manual control characteristics

• SWAT– Dimension based instrument

• NASA– 6-D assessment scales