Alt 6: Attention and workload

Question 1

What is workload?

Answer 1

Mental workload (referred to as just workload) is a general term used to describe the cost of accomplishing task requirements:

Question 2

Workload varies as a function of

Answer 2

task demands placed on the human operator
AND
the operator’s capacity to meet those demands

Question 3

Task demands influenced by factors:

Answer 3

Task Difficulty
Task Priority
Situation

Question 4

Operator capacity

Answer 4

Individual operator differences:
Each operator has a supply of mental resources
Mental resources shape how we cope with task
demands

Question 5

excessive workload:

Answer 5

overload

Question 6

sustained low workload:

Answer 6

underload

Question 7

Underload can cause:

Answer 7

(1) Increased fatigue
(2) Lower task engagement
(3) Lower vigilance
(4) Generally reduces operators capacity to deal
with the unexpected (spare capacity)

Question 8

Why measure workload?

Workload prediction

Answer 8

To maintain workload within acceptable limits

• Safety
• Change management: Know in advance what effect changes will have

Question 9

Why measure workload?

Equipment assessment

Answer 9

Optimize the system to suit operator

• Designers may want to know what workload will be at the design, production, or usage stages
• Identify problem areas where performance may decline

Question 10

Why measure workload?

Employee selection

Answer 10

Choose the right operators, or further training

- Can train to improve some capacity, but only up to a point

Question 11

There are three major categories of workload measures:

Answer 11

1. Performance
2. Subjective
3. Physiological

Question 12

Performance measures

Answer 12

System designers are typically concerned with performance, some might argue workload is only important if it affects performance

Question 13

Primary task performance

Answer 13

Common general measures: Accuracy, Response time, Signal detection
Task specific measures: Mouse movements, Altitude deviation, Braking time,

Question 14

Primary Task performance measurement advantages

Answer 14

Workload reflected directly by performance outcome
Non-invasive and non-interfering
Tracks changes in workload dynamically. (i.e., as performance proceeds)
Uncontaminated by memory issues

Question 15

Primary Task performance measurement disadvantages

Answer 15

Mental workload is not the only thing that can influence performance
Doesn’t take effort into account
Might not always have the technology or interface
available to monitor performance

Question 16

Secondary task performance

Answer 16

Purpose: To measure the spare capacity not being used by the primary task
Usually, an increase in primary task workload is associated with a decrease in secondary task perf.
Potential measures including: Rhythmic tapping task, Probe reaction tasks, Auditory monitoring

Question 17

Secondary task performance measurement advantages

Answer 17

The same secondary task can be used with very different primary tasks
There are a collection of available (and validated) secondary tasks
Provide a measure of space capacity
Useful when there is little primary task data available
(e.g. monitoring jobs, baggage scanner)

Question 18

Secondary task performance measurement disadvantages

Answer 18

Only relevant when secondary task taps into the same resources as the primary task
It adds in another task to the work environment (could increase workload)
Can interfere/interrupt primary task

Question 19

Subjective measures

Answer 19

Where you ask someone to quantify their personal experience of workload

Question 20

Three variables that are useful to categorise different subjective rating techniques:

Answer 20

Dimensionality (single or multiple)
Evaluation (absolute or relative)
Immediacy (when queried?)

Question 21

Subjective measures advantages

Answer 21

Cheap and simple to administer
No need to interfere with primary task
Reasonably good reliability and validity
NASA-TLX has a huge literature available for comparison

Question 22

Subjective measures disadvantages

Answer 22

People aren’t always aware of workload
People find it difficult not to baseline their workload
Not sensitive to moment-to-moment changes

Question 23

Physiological measures

Answer 23

The assumption is that biological functions can reflect mental work done.

Question 24

Popular Physiological measures include:

Answer 24

Cardiovascular
Ocular
Brain activity

Question 25

Cardiovascular measures

Answer 25

Heart-rate variability shown to increase with workload
Particularly relevant to emotional stress
Potential issues:
• Need to establish a baseline
• Quite a range due to individual differences
• Only sensitive when stress is involved

Question 26

Ocular measures

Answer 26

Pupil diameter increases with workload
Visual scanning patterns and pathways change with workload
Length of time spent fixating on items changes with workload

Question 27

Brain activity measures

Answer 27

It is intuitive that brain activity will reflect mental workload
Brain activity sensitive to different kinds of cognitive demands (e.g. memory, vigilance, flexibility, etc.)
Measures: Electroencephalogram (EEG), Event- related potentials (ERP), and Cerebral blood flow

Question 28

Physiological measures advantages

Answer 28

Provide a relatively continuous measure over time
Objective
Many different techniques available

Question 29

Physiological measures disadvantages

Answer 29

High cost
Often obtrusive
Cannot be used to determine how the operator feels about the task (can be important)

Question 30

Multiple Resource Theory

Answer 30

If two (or more) tasks are similar they will draw on a common resource pool. This will affect performance negatively
If the two (or more) require different resources, then performing the tasks at the same time will have little negative consequence

Question 31

Multiple resource theory assumptions (3)

Answer 31

1. There is a common, finite pool of resources that can be flexibly allocated to tasks
2. Allocating more resources to a task speeds up the rate of processing of that task
3. The quantity of resources made available can be increased or decreased

Question 32

Multiple resource theory

Stages of processing:

Answer 32

Perception (I can see a car stopped ahead…)
• Cognition (…I predict that car will be a problem…)
• Response (…slows down)

Question 33

Multiple resource theory

Codes of processing

Answer 33

(relevant in all stages)
Spatial (e.g. pointing out a car)
Verbal / Linguistic (e.g. describing a car)

Question 34

Multiple resource theory

Modalities

Answer 34

(only relevant for perception stage)
Auditory perception (e.g. listening to radio)
Visual perception (e.g. looking for a sign)

Question 35

Multiple resource theory

Visual channels

Answer 35

(only relevant in visual modality)
Focal channel (focus of attention, e.g. car in front)
Ambient channel (peripheral vision, e.g. cars on either side)

Question 36

Driver safety

Answer 36

Driving provides an example of a practical task domain where competition for limited resources is common