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Cognitive Engineering PSYC 530 Vigilance. Raja Parasuraman. Overview. Historical Background Theories of Vigilance Signal Detection Theory and Vigilance Enhancing Vigilance in Real World Systems. Historical Background. Origins of Vigilance Research (1940s).

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overview
Overview
  • Historical Background
  • Theories of Vigilance
  • Signal Detection Theory and Vigilance
  • Enhancing Vigilance in Real World Systems
origins of vigilance research 1940s
Origins of Vigilance Research (1940s)
  • German submarines sinking Allied naval and cargo ships in English Channel and Bay of Biscay
  • Royal Air Force (RAF) reconnaissance and anti-submarine warfare flights
  • Radar and sonar operators on board watching or listening for U-boat contacts
origins of vigilance research contd
Origins of Vigilance Research (Contd.)
  • Low probability of contact —most missions ended without locating a German submarine
  • When a contact was missed, most often towards the end of a flight
  • False reports--leading to bombing of friendly vessels or large marine life
norman mackworth s studies
Norman Mackworth’s Studies
  • Field observations of airborne radar and sonar operators
  • Conducted simulation experiments at MRC Applied Psychology Unit (he was first Director of the Unit) with the Clock Test
  • Did first laboratory experiments demonstrating the vigilance decrement phenomenon
mackworth clock test

Double Jump = Signal

Single Jumps = Neutral events

Signals occur unpredictably and infrequently (12 every 30 minutes)

Mackworth Clock Test
results mackworth 1948
Results (Mackworth, 1948)

“Alerted Detection”

Subjects: RAF and Naval personnel (25 each)

Clock Test: 12 signals/30 min

Following training, 2 hour test

100

90

Vigilance Decrement

80

Proportion of Signals Detected (%)

70

60

50

30 60 90 120 minutes

Time on Task

characteristics of vigilance
Characteristics of Vigilance
  • Low probability of occurrence of signal (< 5%)
  • Frequent non-signal (noise) or neutral events
  • Temporal uncertainty of signal (minutes to days)
  • Prolonged period of performance (30 min - 1 hr)
  • Need to consider both
    • vigilance decrement and
    • overall vigilance level

Vigilance Decrement

Yes

No

High

Vigilance Level

time

Low

Minimum acceptable level of performance

types of vigilance task
Types of Vigilance Task
  • Low vs. High Event Rate (Number of non-signal events per unit time)
  • Simultaneous vs. Successive (Memory load imposed in successive tasks)
  • Sensory vs. Cognitive (Signal defined on physical vs. symbolic or semantic level)
typical vigilance results
Typical Vigilance Results

Reaction Time

Detection Rate

100

1000

80

800

60

600

Proportion of Signals Detected (%)

Mean Reaction Time for Detected Signals (ms)

40

400

20

200

0

0

10 20 30 40 minutes

10 20 30 40 minutes

Time on Task

Time on Task

leading vigilance researchers

Donald Broadbent, MRC Applied Psychology Unit (deceased)

Roy Davies,

Aston University (retired)

Peter Hancock, University

of Central Florida

Early photo of some guy at George Mason University

Joel Warm,

University of Cincinnati

Leading Vigilance Researchers

Norman Mackworth, MRC Applied Psychology Unit (deceased)

theories of vigilance14
Theories of Vigilance
  • Arousal Theory
  • Habituation Theory
  • Expectancy Theory
  • Attentional Resource Theory
  • Multi-Component Theories
arousal theory
Arousal Theory
  • Decline in detection rate over time (vigilance decrement) is due to a decrease in physiological arousal due to the repetitive nature of the task
  • Ascending Reticular Activating System — Brain stem activates diverse regions of cortex
arousal theory pros
Arousal Theory: Pros
  • Behavioral (activity measures), physiological (EEG theta, skin conductance, etc.), and subjective report measures all point to decreased arousal with time on task
  • Overall level of vigilance is significantly affected by factors that influence arousal (: Caffeine, other stimulant drugs; morning vs. late night performance; varied auditory stimulation, etc. : Alcohol, other depressant drugs; sleep deprivation; loud noise).
arousal theory cons
Arousal Theory: Cons

Detection performance

Arousal decline: task performance

Arousal decline: no task imperative

  • Decline in arousal correlates with vigilance decrement, but causal relation difficult to show and opposite causal relation is possible(vigilance decrement  arousal decline)
  • Many factors that change arousal level do not affect the vigilance decrement over time.

Stimulant drug: actual

Control

predicted

Control

Depressant drug

expectancy theory pros
Expectancy Theory: Pros
  • Subjects perceive and expect signals to occur at a very low rate (Baker, 1961). As a result, they become more “conservative” in responding (in an SDT sense), and adjust their criterion upwards
  • Leads to a greater likelihood of missing a signal
  • This further reduces expectancy for a signal, and so on in a “vicious cycle” (Broadbent, 1971)
  • Support for theory in Reaction Time (RT) and SDT (ß) measures
  • Support for theory when signal probability is lowered, detection rate decreases and vigilance decrement increases

Low expectancy for signal

Upward criterion adjustment

Further reduction of expectancy for signal

Missed signals

expectancy theory cons
Expectancy Theory: Cons
  • Vigilance decrement occurs even when subjects are specifically trained to match their “expectancy” to the actual signal rate (Baddeley & Colquhoun, 1964)
  • No independent measure of the construct of “expectancy”
  • The theory cannot account for sensitivity decrement over time in vigilance
hit and false alarm rates in vigilance tasks
Hit and False Alarm Rates in Vigilance Tasks

Detection Rate

False Alarm Rate

100

10

80

8

60

6

Proportion of Signals Detected (%)

Proportion of Non-Signals Responded To (%)

40

4

20

2

0

0

10 20 30 40 minutes

10 20 30 40 minutes

Time on Task

Time on Task

  • Early vigilance studies did not report FA rates
  • If they did, they treated them as “guesses” or computed biased measures of accuracy
two possible sources for the vigilance decrement
Two Possible Sources for the Vigilance Decrement

1.0

A. Criterion Shift. The vigilance decrement in hit rate is due to an increase in the criterion ( ß), resulting in “downward movement” along a single ROC

Increasing Criterion, Fixed Sensitivity

time

P(H)

0

P(FA)

1.0

1.0

B. Sensitivity Decrement. The vigilance decrement in hit rate is due to a reduction in d’, represented by points on ROCs with lower sensitivity

time

P(H)

Decreasing Sensitivity

0

P(FA)

1.0

sources of the vigilance decrement
Sources of the Vigilance Decrement

A. Criterion Shift

d’

ß

100

Vigilance Decrement in Hit Rate

80

60

Proportion of Signals Detected (%)

or

40

B. Sensitivity Decrement

20

0

10 20 30 40 minutes

Time on Task

ß

d’

sensitivity decrement parasuraman 1979
Sensitivity Decrement (Parasuraman, 1979)
  • High event rate (> 24/minute)
  • Successive vs. simultaneous task
  • Dual-task probe RT task suggests that sensitivity decrement is due to depletion of attentional resources with time on task
tcds study of cerebral hemovelocity in an air traffic control vigilance task
TCDS Study of Cerebral Hemovelocity in an Air Traffic Control Vigilance Task

Target Cue Provided

Just Before Critical

Event:

100% Valid

70% Valid

No Cue

slide27

1.05

1.00

.95

.90

0.85

0.8

0

0

10

20

30

Hitchcock et al. (2000)

100% Valid Cue

70% Valid Cue

No Cue

No Task Control

Cerebral Hemovelocity Score

40

Time on Task (minutes)

multi component theory arousal attentional resources and expectancy parasuraman 1985
Multi-Component Theory: Arousal, Attentional Resources, and Expectancy (Parasuraman, 1985)
  • Arousal controls the overall level of vigilance, but not the decrement
  • The vigilance decrement can be due to either a sensitivity decrement (d’ decrement) or a criterion shift with sensitivity remaining stable (ß increase)
  • Sensitivity decrement is due to depletion of attentional resources over time. Sensitivity decrement is greater for:
    • high event rate (observation load)
    • successive discrimination (memory load)
    • low signal salience (perceptual load)
  • Criterion shift is due to expectancy
air traffic control
Air Traffic Control

Signal: Two aircraft in “conflict” (within 1 mile vertically or 5,000 ft horizontally)

industrial inspection and quality control
Industrial Inspection and Quality Control

Signal: Manufactured product with specified flaw

techniques to combat loss of vigilance
Techniques to Combat Loss of Vigilance
  • Show signal examples (reduce memory load)
  • Increase signal salience (reduce perceptual load)
    • Blinking
    • Adding coherent motion
    • Alternate sensory modalities
  • Lower event rate (if possible)
  • Insert false signals (TSA program for baggage screeners)
  • Allow reporting with multiple levels of confidence