Application of Cognitive Modeling to Fatigue Management

4th Panhellenic Conference on Aerospace MedicineAthens, 29 February 2008

James C. Miller, Ph.D., CPEmillergonomics.com

jcmiller@millergonomics.com(USAF Research Lab, Retired)

Topics

Fatigue context

Quantitative modeling of fatigue (SAFTE)

FAST software (Windows)

F/PAS Web site

Modeling examples

The Human in the Loop

The most unpredictable component in any weapon system is human cognition

After training and currency, the greatest contributor to that human variability is fatigue

Good human-machine system design exploits human strengths and protects the system from human weaknesses

The Human in the Loop

Human Strengths: Better pattern recognition capabilities and decision-making skills than can be provided in software

Human Weaknesses: Much more performance variability than one finds in software and modern hardware, primarily in attention and vigilance

Sources of Fatigue Variability

Large amplitude, moment-to-moment fluctuations in attentiveness associated with fatigue; average performance may be at an acceptable level

Brief periods when responses are extraordinarily delayed or absent for a half-second to a minute ("lapses"); often called "distractibility;" fatigued system operators are more easily distracted than non-fatigued operators

Microsleeps; i.e., falling asleep on the job for more than a minute

Types of Fatigue

Fatigue and sleepiness are caused primarily by lack of sleep, with the exception of physical fatigue caused by brief physical work and task-specific fatigue

For practical purposes, we sort the generators of fatigue into six categories:

Physical Circadian Acute Cumulative Chronic Task-specific

Types of Fatigue

Circadian Effects. Malaise and fatigue due to: Night Work. the pre-dawn period when sleep drive and

sleepiness are highest and body temperature and alertness are lowest.

Jet Lag. a time zone change that is faster than about one time zone per day and exceeds about three time zones; re-synchronization of internal circadian rhythms to new external time cues, especially the daylight-darkness cycle.

Shift Lag. a change from day work to night work and vice versa. The main external time cue, the daylight-darkness and social cycles, inhibits re-synchronization. For most night workers, re-synchronization never occurs

Types of Fatigue

Acute Fatigue. Acute fatigue builds up normally and unavoidably within in one waking period; recovery from acute fatigue occurs as the result of one good-quality, nocturnal sleep period

Cumulative Fatigue. Cumulative fatigue builds up across major waking and duty periods when there is inadequate recovery (due to inadequate sleep) between the duty periods; recovery from cumulative fatigue cannot be accomplished in one good-quality, nocturnal sleep period

Types of Fatigue

The only known cure for physical fatigue, acute fatigue, cumulative fatigue, jet lag, and shift lag is good-quality nighttime sleep

All other treatments, called fatigue countermeasures (including prescription drugs), are "Band-Aids" that counter the symptoms of fatigue

Eventually, the individual must sleep to recover from these types of fatigue

Nature of Fatigue

Ubiquitous: fatigue affects everybody

Pervasive: fatigue affects everything we do, physically and cognitively

Insidious: often when we are fatigued, we are quite unaware of how badly we are performing

Fortunately, the biological changes and rhythms that cause fatigue-induced declines, lapses and variability in human performance are predictable; thus, we may model them

Predictive Model

Quantitative Predictions of Fatigue

A world-class applied model (or simulation) was developed during the 1990s, primarily with US DoD funding

The Sleep, Activity, Fatigue and Task Effectiveness (SAFTE) is a 3-process, applied model of human cognitive performance effectiveness (Hursh et al., 2004):

Circadian rhythms in metabolic rate and alertness Cognitive performance recovery rates associated with

sleep, and cognitive performance decay rates associated with wakefulness

Cognitive performance effects associated with sleep inertia

Quantitative Predictions of Fatigue

Validation Example

Predictive Software:FAST

Quantitative Predictions of Fatigue

The Fatigue Avoidance Scheduling Tool (FAST) was based upon the SAFTE applied model

It is a Windows® program that estimates the average effects of various work-rest schedules on human cognitive performance by examining manually-entered work and sleep data in any of several formats

Geophysical model allows jet lag calculations

‘Autosleep’ function fills in best sleep estimate when needed

Quantitative Predictions of Fatigue

FAST was developed initially as a US Air Force product to deal specifically with R&D on Air Force mission-scheduling issues (Dr. Miller was the Government contract technical monitor)

The FAST software development effort concluded in 2006 with version 1.5; FAST is available commercially

FAST

Cognitive performance (%)Cursor for I/O“Dashboard”Sleep (blue; model input)Work (red; captures data output)Daylight/darkness (gray)Circadian phase (thin red curve)

FAST (zoom & variability)

Zero suppression * Copy/Paste * -30 percentile

FAST

Click and drag “grid” input function

FAST

Start End StatsDay Date Time Day Date Time Dur Eff %BCLFriz 11/9/2007z 13:00z Friz 11/9/2007z 20:59z 480 97.97 0Satz 11/10/2007z13:00z Satz 11/10/2007z20:59z 480 97.97 0Sunz 11/11/2007z21:00z Monz 11/12/2007z04:59z 480 96.42 0Monz 11/12/2007z21:00z Tuez 11/13/2007z04:59z 480 97.7 0Wedz 11/14/2007z05:00z Wedz 11/14/2007z12:59z 480 75.82 67.29Thuz 11/15/2007z05:00z Thuz 11/15/2007z12:59z 480 73.04 71.25Friz 11/16/2007z06:00z Friz 11/16/2007z12:59z 420 71.72 75

471.43 87.52 29.7

Tabular output

Copy/paste work period data

Predictive Software:F/PAS

Quantitative Predictions of Fatigue

A follow-on contract was awarded by the USAF in 2006 to create the "son of FAST" software (Dr. Miller was the Government contract technical monitor)

Its working name was the Intelligent Scheduling Tool (IST)

FAST is Windows-based; the IST is browser/Web-based

This new software is now called the “Fatigue/Performance Assessment System (F/PAS)”

Quantitative Predictions of Fatigue

F/PAS uses the SAFTE model and its core software has all of the functions of FAST

F/PAS gains two new functions that were unavailable in FAST:

Pharmaceutical effects (caffeine, go pill, no-go pill) Generalization of the Autosleep function from a single

time zone to transmeridian travel

Quantitative Predictions of Fatigue

F/PAS also gains three new interfaces that are being designed with a user-centered method

The new interfaces replace the original, graphic interface in FAST that was designed to support fatigue scientists

The interfaces include the: Mission Scheduler Interface for aircrews, mission

schedulers, and flight surgeons; irregular schedules Mishap Investigation Interface for both air and ground

mishaps Shiftwork Scheduling Interface; regular, cyclic schedules

F/PAS Mission Scheduling InterfaceUnder Construction.

Display looks much like FAST graph.Rapid input by Outlook-style Calendar.

F/PAS Mishap Investigation Interface (Questions)

F/PAS Mishap Investigation Interface (Mission Log)

F/PAS Mishap Investigation Interface (Dashboard)

F/PAS Mishap Investigation Interface (Graphic Output)

F/PAS Shiftwork Scheduling Interface (Known Plans)

F/PAS Shiftwork Scheduling Interface (Plan Options)

F/PAS Shiftwork Scheduling Interface (New Plan Wizard)

F/PAS Shiftwork Scheduling Interface (Analysis)

FAST-to-F/PAS Transition

Presently, the user interfaces are in early ‘alpha’ phase and usability testing; thus, too early for formal plan and schedule

F/PAS will read the ‘fas’ data files created by FAST

For owners of FAST, there will probably be a discounted upgrade program to F/PAS

Modeling Examples

Ground Mishap in FAST (Phase)

Ground Mishap in FAST (BAC)

Dr. Miller’s Trip to Athens

Shiftwork

Additional Information

FAST (from NTI, Inc.): www.ntiinc.ms11.net

Dr. Miller: www.millergonomics.com(Presently, a consultant to NTI for F/PAS development)