DOT/FAA/AM-02/13

Crystal E. Cruz

Albert Boquet

Cristy Detwiler

Thomas E. Nesthus

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

July 2002

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, VA 22161.

A Laboratory Comparison of

Clockwise and CounterClockwise Rapidly Rotating Shift

Schedules, Part II: Performance

Office of Aerospace Medicine

Washington, DC 20591
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents thereof.
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AM-02/13

4. Title and Subtitle 5. Report Date

A Laboratory Comparison of Clockwise and Counter-Clockwise Rapidly

Rotating Shift Schedules, Part II: Performance

July 2002

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

Cruz, C., Boquet, A., Detwiler, C., and Nesthus, T.

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aerospace Medical Institute

P.O. Box 25082

Oklahoma City, OK 73125 11. Contract or Grant No.

12. Sponsoring Agency name and Address 13. Type of Report and Period

Covered

Office of Aerospace Medicine

Federal Aviation Administration

800 Independence Ave., S.W.

Washington, D.C. 20591 14. Sponsoring Agency Code

15. Supplemental Notes

This work was performed under Task AM-A-00-HRR-519.

16. Abstract:

INTRODUCTION. Many Air Traffic Control Specialists (ATCSs) work a relatively unique counter-clockwise, rapidly

rotating shift schedule. Although arguments against these kinds of schedules are prevalent in the literature, few studies

have examined rotating shifts such as those seen with ATCSs. The present study directly compared clockwise and

counter-clockwise rapidly rotating shiftwork schedules on measures of complex task performance from the Multiple

Task Performance Battery (MTPB) and vigilance from the Bakan Vigilance Task. METHODS. Participants (n=28)

worked day shifts for the first week of the study (0800-1600), followed by two weeks of either a clockwise (n = 14) or

counter-clockwise (n = 14) shiftwork schedule. Participants completed three 1.5-hour sessions on the MTPB on each

shift following the first day of training. Each session contained low, medium, and high workload periods, as well as

active- and passive-task components. In addition, participants completed a .5-hour Bakan Vigilance Test at the

beginning and end of each shift. RESULTS. There were no group differences in the overall or passive task composite

scores for the MTPB. Instead, a shift by session interaction, F (8, 19) = 5.2, p = .001, indicated that performance was

maintained across the afternoon shifts, was lower at the end of the early morning shifts, but fell by a much greater

margin at the end of the midnight shift. Results for the active task composite scores indicated a 3-way interaction

between week, shift, and rotation condition, F (4, 23) = 4.7, p = .006. This complex relationship indicated that

performance was consistently higher in the counter-clockwise rotation and was less variable across shifts than in the

clockwise rotation. Results of the Bakan Vigilance Task revealed a significant Rotation Condition by Shift interaction,

F (4, 23) = 6.2, p = .001. While the counter-clockwise group appeared to perform consistently better than the clockwise

group across all shifts, results of the simple effects analyses indicated a significant difference only on the first afternoon

shift. DISCUSSION. These data do not support the hypothesis that a clockwise rotation will result in better outcomes

on complex or vigilance task performance. In fact, performance in the two groups was generally equivalent, with a few

exceptions in which the counter-clockwise group performed better. The empirical evidence gained from this study

suggest that particular shifts, such as early morning and midnight shifts, may adversely affect sleep and performance

more than the direction of shift rotation.

17. Key Words 18. Distribution Statement

Document is available to the public through the

National Technical Information Service

Shiftwork, Shift Rotation, Vigilance, Complex

Task Performance, Workload

Springfield, Virginia 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 33

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

iii

ACKNOWLEDGMENTS

The authors acknowledge Pamela Della Rocco, Ph.D., for her foundational work in shiftwork and

fatigue research at the Civil Aerospace Medical Institute, for proposing this project as part of the

larger research program, and for her contributions to the protocol for this study. In addition, we

thank Mr. Blake Sanders for his contribution to the data collection and test administration for this

study, Ms. Susan Buriak for her work to append and reduce the database for the Multiple Task

Performance Battery, and Mrs. Jane Brooks for providing the food service for the study.

1

A LABORATORY COMPARISON OF CLOCKWISE AND COUNTER-CLOCKWISE

RAPIDLY ROTATING SHIFT SCHEDULES, PART II: PERFORMANCE

This report is the second in a series on the findings

from a laboratory study comparing clockwise and

counter-clockwise rapidly rotating shiftwork schedules. As discussed in the first report, debate exists in

the shiftwork literature regarding the benefit of rotating versus fixed-shift schedules (Folkard, 1992;

Wedderburn, 1992; Wilkinson, 1992), but there is

little debate that if shift schedules are to rotate, they

should do so in a clockwise direction (Barton &

Folkard, 1993; Czeisler, Moore-Ede, & Coleman,

1982; Folkard, 1989; Knauth, 1993). Akerstedt (1990)

and Barton and Folkard (1993) have conceded, however, that there is very little empirical evidence to

support the arguments against counter-clockwise rotations. This is especially true with regard to measures

of performance.

Air traffic control specialists (ATCSs) in the United

States have worked variations of counter-clockwise,

rapidly rotating shift schedules since the early 1970s.

The most common and well-known of these schedules

is called the 2-2-1 (Cruz & Della Rocco, 1995) and

involves working two afternoon shifts, followed by

two morning shifts, followed by one midnight shift.

Summarizing laboratory and field research on the 2-

2-1 schedule, Della Rocco, Cruz, and Schroeder (1995)

demonstrated that vigilance, problem solving, and

reaction time on the 2-2-1 schedule occurred primarily during the midnight shift, with performance

declining progressively across the night. There was

some evidence that reaction times might also be negatively affected on the first morning shift of the schedule following the “quick turn” (Schroeder, Rosa, &

Witt, 1995). None of these findings was particularly

surprising since performance decrements are expected

during the midnight shift in any shift schedule configuration (Akerstedt, 1988; Klein, Bruner, &

Holtman, 1970; Monk, 1990).

Specifically, Akerstedt (1996) reported that “reaction time, computation and problem solving ability

are markedly less satisfactory during night work.”

Erroneous monitoring of meters, single vehicle accidents, and a number of major environmental disasters

like the Exxon Valdez oil spill and the Three Mile

Island accident were also reported to be associated

with sleepiness and decrements in performance on the

night shift. In a review of shiftworker performance,

Monk (1990) described performance rhythms as the

result of complex processes involving circadian rhythmicity, sleep disruption, social and domestic disruptions, and such differences in shift-related variables as

supervision levels, motivation levels, and group morale. In addition, different kinds of tasks have demonstrated different performance rhythms. For example,

performance on immediate memory tasks is generally

better in the morning than in the afternoon or evening,

whereas performance on long-term memory and perceptual-motor tasks tends to follow the circadian

temperature rhythm more closely, resulting in better

performance in the afternoon.

Still, while most researchers will agree that performance is worse during the night than during the day

(Bjerner & Swensson, 1953; Folkard & Monk, 1979;

Hildebrandt, Rohmert, & Rutenfranz, 1974), the

impact of shift rotation, particularly with regard to

rapidly rotating shiftwork schedules, remains unresolved. Indeed, of the limited studies examining the

direction of rotation, none appear to include information regarding the performance of individuals working these schedules. A survey conducted by Barton

and Folkard (1993) of shiftworkers in five different

industries indicated that those working advancing

(counter-clockwise) rotation schedules reported poorer

physical and psychological health, greater sleep disruption, more social and domestic disruption, and

lower job satisfaction than those working delaying

(clockwise) shift rotation schedules. Likewise, a study

of microelectronic factory workers as they moved

from a counter-clockwise to a clockwise shift rotation

(with 5 days on each shift) indicated that results for

the sleep-wake cycle and subjective measures of fatigue supported the clockwise rotation of shifts (Lavie,

Tzischinsky, Epstein, & Zomer, 1992). And finally, a

study of 14 air traffic controllers in the US Air Force

(USAF) working a rapidly rotating (i.e., two days on

each shift type), clockwise shiftwork schedule found

that diurnally oriented circadian rhythms were maintained (Luna, French, Mitcha, & Neville, 1994).

However, as with the other studies mentioned here,

no performance data were reported.

The present study was conducted to address the

need for more research regarding direction of rotation

in rapidly rotating shift schedules. The purpose of the

study was to directly compare clockwise and counterclockwise rapidly rotating schedules in the laboratory
2

to provide empirical evidence (quantitative as well as

qualitative) regarding a variety of outcomes relevant

to shiftwork. Specifically, Part 2 in this series of

reports examined the effects these schedules had on

vigilance and multiple task performance.

METHODOLOGY

A 3-week protocol was designed for a laboratory

comparison of rapidly rotating clockwise and counterclockwise shift schedules. Data were collected using

groups of five participants at a time. The direction of

rotation was balanced such that the first group was

assigned to the clockwise rotation; the second group

was assigned to the counter-clockwise rotation, and so

on. Although the experiment was extensive, including

multiple computer tests, physiological measures, and

saliva sampling, this paper will focus on only those

variables related to vigilance and complex task performance measures.

Participants

Thirty participants between the ages of 20 and 55

(M = 41.2 years) were recruited and screened from the

general population to participate in the study. Participants gave informed consent to participate in the

study and were paid for their participation. Two

participants withdrew before completing the study.

The remaining participants were assigned to either the

clockwise (n = 14) or the counter-clockwise (n = 14)

rotation condition based on the order in which they

were recruited. The clockwise rotation included 7

males and 7 females with an average age of 40.6 years

(sd = 9.4 yrs.), while the counter-clockwise rotation

included 5 males and 9 females with an average age of

41.9 years (sd = 9.0 yrs.). All participants were nonsmokers and light- or non-users of caffeine and alcohol. Additional details regarding the participant

sample, their recruitment, and selection can be found

in Part 1 of this series of reports (Cruz, Detwiler,

Nesthus, & Boquet, in press).

Procedures and Apparatus

Participants in the study reported to the laboratory

at the Civil Aerospace Medical Institute (CAMI) for

8 hours per day, 5 days per week, for 3 weeks. The first

week (Monday-Friday) for both shift rotation conditions was comprised only of day shifts (0800-1600).

During this week, participants were trained on computerized tasks and habituated to the laboratory environment and to wearing a physiological monitor.

During the next two weeks, participants worked 1 of

the shift rotation schedules shown in Table 1, as

determined by their group assignment. The clockwise

rotation allowed 24 hours off at each shift rotation

and a 48-hour weekend before returning to work on

Monday. The counter-clockwise rotation allowed only

8 hours off at each shift rotation and an 80-hour

weekend before returning to work again.

On the first day of the study, participants were

provided with an orientation to the laboratory and a

detailed daily schedule for the study. Two one-time

questionnaires were completed, a MorningnessEveningness Questionnaire (Horne & Ostberg, 1976)

and a biographical questionnaire. In addition, participants were given physiological monitoring devices

and daily logbooks and were trained on their use.

Finally, participants were trained on the Multiple

Task Performance Battery (MTPB) and the Bakan

Vigilance Task. The physiological monitors and all

sensors, except the chest band, were worn 22.5 hours

per day to accommodate a 1.5-hour break for showers

and leisure activities. The only restriction was that the

monitor should not be removed while sleeping or

napping. The chest band sensor was only worn while

working at the laboratory. The Bakan Vigilance Task

Table 1.

Clockwise and Counter-Clockwise Shift Rotation Schedules

Clockwise Rotation Counter-Clockwise Rotation

Day Work Hours Hours Between Day Work Hours Hours Between

Monday 0600-1400 16 Monday 1400-2200 16

Tuesday 0600-1400 24 Tuesday 1400-2200 8

Wednesday 1400-2200 16 Wednesday 0600-1400 16

Thursday 1400-2200 24 Thursday 0600-1400 8

Friday-Sat 2200-0600 Thur-Friday 2200-0600
3

was administered at the beginning and end of each

workday, and the MTPB was performed 3 times each

day. The daily protocol is presented in Table 2.

Participants were instructed to treat their participation in the study as a full-time job and to refrain

from drinking alcohol or taking any drugs or medications during the course of the study, with the exception of ibuprofen, birth control pills, estrogen

replacement, and/or a non-drowsy formula allergy

medications such as ClaritinTM. In addition, subjects

were instructed not to consume any caffeinated beverages or chocolate and were not allowed to eat bananas because of potential interference with the

radioimmunoassays for cortisol. Diet was not otherwise controlled in the study. Participants were tested

with the Intoxilyzer 9000TM breath alcohol test at the

beginning of each workday to ensure compliance with

the study protocol. None of the participants tested

positive during the study. A final day of testing on

Day 22 of the study included a final Bakan test

session, checking in of equipment, an exit questionnaire regarding the study experience, and a group

cohesiveness questionnaire. Bringing participants back

to the laboratory on this final day was done to mitigate

an end-of-study effect at the end of the previous week

and to allow for data collection on the weekend

following the last shiftwork week.

Bakan Vigilance Task

On Day 1 of the study, participants were trained on

a modified version of the Bakan Vigilance Task (Dollin

et al., 1993; Figure 1). The Bakan test had two

components: a stimuli comparison and an estimation

task. A sequence of 3-digit numbers was presented on

Table 2.

Daily Experimental Protocol

Time (in hours) Activity

Start End

00:00 00:30 Download & initialize Miniloggers; Subjective ratings; Collect saliva

00:30 01:00 Bakan Session 1

01:00 02:30 MTPB Session 1

02:30 02:45 Subjective ratings; Collect saliva

02:45 03:15 Break

03:15 04:45 MTPB Session 2

04:45 05:00 Subjective ratings; Collect saliva

05:00 05:30 Meal Break

05:30 07:00 MTPB Session 3

07:00 07:30 Bakan Session 2

07:30 08:00 Download & initialize Miniloggers; Subjective ratings; Collect saliva

(Computer Screen Image)

2 5 7 A

(Example sequence)

1 3 6 E

2 3 6 1

2 3 6 A

2 4 6 3

8 4 6 4

(Action Taken)

←Press Spacebar

Figure 1. Illustration of Bakan Vigilance Task Computer Screen Image and Example of Sequence
4

a computer screen every 1.5 seconds for 30 minutes.

When a sequence of 3-digit numbers was repeated in

sequence, depressing the space bar on the keyboard

indicated a correct response. In addition, a single digit

or letter was presented simultaneously to the right of

the 3-digit stimuli. At the end of each 5-minute block

of trials, subjects were required to indicate the proportion of numbers to letters presented in the secondary

task during that block. The configuration for this

study involved 132 possible correct responses on the

primary task out of 1200 total stimuli (6 blocks of 200

stimuli each) for a 30-minute session. Participants

were given one practice session on the Bakan on day

1, with an experimenter watching to make sure they

understood when to press the spacebar. For the remainder of the study, participants completed a 0.5-

hour Bakan test at the beginning (session a) and end

(session b) of each shift.

For these analyses, only the number of correct

responses, or “hits” on the primary stimuli comparison task, were analyzed. The secondary estimation

task was not included in the analyses primarily because the data were compromised due to an error in

the setup procedure for the task. The manual for the

task recommended using a set-up file for each subject

to avoid re-entering subject and testing configuration

information. Unfortunately, by using the set-up feature of the program, the proportions for the letter

estimation task were no longer randomly generated on

each trial. Instead, the initial randomly generated

proportions were used for each subsequent test. This

problem was identified during testing for the fourth

group of subjects; therefore, all data for the letter

estimation task for these groups was considered contaminated, and the decision was made not to analyze

these data.

Multiple Task Performance Battery (MTPB)

The CAMI MTPB was used as the synthetic work

environment in this study. The MTPB provided an

established approach to an intrinsically motivating

synthetic work situation requiring time-shared performance of several tasks under varying workload

conditions (Chiles, Alluisi, & Adams, 1968). Timesharing and variations in workload are essential features of the ATC work environment. The MTPB

consists of 5 tasks including static and dynamic monitoring, mental arithmetic, a complex visual discrimination task, and a problem-solving procedural task. A

full description of each task is provided below. These

tasks measure basic psychological or behavioral functions relevant to control of complex systems in general

and ATC and pilot tasks in particular. The tasks were

computerized to control all signal presentations. The

laboratory included 5 personal computer workstations and 1 controller station, using Pentium processors and 21” touch-screen monitors. Inputs were

made via the touch screen and the 10-key pad on the

keyboard.

Red and green light monitoring

Five pairs of boxes or “lights”(1 red and 1 green per

pair) were graphically represented at each corner and

in the center of the touch screen monitor. The red box

was directly over the green box. The normal state of

the red “light” was off, displayed as a red outline of a

box. The normal state of the green “light” was on,

displayed as a filled in, green box. A signal consisted

of a change in the normal state of either box to “on”

in the case of the red light or to “off” in the case of the

green light. The subject was instructed to respond to

the signal by touching the box that changed. A correct

response returned the signal to the normal state. The

box automatically returned to the normal state if no

response was initiated within 15 seconds of signal

onset. Response time was recorded in milliseconds

separately for red and green lights.

Meter monitoring

Four graphic representations of meters with fullscale values of –50 to +50 were presented in the upper

quarter of the touch screen monitor. A red needle on

each meter fluctuateed at random with an average

position of zero. A signal was present when the needle

deflected by an identifiable amount to the left or right

and began to fluctuate with an average position at a

non-zero value. Each subject was asked to respond to

a signal by pressing one of two white boxes above each

meter on the side of the meter to which the signal was

deflected (i.e., left or right of zero). When the correct

box was pressed, the pointer stopped on its “true”

average value, giving immediate feedback as to the

accuracy of the response. The pointer then began to

fluctuate again. The response time was recorded in

milliseconds.

Mental arithmetic

Arithmetic problems were presented about onethird of the distance from the bottom of the screen.

Problems consisted of three 2-digit numbers in the

following form, “XX + YY – ZZ = .” Each subject was

instructed to perform the computation mentally and

to enter the answer in reverse serial order through the

“10 key” keypad on the keyboard. The response was

displayed on the screen and the subject could correct

the answer before pressing the enter key by using the
5

backspace key. If the answer was correct, a blue box

appeared next to the answer. If the response was

incorrect, a yellow-orange box appeared. Response

time was measured between the time the problem was

presented and a press of the enter key.

Target identification

A standard histogram pattern was displayed in the

upper center portion of the screen on a 6 x 6 cell matrix

such that each bar length of 1 to 6 units appeared only

once. A “target” pattern was displayed, followed by

successive presentations of 2 comparison patterns that

could be rotated 0, 90, 180, or 270 degrees. Subjects

were instructed to decide if one, both, or neither of the

comparison patterns matched the initial target pattern and then to press the box on the screen with the

correct response (i.e., 0, 1, or 2) to indicate their

answer. If the response was correct, a blue box appeared

next to the task. If the response was incorrect, a yelloworange box appeared with the correct answer inside.

Code lock

At the bottom of the screen, 5 white boxes labeled

A through E were displayed when this task was active.

Just above these boxes, feedback/response boxes appeared that were white, red, or orange-yellow. The

subject was instructed to decode a series of 5 letters

using a left-to-right search pattern. This resulted in a

predictable number of errors if the subject maintained

the requested search pattern. As in previous tasks, a

correct response resulted in a blue box on the screen;

an incorrect response resulted in the presentation of a

yellow-orange box. When a subject received an indication of an incorrect response, he/she was instructed

to enter the portion of the sequence already decoded

and then proceed with the left to right search pattern

to find the next letter. After the correct sequence was

entered, a 15-second delay occurred, and the subject

was instructed to enter the correct sequence again

(short-term recall).

MTPB Training

On the first day in the laboratory, participants

received standardized training on the MTPB including a training manual that described each task in

addition to receiving 30 minutes of part-task training

on each task individually followed by the full 1.5-

hour schedule of tasks (Table 3). Participants were

briefed about the importance of this research in the

context of ATC, as well as the relationship of the

MTPB tasks to the complex tasks performed by ATCSs

in an attempt to maintain the motivating qualities of

the synthetic work environment. Beginning on the

second day and throughout the remainder of the

study, three 1.5-hour sessions on the MTPB were

completed each day. A previous study suggested that

75% of the improvement in performance on the

MTPB was attained in 12 to 14 hours of practice and

that overall composite scores stabilized after 16 hours

of practice (Cruz, Della Rocco, & MacLin, 1993).

Therefore, participants completed 19.5 hours of practice on the MTPB by the end of the training week and

received a feedback report of their performance through

the fourth day of training.

MTPB scoring

Dependent variables for each task of the MTPB

included a percent correct and reaction time measure.

The scores from the shiftwork weeks were combined

into 3 composite scores: 1) active task composite, 2)

passive task composite, and 3) overall composite.

Composite scores were computed using the procedure

reported by Mertens, McKenzie, and Higgins (1983),

which computed the standardized score for each meaTable 3.

Schedule of MTPB Tasks by 15-minute Segment

Segments (in minutes)

Tasks 1-15 16-30 31-45 46-60 61-75 76-90

Light Monitoring xxxxxx

Meter Monitoring xxxxxx

Mental Arithmetic x x

Target Identification x x

Code Lock x x
6

sure with a mean of 500 and a standard deviation of

100. Reaction time scores were multiplied by negative

one (-1) so that higher scores indicated faster response

times. In addition, efficiency ratios were calculated

for all tasks except code lock in order to examine the

speed-accuracy trade-off. These ratios were calculated

using the standardized scores for the percent correct

measures in the numerator and the standardized scores

for the reaction time measures (not multiplied by –1)

in the denominator. In this way, high accuracy and

low reaction time scores combine into efficiency ratios greater than 1, while low accuracy and high

reaction time scores combine into efficiency ratios less

than 1. Efficiency ratios were not calculated for the

code lock measures due to severely skewed distributions for the reaction time measures. This problem

may have influenced the findings for the active and

overall composite scores as well. A number of transformations were considered to alleviate the problem;

however, none resulted in an impact on the statistical

outcome. Therefore, the composite scores were computed as they have been in the past (Mertens,

McKenzie, & Higgins, 1983).

Design and Data Analysis

The design of the study was a mixed model repeated measures design where schedule rotation represented the between-groups variable, and week, shift,

and session represented the within-subjects, repeated

measures. Due to the nature of the shiftwork schedule

design in this study, shift type and day of the week

were inherently confounded. Therefore, for purposes

of analysis, data were organized by shift type instead

of day of the week. The majority of analyses utilized

the General Linear Model (GLM) for Repeated Measures procedure. To mitigate inflated alpha due to the

large number of repeated measurements in this design, the Greenhouse-Geisser correction (Greenhouse

& Geisser, 1959) to the ANOVA for repeated measures was selected. Post-hoc comparisons using the

Bonferroni adjustment for multiple comparisons were

conducted for main effects. Simple effects analyses

and Bonferroni multiple comparisons were conducted

to investigate significant interactions. Given the suggestion by Akerstedt (1996) that shiftwork may become more intolerable after one’s mid-40s, follow-up

analyses examining the effects of age were also conducted. Splitting the sample at age 40 produced 2

nearly evenly split age groups, with 15 participants

under age 40 (n = 7 clockwise; n = 8 counter-clockwise) and 13 participants over age 40 (n = 7 clockwise;

n = 6 counter-clockwise).

RESULTS

Results of the analysis of the Bakan Vigilance Task

and the Multiple Task Performance Battery are presented. Each dependent measure was assessed in terms

of potential performance differences between the 2

rotation conditions and patterns of performance within

each condition.

Bakan Vigilance Task

Participants received a total of 4.5 hours of training

(9 sessions) on the Bakan test during week 1 of the

study and completed 20 additional sessions during

weeks 2 and 3 of the protocol. Twelve out of 812 data

points were missing (1.5%). A system failure on Day

2 of the training week in 1 group and an electrical

storm on the first midnight shift in another group

caused trials for the participants in those groups to be

lost. In addition, two participants arrived late on 1

occasion. The lost training session data were replaced

with the average of the session scores immediately

before and after the missing session. All other missing

data were replaced with the average of each participant’s

own same session- and shift-type scores (i.e., beginning or end of shift and early morning, afternoon, or

midnight shift) across all non-training trials.

Analysis of variance and multiple comparisons indicated that there were no significant differences

between rotation conditions on any of the trials during the training week. In addition, while the scores do

not appear to have achieved complete asymptote (See

learning curve figure in Appendix A.), there were no

significant within-group differences between the sessions on days 4 and 5 of the training week at the

beginning or end of the day.

A MANOVA was conducted on the 2 (Week) x 5

(Shift) x 2 (Session) x 2 (Rotation Condition) factorial. A main effect for Week, F (1, 26) = 7.0, p = .014,

indicated that performance during the first week of

shiftwork was significantly better (M = 101.7) than

during the second week of shiftwork (M = 97.5). In

addition, a main effect for Session, F (1, 26) = 15.8,

p = .000, indicated that performance was significantly

better at the beginning of shifts (M = 102.8) than at

the end (M = 96.4). There was also a significant

interaction for Rotation Condition by Shift, F(4,23)

= 6.2, p = .001. The data for this interaction are

presented in Figure 2. While it appears that the

counter-clockwise group performed consistently better than the clockwise group across all sessions, results

of the simple effects analyses indicated a significant

difference only on the first afternoon shift, where the
7

counter-clockwise group (M = 113.5) performed significantly better than the clockwise group (M = 90.2),

F (1, 26) = 7.2, p=.012. This shift was the first day of the

workweek for the counter-clockwise rotation condition

and the third day for the clockwise rotation condition.

Multiple Task Performance Battery

Participants received 19.5 hours of training (13

sessions) on the MTPB during Week 1 of the study

and completed 30 additional sessions on the MTPB

during Weeks 2 and 3 of the protocol. Fifteen out of

1,204 session data points were missing (1.2%). The

same system failures and electrical storm that affected

the Bakan Vigilance Test also impacted the MTPB

and accounted for the bulk of the missing data.

Missing data during the shiftwork trials were replaced

with the average of each participant’s own same shiftand session-type scores (i.e., morning, afternoon, or

midnight shift and sessions 1, 2, or 3).

To ensure that the groups were not different at

baseline, unadjusted t-tests were conducted on the

Day 4 (Thursday) data for each measure. The only

significant difference between groups was on the

response time measure for the recall portion of the

code lock task on the first session of the day, t (26) =

2.2, p = .037. Response time in the clockwise condition (M = 13.9 sec.) was significantly slower on this

session than in the counter-clockwise condition (M =

8.1 sec.). There were no differences, however, for

sessions 2 or 3 of that same day or any other baseline

training day for any of the measures, indicating that

the two groups were not significantly different from

each other at baseline. In addition, examination of the

learning curves for each measure (See learning curve

figures in Appendix A.) shows that the majority of

improvement in performance had occurred by Day 5

of the training week. Unadjusted t-tests were conducted within each rotation condition to compare

Day 4 performance with Day 5 performance. Within

the clockwise rotation there was no significant improvement between Days 4 and 5 on any of the

measures. Within the counter-clockwise rotation,

however, the green light monitoring task did show

significant improvement from Day 4 (M = 93.5%, 4.7

sec.) to Day 5 (M = 98.5%, 3.7 sec.), t (13) = 2.2, p =

.049 and t (13) = 2.2, p = .045 on the second session

of the day. There were no differences on any of the

other tasks or on sessions 1 or 3.

Results of each measurement from the MTPB are

discussed individually below. In order to give an

overview of the data for the numerous measurements

analyzed from the MTPB, however, the Shift by

Session means for each variable are presented in Figure 3. The graphs for the overall composite, passive

composite, red light ratio, probability meter ratio,

and target identification ratio represent statistically

significant Shift by Session interactions. The other 3

variables (active composite, green light ratio, and

arithmetic ratio) are also presented for a full picture of

this relationship. In addition, the Rotation Condition

by Shift means for each variable are presented in

Figure 4. Only the green light ratio graph represents

a statistically significant Rotation Condition by Shift

interaction; however, both the active composite and the

arithmetic ratio resulted in significant three-way interactions that included Rotation Condition and Shift.

0

33

66

99

132

EM1 EM2 A1 A2 M

Shift

Number of 

Correct 

Responses

Clockwise Counter-Clockwise

Figure 2. Rotation Condition by Shift Interaction on the Bakan Vigilance Task
8

450

470

490

510

530

123

Session

EM1

EM2

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A2

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EM2

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0.85

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Session

EM1

EM2

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A2

M

Figure 3. Shift by Session Interaction for Each Measure of the MTPB
9

450

470

490

510

530

Shift

Clockwise

CounterClockwise

 

0.85

0.9

0.95

1

1.05

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CounterClockwise

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CounterClockwise

 

0.85

0.9

0.95

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1.05

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1.15

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Clockwise

CounterClockwise

Figure 4. Rotation Condition by Session Interaction for Each Measure of the MTPB
10

Composite Scores

Analysis of both the overall composite and passive

task composite scores revealed a significant Shift by

Session interaction, F (8, 19) = 3.4, p = .01 and F (8,

91) = 5.2, p = .001, respectively (Figure 3). Simple

interaction effects analyses of the overall composite

scores revealed a significant main effect for Shift on

the third Session, F (4, 23) = 4.3, p = .019 as well as

a significant main effect for Session on the midnight

shift, F (2, 25) = 9.7, p=.000. Bonferroni pairwise

comparisons revealed that performance at the end of

the second afternoon shift (M = 510.2) was significantly higher than at the end of the first early morning

shift (M = 490.1) and that performance at the end of

the midnight shift (M=470.9) was significantly lower

than at the beginning of the midnight shift (M =

503.9). Simple interaction effects analyses of the

passive composite scores also revealed a significant

main effect for Shift on the third Session, F (4, 23) =

7.0, p = .002 as well as a significant main effect for

Session on the midnight shift, F (2, 25) = 16.5, p =

.000. Bonferroni pairwise comparisons revealed that

performance at the end of the 2 afternoon shifts (M =

509.4 and 513.6, respectively) was significantly better

than at the end of either the first early morning shift

(M = 483.8) or the midnight shift (M = 458.6). In

addition, performance showed a significant decline across

the midnight shift, such that performance on the first

session (M = 508.3) was significantly better than performance on either the second (M = 487.7) or third sessions

(M = 458.6) and performance on the second session was

significantly better than on the last session.

Analysis of the active task composite scores revealed a significant Rotation Condition by Shift by

Session interaction, F (8, 19) = 3.0, p = .019. Simple

interaction effects analyses of the 3-way interaction

were conducted for each Session (Figure 5). On Session 1, there was no significant effect of rotation

condition. On Session 2, there was a significant effect

for rotation condition on the first early morning shift,

F (1, 26) = 4.3, p = .049, with the counter-clockwise

rotation (M = 525.9) performing better than the

clockwise rotation (M = 483.0). On Session 3, there

was a significant effect for rotation condition on the

first afternoon shift, F (1, 26) = 5.2, p = .032, with the

counter-clockwise rotation (M = 534.1) performing

better than the clockwise rotation (M = 464.8).

Efficiency Ratios

Green Light Efficiency. Analysis of the green light

ratio data revealed a significant Rotation Condition

by Shift interaction, F (4, 23) = 3.2, p = .027 (Figure

4). Examination of the figure indicates that efficiency

for the clockwise rotation was lower than for the

counter-clockwise rotation on both early morning

shifts and the midnight shift but was higher on the 2

afternoon shifts. Multiple comparisons to examine

these differences, however, were not statistically significant. In addition to the interaction, there was a

significant main effect for Week, F (1, 26) = 13.4, p =

.001, indicating that efficiency in the second week of

shiftwork (M = 1.08) was significantly better than in

the first week of shiftwork (M = 1.03). There was also

a significant main effect for Session, F (2, 25) = 4.1,

p = .025, such that efficiency on Session 2 (M = 1.08)

was significantly higher than on Session 3 (M = 1.03).

Red Light Efficiency. Analysis of the red light ratio

data revealed a significant Shift by Session interaction, F (8, 19) = 2.8, p = .018 (Figure 3). Simple effects

analyses revealed a significant main effect for Shift at

the third Session, F (4, 23) = 7.5, p=.000 and a

significant main effect for Session on the midnight

shift, F (2, 25) = 12.7, p=.000. Bonferroni multiple

comparisons revealed that performance at the end of

the first afternoon shift (M = 1.095) was significantly

higher than at the end of the first early morning shift

450

470

490

510

530

550

Session 1 Session2 Session 3

Shift

Counter-Clockwise

Clockwise

Figure 5. MTPB Active Task Composite Scores for Rotation Condition

by Shift Interaction for Sessions 1, 2, & 3
11

(M = 0.954) and that performance at the end of both

the afternoon shifts (M = 1.095 and 1.106, respectively) was significantly higher than at the end of the

midnight shift (M = 0.889). In addition, performance

on the last session of the midnight shift (M = 0.889)

was significantly lower than on either the first (M =

1.071) or second (M = 1.029) sessions of the midnight

shift. In addition to the interaction, there was also a

significant main effect for Week, F (1, 26) = 10.67, p

= .003, indicating that efficiency in the first week of

shiftwork (M = 1.08) was significantly higher than in

the second week of shiftwork (M = 1.02).

Probability Meter Efficiency. Analysis of the Probability Meter ratio data revealed a significant Shift by

Session interaction, F (8, 19) = 2.81, p = .012 (Figure

3). Simple effects analyses revealed a significant main

effect for Shift on the second and third Sessions, F (4,

23) = 3.0, p= .029 and F (4, 23) = 7.9, p = .000,

respectively. Bonferroni multiple comparisons revealed

that performance on the second and third sessions of

both afternoon shifts (M = 1.11 and 1.105 respectively for Session 2 and M = 1.086 and 1.099, respectively for Session 3) was significantly higher than on

the second and third sessions of the midnight shift (M

= 1.019 and 0.948, respectively). In addition, simple

effects analyses revealed a significant main effect for

Session on the second early morning shift, F (2, 25) =

3.6, p = .039 and the midnight shift, F (2, 25) = 9.1,

p = .001. Bonferroni multiple comparisons revealed

that performance on the last session of the second

early morning shift (M = 1.03) was significantly lower

than performance on the second session (M = 1.101),

and performance on the last session of the midnight

shift (M = 0.948) was significantly lower than performance on the first session (M = 1.087).

Arithmetic Efficiency. Analysis of the Arithmetic

ratio data revealed a significant Rotation Condition

by Week by Shift interaction, F (4, 23) = 2.90, p = .032

(Figure 6). Simple effects analyses, however, revealed

only a main effect for Week for the first early morning

shift, F (1, 26) = 6.3, p = .018, indicating that

performance on the first early morning shift was

significantly better during the second week of shiftwork

(M = 1.097) than for the first week (M = 1.017). No

simple effects of rotation condition were significant.

Target Identification Efficiency. Analysis of the Target Identification ratio data revealed a significant

Shift by Session interaction, F (8, 19) = 2.64, p = .021

(Figure 6). Simple effects analyses revealed a significant main effect for Shift at the third Session, F (4, 23)

= 6.4, p = .000 such that performance at the end of the

second afternoon shift (M = 1.134) was significantly

better than performance at the end of either of the two

early morning shifts (M = 1.008 and 1.006, respectively) or the midnight shift (M = 0.979).

Age Effects

To account for the potential confound of age with

rotation condition, a number of subsequent analyses

were conducted. Although group sizes were made

relatively small by the addition of the age category,

analyses were conducted using age as an additional

between-subjects factor in order to determine if there

were any interactions of age with rotation condition.

No interactions between rotation condition and age

group were statistically significant for either number

of correct responses on the Bakan vigilance task or any

of the MTPB measures. A number of interactions

between age group and week, shift, and session were

identified, but given the small sample sizes, the complexity of the model (i.e., 5 factors with 2 betweensubjects), and the fact that these interactions did not

speak to the question of interest in the study, these

findings were not investigated further. Subsequent

analyses of each full model with age as a covariate were

conducted, however, in order to hold the effects of age

constant. Again, these analyses did not reveal any new

relationships with regard to rotation condition.

0.8

0.9

1

1.1

1.2

EM1 EM2 A1 A2 M

Shift

Efficiency Ratio

Clockwise

Week1

Clockwise

Week 2

Counter-CW

Week 1

Counter-CW

Week 2

Figure 6. Arithmetic Efficiency Ratio for Rotation Condition

by Week by Shift Interaction
12

DISCUSSION

This study represents one of the first experimentally controlled investigations of direction of rotation

in rapidly rotating shift schedules. The purpose of this

paper was to directly compare individual performance

on a vigilance and complex, time-shared task while

working clockwise and counter-clockwise rapidly rotating shift schedules to test the hypothesis that the

clockwise rotation results in better outcomes. Measures included in this report did not support the

hypothesis. Instead, results of the study indicated that

for the most part, performance was similarly affected

on each shift for both rotation conditions, and that if

anything performance was actually better during the

counter-clockwise condition. Results of the study

were similar to past research on the 2-2-1 schedule

performed by Della Rocco and Cruz (1996) indicating that performance is maintained on early morning

and afternoon shifts and drops more dramatically

across the midnight shift. Again, Monk (1990) and

others (Akerstedt, 1988; Klein, Bruner, & Holtman,

1970) have consistently found that performance decrements on the midnight shift are to be expected in

any shift schedule configuration. A significant benefit

of the 2-2-1 schedule worked by many ATCs, then, is

that it generally includes only one midnight shift,

which is placed at the end of the workweek and is

followed by several days off. This is in keeping with

European recommendations that no more than 2 to 4

midnight shifts should be worked in succession

(Wedderburn, 1991).

For obvious reasons, vigilance is a concern within

the field of air traffic control. Our investigation here

suggests that the only significant difference between

rotation conditions was observed on the first afternoon shift of the workweek, such that correct responses were higher in the counter-clockwise than in

the clockwise rotation condition. An examination of

Figure 2 reveals that performance remained relatively

stable across the week for the clockwise rotation

condition, but it changed more according to shift type

for the counter-clockwise condition. Specifically, in

the clockwise rotation condition, the number of correct responses ranged from a high of 96 to a low of 89,

which represents a 7.3% decline in performance from

the first early morning shift (Day 1) to the midnight

shift (Day 5). In comparison, the number of correct

responses in the counter-clockwise condition ranged

from a high of 114 to a low of 98, which represents a

14.0% decline in performance from the first afternoon shift (day 1) to the midnight shift (day 5).

Although scores in the counter-clockwise condition

were still not lower than the clockwise condition on

the midnight shift, the larger decrease in performance

for that shift may suggest that performance on the

midnight shift is more problematic in the counterclockwise rotation. Because of the compressed nature

of the schedule, the counter-clockwise rotation may

be less tolerant of disruptions such as family illness,

etc. Therefore, the natural decline in performance on

the midnight shift might be exaggerated if workers

encountered unexpected time demands that did not

allow them to rest during the time off before the

midnight shift.

As with the Bakan Vigilance Task, most of the

measures on the MTPB indicated that the direction of

shift rotation was not a significant factor in terms of

performance. Instead, shift type and session interacted in similar ways for both rotation conditions. For

the overall and passive task composite scores, a shift

by session interaction revealed that performance was

better at the beginning of the midnight shift than at

the end, and that performance at the end of the

afternoon shifts was better than performance at the

end of the midnight shift. This relationship was also

true for efficiency ratio scores for the red light monitoring task and the probability meters task. Both of

these tasks were passive in nature, requiring vigilance

to the presence of a signal. The efficiency score for the

target identification task also revealed a shift by session interaction; however, performance did not decline across the midnight shift as dramatically as it did

for the passive tasks. This was most likely because

subjects were better able to protect their performance

on the active tasks than the passive tasks during the

midnight shift. Della Rocco and Cruz (1996) reported a similar trend in an earlier study of the 2-2-1

schedule utilizing the MTPB.

In addition to findings regarding the midnight

shift, the shift by session interactions also revealed

that performance at the end of the first early morning

shift was often significantly lower than performance

at the end of one or both afternoon shifts. This was

true for the overall and passive composite scores as

well as for the red light monitoring and target identification efficiency scores. Given the reduced sleep

duration obtained during the quick-turn-around before the first early morning shift in the counterclockwise rotation (Cruz, Detwiler, Nesthus, &

Boquet, in press), these differences in performance

would have been expected. In the clockwise rotation

condition, however, the first early morning shift follows the weekend, when sleep might have been expected to be adequate. Sleep duration, however, was

similarly reduced in the clockwise rotation for the first
13

early morning shift; the result of a weekend effect (Cruz,

Detwiler, Nesthus, & Boquet, in press). Therefore, we

see a reduction in sleep duration and performance on the

first early morning shift in both rotation conditions.

Two of the active task scores from the MTPB

revealed more complex relationships. The active task

composite score revealed a 3-way interaction with

rotation condition, shift, and session. This interaction indicated that those in the counter-clockwise

condition performed better on the second session of

the first early morning shift and on the last session of

the first afternoon shift than those in the clockwise

condition. One reason that performance may have

been better in the counter-clockwise condition at the

end of the first afternoon shift is that the first afternoon shift was also the first day of the workweek for

this condition, as compared with the third day for the

clockwise condition. The fact that performance was

also better on the second session of the first early

morning shift, however, does not follow because this

shift was the third day of the workweek, following an

8-hour quick-turn-around. Indeed, individuals in the

counter-clockwise condition might have been expected to perform more poorly than those in the

clockwise condition, for whom the first early morning

shift was also the first day of the workweek following

a weekend. Taken together, these data do not support

the suggestion that performance in the counter-clockwise condition was better due to a day-of-week effect,

but rather indicate that performance in the counterclockwise condition was simply at least as good as or

better than performance in the clockwise condition

on all shifts.

Summary

The results from the performance tasks in this

study do not support the suggestion that clockwise

rotations should be preferable to counter-clockwise

rotations. Instead, these results support more recent

suggestions that there may be fewer differences in

these kinds of schedules than was once thought

(Tucker, Smith, Macdonald, & Folkard, 2000). In

addition, the results agree with the findings from the

first report in this series, which showed that rotation

condition did not significantly affect sleep duration,

sleep timing, or subjective reports of mood and fatigue. In short, evidence is growing that direction of

rotation, particularly in rapidly rotating shift schedules, does not affect outcomes such as sleep, subjective

ratings of fatigue, and performance. Replications of

this kind of research in the laboratory and the field are

needed to make reliable conclusions with regard to

shift rotation.

While the schedules examined in this study are

relevant to real-world shiftwork scheduling practices,

one limitation of this study is that it only represents

short-term adaptation to the clockwise and counterclockwise rotation schedules investigated. It is not

clear that performance would be similar for experienced shiftworkers or over longer periods of exposure

to these shift schedules, although the results for the

counter-clockwise group are similar to the results

obtained in field studies of air traffic controllers

(Schroeder, Rosa, & Witt, 1995). Nevertheless, the

results from this study indicate that the counterclockwise shiftwork schedules currently in use by air

traffic controllers in the United States would not

likely be improved by reversing the direction of rotation. Perhaps, more importantly, it is clear that midnight and early morning shifts remain the major concern

for maintaining performance in both clockwise and

counter-clockwise rapidly rotating shift schedules.

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A1

APPENDIX A

Learning Curves for Bakan and MTPB Tasks

Figure A1. Bakan Vigilance Task Learning Curve for Correct Responses

0

80604020

120100

1a 2a 2b 3a 3b 4a 4b 5a 5b 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 1a 1b 2a 2b 3a 3b 4a 4b 5a 5b

Day of Workweek

Number of Correct Responses

Clockwise Counter-clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork

"a"=Session a, "b"=Session b
A2

Figure A2. Red Lights Learning Curve (Percent Correct)

95908580757065605550

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Wek 3 Shiftwork
A3

Figure A3. Red Lights Learning Curve (Reaction Time)

6543210

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A4

Figure A4. Green Lights Learning Curve (Percent Correct)

95908580757065605550

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A5

Figure A5. Green Lights Learning Curve (Reaction Time)

876543210

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A6

Figure A6. Probability Meters Learning Curve (Percent Correct)

95908580757065605550

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A7

Figure A7. Probability Meters Learning Curve (Reaction Time)

86420

1816141210

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A8

Figure A8. Arithmetic Learning Curve (Percent Correct)

95.0090.0085.0080.0075.0070.0065.0060.0055.0050.00

100.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A9

Figure A9. Arithmetic Learning Curve (Reaction Time)

8.006.004.002.000.00

18.0016.0014.0012.0010.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A10

Figure A10. Target ID Learning Curve (Percent Correct)

95.0090.0085.0080.0075.0070.0065.0060.0055.0050.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A11

Figure A11. Target ID Learning Curve (Reaction Time)

4.003.503.002.502.001.501.000.500.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A12

Figure A12. Code Lock Solution Learning Curve (Percent Correct)

95.0090.0085.0080.0075.0070.0065.0060.0055.0050.00

100.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A13

Figure A13. Code Lock Solution Learning Curve (Reaction Time)

0.00

90.0080.0070.0060.0050.0040.0030.0020.0010.00

100.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A14

Figure A14. Code Lock Recall Learning Curve (Percent Correct)

95.0090.0085.0080.0075.0070.0065.0060.0055.0050.00

100.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Percent Correct

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork
A15

Figure A15. Code Lock Recall Learning Curve (Reaction Time)

0.00

70.0060.0050.0040.0030.0020.0010.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Session

Reaction Time (seconds)

Clockwise Counter-Clockwise

Week 1 Training Week 2 Shiftwork Week 3 Shiftwork