Pergamon Computers ind. Engng Vol. 27, Nos 1--4, pp. 389-392, 1994

0 3 6 0 - 8 3 5 2 ( 9 4 ) 0 0 0 9 0 - 5 Elsevier Science Ltd. Printed in Great Britain

Individual Differences on Diurnal Variations of the Task

Kazushige ARAKAWA, Touru ISHIKAWA Yasuhiko SAITO and Toshinori KOBAYASHI

Department of Systems and Industrial Engineering Ashikaga Institute of Technology

Ashikaga 326, Japan

Performance

Abs t r ac t : In order to understand psychophysiological background of the individual differences on the diurnal variation of task performance, the task performance (i.e. the number of a simple adding calculation performed in one minute) was measured from 09:30 in the morning to 21:30 in the late evening for 9 healthy university male students. Heart rate (HR) and body temperature were also continuously recorded for 35 hours. There were two different types in the diurnal variation of the task performance; the morning type who shows the best performance in the morning, and the evening type who shows it in the evening. The body temperature curve during daytime in the evening type goes gradually up to the evening, on the contrary, that in the morning type rapidly rises to the maximum point in the morning or the aftemoon. HR during daytime were higher in the morning type than the evening type. These results indicate that the morning type has a tendency of the higher mental tension compared with the evening type. And they also suggest that the individual differences on the task performance with a large mental concentration are caused by some kinds of subject's psychosomatic state.

K e y w o r d s : performance, body temperature, heart rate, mental tension.

1 Introduction

When we work all day long in our office, someone has a good

concentration on his work in the morning, and someone has a

good concentration in the evening. It seems that there are some kinds of individual differences in the diurnal variation of the task performance in our office work. It has been reported that the task performance shows a diurnal variation [1,2,5],

which was closely related to the body temperature curve [3,6].

So, it was examined whether there was an individual difference

in the task performance or not, if an individual difference

existed, what kind of the individual differences there were. Kleitman (1963) has reported that the task performance was

closely related to body temperature curve during daytime. The task performance was indirectly controlled by the circadian oscillator [3]. So tha t , the circadian body temperature curve

389

was continuously recorded, and simultaneously, the intelligent task performance ( the simple adding task) was recorded during daytime. The phase relationship between the circadian curve of

body t empera tu re and the d iurnal var ia t ion of the task performance was examined. If the individual dif ferences

existed, what causes the individual differences in the task

performance found in our office work, was psychophysiologi- tally discussed.

2 Method

The exper iment was per formed according to the schedule

shown in F ig . l for nine male heal thy universi ty s tudents

1st day START ~--

,1 SLEEP, Iv ,* ,v I 2nd clay BT nn~ HR

,t'ii SLEEp, I, '"'". v '" '" '"" , , ' " ' " t 3rd day

END

/ ' I 'SLEEP IV V | | | f

|

00 06 12 18 Time of day

BT : Body temperature, HR : Heart rate, T Meals

taskJ Psychological te:t:i ! Adding

Fig. 1 A schedule for the experiment.

t O0

390 Selected papers from the 16th Annual Conference on Computers and Industrial Engineering

( ranged from 19 to 23 years of age). Subjects spent the three days for the experiment. In the first day, in order to check the behavior in his daily life, they took 8 hrs night sleep in the laboratory, and spent a time out of the laboratory during daytime as they did in their dally life. In the second day, after taking 8 hrs night sleep, in order to check effects of the task during daytime on the sleep, they performed the task and the psychological test in every 30 min from 09:30 to 21:30. After finished all the task and the psychological test, they took 8 hrs night sleep to the morning of the 3rd day. Body temperature and heart rate (HR) are continuously recorded for 35 hours; from 11:00 PM at the first day to 10:00 AM at the 3rd day. The task performance was measured as the number of a simple

adding task (i.e. the sequence of a figure adding calculation as Kraepelin diagnosis test) which they performed for one minute. Before every the task, subjects received the psychological test in order to check their subjective mood and sleepiness. All subjects performed this schedule twice with the interval of 3 or 4 days.

3 Results

numbers of adding ca lcu la t ion and the re la t ive values normalized by the maximum actual performance in each subject. From table 1, subjects could be divided into two d i f f e r en t groups ; six of nine sub jec t s show the best performance in the morning, the rest of them in the evening. So, the former group is called as the morning type, the later one as the evening type.

In the morning type, the body temperature goes rapidly up in the morning, and reaches the maximum value in the late

morning or in the early afternoon, and the maximum value

continues to the evening (Fig.2-A). On the other hand, in the evening type, the body temperature goes gradually up to the evening and reaches the maximum values there (Fig.2-B). HR during daytime in the morning type was higher than the evening type (Fig.2-C,D). And the amplitude of diurnal variation of HR in the morning type was higher than the evening type (Fig.2-C,D).

The phase relationship between the diurnal variation of the task performance and the body temperature curve was shown in Fig.3. The task performance became the highest at just before the maximum body temperature in both the morning and evening types.

In order to find the diurnal variation of the task performance, the 2rid day of the experiment was divided into 4 sessions; 1st

session is in the morning (09:30-12:00), 2nd session in the

a f t e r n o o n ( 1 3 : 0 0 - 1 5 : 3 0 ) , 3rd se s s ion in the e v e n i n g (16:00-18:00), and 4th session in the late evening (19:00-21:30). The task performance of each session was shown in table 1. The values of the performance is represented by both the actual

4 Discussion

In order to examine the psychophysiological background of this individual difference in the task performance, HR and the body temperature were simultaneously recorded for 35 hours. As'the

Table 1. The task performance on each session.

Subject 1 st [o930 -

S e s s i o n

2nd 3rd 4th 1200 ] [1300- 1530] [1600 - 1800] [1900 - 2130]

Morning type

1 lOO 2 lOO 3 lOO 4 lOO 5 lOO 6 lOO

(67.2) 0 (62.2) 30.4 (63.8) 30,8 (63.9) (67.0) 18.1 (60.5) 23.5 (60.9) 0 (59.0) (81.6) 39.6 (75.2) 11.3 (72.2) 0 (71.0) (63.7) 67.2 (60.9) 0 (55.2) 18.6 (56.8) (62.6) 74.5 (60.4) 5.9 (54.4) 0 (53.9) (67.2) 80.8 (66.1) 22.1 (62.9) 0 (61.7)

Evening type

7 8 9

0 (62.1) 66.9 (65.8) 100 (67.7) 24.7 (63.5) 46.7 (61.7) 55.4 (62.2) 100 (63.9) 0 (60.2) 87.7 (56.6) 73.2 (55.6) 100 (57.5) 0 (50.7)

Relative value ( Mean of actual number )

Selected papers from the 16th Annual Conference on Computers and Industrial Engineering 391

Morning type Evening type

I - ' -

( 'C

38

37

36

[A] ('C

38

0000

37

36

35 35 0000 12"00 0000 12"00

[ B ]

0000

( b p m ) [ C ] ( b p m )

lOO- lOO-

50"

0000 1200 0000

T i m e o f d a y

Fig. 2 The diurnal variation of the body temperature (BT) and heart rate (HR).

50'

0000 12"00

[ D ]

0000

T i m e o f d a y

I----

IX:I

I---- rn

Fig. 3

Morning type m

8 y

" t =

]SLEEP I I.-

0000 1200 0000

Evening type

]

0000 1200 0000

The phase relationship between the diumal variation of

the task performance and the body temperature curve.

result, both HR and the body temperature of the morning type

were higher in the morning than that of the evening type. This

indicates that there were individual differences on the diurnal

variation of the body temperature and HR. It is possible to be

considered that the high HR found in the morning type is caused by a high mental tension. Because, in spite of nothing any physical movements except for the finger movements, the

HR is very high. The high HR could be understood as the response of the autonomic nervous system due to some kind of mental tension [4,7]. Thus, the morning type persons either easily response to the experiment circumstances or always keep a higher tension, compared with the evening type. It can be understood that the diurnal curve of body temperature is also

modified by the autonomic nervous system response, which is some kinds of a mental tension. It is well known that circadian curve of body temperature varied by the mental condition in

depressive persons [8]. Thus, the individual differences on the

p e r f o r m a n c e of the task accompan ied with a mental concentration is caused by some kinds of a mental tension.

The same phase relationship between the diurnal variation of

the task performance and that of the body temperature was

found in both types (Fig.3). The task performance showed the highest at just before the maximum body temperature in this study. This result was coincident with the study by Kleitman (1963).

392 Selected papers from the 16th Annual Conference on Computers and Industrial Engineering

5 Conclusion

The large individual differences is found in the diurnal variation of the task performance accompanied with a mental concentration; there is two different patterns of the diurnal variations; the one is the best performance in the morning, the another one in the evening. The individual differences in this kind of task performance is caused by some kinds of a mental tension.

REFERENCES

[I] Baddeley, A., Hatter, J. E., Scott, D. and Snashall, A. Memory and time of day, Q. L Exp. Psychol., Voi.22, pp.605-609, 1970.

[2] Blake, M. L F. Time of day effects on porformance in a range of task, Phychon. Sci., Vol.9, No.6, pp.349-350, 1967.

[3] Johnson, M. P., Duffy, J. F., Dijk, D. J., Ronda, J. M., Dyal, C. M. and Czeisler, C. A. Short-term memory, alertness and performance: a reappraisal of their relationship to body temperature, J. Sleep Res., Vol.1, No.l, pp.24-29, 1992.

[4] Ettema, J. H. and Zielhuis, R. L. Psychological parameters of mental load, Ergonomics, VoL 14, pp.137-144, 1971.

[5] Folkard, S. and Monk, T. H. Circadian rhythms in human memory, Br. J. Psycho1., Vol.71, pp.295-307, 1980.

[6] Kleitman, N. Sleep and Wakefulness, University of Chicago press., Chicago, 1963.

[7]Turner, J. R. and Carroll, D. Heart rate and oxygen consumption during mental arithmetic, a video game and graded exercise: Further evidence of metabolically- exaggerated cardiac adjustments ?, Psychophysiology, Vol.22, No.3, pp.261-267, 1985.