Czeisler et al

Question 1

Aim:

Answer 1

if exposure to bright light during night shift will help shift workers resynchronise their body clock.

Question 2

Procedure

Answer 2

8 men ages 22-29 (later 6)

There were two conditions for night shift working; a control condition with low-level lighting and an experimental condition with high-level lighting.

In the control condition, the men were asked to use their home setting for any daytime sleeping they required. For this, sleeping was left unregulated and naturalistic.

In the experimental condition, the participants’ daytime sleeping at home was treated to having opaque windows and artificial darkness enforced.

Men in the experimental group were exposed to very bright light during the night shift (12,000 lumens of brightness compared to approximately 150 lumens of normal artificial room lighting).

Question 3

Findings

Answer 3

Biological measures such as body temperature showed that the experimental group had had their circadian rhythms adjusted forward by 9 hours, while the control group stayed roughly the same. This suggests that their circadian rhythms adapted.

There was a significant improvement in alertness and night shift work performance, as measured, at night, by repeated testing on cognitive skills.

The experimental group on average slept two hours longer at night. A loss of two hours sleep over 7 days equates two 2 days sleep missed which can be harmful.

Question 4

Conclusion

Answer 4

The conclusion of this experiment was that usual circadian maladjustment to night shift work can be treated and reversed with exposure to light at night and dark during the day.

Question 5

Evaluation strengths

Answer 5

This study can be applied directly to shift work patterns. It has important implications for improving night-worker productivity. It could also reduce the risk of accidents at work during the night and increase workers’ health and safety.

The time difference between the mean low points of body temperature of the control versus the experimental group was huge, and statistically unlikely to have occurred by chance.

Question 6

Evaluation weaknesses

Answer 6

EVALUATION - WEAKNESSES
Small sample size.

Gender biased, making it hard to generalise the results.

The night shift work was simulated in a lab which may not have reflected typical working conditions. The work involved sitting in a chair for the duration of the night. This may lack ecological validity for some types of night shift work.

Several extraneous variables were not fully controlled; for example, when they ate breakfast or how much time they slept for. further, things like how noisy it was could not be controlled.

This theory is biological reductionism.

it still took three days to adapt which is not good for regular shift changes.