Cognitive performance of grass trimmers in noisy conditions - the effect of user age
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environment to conduct the experiment.
2.3. Personal interview
Before the actual experiment personal interview was conducted to qualitatively assess noise-induced effects on the grass trimmers. Workers were questioned about such matters as
the feeling of annoyance, quality of sleep, whether they were well-rested after sleep, and enjoyment of leisure time. Workers were also asked their age, the period for which they had
worked as grass trimmers, and whether they were had had health problem before entering in the profession. Only those who reported no health complaints before entering in this
profession were used in the experiment. Workers who had been grass trimmers for more than five years or so mostly reported sleep disturbances, irritability, inability to fully enjoy leisure
time, not feeling fresh even after sleep. These complaints were less frequent in workers who had been grass trimmers for less than two years. New workers did not report such effects.
2.4. Difficulty Index
Three difficulty indices were defined in this study: level 1 one possible response; difficulty; index 2 two possible responses and level 3 three possible
responses.
Figure 1.
Observation sheet showing example of noise level during grass trimming operation
ZULQUERNAIN MALLICK AJE Vol.9 2009 33-48
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2.5. Noise levels
In a preliminary study to determine the level of noise to which operators were subjected while trimming grass, the level of noise varied from 116 dBA to 145 dBA;
therefore the noise levels in this experiment were set at 116, 126, 136 and 145 dBA.
2.6. Experimental set-up
Experiment was conducted in a 4.9 x 4.6 x 2.9 m L x W x H room. The temperature was maintained approximately at 25 ± 2° C. Light reflection from
windows and doors was eliminated. When the room was closed, it was acoustically sealed from the outside environment. A human response measurement system
Figure 2 was used to measure reaction times in milliseconds. Circuit-1 and Circuit-2 were part of the experimental set-up that included LEDs of different
colors.
2.7. Stimuli and general experimental procedure
Circuit-1 and Circuit-2 Figure 2 were fabricated specially for this experiment on two plastic boards and were placed in front of the subjects when they were
required to perform the experimental task. Circuit-1 was used for presenting the stimuli to the subjects, and Circuit-2 was used to measure their responses. Before the
actual experimentation, a pilot study was undertaken. During this study, each subject was briefed about the objective of the experiment, and the methods used.
Subjects were instructed to adopt a normal sitting posture while performing the experimental task. Each subject was given a training session to familiarize him with
the experimental procedure.
Circuit-1 Circuit-2
Human response measurement system
Power Supply
Experimenter Subject
600 mm
560 mm
6 8
m m
Figure 2.
Schematic diagram of the experimental setup
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