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
Cognitive performance of grass trimmers in noisy conditions - the effect of user age
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Three tasks were assigned, which had different levels of difficulty. In all tasks, subjects were required to switch on the same color of LED at Circuit-2 by observing
the glowing LED and its color at Circuit-1. In the simplest task Difficulty Index 1, subjects were required to observe the color of the LED on Circuit-1, and to light the
LED on Circuit-2 that had the same color; this trial provided a simple reaction time.
In the second task Difficulty Index 2 two LEDs of different color were lit on Circuit-1, and subjects were required to switch on an LED of one of the two colors
on Circuit-2. In the third task Difficulty Index 3 three LEDs of different color were lit and subjects were required to switch on an LED of one these colors on Circuit-2.
The locations of the LEDs on Circuit-2 were clearly labeled. Subjects were trained during a trial session to switch on the appropriate LED. All reaction times in
milliseconds and user errors were measured using an electronic device designed and developed for this purpose Appendix A However subjects committed a
negligible number of errors 2. After the subject had taken his seat, the following steps were followed in order for both the training and experimental
sessions.
Step 1: A Start signal was given to the subject. Step 2: The stimulus was presented to the subjects by the experimenter.
Step 3: The subject responded by switching on the appropriate LED on
Circuit-2. Step 4: The reaction time was recorded by the experimenter.
The experiment was conducted for three categories of subjects: Novice, Intermediate and Experienced workers. The noise during grass trimming operation
in a real environment was recorded on an audio-cassette. The pre-recorded noise was subsequently played in the experimental chamber during the experiments. The
noise level was maintained at a pre-specified value. Training was rigorous for older subjects so that they were made fully aware of the experimental procedure.
2.8. Experimental Design
In all the three studies undertaken in the present work, human performance dependent variable was measured in milliseconds for reaction time, choice
reaction time and choice reaction time for difficulty index three. Independent variables were difficulty index, noise levels and subject age category. A three-factor
repeated-measures analysis of variance ANOVA was used to analyze the data.
3. Results
Three experiments were conducted to study the effect of age on cognitive performance of subjects.
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