Chapter - IV

Design and Methodology

The present investigation was conducted upon

the students of M.D.University, Rohtak by adopting

multigroup design.

Sample:

Two hundred post graduate students were admini-

stered the Indian adaptation of Weinstein's (1978)

noise sensitivity scale in order to estimate the noise

sensitivity level of each S. On the basis of their

noise sensitivity scores and the Indian norms of the

scores they were assigned to high and low noise

sensitivity groups. Further, each selected S was

given an audiometric test so as to retain only those

Ss for experimentation who fell within the normal

hearing range. Out of the Ss thus left in the high

and low noise sensitivity groups, 75 Ss were assigned

to each low and high noise sensitivity groups with

the help of a table of random numbers. Although only

100 Ss were required in all, but additional 25 Ss

were kept in each of the two groups in order to

compensate for any sample loss. Ss of each of the

two groups were then subsiquently divided randomly

in five equal sized sub - groups each having

53

15 Ss. After collecting data, however, each sub-group

was reduced to a size of 10 Ss by taking out Ss at

random.

In view of the applied utility of noise and

the earlier contradictory results about the effect of

noise on work efficiency the present investigator

got interested in investigating the effect of factory

and camp ( continuous as well as intermittent) noise

on mental work by adopting a design which could equate

Ss on noise sensitivity level, so that any change

in the dependent variable could be directly ascribed

to noise. In the case of between group design or within

group design where the same subject is to be assigned

same work in different conditions, it may not be always

necessary to measure the noise sensitivity level of

individual subject before starting the e"^periment.

However, in the case of two randomized or multigroup

design (which as followed in the present work) where

different siibjects are to be used in different conditi-

ons, Ss must be eqtiated on noise sensitivity.

The importance of matching Ss on noise sensitivity

can not be exaggerated. However, the earlier investi-

gators did not pay much attention to it. The reason

might be the non availability of any standardised tool

for measuring the noise sensitivity of subjects or

5^

sheer ignorance. Although they adopted randomization

technique, but it could be effective only where the

samples are reasonably large. Since in laboratory

situation, only a restricted sample can be used, there-

fore, inspite of the use of randomization technique, the

noise sensitivity variable would have remained unbalanced

in the earlier work on noise. Due to this reason

which in turn might have led to contradictory results

regarding effect of noise on work. The present investi-

gator did not opt for within group design due to its

major drawback of practice and boredom carry over effect

from one condition to another. The multigroup design

was thought to be most appropriate for the present study.

The investigation was conducted in the following

manner by adopting multigroup design with five groups

each for high and low noise sensitivity. Different sub-

groups of Ss were required to work under one of the fol-

lowing conditions — Quiet, Camp continuous. Camp intemit-

tant, Factory continuous or Factory intermittent noise

condition. Working session of twenty minutes was fixed

during which S performed the mental task of decoding

letters. The same task was done by different Ss

in different ridisy conditions. The overall

design for investigation was as follows:

55

Low noise sensitivity group,

Group A Decoding of letters for 20 minutes under nA = 15 Quiet condition

Group B Decoding of letters for 20 minutes under nB = 15 Camp continuous noise condition

Group C Decoding of letters for 20 minutes under nC = 15 Camp intermittent noise condition

Group D Decoding of letters for 20 minutes under nD = 15 Factory continuous noise condition

Group E Decoding of letters for 20 minutes under nE = 15 Factory intermittent noise condition

In the same manner five sub-groups of high noise

sensitivity Ss were made to work under exactly similar

conditions. After collecting the data, these sub-groups

were reduced to the required size of 10 Ss by taking out

Ss on random basis.

All the four types of noise, were played at 110

decibles (as 120 decibles is the pain threshold).

Instroamentation:

1. Indian adaptation (in Hindi) of Weinstein's(1978)

noise sensitivity scale.

2. Philips Stereo Cassette Deck F. 6121.

3. Philips integrated amplifier 15 AH 824 fitted

with sensitive power meters.

4. Final Selection of Camp(continuous) Camp(inter-

56

mittent), Factory (continuous and Factory

(intermittent), noises was made from a large

recorded collection of noise from actual indu-

strial set up and camp area in the neighbour-

hood of Medical College, Rohtak.

5. A-udiometer Arphi (Clinical Diagnostic Audiometer

model 700 Mark IV.

6. Benedict Roth Apparatus.

7. Noise Meter.

8. Stop Watch.

Noise Sensitivity Scale:

It is the Indian adaptation of Weinstein's (1978)

noise sensitivity scale prepared by Bhatia et al. (1986).

It is a self-reporting questionnair of items in Likert

format. This scale measures objectively the noise sens-

itivity of Ss. According to the norms, Ss scoring above

76.45 were considered highly sensitive and below 60.75

as having low noise sensitive.

Philips F 6121 Stereo Cassette Deck:

In four out of five conditions the Ss had to

perform mental work under either camp(continuous), camp

(intermittent) factory (continuous) or factory (intermittent)

57

noise conditions. It was important to record and then

replay these noises with as much of realism as possible

to avoid the artificiality factor which has polluted the

results of many earlier laboratory conducted experiments,

With this aim all recordings were done with a highly sen-

sitive stereo recording device. Philips F 6121 Cassette

deck with the following specifications was found to be

quite suitable for the purpose:

Tape travel speed : 4.76 cm/sec

Maximum speed variation : 1.5%

Wow and flutter : 0.2% (DIN), 0.07% (WRMS)

Distortion at maximum lelvel : 0.5%

Distortion at nominal level : 1.2%

Fitted with Dolby noise reduction system

(It was used both during recording and playing)

VU Meters (Both the recording and playing chan-

nels fitted withVU meters) to avoid overloading

the tapes at peak levels.

Power supply : 230 volts AC, 50-60 Hz.

The recordings were done through two highly sen-

sitive microphones (AKG-D 190 C).

Philips Integrated Amplifier AH B24:

58

Output power (into 4 ohms load/channel at less

than 10% distortion both channels driven) : 300 watts

Total harmonic distortion (THD): 1% at 40 W rms (typical

0.3%) .

Power bandwidth: 40 Hz-20 KHz (+ 3 dB).

Frequency response: 30 Hz-20 KHz (+ 3 dB)•

Power Indicator: (Average reading power meters, separate

for each channel. Calibration markings in dB and %).

Signal to-noise ratio: 75 dB (weighted wrt 40 watts rms).

Main Power Supply: 240 V, 50/60 Hz Ac.

Loud Speaker: Matched with Philips 15 Ah 426, 3 way 3-speaker

Bass Reflex enclosure: (Four such enclosures could be

simultaneously connected to the amplifier). Each speaker

enclsoure fitted with the following:

1. 1x20 cm woofer

2. 1x12.4 cm squawker

3. 1x2.54 cm done twelth

4. 50 segment LED bar graph graduated for power

levels.

Audiometer:

Arphi Model 700 Mark-IV is a modern advanced

clinical diagnostic audiometer incorporating the very

59

latest transistor tachnolo^ and electronic development.

It has a special feature for greater accuracy of diagno-

sis. The hearing loss attenuator (intensity dial) is"

calibrated for hearing loss of 10 dB to 100 dB in 5 dB

steps. The selection of almost all major tests and

functions are arranged on just one knob.

Testing Procedure:

For testing the hearing of different Ss, frequen-

cy dial was initially set at 1000 Hz and the hearing

loss attenuator (intensity dial) at 25 dB. After chec-

king whether the subject heard the tone at this frequency,

the tone interrupter was released and the frequency dial '

was changed to 2000 Hz. The tone was then reintroduced

by operating the tone interrupter. In a similar way the

frequency dial was changed to 4000 Hz then to 6000 Hz,

8000 Hz, 500 Hz and 250 Hz respectively to check normal

hearing throughout these entire frequency ranges. Since

the tone was presented at 25 dB at all the frequencies,

any subject with a hearing impairment in any of the fre-

quencies was easily detected with the help of following

norms:

Opto 25 dB loss - normal hearing

40 dB loss - Mild hearing loss

60 dB loss - Moderate loss

75 dB loss - Severe hearing loss

110 dB loss - Profound

PULLEY

FLOATING D R U M OXYGEN CHAMBER

SUBJECT

RECORDING DRUM

WATER

COUNTER BALANCING WEIGHT

FACE MASK

UNIDERICTIONAL VALVE

BENEDICT ROTH APPARATUS

F I G . 1.

60

Above 110 dB - Total hearing loss.

Benedict Roth Apparatus:

This apparatus records the respiratony movement

and oxygen consumption graphically. Expired carbon-dio-

xide is removed from the circuit by soda-lime re-absorp-

tion. The apparatus as shown in figure 1 consists

of a light cylindrical metal ball which fits lossely

into a narrow space between two concentric cylinders;

the water which fills this space forms an airtight seal

but allows free movement. The bell is counterpoised

by a weight connected to it by a chain which runs over

a pulley. In this way the bell can move freely to acco-

modate the oxygen within it at atmospheric pressure. An

ink writing pen attached to the counterpose weight records

the volume of gas in the bell on a specially hinted chart

calibrated with horizontal lines for voliime (Km-300W)

and vertical lines for times (0.66 mm/sec.)

The bell is first filled with oxygen from a cyli-

nder provided with a reducing value. The subject is

then connected to the apparatus by two large diameter

tubes through unidirectional valves inserted into a face

mask. He inspires oxygen from the bell through one tube

and expires through the other tube through soda-lime and

61

and back into the bell. The back flow of gas being

prevented by values. The respiratory circuit is thus

cut off entirely from the outside air. The bell moves

up and down with each respiration and slowly sinks as

the oxygen is used up. The rate of fall measures the

rate of oxygen consumption.

Sound level meter:

The sound level meter is a self-contained instrument

for the objective measurements of sound and noise levels.

These are the basic instruments for experimental acous-

tics. Experience and knowledge of the precise meter

specification will additionally permit allowance to be

made for pos.sible peaks in the noise. In use, the

meter should be pointed roughly towards the sound source,

and held away from the body to reduce the effect of

reflections.

In present experiment Moraj sound level meter

(type-3003) was used. Although the integrated amplifier

had VU meters attached to each of the two channels still

the noise level adjustment at 110 decibels was checked

through an independent noise level meter so that exact

intensity of noise reaching Ss ear could be precisely

controlled at 110 decibels.

62

The Moraj sound level meter has the following

specification:

Sound Level Range

Frequency

Microphone

Power supply

Box

Input Impendence

Indication

20 dB to 120 dB.

10 Kc/s

Undirectional-dynamic

Battery operated

Wooden Box with carrying

handle.

500 ohms.

50mm rectangular panel

meter.

Procedure:

About 200 postgraduate students of M-D. University,

Roh-tak—we-re—admi-ni-s±ered-^rhe [-ndian—atiaptartion- of-

Weinstein's (1986) noise sensitivity scale. With the

help of the scoring key of the scale, the noise sensi-

tivity score of each S was worked out.

After categorizing the Ss into high or low sensiti-

vity groups, each S was given an audiometeric screening.

The S with normal hearing threshold were selected for

experimentation. In this way 75 Ss were taken for

each low and high noise sensitivity group. Each of the

two main groups were divided randomly in five sub-groups.

.. . :: ' 1 t -ilTT ^ r (

/ 4

63

each consisting of 15 Ss. Since Ss were assigned

randomly to different sub-groups from the main group,

it was assumed that in every sub-group Ss had approxi-

mately equal mean sensitivity level. In order to take

into account noise sensitivity inequalities in the

two groups, the changes in the oxygen consumption during

the experiment were expressed in terms of percentage

to the initial basal indices. This aspect would be

dealt with details while dealing with the analysis of

results in Chapter V.

After the formulation of sub-groups, each S was

individually brought in the laboratory and was allowed

to relax for about 10 minutes during which an effort

was made to establish rapport with him. Every S was

then explained the procedure for task (decoding of

letters) which he had to perform during the work session.

The E continued explaining the method of doing the task

to S till he fully understood it. After ascertaining

that S had clearly understood the procedure, the facial

mask was put on the face of the S. It was done when the

S was fully relaxed and was not performing any task.

Initial oxygen consumption for one minute(basal) was

recorded on the special printed chart in the Benedict

Roth apparatus.

After taking 1 minute Basal, the S was handed over

6/i

the task with the instructions that he should keep

on working at the maximum speed till he was asked to

stop. Simultaneously the type of the noise to be played

was switched on. Working session of 20 minutes was

kept constant. During the whole session S had to

breath through mask and recording of oxygen consumption

for the entire 20 minutes period was taken on the chart.

Any extreneous sound which could contaminate the

results was fully controlled.' In the case of quiet

condition no noise was played. The experiment was done

in an air conditioned room which had negligible external

noise. In this way the experiment was conducted on all

the Ss and the obtained data were subjected to statistical

analyses. The same procedure was adopted for both low

and high noise sensitivity groups. An introspective

report was taken from every S after the completion of

the experiment. The procedure for both the low and high

noise sensitivity groups were exactly identical. After

collecting data for both low and high noise sensitivity

groups, each sub-group was reduced to a size of 10 Ss

randomly and work efficiency of each S was calculated.

With this background we may now pass on to the

next chapter dealing with the results and discussion.