**5. Result and discussion**

202 Fuzzy Inference System – Theory and Applications

The membership functions are then aggregated using T-norm product to construct fuzzy IF-THEN rules that have a fuzzy antecedent part and constant consequent, The total number

Fig. 4.12. Typical rules and their graphic representations in Sugeno approach.

Fig. 4.11. (b) Membership functions of cognitive task type.

Fig. 4.11. (c) Membership functions of age group.

for rules is 27. Some of the rules are given below:

The model was trained for 250 epochs and it was observed that the most of the learning was completed in the first 190 epochs as the root mean square error (RMSE) settles down to almost 0% at 190 th epoch. Figure 5.1(a) shows the training RMSE curve for the model after training the fuzzy inference system. It is found that the shape of membership functions is slightly modified.

Fig. 5.1. (a) Training root means squared error.

Fig. 5.1. (b) Data testing

Some Studies on Noise and Its Effects on Industrial/Cognitive Task Performance and Modeling 205

Fig. 5.2. (b) Reduction in cognitive task efficiency as a function of noise level at 'moderate'

Fig. 5.2. (c) Reduction in cognitive task efficiency as a function of noise level at 'complex'

An alternative representation to Figure 5.2(a-c) discussed above is shown in Figure 5.3(ac), in which the reduction in cognitive task efficiency with noise level for 'low', 'medium' and 'high' cognitive task at deferent ages is presented besides this following inference are

1. If age is 'young' as shown in Figure 5.3(a) the cognitive task efficiency reduces to 21.5% for 'moderate' and 36% for 'complex' cognitive tasks while it reduces 9.22% for 'simple'

2. In case of 'medium' age, the cognitive task efficiency is reduced to 30.1%, 49.4%, and 68.3% at 100 dB (A) for 'simple', 'moderate' and 'complex' cognitive tasks, respectively

3. For 'old' age, the reduction in cognitive task efficiency occurs even at much lower noise levels as can be observed from Figure 5.3(c). It is 36.2%, 71.9%, and 91% at 100 dB (A)

for 'simple', 'moderate' and 'complex' cognitive tasks, respectively.

cognitive task at 90 dB (A) and above noise levels.

as is evident from Figure 5.3(b).

cognitive task for various ages.

cognitive task for various ages.

readily down:

This is because of the close agreement between the knowledge provided by the expert and input/output data pairs. While, Figure 5.1(b) shows data testing to check data validity. Hence, the impact of the noise level on cognitive human work efficiency is represented in the form of graphs in Figure 5.2, with the ages as parameters for different cognitive task type. The reduction in cognitive task efficiency up to the noise level of 75 dB (A) is almost negligible for all ages irrespective of cognitive task. Assuming effects of 25% reduction in cognitive work efficiency as low effect Figure 5.2(a) Show the reduction in cognitive task efficiency versus noise level with 'simple' cognitive task for 'young', 'medium', and 'old' ages. The cognitive work efficiency reduce to almost 29.6% at 90 dB (A) and above noise levels for 'old' ages but the 'young' and 'medium' age remain 'unaffected'.

It is to be observed from Figure 5.2(b) that the cognitive task efficiency is low (only 14.8%) at 85 dB (A) for 'young' age whereas for 'medium' and 'old' ages, the reduction in cognitive task efficiency is 26% and 45.9% respectively at the same noise levels for 'moderate' cognitive task . However the reduction in cognitive task efficiency is almost 21.5%, 38.9%, and 60.2% for 'young', 'medium' and 'old' ages, respectively at 90 dB (A) and above noise levels.

Figure 5.2(c) depicts the reduction in cognitive task efficiency with noise level at 'complex' cognitive task for 'young', 'medium', and 'old' ages. It is evident from this figure that the reduction in cognitive task efficiency is negligible up to the noise level of 80 dB (A) for 'young' age while it is about 26.4%, 34.1% for 'medium' and 'old' ages the cognitive task efficiency start reducing after 80 dB (A) even for 'young' and 'medium' ages. At 90 dB (A), cognitive task efficiency reduces to 36% , 56.7% and 75.1% for 'young', 'medium' and 'old' ages, respectively . There is significant reduction in cognitive task efficiency after 95 dB (A) for all ages. When noise level is in the interval of 100-105 dB (A), it is 45.6% for 'young', 68.3% for 'medium', and 91% for 'old' ages, respectively.

Fig. 5.2. (a) Reduction in cognitive task efficiency as a function of noise level at 'simple' cognitive task for various ages.

This is because of the close agreement between the knowledge provided by the expert and input/output data pairs. While, Figure 5.1(b) shows data testing to check data validity. Hence, the impact of the noise level on cognitive human work efficiency is represented in the form of graphs in Figure 5.2, with the ages as parameters for different cognitive task type. The reduction in cognitive task efficiency up to the noise level of 75 dB (A) is almost negligible for all ages irrespective of cognitive task. Assuming effects of 25% reduction in cognitive work efficiency as low effect Figure 5.2(a) Show the reduction in cognitive task efficiency versus noise level with 'simple' cognitive task for 'young', 'medium', and 'old' ages. The cognitive work efficiency reduce to almost 29.6% at 90 dB (A) and above noise levels for 'old' ages but the 'young' and 'medium' age remain

It is to be observed from Figure 5.2(b) that the cognitive task efficiency is low (only 14.8%) at 85 dB (A) for 'young' age whereas for 'medium' and 'old' ages, the reduction in cognitive task efficiency is 26% and 45.9% respectively at the same noise levels for 'moderate' cognitive task . However the reduction in cognitive task efficiency is almost 21.5%, 38.9%, and 60.2% for 'young', 'medium' and 'old' ages, respectively at 90 dB (A) and above noise

Figure 5.2(c) depicts the reduction in cognitive task efficiency with noise level at 'complex' cognitive task for 'young', 'medium', and 'old' ages. It is evident from this figure that the reduction in cognitive task efficiency is negligible up to the noise level of 80 dB (A) for 'young' age while it is about 26.4%, 34.1% for 'medium' and 'old' ages the cognitive task efficiency start reducing after 80 dB (A) even for 'young' and 'medium' ages. At 90 dB (A), cognitive task efficiency reduces to 36% , 56.7% and 75.1% for 'young', 'medium' and 'old' ages, respectively . There is significant reduction in cognitive task efficiency after 95 dB (A) for all ages. When noise level is in the interval of 100-105 dB (A), it is 45.6% for 'young',

Fig. 5.2. (a) Reduction in cognitive task efficiency as a function of noise level at 'simple'

68.3% for 'medium', and 91% for 'old' ages, respectively.

cognitive task for various ages.

'unaffected'.

levels.

Fig. 5.2. (b) Reduction in cognitive task efficiency as a function of noise level at 'moderate' cognitive task for various ages.

Fig. 5.2. (c) Reduction in cognitive task efficiency as a function of noise level at 'complex' cognitive task for various ages.

An alternative representation to Figure 5.2(a-c) discussed above is shown in Figure 5.3(ac), in which the reduction in cognitive task efficiency with noise level for 'low', 'medium' and 'high' cognitive task at deferent ages is presented besides this following inference are readily down:


Some Studies on Noise and Its Effects on Industrial/Cognitive Task Performance and Modeling 207

In order to observe the data behavior, we have compared some of our model results with deduction based on the criterion of Safe Exposure Limited recommended for industrial workers. The Recommended Exposure Limit (REL) for workers engaged in occupation such as engineering controls, administrative controls, and/or work practices is 85 dB (A) for 8 hr duration NIOSH (36), also recommended a ceiling limit of 115 dB(A). Exposures to noise levels greater than 115 dB (A) is not permitted regardless of the duration of the exposure time. There is almost no (0%) reduction in work efficiency when a person is exposed to the maximum permissible limit of 85 dB (A) for 8 hr and maximum (100%) reduction in work

NIOSH OSHA

Reduction in work efficiency(%)

1 85 100 0 55.7 moderate 2 90 200 25 75.1 high 4 95 400 50 88.2 high 5 100 800 75 91 Very high 6 105 1600 100 91.6 Very high 7 110 3200 100 92.2 Very high 8 115 6400 100 92.2 Very high Table 5.1. Data behavior comparison of the Results Based on Recommended Exposure Limit

The main thrust for the present work has been to develop a neuro-fuzzy model for the prediction of cognitive task efficiency as a function of noise level, cognitive task type and age. It is evident from the graph that the cognitive task efficiency, for the same cognitive task, depends to a large extent upon the noise level and age. It has also been verified that young age are slightly affected even at medium noise level while old ages get significantly affected at much lower noise level. It is to be appreciated that the training done using ANFIS is computationally very efficient as the desired RMSE value is obtained in very less number of epochs. Moreover, minor changes are observed in the shape of the membership functions after training the model. This is because of close agreement between the knowledge provided by expert and input/output data pairs.The present effort also establishes the usefulness of the fuzzy technique in studying the ergonomic environmental problems where

1. The study may also be done by changing the input parameters such as: type of task, gender of the workers, environmental conditions (light, temperature, vibration,

2. Data should collect from noisy environment for different ages for workers doing cognitive tasks, and the questionnaire form must be filled carefully to simulate high

model results

Fuzzy value

numerical value (%)

efficiency for a noise exposure of 105-115 dB (A) for 8 hr.

Acoustic energy Dose(%)

(REL) and the neural fuzzy model for moderate task.

the cause-effect relationships are inherently fuzzy in nature.

**6.1 Scope for future research** 

performance model.

humidity) etc.

S.No. Noise

**6. Conclusion** 

levels dB(A)

Fig. 5.3. (a) Reduction in cognitive task efficiency as a function of noise level for 'young' age for various cognitive tasks.

Fig. 5.3. (b) Reduction in cognitive task efficiency as a function of noise level for 'medium' age for various cognitive tasks.

Fig. 5.3. (c) Reduction in cognitive task efficiency as a function of noise level for 'old' age for various cognitive tasks.

In order to observe the data behavior, we have compared some of our model results with deduction based on the criterion of Safe Exposure Limited recommended for industrial workers. The Recommended Exposure Limit (REL) for workers engaged in occupation such as engineering controls, administrative controls, and/or work practices is 85 dB (A) for 8 hr duration NIOSH (36), also recommended a ceiling limit of 115 dB(A). Exposures to noise levels greater than 115 dB (A) is not permitted regardless of the duration of the exposure time. There is almost no (0%) reduction in work efficiency when a person is exposed to the maximum permissible limit of 85 dB (A) for 8 hr and maximum (100%) reduction in work efficiency for a noise exposure of 105-115 dB (A) for 8 hr.


Table 5.1. Data behavior comparison of the Results Based on Recommended Exposure Limit (REL) and the neural fuzzy model for moderate task.
