Study on an evaluation index for noise susceptibility. II. Reduction of [ART1k-ARTWN] and critical bandwidth in acoustic reflex.

Effects of noise exposure on the difference between ART1k (acoustic reflex threshold) and ARTWN [( ART1k-ARTWN]), and on the critical bandwidth (CBW) in acoustic reflex (AR) were investigated. One hundred and eleven workers using hand-held vibrating tools (exposed group) served as subjects. The results were compared with the values obtained in the control group reported by the authors previously (Miyakita and Miura 1985). The exposed group was classified into four groups according to their hearing levels (HL) at 4 and 8 kHz; i.e. Group A (HL(4k + 8k)/2 less than 25 dB), Group B (25 dB less than or equal to HL (4k + 8k)/2 less than 50 dB), Group C (50 dB less than or equal to HL (4k + 8k)/2 less than 75 dB), and Group D (HL (4k + 8k)/2 greater than or equal to 75 dB). [ART1k-ARTWN] was reduced significantly (p less than 0.001) in the exposed groups; i.e. 12.4 dB in the control group, 6.7 dB in Group A, 2.3 dB in Group B, -0.3 dB in Group C, and -1.3 dB in Group D. On the other hand, a significant widening of the CBW was observed in the exposed group compared to that of the control group (p less than 0.05); i.e. 1138 Hz in the control group, 1410 Hz in Group A, 3287 Hz in Group B, and greater than or equal to 4000 Hz in Groups C and D. In addition, we confirmed that the reduction of [ART1k-ARTWN] might be the result of the widening of the CBW in AR.(ABSTRACT TRUNCATED AT 250 WORDS)