Physiological noise masking effect. The physiological noise (PN) includes all noises for which the source is in the body (for ex- ample breath, heartbeats). The PNME is the masking due to this PN. This effect is more important in occluded ear than in open ear. When the subject is wearing a hearing protec- tor, the low frequency increases in SPL due to the ear canal occlusion affects the PN. The maximum level of the PN under diverse hearing protectors is less than 35 dB SPL around 80 Hz according to Xxxxxx and Xxxxxxx (1983), then it decreases with frequencies to reach 20 dB SPL at 250 Hz. The PN in opened ear is lower; in his experiments, Xxxxxx and Xxxxxxx (1983) found that it was even lower than the instrumentation noise of his measurement system (about 24 dB SPL at 80 Hz). For both open and occluded ear, the PNME can be written as A2 = A2b = A2a + A2PNME where A2PNME represents the PNME that affects the A2 pathway. The masking effect due to a 250 Hz pure tone at 40 dB SPL is present below 1 kHz and its effect is equivalent to the one due to a narrow band noise (Xxxxxxx (2004) and Ehmer (1959)). Consequently, the A2PNME decreases the importance of the A2 at low frequencies (a little in opened ear A2PNMEop ≤ 0 and more in occluded ear A2PNMEoc < 0), whereas it has nearly no effect at high frequencies (A2PNME ≈ 0). We can therefore write A2 < A2a at low frequencies and A2 ≈ A2a at high frequencies.
