In Brief:
This study examined the effects of decreased audibility in low frequency spectral regions produced by low-pass noise masking on cortical event-related potentials (ERPs) to the speech sounds /ba/ and /da/. Subjects were normal-hearing adults (n = 10), and the speech sounds were presented in the following low-pass noise masking conditions: quiet (no masking), low-pass noise cutoff frequencies of 250, 500, 1000, 2000, and 4000 Hz, and broadband noise. As the cutoff frequency of the low-pass noise masker was raised, ERP latencies increased and amplitudes decreased. The low-pass noise affected N1 gradually as the LPN cutoff was raised, whereas MMN, N2, P3 and behavioral measures showed latency increases and amplitude decreases only when the noise masked the acoustic cues differentiating /ba/ from /da/. This study provides insight into the changes in brain processes and behavioral performance which occur when audibility is reduced, such as with low frequency hearing loss.
