Bars show the percentage of loci with sensitivity loss ≥ 6 decibels (dB) during treatment as a function of baseline sensitivity. On the x-axis, parentheses beneath each group of 3 bars is the range of locus baseline sensitivity for that group: [6,8] = 6 to 8 dB, (8,12] = >8 to 12 dB, (12,16] = >12 to 16 dB, (16,20] = >16 to 20 dB, (20,24] = >20 to 24 dB, (24,28] = >24 to 28 dB, (28,32] = >28 to 32 dB, and (32,36] = >32 to 36 dB. The dose of NAC for each cohort was 600 mg bid for 3 months followed by 600 mg tid for 3 months for cohort 1, 1200 mg bid for 3 months followed by 1200 mg tid for 3 months for cohort 2, and 1800 mg bid for 3 months followed by 1800 mg tid for 3 months for cohort 3.