Influence of M level on EABR latency

The latencies of the various EABR responses were compared using 2-way ANOVAs for M levels versus duration of deafness. The M levels were separated into groups in such a way that each group contained the same number of data. The first group consisted of the M levels data below 90 CU. For the groups 2, 3, and 4, the M levels were respectively between, 90 CU and 145 CU; 146 CU and 197 CU; and 198 CU and 272 CU. The same groups as for analysis of electrode sites on latency (also presented in Table I) were used for deafness duration. For waves IIIe and Ve, latencies were significantly influenced by the M levels (respectively F = 8.9, df = 3, p = 0.048 and F = 3.3, df = 3, p = 0.024). However, for interval IIIe-Ve latencies, there was no effect of M level (F = 2.2, df = 3, p = 0.091). ANOVAs’ normality test passed for analysis about wave IIIe (p > 0.05), wave Ve (p > 0.05), and interval IIIe-Ve (p > 0.05), while the equal variance test failed for waves IIIe (p ≤ 0.001) and Ve (p ≤ 0.001) and passed for interval IIIe-Ve (p > 0.05). Post hoc comparisons (Student-Newman-Keuls test) for M level were significant for M level group 1 versus 2, 3, and 4, as well as for M level group 4 versus 2 and 3 for both wave IIIe and wave Ve. Figure 7 shows latencies of wave IIIe (7a), wave Ve (7b), and interval IIIe-Ve (7c) averaged across subjects and electrodes as a function of the four groups of M levels.

Figure 7. Mean latencies of EABR waves IIIe (a), Ve (b), and interval IIIe-Ve (c) averaged across subjects and electrodes within four groups of M levels (ML) indicated in abscissa. Group 1: 0 CU < ML ≤ 89 CU; group 2: 89 CU < ML ≤ 145 CU; group 3: 145 CU < ML ≤ 197 CU; group 4: 197 CU < ML ≤ 272 CU. Vertical bars denote the standard error around each mean. * represents significant differences among the M groups (p < 0.05).
Figure 7. Mean latencies of EABR waves IIIe (a), Ve (b), and interval IIIe-Ve (c) averaged across subjects and electrodes within four groups of M levels (ML) indicated in abscissa. Group 1: 0 CU < ML ≤ 89 CU; group 2: 89 CU < ML ≤ 145 CU; group 3: 145 CU < ML ≤ 197 CU; group 4: 197 CU < ML ≤ 272 CU. Vertical bars denote the standard error around each mean. * represents significant differences among the M groups (p < 0.05).

ANOVAs for M levels and duration of deafness showed significant interactions for latencies of wave IIIe (F = 13.4, df = 3, p < 0.001), wave Ve (F = 15.7, df = 3, p < 0.001), and interval IIIe-Ve (F = 4.9, df = 3, p = 0.003). Post hoc comparisons (Student-Newman-Keuls test) were significant for the M levels group 4 versus groups 1, 2, and 3 for subjects with more than seven years of deafness for waves IIIe (p < 0.05) and Ve (p < 0.001). For interval IIIe-Ve, latencies of M levels group 4 differed significantly from groups 1 and 2 (p < 0.05) for those subjects. Pearson correlation coefficient (r) determined whether a relationship existed between evoked potentials latency and the M level averaged across subjects for each electrode site. There were significant correlations for wave IIIe (r = 0.83, p < 0.001) and wave Ve (r = 0.81, p < 0.001) but not for interval IIIe-Ve (r = 0.00, p = NS). Figure 8 displays latency plotted against M level for each stimulation site for wave IIIe (8a), wave Ve (8b), and interval IIIe-Ve (8c). The slopes estimated by linear regression are 0.62 µs per mm of cochlea (p < 0.05) for wave IIIe, 0.61 µs per mm of cochlea (p < 0.05) for wave Ve, and -0.02 µs per mm of cochlea (p = NS) for interval IIIe-Ve.

Figure 8. Mean latencies of waves IIIe (a), Ve (b), and IIIe-Ve (c) averaged across the subjects for each electrode as a function of the M levels. Vertical bars denote the standard error around each mean. Linear regression was applied on mean values: the equation of the resulting line is y = 0.0062x + 1.36 with R² = 0.68 (p < 0.005) for figure a, y = 0.0061x + 3.19 with R² = 0.66 (p < 0.005) for figure b, and y = - 0.0002x + 1.82 with R² = 0.00 (p = NS) for figure c. Electrode numbers are indicated next to each point.
Figure 8. Mean latencies of waves IIIe (a), Ve (b), and IIIe-Ve (c) averaged across the subjects for each electrode as a function of the M levels. Vertical bars denote the standard error around each mean. Linear regression was applied on mean values: the equation of the resulting line is y = 0.0062x + 1.36 with R² = 0.68 (p < 0.005) for figure a, y = 0.0061x + 3.19 with R² = 0.66 (p < 0.005) for figure b, and y = - 0.0002x + 1.82 with R² = 0.00 (p = NS) for figure c. Electrode numbers are indicated next to each point.