Objectives-The primary goal of this study was to determine if physiological forward-masking patterns in cochlear implants are predictive of psychophysical forward-masking patterns (PFM). It was hypothesized that the normalized amount of physiological masking would be positively correlated with the normalized amount of psychophysical masking for different masker-probe electrode separations. A secondary goal was to examine the relation between the spatial forwardmasking patterns and speech-perception performance. It was hypothesized that subjects with less channel interaction overall (either psychophysically or physiologically) would have better speechperception ability due to better spectral resolution.Design-Data were collected for 18 adult cochlear implant recipients (N = 9 Clarion CII or HiRes 90K, N = 9 Nucleus 24R[CS]). Physiological spatial forward-masking patterns were obtained with the electrically evoked compound action potential (ECAP) through the implant telemetry system. PFM patterns were obtained using a 3-interval, 2-alternative forced-choice adaptive procedure. Both measures used a fixed probe electrode with varied masker location. For each subject, spatial forwardmasking patterns were obtained for three probe electrodes with five masker locations per probe.Results-On an individual basis, the correlation between ECAP FM and PFM was strong for 10 subjects (r = 0.68 to 0.85, p ≤ 0.02), moderately strong for two subjects (r = 0.54 to 0.55, p = 0.06 to 0.07), and poor for six subjects (r = 0.13 to 0.45, p > 0.14). Results across subjects and electrodes showed a highly significant correlation between ECAP FM and PFM (r = 0.55, p < 0.0001); the correlation was strongest for basal electrodes. There was no significant correlation between speech perception and ECAP FM or PFM. Subjects whose ECAP FM patterns correlated well with PFM patterns generally had the poorest speech perception and subjects with the poorest correlations had the best speech perception.Conclusions-ECAP FM and PFM patterns correlated well for two-thirds of the subjects. Although the group correlation was statistically significant, ECAP FM patterns only accounted for 30% of the variance in the PFM measures. This suggests that the ECAP measures alone are not sufficient for accurately predicting PFM patterns for individual subjects.

Objectives Spread of excitation within the cochlea in response to electrical stimulation can be measured with the electrically evoked compound action potential (ECAP). Different spread-of-excitation measurement techniques have been reported in the literature. One method uses a fixed stimulus location while varying the recording electrode along the length of the implanted array. This results in a relatively coarse estimate of spatial spread (SS) along the cochlea. Another method uses a forward-masking paradigm to evaluate the relative overlap of stimulated neural populations between electrodes. Both the probe and recording electrodes are fixed in location while a masker stimulus is systematically applied across electrodes. This method, which yields a more precise estimate of spatial excitation patterns, is termed spatial masking (SM). Five experiments were conducted to examine potential effects of stimulus and/or recording parameters on SS and SM patterns. Experiment 1 examined whether SS patterns were systematically broader than SM patterns across electrodes and subjects. Experiments 2 and 3 evaluated the effects of stimulus level on SS and SM patterns, respectively, to determine whether increased stimulus level systematically resulted in broader patterns. Experiment 4 evaluated whether recording electrode location affected SM patterns, and Experiment 5 evaluated whether SM patterns varied significantly across repeated trials within a test session. Design Data were collected for 27 ears in 26 adult and teenage subjects [N=6 ears with Advanced Bionics CII, N=8 ears with Advanced Bionics HiRes 90K, N=10 ears with Nucleus 24R(CS), N=3 ears with Nucleus 24RE(CA) Freedom]. A standard forward-masking subtraction paradigm was used for all ECAP measures. For SS patterns, the masker and probe were fixed on the same electrode at the same level while the recording electrode varied across the remaining electrodes in the array. For SM patterns, the probe and recording locations were fixed while the masker location varied across all electrodes except the recording electrode. Results In Experiment 1, SS patterns were broader than SM patterns. Subjects with Advanced Bionics devices exhibited relatively broad patterns for both measures, whereas Nucleus subjects typically exhibited narrower SM functions relative to SS functions. In Experiments 2 and 3, there was a significant effect of stimulus level on the spread of both SS and SM patterns in roughly one-third of measures in each experiment. In Experiment 4, there was a significant effect of recording electrode location on the width/ spread of SM patterns for only 11.5% of comparisons. In Experiment 5, there were no significant differences in SM amplitudes across repeated trials for 94% of comparisons, which suggests that ECAP measures are highly robust within a test session. Conclusions Results showed that SS functions were generally broader than SM functions, which suggests that SS measures reflect volume conduction of the ECAP response along the length of the cochlea. ...