Psychophysical Versus Physiological Spatial Forward Masking and the Relation to Speech Perception in Cochlear Implants

Abstract

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.

Pitch ranking, electrode discrimination, and physiological spread of excitation using current steering in cochlear implants

“…Because ECAPs generally require higher current levels to evoke a response, there can be greater spread of excitation in the cochlea compared with lower current levels for psychophysical tasks. A study by Hughes and Stille (2008), using a forward-masking paradigm, showed that excitation patterns for ECAP measures were broader than those obtained for psychophysical (pulsetrain) measures. Therefore, the ECAP may be less sensitive for measuring overlap of neural excitation patterns produced by relatively high-level stimulation of closely spaced electrodes such as adjacent physical electrodes.…”

Pitch ranking, electrode discrimination, and physiological spread-of-excitation using Cochlear's dual-electrode mode

“…The ECAP SOE function reflects the neural excitation pattern elicited by a probe electrode resolved using a forward-masking paradigm. It has been shown that neural excitation measured by the ECAP SOE is comparable to that measured psychophysically using a forward-masking paradigm (Cohen et al, 2003;Hughes and Stille, 2008). In Hughes and Abbas (2006a), the width of the SOE function (calculated as 75% of the normalized amplitude) was compared to the slope of the electrode pitchranking (2IFC) function in ten subjects.…”

Current Steering with Partial Tripolar Stimulation Mode in Cochlear Implants

“…A more straightforward way to explain the variable perceptual data is to directly estimate the excitation patterns of steered pTP stimuli with different α in each subject. This can be achieved by measuring the forward masking patterns of steered pTP stimuli using psychophysical methods (e.g., Chatterjee and Shannon 1998; Kwon and van den Honert 2006b; Srinivasan et al 2010;Landsberger et al 2012) or using electrically evoked compound action potentials (e.g., Cohen et al 2003;Hughes and Stille 2008).…”