Modeling the relationship between psychophysical perception and electrically evoked compound action potential threshold in young cochlear implant recipients: clinical implications for implant fitting

• Published in: Clinical neurophysiology 2004-12, Vol.115 (12), p.2811-2824
• Main Authors: Thai-Van, Hung, Truy, Eric, Charasse, Basile, Boutitie, Florent, Chanal, Jean-Marc, Cochard, Nadine, Piron, Jean-Pierre, Ribas, Sébastien, Deguine, Olivier, Fraysse, Bernard, Mondain, Michel, Uziel, Alain, Collet, Lionel
• Format: Article
• Language: English
• Subjects: Action Potentials; Agricultural sciences; Auditory Perception; Auditory Threshold; Biological and medical sciences; Child; Child, Preschool; Cochlear implant; Cochlear Implantation - methods; Compound action potential; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Ear, auditive nerve, cochleovestibular tract, facial nerve: diseases, semeiology; Electrodiagnosis. Electric activity recording; Evoked Potentials, Auditory; Female; Fundamental and applied biological sciences. Psychology; Hierarchical regression analysis; Humans; Infant; Investigative techniques, diagnostic techniques (general aspects); Jack-knife validation; Life Sciences; Male; Medical sciences; Models, Theoretical; Nervous system; Neural response telemetry; Non tumoral diseases; Otorhinolaryngology. Stomatology; Psychophysical levels; Psychophysics; Regression Analysis; Soil study; Vertebrates: nervous system and sense organs
• ISSN: 1388-2457; 1872-8952
• DOI: 10.1016/j.clinph.2004.06.024

Objective: In cochlear implant recipients, the threshold of the electrically evoked compound action potential (ECAP) has been shown to correlate with the perceptual detection threshold and maximum comfortable loudness levels (respectively, T- and C-levels) used for implant programming. Our general objective was to model the relationship between ECAP threshold and T/ C-levels by taking into account their relative changes within each subject. In particular, we were interested in investigating further the validity of ECAP threshold as a predictor of psychophysical levels, depending on intra-cochlear electrode location and time of testing (from 1 to 18 months post-implantation). Methods: A total of 370 ECAP thresholds, measured in 49 children, using a Nucleus ® 24 cochlear implant, were compared with the corresponding T- and C-levels obtained at the same visit, for the same electrode. Response profiles for the whole group of patients were modeled across four test electrodes spaced equally along the electrode array from base towards apex. A linear regression model was constructed and the quality of the ECAP threshold-based predictions was assessed by testing for correlation between measured and predicted psychophysics. Comparison was made with a more simplistic model (described here as the ‘parallel profiles method’) stipulating, within each subject, a 1 μA increase in psychophysical levels for every 1 μA increase in ECAP threshold. Results: Offset between ECAP threshold and psychophysics profiles was found to vary significantly along the electrode array for the T-, but not for the C-level. In contrast with the parallel profiles method, our regression model predicted, within each subject, an average increase of 0.23 μA (95% confidence interval: 0.18–0.28) in T-level for every 1 μA increase in ECAP threshold. This correction improved the quality of T-level prediction when our model was run using measured T-level and ECAP threshold from a reference electrode ( r=0.77 vs. r=0.62). The shorter the distance between the electrode for which T-level was predicted and the one used as reference, the stronger the correlation between measured and predicted T-levels. In addition, poorer T-level predictions were obtained at the basal end of the array during the first 3 months post-implantation. In contrast to T-level, individual changes in C-level with ECAP threshold exhibited heterogeneous patterns across subjects so that no common coefficient could account for these change