Relation Between Neural Response Telemetry Thresholds, T- and C-Levels, and Loudness Judgments in 12 Adult Nucleus 24 Cochlear Implant Recipients

Abstract

The results of this study provide important insight into the relation between NRT thresholds and loudness judgments for different stimulation rates and T- and C-levels at various MAP rates. The loudness judgment dynamic range and MAP dynamic range (T- and C-levels) varied notably for different stimulation rates. As a result, the relation of NRT thresholds to these measures also varied with stimulation rate. Overall, the mean vNRT thresholds fell higher in the loudness judgment dynamic range than the tNRT thresholds. Mean NRT thresholds fell between the judgments of medium soft and maximum acceptable loudness for all stimulation rates. Mean vNRT thresholds fell above C-levels, whereas almost half of tNRT thresholds fell just below C-levels. However, the relation between NRT thresholds and C-levels varied substantially for different MAP stimulation levels. In addition, there is substantial individual variability in the relation between NRT thresholds and MAP levels that is not reflected in the group data. The prediction of the contour of T- and C-levels from the contour of NRT thresholds across electrodes would not be appropriate for half of the subjects. Therefore, great care should be taken when applying a fitting rule that incorporates NRT thresholds without considering these individual differences. For adults who can provide appropriate loudness judgments and threshold responses it appears to be most efficient to primarily use behavioral measures to create MAPs.

Cochlear Implants: System Design, Integration, and Evaluation

“…The ECAP threshold is typically between the behaviorally measured T and C levels, and can be used to create a map without any subjective responses from the patient. Such objectively created maps are especially valuable to the increasing pediatric implant populations as well as those who cannot give accurate behavioral responses, but their speech performance is still sub-optimal compared with the behaviorally created maps [171][172][173]. Another measure under investigation for objective mapping is acoustic reflex, which contracts the middle ear muscle to attenuate a loud sound, but its clinical acceptance appears to be at least several years away [174,175 ].…”

Is Electrode-Modiolus Distance a Prognostic Factor for Hearing Performances after Cochlear Implant Surgery?

“…Another important electrophysiological parameter is the electrically evoked compound action potential (ECAP), which has been reported to be modified by the position of the electrode inside the cochlea [van Wermeskerken et al, 2009]. Even if the relation between ECAP and stimulation levels is not constantly observed, the ECAP threshold is routinely used to estimate threshold and comfortable stimulation levels [Potts et al, 2007].…”

Postimplantation Changes of Electrophysiological Parameters in Patients with Cochlear Implants

“…Different researchers tried to use electrically-evoked auditory brainstem responses, electrically-evoked stapedius reflex thresholds or measurements of the electrically-evoked compound action potentials (ECAP) [Mittal and Panwar, 2009;Muhaimeed et al, 2010;Pau et al, 2011;Van Den Abbeele et al, 2012]. Even though the correlations of these measures with the behavioural thresholds (T levels) and hearing comfort levels (C levels) are relatively weak [Holstad et al, 2009;Potts et al, 2007;Smoorenburg et al, 2002;Tao et al, 2011] for particular electrodes, fittings based on the objective profiles with subsequent behavioural adaptation of the 'shift and tilt' [Hughes et al, 2001;King et al, 2006;Smoorenburg et al, 2002] are widely used and currently rank among the best available options.…”