Cochlear implant input-output functions can be non-monotonic at high levels

Evidence

Closer inspection of the data revealed that the input/output growth functions sometimes had non-monotonic shapes. An example obtained for G7 1 month after deafening is illustrated in Fig. 4c for RPS-A and RPS-C. The function for RPS-C shows, at some point in the dynamic range, a decrease in response amplitude with increases in level. In this case, the cathodic pulse was more effective than the anodic pulse at low levels but less effective at high levels. Such non-monotonicities were observed in seven of the ten subjects but only in about 13 % of the cathodic and 4 % of the anodic growth functions. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2295

Categorization

• QUESTION: Why would increasing stimulation current reduce response amplitude? This suggests a mechanism worth investigating—perhaps differential fiber recruitment ordering or refractoriness.