Fitting based on Objective Measures: The objective offset (or ‘Brown’) method

Since this method was developed for Nucleus implants the terminology in this section is Nucleus focused.
Carolyn Brown noted that in her data the weak correlation between T and C levels and ECAP is mostly determined by large individual shifts in the profiles, this means that the ECAP cannot predict the absolute level of T and C levels, but it could predict the shape of the profile (Brown et al., 2000). Brown et al. proposed a method in which the ECAP profile was used in combination with one classical T and C level measurement in the centre of the array. By adding/subtracting a constant offset to each channel, the profile was shifted to match the measured T and C level. Using this method they found (not surprisingly) that the average group correlation between the ‘predicted’ T and C level and the measured T and C level was higher than when using the uncorrected ECAP. However, Cafarelli-Dees et al. (2005) showed that the expected difference between predicted and real T and C level (the mapping error) was still unacceptably large. Furthermore it was shown that when using a profile determined by the average across a large group of subjects instead of the ECAP profile, the mapping error was even less. Surprisingly, clinical studies showed no significant drop in performance with maps made following the method proposed by Brown et al. (see for instance Craddock et al., 2003). This is another indication that the measure of how well a mapping method predicts measured T and C level is not a good measure for the quality of the mapping method itself in terms of clinical benefit.
Advantage: Quick, easy to do. Only 1 T and C measurement needed.
Disadvantage: Fixed dynamic range across array. May not be accurate enough for some.
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