Fitting based on Objective Measures: The preset map series (or Almqvist) method

Since this method was developed for Nucleus implants the terminology in this section is Nucleus focused.
When mapping children we assume that methods we know to work for adults should work equally well for children. However, this may not always be the case: first of all congenitally deaf children have no sense of loudness and probably their final C-level is determined by a combination of what is offered to them and how well they adapt to that. Almqvist (personal communication) amongst others put forward the notion that congenitally deaf children have no optimal map but can get accustomed to any map provided:
  1.  The map is audible to them (i.e., elicits neural responses).
  2.  The map has sufficient dynamic range to code loudness differences.
Now, in spite of the weak correlation between ECAP thresholds and T and C levels, we do know that the ECAP threshold always corresponds to an audible level. Furthermore, we also know, that, on average, the offset between ECAP and T-level is about 30 CL (assuming 80 Hz NRT measurement and default 900 Hz map rate).
Based on these notions, the preset map series method uses ONLY the ECAP information to create initial maps for children: The ECAP profile is shifted down 40 CL to determine the T-levels, the C-levels start at T-level+10 CL and are increased over time until they are at the ECAP thresholds. Then after some time the T-levels are checked by measuring a sound field audiogram.
A multicentre study with 100 subjects (children) is ongoing (Ramos et al., 2003). The preliminary results (60 children) show no difference between preset map series and conventional mapping but a significant time saving, especially in the first fitting. This was a randomized trial (randomized for treatment) where the quality of the map was measured both with parental questionnaires and with sound field audiograms.
In adults this method does not work so well, presumably because they have some memory of the sound and dislike any map that is very different from what they remember. In other words: maybe they do not have the plasticity in their brain to adapt to the map, so we have to adapt the map to their brain.
Advantage: very quick, especially for the first map, no behavioural input needed.
Disadvantage: does not always give the best map, so that sometimes specific fine-tuning is needed and such maps should be checked at a later date. Not suitable for adults.
 
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