9Objective measures → the MAP

Everything in this atlas converges here. The impedance sweep clears the interface, the ECAP confirms and quantifies the nerve's response, the ESRT marks the comfortable ceiling — and the question is how to turn those numbers into a MAP: the per-electrode T and C levels and parameters the recipient will actually hear through. Objective measures do not replace behavioural fitting, but they scaffold it: they give the first MAP its shape, cross-check the behavioural one, and carry most of the load when the recipient cannot tell you what they hear.

FThe mapping problem

A MAP is the complete set of programming parameters stored in the sound processor: for every active electrode, a threshold (T) level and a comfortable (C or M) level defining the electrical dynamic range into which sound is compressed, plus the coding strategy, stimulation rate, and pulse width. Ideally every T and C is set behaviourally. In reality — at first fit, in young children, across 12–22 electrodes — full behavioural measurement of every value is slow or impossible, and that is the gap objective measures fill.[2014]

TCObjective anchors for levels

Two anchors sit at different points in the dynamic range, and they are complementary:

The ECAP threshold correlates with behavioural levels but the relationship is loose and offset between individuals; it is better at predicting the relative profile across electrodes than the absolute value on any one. The ESRT, sitting near C/M, is a stronger predictor of the comfortable ceiling. Used together they bracket the dynamic range from both ends.[2000, 2002, 1997]

CProfile-based & scaled fitting

A key practical refinement is to use the ECAP not value-by-value but as a profile. The shape of the tNRT across the array — which electrodes need more current and which less — tends to track the shape of the behavioural T/C profile, even when the absolute offset is unknown. So a clinician can measure behavioural levels on a few electrodes, then use the ECAP profile to interpolate the rest, rather than measuring all of them.[2010]

This scaled-profile approach — anchor with a small number of behavioural measurements, shape with the objective profile — is more accurate than applying a single fixed offset to the whole ECAP profile, and it is the most clinically useful way the ECAP feeds the MAP.

TCPaediatric fitting — where objective measures carry the load

In infants and young children, reliable loudness scaling is impossible and even conditioned-response audiometry is limited. Here objective measures move from supporting role to lead:

• ESRT anchors the comfortable ceiling so the child is not over-stimulated.
• ECAP thresholds / profile shape the level map across electrodes.
• eABR / cortical responses confirm the pathway conducts and matures (Modules 6–7).
• Behavioural observation then refines the MAP progressively as the child develops testable responses.

The recommended practice is a battery — no single objective measure suffices, but combined they produce a safe, audible starting MAP that behavioural refinement then optimises.[2004]

TA combined workflow

1. Impedance — confirm intact contacts; deactivate opens/shorts (Module 2).
2. ECAP — obtain thresholds/profile across the array (Modules 3–4).
3. ESRT — anchor the C/M ceiling where obtainable (Module 5).
4. Set a starting MAP — C/M from ESRT, profile shape from ECAP, T-levels conservatively below.
5. Refine behaviourally — loudness balancing, comfort checks, and (in children) observation and serial visits.

CThe limits of objective-only programming

The recurring honest caveat of this atlas applies most sharply here. Objective measures tell you the system can deliver an audible, comfortable signal; they do not guarantee speech understanding, optimal loudness balance, or the best spectral allocation. A MAP set purely on objective data is a safe starting point, not an optimised one. Where the recipient can give reliable behavioural responses, those take precedence; objective measures earn their place by getting the MAP close, fast, and safely — and by carrying programming when behaviour cannot.[2014]