Effects of stimulation rate with the Nucleus 24 ACE speech coding strategy

Area of Science:

• Audiology
• Biomedical Engineering
• Neuroscience

Background:

• Cochlear implants (CIs) are vital for restoring hearing in individuals with severe to profound sensorineural hearing loss.
• The Advanced Combination Encoder (ACE) speech coding strategy in Nucleus 24 devices allows for adjustable electrical stimulation rates.
• Optimizing stimulation rates is crucial for maximizing speech understanding in CI users.

Purpose of the Study:

• To compare speech recognition performance in cochlear implant users at two electrical stimulation rates: 720 pulses per second per channel (pps/ch) and 1800 pps/ch.
• To investigate the relationship between psychophysical measures and program (MAP) stimulation levels for each rate.
• To assess the stability of MAP levels over a 14-week period.

Main Methods:

• Eight postlinguistically deaf adults with Nucleus 24 CIs participated.
• Speech recognition was tested using words in quiet and sentences in noise at various sound levels.
• Psychophysical measures (threshold, maximum acceptable loudness) were obtained to set and adjust MAPs for each stimulation rate.

Main Results:

• Significantly better group scores for phonemes and sentences in noise at 50 dB SPL were observed with 1800 pps/ch compared to 720 pps/ch.
• No significant differences were found for words at any level or for sentences at higher noise levels.
• Individual performance varied, with some subjects favoring 720 pps/ch and others 1800 pps/ch; subjective preferences were also mixed.

Conclusions:

• Individualized programming is essential, as over half of subjects preferred one rate over the other, and performance varied significantly.
• MAPs should incorporate both moderate (720 pps/ch) and fast (1800 pps/ch) rates within the ACE strategy during initial device use.
• Adjustments to MAP minimum and maximum levels are necessary to ensure clear and comfortable sound perception across different listening conditions.