Hearing Preservation in cochlear implantees

Lendra Friesen

Background/Aims

Recent studies have demonstrated that low-frequency hearing preservation is possible with cochlear implanted patients using new electrode technology and a soft surgical technique. Studies are beginning to reflect benefit in clinical outcomes. However, the neural mechanisms underlying this benefit are unknown. Our aims in this study were to measure: 1) sentence recognition in quiet and noise, 2) just noticeable
differences (JNDs) of pulse phase duration (PPD), which has been shown to decrease in animals with increased auditory nerve damage and, 3) cortical sensitivity to the obtained behavioral PPD JNDs with the N1-P2 and ACC responses.

Methodology

We examined the psychophysical just noticeable difference (jnd), using stimulus ppd (400 ms pulse trains) on basal, medial, and apical electrodes using a lower reference range (30-80us) and a higher reference range (345-395 us) of the ppd using a 3 down, 1 up alternative-forced choice procedure. We then recorded the N1-P2 and the Acoustic Change Complex (ACC) on basal, medial, and apical electrodes for both the low and high range of phase durations to determine the relationship to the behavioral jnd. An 800 ms pulse train was used, where the first 400 ms of the stimulus was the standard and the second 400 ms was the jnd of the phase duration. We also tested patients’ sentence recognition in soundfield in quiet and at a +5 S/N to examine the relationship to the jnds and the cortical responses.

Results/Conclusions/Significance

No significant differences were observed between the individuals with hearing preservation auditory thresholds and those without for any of the measures conducted. Only a significant main effect for amplitude between the shorter duration stimuli and the longer duration stimuli was noted. The current standard to define individuals with hearing preservation is based on their auditory thresholds. However, this might not be the best method of separating this group of individuals. Based on our results, it appears that there is little difference between the individuals having low-frequency hearing preservation and those without. It could also be that we are not using measurements that accurately assess the differences between these two groups.