Place-pitch discrimination of single- versus dual-electrode stimuli by cochlear implant users

Abstract

Simultaneous or near-simultaneous activation of adjacent cochlear implant electrodes can produce pitch percepts intermediate to those produced by each electrode separately, thereby increasing the number of place-pitch steps available to cochlear implant listeners. To estimate how many distinct pitches could be generated with simultaneous dual-electrode stimulation, the present study measured place-pitch discrimination thresholds for single- versus dual-electrode stimuli in users of the Clarion CII device. Discrimination thresholds were expressed as the proportion of current directed to the secondary electrode of the dual-electrode pair. For 16 of 17 electrode pairs tested in six subjects, thresholds ranged from 0.11 to 0.64, suggesting that dual-electrode stimuli can produce 2-9 discriminable pitches between the pitches of single electrodes. Some subjects demonstrated a level effect, with better place-pitch discrimination at higher stimulus levels. Equal loudness was achieved with dual-electrode stimuli at net current levels that were similar to or slightly higher than those for single-electrode stimuli.

Current Steering with Partial Tripolar Stimulation Mode in Cochlear Implants

“…However, as revealed by the above analysis of the d′ values, the change in cumulative d′ with a 0.1 interval in α was not significantly different across α. The overall Donaldson et al (2005), it was found that steered pTP mode created on average six pitch steps on a main electrode in this study. A one-way RM ANOVA revealed no significant effect of electrode (F 2,8 00.17, p00.85) on the overall cumulative d′, indicating similar pitch changes with steered pTP stimuli on different main electrodes.…”

“…Higher pitch percepts were elicited with increasing α (i.e., more current injected to the basal main electrode). CI users perceived on average five intermediate pitch sensations per electrode pair (e.g., Donaldson et al 2005), but their speech recognition only slightly improved with speech processing strategies using the MP-mode current steering (e.g., Firszt et al 2009). The large current spread of MP stimulation may have limited the number of independent spectral channels with MP-mode current steering.…”

Threshold Levels of Dual Electrode Stimulation in Cochlear Implants

“…Donaldson et al (2005) showed that for most of the subjects no current correction was needed for creating the same loudness for e (monopolar stimulation) and e+1 with α=0.5. This finding was confirmed by a previous study from our group (Snel-Bongers et al 2011), but it was demonstrated that higher current levels were required to reach MCL levels for e+x up to an excitation width of 4.4 mm (e+4).…”

“…In addition, TL is part of the clinical fitting procedure. At MCL, a current correction is needed to maintain constant loudness for non-simultaneous DES on adjacent electrodes, while it is not for most simultaneous DES (Donaldson et al 2005;Frijns et al 2009b;Snel-Bongers et al 2011;Snel-Bongers et al 2012). Based on the findings with our computational model described above ( Figure 1A, B), it was hypothesized that such a current correction is also needed when current steering is employed close to TL.…”

“…One reason for this might be reduced spectral resolution caused by the limited number of physical electrodes in the array (Brendel et al 2009;Hughes and Goulson 2011). Dual electrode stimulation (DES), either simultaneous (Donaldson et al 2005;Townshend et al 1987) or sequential (Kwon and van den Honert 2006;McDermott and McKay 1994), has been proposed as a method to increase the number of perceivable pitches with CIs. In simultaneous DES (also called current steering), the summation of two electrical fields produces excitation of nerve fibers intermediate to the stimulated contacts.…”