HiResolution^TM and Conventional Sound Processing in the HiResolution^TM Bionic Ear: Using Appropriate Outcome Measures to Assess Speech Recognition Ability

Abstract

Objective: This study compared speech perception benefits in adults implanted with the HiResolution^TM (HiRes) Bionic Ear who used both conventional and HiRes sound processing. A battery of speech tests was used to determine which formats were most appropriate for documenting the wide range of benefit experienced by cochlear-implant users. Study Design: A repeated-measures design was used to assess postimplantation speech perception in adults who received the HiResolution Bionic Ear in a recent clinical trial. Patients were fit first with conventional strategies and assessed after 3 months of use. Patients were then switched to HiRes sound processing and assessed again after 3 months of use. To assess the immediate effect of HiRes sound processing on speech perception performance, consonant recognition testing was performed in a subset of patients after 3 days of HiRes use and compared with their 3-month performance with conventional processing. Setting: Subjects were implanted and evaluated at 19 cochlear implant programs in the USA and Canada affiliated primarily with tertiary medical centers. Patients: Patients were 51 postlinguistically deafened adults. Main Outcome Measures: Speech perception was assessed using CNC monosyllabic words, CID sentences and HINT sentences in quiet and noise. Consonant recognition testing was also administered to a subset of patients (n = 30) using the Iowa Consonant Test presented in quiet and noise. All patients completed a strategy preference questionnaire after 6 months of device use. Results: Consonant identification in quiet and noise improved significantly after only 3 days of HiRes use. The mean improvement from conventional to HiRes processing was significant on all speech perception tests. The largest differences occurred for the HINT sentences in noise. Ninety-six percent of the patients preferred HiRes to conventional sound processing. Ceiling effects occurred for both sentence tests in quiet. Conclusions: Although most patients improved after switching to HiRes sound processing, the greatest differences were seen in the ‘poor’ performers because ‘good’ performers often reached ceiling performance, especially on tests in quiet. Future evaluations of cochlear-implant benefit should make use of more difficult measures, especially for ‘good’ users. Nonetheless, a range of difficulty must remain in test materials to document benefit in the entire population of implant recipients.

Cochlear implants: A remarkable past and a brilliant future

“…Among these are the n-of-m and SPEAK strategies also mentioned before in section 2, and the advanced combination encoder (ACE) (Kiefer et al, 2001) and "HiResolution" (HiRes) strategies (Koch et al, 2004), which were developed more recently. The n-of-m, SPEAK, and ACE strategies each use a channel-selection scheme, in which the envelope signals for the different channels are "scanned" prior to each frame of stimulation across the intracochlear electrodes, to identify the signals with the n-highest amplitudes from among m processing channels (and associated electrodes).…”

A Review of Stimulating Strategies for Cochlear Implants

“…In the cochlear implant system, the stimulating strategy plays an extremely important role in generating the sounds heard by users (Wilson et al, 1991;Kiefer et al, 2001;Koch et al, 2004;Wilson & Dorman, 2008). It functions to convert sounds into a series of electric impulses which determines which electrodes should be activated in each cycle.…”

“…When two (or more) neighboring electrodes are stimulated in a suitable manner, intermediated channels, also known as virtual channels, are created between the electrodes. These virtual channels can enable CI users to perceive different frequencies between two fixed channels (Koch et al, 2004;Choi & Hsu, 2009). Using the virtual channel technique not only allows for more stimulating space, but also improves the reproduction of the original spectrum.…”

“…The original spectrum is reproduced by 15 virtual channels, and all electrode pairs are turned on in a predefined sequence within 15 consecutive clock cycles. CI users with the HiRes120 strategy devices usually have better hearing performance compared to those with the CIS strategy devices (Koch et al, 2004;Wilson & Dorman, 2008), indicating that applying virtual channel technique does improve the perceptual quality of CI users. However, since the HiRes120 strategy only adjusts the current level ratio of two neighboring electrodes, its spectral resolution is actually not high enough due to the relatively wider stimulation region of the immediate channels.…”

Speech perception scores in cochlear implant recipients: An analysis of ceiling effects in the CUNY sentence test (Quiet) in post-lingually deafened cochlear implant recipients

“…Firstly, when two different conditions, such as two speech coding strategies or two different programs are compared, reaching the ceiling scores leaves no room for such comparisons (Koch et al, 2004, Spahr and Dorman, 2005, Spahr and Dorman, 2004, Bassim et al, 2005, Amoodi et al, 2012. Secondly, when a recipient receives the highest possible score during the earlier assessments, identifying the further changes in their performance over time will become a problem.…”