Page 59 - Spring2019

Figure 3. Means and SEMs for recognition of monosyllabic words (solid circles) and sentences (open circles) by implant subjects. The sentences included the AzBio sentences (green circles and lines) and the Hochmair-Schultz-Moser (HSM) sentences in German or their equivalents in other languages (blue circles and lines). See text for additional details about the tests and sources of data. From Wilson and Dorman (2018b), with permission.
interval for the two monosyllabic word tests; and (5) lower scores for the word tests than for the sentence tests.
The improvements over time indicate a principal role of the brain in determining outcomes with CIs. In particular, the time course of the improvements is consistent with changes in brain function in adapting to a novel input (Moore and Shan- non, 2009) but not consistent with changes at the periphery such as reductions in electrode impedances that occur during the first days, not months, of implant use. The brain makes sense of the input initially and makes progressively better sense of it over time, out to 3-12 months and perhaps even be- yond 12 months. (Note that the acute comparisons in Figure 2 did not capture the improvements over time that might have resulted with substitution of the new processing strategy on a long-term basis; also see Tyler et al., 1986.)
The results from the monosyllabic word tests also indicate that the performance of unilateral CIs has not changed much, if at all, since the early 1990s, when the new processing strat- egies became available for clinical use (also see Wilson, 2015, for additional data in this regard). These tests are particularly good fiducial markers because the scores for the individual subjects do not encounter ceiling or floor effects for any of the modern CIs and processing strategies tested to date.
Figure 4. Recognition by subjects with normal hearing (NH; black circles) and CI (blue circles) subjects of AzBio sentences presented in an otherwise quiet condition (left) or in compe- tition with environmental noise at the speech-to-noise ratios (SNRs) of +10 dB (center) and +5 dB (right).Horizontal lines, means of the scores for each test and set of subjects. From Wil- son and Dorman (2018b), with permission; data courtesy of Dr. René Gifford.
An additional aspect of performance with the present-day unilateral CIs is seen in Figure 4, which shows the effects of noise interference on performance. These data also are from VUMC and again kindly provided by Dr. Gifford. The subjects include 82 adults with normal hearing (NH) and 60 adult users of unilateral CIs from the same corpus men- tioned previously or implanted later at the VUMC. The Az- Bio sentences were used and were presented in an otherwise quiet condition (Figure 4, left) or in competition with envi- ronmental noise at the speech-to-noise ratios (SNRs) of +10 (Figure 4, center) and +5 dB (Figure 4, right). Scores for the individual subjects are shown along with the mean scores in- dicated by the horizontal lines.
The scores for the NH subjects are at or near 100% correct for the quiet and +10 dB conditions and above 80% correct for the +5 dB condition. In contrast, scores for the CI sub- jects are much lower for all conditions and do not overlap the NH scores for the +10 and +5 dB conditions. Thus, the present-day unilateral CIs do not provide NH, especially in adverse acoustic conditions such as the ones shown and such as in typically noisy restaurants or workplaces. However, the CIs do provide highly useful hearing in relatively quiet (and reverberation-free) conditions, as shown by the data in Fig- ure 4, left, and by the sentence scores in Figure 3.
Adjunctive Stimulation
Although the performance of unilateral CIs has been rela- tively constant for the past 2+ decades, another way has been found to increase performance and that is to present stimuli in addition to the stimuli presented by a unilateral CI. As noted in A Snapshot of the History, this additional (or ad- junctive) stimulation can be provided with a second CI on the
Spring 2019 | Acoustics Today | 57