van Hoesel Richard, Böhm Melanie, Battmer Rolf D, Beckschebe Jens, Lenarz Thomas
Cooperative Research Centre for Cochlear Implant and Hearing Aid Innovation, Melbourne, Victoria, Australia.
Ear Hear. 2005 Aug;26(4):381-8. doi: 10.1097/00003446-200508000-00002.
A study was conducted examining the effects of amplitude-mapping adjustments on speech intelligibility with bilateral cochlear implant users, for both unilateral and bilateral device use. The main motivation for this study was the consideration that bilateral loudness summation may result in sounds becoming too loud if no adjustments are made to standard monaural amplitude-mapping functions (maps) when used bilaterally. In that case, reductions of the stimulation levels may be needed. The objective was to assess the impact of such adjustments on speech intelligibility in noise and in quiet.
Four different maps were compared in eight bilateral users of the Nucleus 24 system. Each map variation was taken home for 1 week and used bilaterally. After each week, the map used was tested both unilaterally and bilaterally using an adaptive speech-in-noise test and bilaterally for low-level speech in quiet. For the tests in noise, both speech and noise were presented from the same loudspeaker placed directly in front of the listener (S0N0). One of the maps evaluated was a standard clinical map, fitted as if only one ear were to be used. The three other maps used stimulation levels that were reduced more near the maximal stimulation levels, near thresholds, or else by a similar amount over the entire dynamic range.
The data showed a modest but statistically significant decrease in performance when stimulation levels were lowered. This was true both in noise and in quiet. For level reductions corresponding to binaural loudness summation effects, the performance decrease was on the order of 1 to 2 dB. Altering the slope of the map had relatively little effect on performance. Comparison of unilateral with bilateral performance using the same map (i.e., no compensation for bilateral loudness summation) and with speech and noise both presented from in front of the listeners showed a modest but statistically significant improvement in the bilateral condition.
Using higher stimulation levels in amplitude-mapping functions can improve both monaural and binaural speech perception performance in quiet and in noise, even when the slope of the acoustic to electrical amplitude-mapping function is held constant (i.e., when the electrical signal-to-noise ratio remains constant). The results in noise can be understood if we assume that the relation between electrical stimulation levels and loudness grows faster at higher stimulation levels. When comparing the monaural better ear with binaural performance in noise (S0N0) by using the same map, that is to say, when no adjustments were made in the bilateral condition for bilateral loudness summation, an average signal-to-noise ratio benefit of 1.4 dB was found in the bilateral condition. These findings indicate that when fitting bilateral devices clinically, although binaural performance may decrease slightly if levels need to be reduced to compensate for binaural loudness summation, the binaural S0N0 advantage over the better ear will offset this. Consequently, performance with both ears after adjustment is likely to remain at least as good as for the better ear alone without level adjustment, even in the S0N0 condition where binaural advantages are minimized.
开展一项研究，探讨幅度映射调整对双侧人工耳蜗使用者单耳和双耳使用时言语可懂度的影响。开展这项研究的主要动机是考虑到，如果在双侧使用时不对标准单耳幅度映射功能（图谱）进行调整，双侧响度总和可能会导致声音变得过大。在这种情况下，可能需要降低刺激水平。目的是评估此类调整对噪声环境和安静环境中言语可懂度的影响。
在8名使用Nucleus 24系统的双侧使用者中比较了4种不同的图谱。每种图谱变体被带回家使用1周，并双侧佩戴。每周之后，使用的图谱会通过自适应噪声环境言语测试进行单耳和双耳测试，并通过安静环境下的低强度言语测试进行双耳测试。对于噪声环境测试，言语和噪声都通过直接放置在聆听者正前方的同一个扬声器呈现（S0N0）。评估的图谱之一是标准临床图谱，其拟合方式就好像只使用一只耳朵一样。其他三种图谱在接近最大刺激水平、接近阈值时或在整个动态范围内以相似幅度降低了刺激水平。
数据显示，当刺激水平降低时，表现出现了适度但具有统计学意义的下降。在噪声环境和安静环境中都是如此。对于与双耳响度总和效应相对应的水平降低，表现下降幅度约为1至2分贝。改变图谱的斜率对表现的影响相对较小。使用相同图谱（即不对双耳响度总和进行补偿），并在聆听者正前方呈现言语和噪声，比较单耳和双耳表现，结果显示双耳条件下有适度但具有统计学意义的改善。
在幅度映射功能中使用更高的刺激水平可以改善安静环境和噪声环境下单耳和双耳的言语感知表现，即使声电幅度映射功能的斜率保持不变（即电信号噪声比保持不变）。如果我们假设电刺激水平与响度之间的关系在较高刺激水平下增长更快，那么噪声环境下的结果就能得到解释。当通过使用相同图谱比较噪声环境（S0N0）下单耳较好耳和双耳表现时，也就是说，当在双侧条件下不对双耳响度总和进行调整时，发现双耳条件下平均信噪比优势为1.4分贝。这些发现表明，在临床安装双侧设备时，尽管如果需要降低水平以补偿双耳响度总和，双耳表现可能会略有下降，但双耳在S0N0条件下相对于较好耳的优势将抵消这一点。因此，即使在双耳优势最小化的S0N0条件下，调整后双耳的表现可能至少与未进行水平调整时较好耳的表现一样好。
