Effects of Talker Sex Differences on Binaural Summation in Cochlear Implant Users and Normal Hearing Listeners.

The groups of implant users with hearing loss or normal hearing in the other ear had only 8 people each, and the whole study was done at a single centre, so the group averages rest on very few individuals. Only 11 of the 19 bilateral implant users were tested with opposite-sex competing talkers, so that comparison is based on a little over half the group. Testing used speech and competing talkers from the same direction. Benefits that depend on where a sound comes from (head shadow) were not measured at all, so the results do not describe listening in a room where talkers are in different places. All participants were native Mandarin speakers tested with Mandarin sentences, and the authors note that the slope of the listening task may differ in tonal versus non-tonal languages; they say there is no strong evidence binaural summation itself differs, but it has not been tested directly. The model used to explain the results needed the steepness of each listener's performance curve, which could not be measured in these participants; those numbers were borrowed from 10 other bilateral implant users and from published normal-hearing data. Measurements were made on one day in a sound-treated set-up, not in everyday listening, and each threshold came from two runs of a short adaptive task.

The work was funded by Chinese national and institutional grants, including the National Natural Science Foundation of China, the National Key R&D Program of China, the Beijing Natural Science Foundation, Capital Medical University and Beijing Tongren Hospital. The authors declared no conflicts of interest. All implant users in the study wore the same MED-EL device and processor, and implant mappings and microphone settings were left unchanged during testing.

Do not read this as evidence that a second cochlear implant reliably improves hearing in noise. The gains from listening with both ears were small or absent in most conditions and never averaged more than 3.5 dB, the unilateral groups had only 8 people each, and testing used speech and competing talkers coming from the same direction. The suggestion in the discussion that adding a second implant may benefit patients is a proposal from the authors, not something this study tested.