When the First Pulse Fades: 75% Reduction in Precedence Effect in Cochlear Implanted Rats.

This is a study in rats. No person was tested, and the authors' preferred explanation for their result, that the animals never had to use their implants in a world full of echoes, is a hypothesis the experiment cannot test. The numbers are small: 8 neonatally deafened and 4 adult-deafened implant rats, and the comparison data from the 4 hearing rats were taken from an earlier published study rather than collected alongside. Three of the eight neonatally deafened rats could not meet the 75% accuracy criterion at the fastest pulse rate and were dropped, so the data at 900 pulses per second come from fewer animals than the rest. The adult-deafened rats were only tested at the single pulse rate of 300 per second, so it is not known whether their results would look the same at other rates. No echoes or reverberation were ever presented. The rats lateralized isolated bursts of pulses, so the study measures how heavily they weighted the first pulse, not how they actually cope in a reverberant room. The hearing comparison used acoustic clicks delivered through tubes while the implant rats received electric pulses, so the two groups differ in stimulus type as well as in hearing history.

The work was funded by the Hong Kong Health and Medical Research Fund, the Hong Kong General Research Fund, the German Academic Exchange Service with German federal research ministry funds, the EU Seventh Framework Programme Marie Curie actions, the research commission of the medical faculty at the University of Freiburg, and the charity Taube Kinder lernen hören e.V. Eight of the cochlear implant electrode arrays used in the animals were provided by MED-EL Medical Electronics, a company that makes cochlear implants, under a research agreement. The authors declared no conflicts of interest.

Do not read the 75% figure as a measured loss of hearing-in-noise ability in implant users. It is a difference in how heavily 12 rats weighted the first pulse of an isolated burst of pulses, with no echoes present anywhere in the experiment. The authors' explanation for it, that their animals never had to use their implants in a reverberant world, was not tested here.