CHANNEL INTERACTIONS IN PATIENTS USING THE INERAID MULTICHANNEL COCHLEAR IMPLANT

Electrode interactions were investigated on two totally deaf patients fitted with the Ineraid multichannel cochlear implant. Currents were a pplied to the most apical electrode (the 'perturbation' electrode) and their effects on psychophysical thresholds on the other electrodes (t he 'test' electrodes) of the intracochlear array were studied. Two exp erimental protocols were used. In experiment I, we used a detection pr otocol to study how the perception of signals presented on each test e lectrode was affected by subthreshold, simultaneous or non-simultaneou s stimulation of the perturbation electrode. Strong electrode interact ions were observed with simultaneous stimulation and monotonically dec reased as a function of electrode separation. Electrode interactions w ere weak with non-simultaneous stimulation. In experiment II, we used a discrimination protocol to study how the perception of signals prese nted on the test electrode was affected by suprathreshold, non-simulta neous stimulation of the perturbation electrode. Subjects could discri minate stimulation of 'perturbation+test' versus 'perturbation alone' when the level of stimulation on the test electrode was near threshold . These results demonstrate that strong electrode interactions in the Ineraid multichannel cochlear implant system are generated by electric al field summation due to simultaneous stimulation of different electr odes, and that one can reduce electrode interactions by sequential act ivation of the electrodes. These observations might help to understand basic phenomena underlying recent significant improvements in speech recognition scores when switching from simultaneous to interleaved pul satile stimulation in patients wearing the same cochlear implant syste m