ITD Perception With Clinical CI Processors In Bilateral Implantation

Brill, S

Using loudness balanced 50 Hz click trains as dichotic stimulus in a lateralization task, interaural time difference (ITD) resolution of down to 25 us have been observed in two bilaterally implanted CI users. Six other subjects exhibited ITD resolutions of 50 us. This is especially surprising, since non-sychronized clinical processors were used. Both processors were programmed to operate at different stimulation rates, which followed from clinical fitting. Therefore the individual biphasic current pulses from the pulsatile
stimulation on both sides cannot provide any lateralization cues.

Under the assumption that individual pulses can be resolved by the auditory system, they should disturb lateralization capability because their temporal relation is arbitrary and changes over time and within the duration of the stimulus. Since the lateralization capability is only moderately affected in comparison to the performance of normal hearing subjects in the same task, we may conclude that individual current pulses at these rates are either ignored or not perceived at all by the auditory pathways performing the lateralization task. The only cue available is a temporal difference of the envelope signals of the two sides.

Contact Information

Stefan Brill
Institute of Applied Physics, University of Innsbruck,
Technikerstr. 25, A-6020 Innsbruck, Austria
Phone: +43/512/507-6407
Fax: +43/512/507-2922
E-mail: Stefan.M.Brill@uibk.ac.at