Pitch perception in cochlear implants with different filter bank designs

Cochlear implant subjects have problems discriminating the fundamental frequency or the pitch of harmonic sounds using current speech processors. The present study investigated the effect of the filter bank in the speech processor on pitch perception. Four filter banks were examined with respect to the discrimination of fundamental frequency of single formant stimuli in 4 Nucleus CI24 subjects. All experiments were done with and without the presence of temporal pitch cues to assess the effects of temporal and place pitch separately. The results indicate that the transmission of F0 by means of place pitch is possible if the filter bank has enough resolving resolution in the F0 frequency register. The filter shape did not have a significant effect. In order to correctly transmit the fundamental frequency using temporal pitch cues, the higher harmonics had to be unresolved. If higher harmonics were resolved the modulation of the envelope of the electrical stimuli also contained components at the harmonic frequency and this may perturb the pitch percept. The results of the data without temporal pitch cues can be explained by a model that compares the centroid of the excitation patterns along the electrode array.