ABSTRACT: The frequency-to-channel mapping for Cochlear implant (CI) signal processors was originally designed to optimize speech perception
and generally does not preserve the harmonic structure of music sounds. An algorithm aimed at restoring the harmonic relationship
of frequency components based on semitone mapping is presented in this article. Two semitone (Smt) based mappings in different
frequency ranges were investigated. The first, Smt-LF, covers a range from 130 to 1502 Hz which encompasses the fundamental
frequency of most musical instruments. The second, Smt-MF, covers a range from 440 to 5040 Hz, allocating frequency bands
of sounds close to their characteristic tonotopical sites according to Greenwood's function. Smt-LF, in contrast, transposes
the input frequencies onto locations with higher characteristic frequencies. A sequence of 36 synthetic complex tones (C3
to B5), each consisting of a fundamental and 4 harmonic overtones, was processed using the standard (Std), Smt-LF and Smt-MF
mappings. The analysis of output signals showed that the harmonic structure between overtones of all complex tones was preserved
using Smt mapping. Semitone mapping preserves the harmonic structure and may in turn improve music representation for Nucleus
cochlear implants. The proposed semitone mappings incorporate the use of virtual channels to allow frequencies spanning three
and a half octaves to be mapped to 43 stimulation channels. A pitch difference limen test was done with normal hearing subjects
discriminating pairs of pure tones with different semitone intervals which were processed by a vocoder type simulator of CI
sound processing. The results showed better performance with wider semitone intervals. However, no significant difference
was found between 22 and 43 channels maps.
Semitone mapping–Melody–Music–Nucleus cochlear implant
EURASIP Journal on Audio Speech and Music Processing 04/2012; 2011(1):1-11. · 0.71 Impact Factor
ABSTRACT: Music perception with a cochlear implant (CI) can be unsatisfactory because current-day implants are primarily designed to enable speech discrimination. The present study aimed at evaluating electrophysiological correlates of musical sound perception in CI users to help achieve the long-term goal of improved restoration of hearing in those individuals.
Auditory discrimination accuracy in adult CI users (n=12) and matched normal-hearing controls (n=12) was measured by behavioral discrimination tasks and mismatch negativity (MMN) recordings. Discrimination profiles were obtained by using a set of clarinet sounds (original/vocoded) varying along different acoustic dimensions (frequency/intensity/duration) and deviation magnitudes (four levels).
Behavioral results and MMN recordings revealed reduced auditory discrimination accuracy in CI users. An inverse relationship was found between MMN amplitudes and duration of profound deafness.
CI users have difficulties in discriminating small changes in the acoustic properties of musical sounds. The recently developed multi-feature MMN paradigm (Pakarinen et al., 2007) can be used to objectively evaluate discrimination abilities of CI users for musical sounds.
Measuring auditory discrimination functions by means of a multi-feature MMN paradigm could be of substantial clinical value by providing a comprehensive profile of the extent of restored hearing in CI users.
Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 12/2010; 121(12):2070-82. · 3.12 Impact Factor
ABSTRACT: The electrically evoked compound action potential (ECAP) amplitude resulting from a train of pulses of finite duration (100 ms or 200 ms) was found to vary inversely to the stimulation rate (pulse rate), corroborating well with neural adaptation results from a previous study (Dillier et al., 2005). Amplitude growth functions based on these adapted responses yield thresholds (TNRT) that increase with increasing pulse rate, contrary to behavioural thresholds, which are known to vary inversely with the stimulation rate. Adaptation effects are therefore a confounding factor that must be accounted for when attempting to compare behavioural and objective measures.
Cochlear implants international 02/2009; 10 Suppl 1:63-7.