Comparison of percepts found with cochlear implant devices

Much of what has been observed in psychoacoustic testing of implanted listeners is similar to that seen in normal or hearing-impaired listeners with only parametric modification. What is lacking is evidence for critical band phenomena and for frequency selectivity. The unique interaction of waveform and sensation level with pitch, loudness, and threshold appears only in implanted listeners. Direct waveform processing, without spectral decomposition, appears to be the means by which information is brought to the nervous system through electrical stimulation. The operations by which this is coded to create percepts of pitch and loudness remain to be elucidated.