Clinical Assessment of Music Perception in Cochlear Implant Listeners

The cochlear implant (CI) restores substantial hearing in profoundly deafened adults and children. Cochlear implant signal processing strategies have been optimized for speech understanding in quiet, such that most postlingually deafened adults with implants can now recognize 70% to 80% of sentences presented in quiet (1). However, music perception and appraisal, although highly variable, remain generally poor for CI listeners (2–5). Still, many CI recipients have indicated that music is an important part of their lives and auditory experience and have expressed a desire to enjoy music again (6). The definition of music differs among various cultures and social milieus. In addition, there are numerous subjective factors influencing enjoyment, including personal preferences for musical genre and situational context, such as the listening environment and the listener’s mood. These subjective factors can all greatly affect music appraisal and thereby render appraisal difficult to measure. Thus, many studies focus on the objective characteristics of sound, which can be described in terms of physical parameters of the acoustic signals (7). Several structural features of music that have been examined with regard to music perception include rhythm, pitch, melody, and timbre. Timbre is the attribute of sound that enables one to differentiate between sounds having the same pitch, loudness, and duration, such as when distinguishing the same musical note played on different instruments. Previous studies have shown that CI recipients have perceptual accuracy similar to normal-hearing adults for simple rhythms presented at a moderate tempo. However, CI recipients are significantly less accurate than normal-hearing adults on perception of pitch, pitch patterns, melodies, and timbre (5–10). In one study on the cases of 49 CI listeners, Gfeller et al. (8) found complex pitch direction discrimination thresholds ranging from 1 semitone to 2 octaves (24 semitones), with a mean of 7.6 semitones. This can be interpreted to indicate that on average, CI users require complex tones to be more than 7 notes apart on the western musical scale to correctly identify which one is higher in pitch. In comparison, normal-hearing listeners demonstrated a mean threshold of 1.1 semitones. Melody and timbre identification are similarly poor: in open-set recognition tasks, CI users scored an average of 12% correct in melodies and 47% correct in instrument recognition, compared with 55% and 91%, respectively, for normal-hearing listeners (8,10). Melody recognition was better for melodies with distinctive rhythms. Gfeller et al. (8) suggest that advanced age and greater length of profound deafness have a negative impact on melody recognition of implant recipients. Timbre recognition has a weak negative correlation with age, length of implant use, speech processing, and cognitive measures of sequential processing (10,11). Appraisal tests have shown that CI listeners give higher ratings to the lower-frequency instruments in each family; however, in identification tasks, CI listeners often mistake instruments from different families for the target item (10,11). No commercial strategy or device has been objectively demonstrated to be superior for music perception. Until recently, CI development has focused on improving speech recognition in quiet. Accordingly, implant technology has implemented a vocoder approach, which preserves the temporal envelope of frequency-specific bands but greatly limits the delivery of temporal fine-structure information important for perceiving music (12). Such information is also important for the understanding of tonal languages (13), speech perception in noise (14), and the perception of interaural time differences for sound localization (15). The delivery of spectral information is also limited to about 6 to 8 functional frequency channels (1). Future technologies that improve the delivery of temporal or spectral information could enhance music perception, and a practical, valid, and reliable test is a necessary tool for evaluation. Because of the importance of music and these related tasks, some tests of music perception have been developed. Gfeller et el. (2,9,16) began by adapting the Primary Measures of Music Audiation test and also developed the Musical Excerpt Recognition Test. These are lengthy tests of open-set recognition and music appraisal, which can take many hours and require trained musical personnel to code the responses. Many other groups have also assembled in-house tests to evaluate novel CI strategies and designs developed by their laboratories (14,17). These instruments used in these studies were designed to address specific research questions regarding perception of different structural features of music. The methodologies used are often similar, but they were not intended to be standardized tests and it is not possible to directly compare the results across laboratories. Thus, we have developed a short, computerized test, the University of Washington Clinical Assessment of Music Perception (CAMP), comprising pitch direction discrimination, melody identification, and timbre identification. In this study, we describe the test stimuli and protocol, discuss considerations in developing a test that is clinically practical, and report preliminary results.