March 5, 2013
There are many effects that cochlear implants have on individuals with impaired hearing. Music is a major aspect of hearing that is affected by the presence of a cochlear implant in these individuals. Characteristics like pitch, rhythm and meter, melodic contour, and timbre are those that most affect the perception of music in those who have cochlear implants. By understanding the differences in musical perception caused by having cochlear implants, researchers can develop technology that will greatly advance the hearing quality of these listeners. This could certainly lead to improvement in speech perception in hearing-impaired individuals.
Previous studies have found that pitch perception is the most difficult aspect of music to distinguish for individuals with cochlear implants (CIs). Pitch is the highness or lowness of a sound. It is described as the perceived frequency of complex tones that is heard by the human ear (Drennan and Rubinstein, 2008). Pitch is also known as the rate of vibrations of a sine wave that travel through the air per second, and it is expressed in Hertz (Hz).
The temporal coding theory states that the repetition rate of a pitch relies on the complexity of the tone. These repetitions that average up to 2,000 Hz correspond to locations on the basilar membrane in the cochlea in normal hearing individuals. In CI listeners, the average pitch repetition does not extend above 300 Hz. This limit of 300 Hz corresponds to the middle-C note on the piano, which implies that it would be more difficult to perceive pitches with a fundamental frequency higher than that note (Looi, McDermott, McKay, and Hickson, 2008). Because of the limited range of frequencies that can be heard clearly in users with CIs, musical perception is skewed. This muddles songs that are composed of complex melodies and makes the melodic patterns difficult to understand. Even changes in dynamics, or the gradual intensity changes of a piece of music that range in loudness from 10 to 20 dB, can affect the pitch perception of hearing-impaired individuals (Drennan and Rubinstein, 2008).
In a test comparing the musical perception of cochlear implant users and hearing aid users, the group of individuals with hearing aids scored better on the tasks that involved pitch perception. This is due to the fact that the pitch filtered through the cochlear implant and the pitch that corresponds to a certain location in the cochlea is not identical (Looi, McDermott, McKay, and Hickson, 2008). The most difficult pitch perception task associated with individuals who have impaired hearing is detecting a change between two pitches or note intervals. In tasks with a single repeating tone, CI listeners could detect a small pitch change of .5 semitones; however, it wasn’t the highness or lowness that changed, but the quality of the sound. CI users only perceived a change in highness and lowness when there was an interval greater than 4 semitones (Vongpaisal, Trehub, and Schellenberg, 2006).
If CI users are able to use more advanced technology to perceive the differences in pitches of music, they would be able to discriminate between speech sounds of their native language and foreign languages more easily. Not only would they have a better ability to perceive speech, speech with background noise would become less of an obstacle to decipher (Vongpaisal, Trehub, and Schellenberg, 2006).
Melody recognition is also a major characteristic that affects the perception of music in hearing-impaired individuals. A melody is a sequence of notes that is played on a musical instrument. Contour or melodic contour is the movement of the melody or pitches in an upward or downward pattern. The results of the Montreal Battery for Amusia (MBEA) showed that CI listeners are not able to effectively perceive...