Music perception with temporal cues in acoustic and electric hearing

The first specific aim of the present study is to compare the ability of normal-hearing and cochlear implant listeners to use temporal cues in three music perception tasks: tempo discrimination, rhythmic pattern identification, and melody identification. The second aim is to identify the relative contribution of temporal and spectral cues to melody recognition in acoustic and electric hearing.

Both normal-hearing and cochlear implant listeners participated in the experiments. Tempo discrimination was measured in a two-interval forced-choice procedure in which subjects were asked to choose the faster tempo at four standard tempo conditions (60, 80, 100, and 120 beats per minute). For rhythmic pattern identification, seven different rhythmic patterns were created and subjects were asked to read and choose the musical notation displayed on the screen that corresponded to the rhythmic pattern presented. Melody identification was evaluated with two sets of 12 familiar melodies. One set contained both rhythm and melody information (rhythm condition), whereas the other set contained only melody information (no-rhythm condition). Melody stimuli were also processed to extract the slowly varying temporal envelope from 1, 2, 4, 8, 16, 32, and 64 frequency bands, to create cochlear implant simulations. Subjects listened to a melody and had to respond by choosing one of the 12 names corresponding to the melodies displayed on a computer screen.

In tempo discrimination, the cochlear implant listeners performed similarly to the normal-hearing listeners with rate discrimination difference limens obtained at 4-6 beats per minute. In rhythmic pattern identification, the cochlear implant listeners performed 5-25 percentage points poorer than the normal-hearing listeners. The normal-hearing listeners achieved perfect scores in melody identification with and without the rhythmic cues. However, the cochlear implant listeners performed significantly poorer than the normal-hearing listeners in both rhythm and no-rhythm conditions. The simulation results from normal-hearing listeners showed a relatively high level of performance for all numbers of frequency bands in the rhythm condition but required as many as 32 bands in the no-rhythm condition.

Cochlear-implant listeners performed normally in tempo discrimination, but significantly poorer than normal-hearing listeners in rhythmic pattern identification and melody recognition. While both temporal (rhythmic) and spectral (pitch) cues contribute to melody recognition, cochlear-implant listeners mostly relied on the rhythmic cues for melody recognition. Without the rhythmic cues, high spectral resolution with as many as 32 bands was needed for melody recognition for normal-hearing listeners. This result indicates that the present cochlear implants provide sufficient spectral cues to support speech recognition in quiet, but they are not adequate to support music perception. Increasing the number of functional channels and improved encoding of the fine structure information are necessary to improve music perception for cochlear implant listeners.