  In multi speakers environments, cochlear implant (CI) users may attend to a
target sound source in a different manner from the normal hearing (NH)
individuals during a conversation. This study attempted to investigate the
effect of conversational sound levels on the mechanisms adopted by CI and NH
listeners in selective auditory attention and how it affects their daily
conversation. Nine CI users (five bilateral, three unilateral, and one bimodal)
and eight NH listeners participated in this study. The behavioral speech
recognition scores were collected using a matrix sentences test and neural
tracking to speech envelope was recorded using electroencephalography (EEG).
Speech stimuli were presented at three different levels (75, 65, and 55 dB SPL)
in the presence of two maskers from three spatially separated speakers.
Different combinations of assisted/impaired hearing modes were evaluated for CI
users and the outcomes were analyzed in three categories: electric hearing
only, acoustic hearing only, and electric+acoustic hearing. Our results showed
that increasing the conversational sound level degraded the selective auditory
attention in electrical hearing. On the other hand, increasing the sound level
improved the selective auditory attention for the acoustic hearing group. In NH
listeners, however, increasing the sound level did not cause a significant
change in the auditory attention. Our result implies that the effect of the
sound level on the selective auditory attention varies depending on hearing
modes and the loudness control is necessary for the ease of attending to the
conversation by CI users.
