Investigation of temporal fine structure information and localization skills in normal hearing and hearing impaired adults

There is an asymmetric coding in the brain with the unilateral transmission of the auditory stimulus in individuals with unilateral total hearing loss and individuals with unilateral cochlear implants. The objective of the present study is to investigate the processing of acoustic temporal fine structure information cues in a holistic manner in individuals with unilateral hearing. 17 individuals with unilateral cochlear implants, 16 individuals with unilateral total hearing loss, and 18 individuals with bilateral normal hearing were included in the study. The Harmonic Intonation/Disharmonic Intonation tests, Azimuth Localization Test, and Hearing in Noise Test were applied to all participants. The results of the tests were compared between the three groups. A significant difference was observed in triple comparisons between groups in all tests (p<0.001). In paired comparisons, individuals with unilateral cochlear implants showed a significant difference with both groups in all tests (pa<0.016). While no significant difference was observed between the Harmonic Intonation/Disharmonic Intonation tests between the individuals with unilateral total hearing loss and individuals with bilateral normal hearing (pa>0.016), a significant difference was observed in the Azimuth Localization Test and Hearing in Noise Test (pa<0.016). It was concluded that although the acoustic temporal fine structure processing capacity was not affected by the asymmetric processing of the auditory input in the presence of unilateral total hearing loss, hearing in noise and localization abilities deteriorated when compared to normal hearing individuals. The weaker performance of individuals with unilateral cochlear implants than both groups revealed the performance weakness in cochlear implant systems. To the best of our knowledge, this study is the first study to reveal the performance of individuals with unilateral total hearing loss and unilateral cochlear implant users, by examining together the temporal fine structure information and the conditions it is related to, and their performances closest to their daily living environment.