4.2 Key findings and clinical applicability
To find whether hearing thresholds influence hearing-aid use, we compared them with hearing-aid use for PTA4 for each AHL subtype. Only one hearing threshold at 1 kHz in the better ear was significantly lower for those who continued hearing-aid use. This is not a commonsense result, but it is interesting. These findings could be explained by the active role of the ipsilateral minor pathway in the central auditory nervous system (CANS).13, 14 The main pathway of a healthy ear goes to the contralateral CANS, but there is a minor pathway to the ipsilateral CANS, which means that an intact auditory pathway in a healthy ear can guarantee binaural interaction when AHL is treated monaurally in the worse ear.15, 16A second explanation comes from the main role of a patient’s better ear in hearing and listening. In many patients with AHL who are fitted monaurally in the worse ear, aided hearing in the worse ear remains supplementary, especially in situations in which the sound of interest is soft and arrives from the side of the worse ear. Sound localization is needed to locate the person speaking in a group conversation or where there are multiple talkers or noise. The better ear still plays the main and crucial role when the sound of interest arrives from the front or the side of better ear, sound localization is needed to locate only one talker, or a single talker is speaking in a noisy place.17
We found only one audiometric parameter (a hearing threshold at 1 Hz for the better ear) that affected the outcome of hearing-aid use for AHL patients with an aid in the worse ear, like previous studies.6 This demonstrated the importance of hearing in the better ear when AHL is amplified monaurally in the worse ear. This result accords with previous reports stating that preserving the ear with the better auditory threshold significantly improves the intelligibility of speech-in-noise.18