In reverberant environments, most hearing impaired listeners are aware to the disturbance of the signals caused by the reverberation. However, when reverberation is minimum, the actual cause of disturbance is not clear to them and hence can be very frustrating.
Localising a sound source in the horizontal plane relies mainly on two different sources of information: The differences in time of arrival of the sound at the two ears, and the level differences at the two ears. These time and level differences are called interaural time differences (ITD) cues and interaural level differences (ILD) cues. Recent improvements in hearing aids, such as compression and filtering, can significantly alter ITDs and ILDs. The digital processing to input signals tend to restrict the availability of fine timing cues, forcing the listener to rely on level cues. The effect of digital processing in hearing aids on the hearing aid wearers use of localisation cues in different listening environments is not well understood.
The aim of this dissertation is to investigate the effect of reverberation on the localisation abilities of normal hearing and hearing impaired listeners. Moreover, to investigate the effect of Siemens Prisma 2M hearing aids utilizing the localisation cues. Two main sets of experiments were conducted, The first set (4 experiments) were performed on normal hearing listeners to study the effect of reverberation and signal onset/offset times on their localisation abilities for different stimuli signals (i.e. Speech, high-pass speech-low-pass speech, pink noise, 4 KHz pure tone, and 500 Hz pure tone and under different reverberant environments. The second set of experiments was conducted on twenty eight Bilateral Siemense Prisma 2M wearers. They were tested under both reverberant and anechoic conditions, with and without the hearing aids.