The Effect of High Frequency Stimulation and Different Masking Bandwidths on Tinnitus Perception

Abstract

Aims and objectives: Tinnitus can be defined as the perception of sound that does not exist in the external environment. A common treatment for tinnitus is use of real sound: sound therapy. Sound therapy is commonly undertaken using ear-level devices, which have a maximum high frequency limit of 6000-8000 Hz, often below tinnitus pitch. Although some researchers believe that the frequency of sound relative to tinnitus pitch is not important, others believe that the most effective therapeutic sound will incorporate the tinnitus pitch range. The devices used in this study (Austar Lenx 16 Receiver-In-The-Ear combination hearing devices) had a masking output up to 16000 Hz. This study was undertaken to explore the effects on tinnitus perception (loudness and annoyance), noise perception and masking function of extending high frequency masking noise. Methods: Sixteen participants had psychoacoustic (e.g. audiometry, pitch, loudness) and psychometric (e.g. Tinnitus Functional Index) assessments. Masking functions were determined by first finding threshold and minimum masking level (MML) for 4 different bandwidths of bilateral therapeutic sound (broadband noise, high pass, low pass and filtered relative to hearing loss), and then having participants rate tinnitus loudness and annoyance, masking noise loudness and annoyance, and mixing point on 11-point rating scales as the level was increased from threshold to MML. Both the rating at MML and the slope (change in rating as a function of masking intensity) were calculated and analysed. Results: There was no significant difference between the noise loudness, noise annoyance or mixing point ratings for the bandwidths. However, there was a statistically significant difference for tinnitus annoyance: at MML, the broadband noise bandwidth resulted in significantly lower tinnitus annoyance than the high pass, low pass or filtered conditions. In addition, the high pass and filter bandwidths yielded less tinnitus annoyance than the low pass condition at MML. Conclusions: Results indicated a broader bandwidth yielded a greater effect of masking stimulation on tinnitus perception.