The effects of informational versus energetic masking on tinnitus minimum masking levels

Abstract

Recent tinnitus research suggests an important role for attention in tinnitus perception, particularly within the context of Auditory Scene Analysis and the relative salience of exogenous and endogenous auditory objects. Similar proposals have been made for mechanisms underlying informational masking, which appears to affect cognitive processing and the ability to focus attention selectively on target auditory streams. Based on these theories suggesting influence of attentional mechanisms on both tinnitus and informational masking, the primary aim of this study was to determine if informational masking would result in lower tinnitus minimum masking levels (MML) than energetic masking. Stimuli known to produce informational masking (one-, four- and seven-talker speech) and energetic masking (one-, fourand seven-talker reversed speech and speech-modulated noise) were randomly presented to 22 participants with constant tinnitus. Tinnitus MMLs for each stimulus was measured and participants were asked to subjectively rate the stimulus. A comparison between speech and reversed speech revealed no difference in tinnitus MMLs in a mild-to-moderate tinnitus severity group, but a lower tinnitus MML for the four-talker speech stimulus was found in a severe tinnitus group. A comparison of the speech and speech-modulated noise stimuli revealed lower tinnitus MMLs for speech in the severe tinnitus group and the opposite effect for the mild-tomoderate tinnitus group. No difference between the reversed-speech and speech-modulatednoise masking stimuli was observed for either tinnitus severity group. In addition, the one-talker masking stimuli across all three masking types resulted in higher tinnitus MMLs than the fourand seven-talker masking stimuli for both tinnitus severity groups. Stimuli preference ratings revealed that, on the whole, the most preferred stimuli resulted in the lowest tinnitus MMLs for the severe tinnitus group; however this was less clear for the mild-to-moderate tinnitus group. Overall, the results suggested that informational masking resulted in lower tinnitus MMLs in individuals with severe tinnitus than the equivalent energetic masking stimuli. These results were interpreted as indicating that in cases of severe tinnitus perception informational masking disrupts the attentional or cognitive resources allocated to tinnitus, resulting in lower tinnitus MMLs. For the mild-to-moderate tinnitus group, the results suggested that acoustically similar, but subjectively different, masking stimuli affected tinnitus MMLs in different, as yet to be determined, ways. The study suggests that individuals experiencing severe tinnitus may constitute a special clinical sub-group. The primary finding of the study, that informational masking resulted in lower tinnitus MMLs in participants with severe tinnitus, could potentially provide insight into the underlying mechanisms of both tinnitus and informational masking.