Examining the Roles of Residuals Under an Adaptation Level Theory Model for Tinnitus Perception

Abstract

Background: Tinnitus is the perception of sound in the absence of sound in the environment (1-4). The precise mechanisms giving rise to tinnitus perception and distress are still not fully known. The Adaptation Level Theory (ALT) model of tinnitus (5, 6) is an ecological framework which takes a holistic approach to understanding tinnitus and its complexity, in which tinnitus magnitude estimates are based on interactions between the focal component (tinnitus), contextual component (any background noise or applied sounds), and residual components (individual cognitive and behavioural characteristics). Aim: To empirically explore the influence and strength of individual residual factors under a novel Adaptation Level Theory (ALT) model of tinnitus perception. Personality traits, emotion and prediction/anticipation of sounds were residuals examined. Methods: Seven studies were undertaken as part of this doctoral thesis: 1) A scoping review investigated key personality traits relevant to tinnitus, and the relationship between affective disorders and tinnitus. 2) A web-based survey was administered to 154 individuals with tinnitus and 61 age, gender and hearing level-matched non-tinnitus controls. The survey measured four key self-reported personality traits (social closeness, stress reaction, alienation and self-control), tinnitus characteristics and hearing handicap. 3) A behavioural experiment (N=22) introduced short-term emotional stimuli, differing along valence and arousal dimensions, and measured tinnitus loudness and annoyance characteristics. Stimuli were presented in two modalities: auditory and visual. 4) A comprehensive narrative synthesis of current research assessed the feasibility of a relationship between auditory memory, predictive coding and tinnitus generation. 5) A short-term adaptation experiment (N=23) and two-week feasibility trial (N=7) compared the effect of predictable and unpredictable amplitude-modulated computer surf sound on tinnitus loudness and annoyance characteristics. 6) An electroencephalography (EEG) study that compared mean ERP amplitudes and oscillatory band activity in response to tone deviants and tone omissions (at the pitch of tinnitus) between individuals with tinnitus (N=16) and hearing-level matched controls (N=14). 7) A randomized tinnitus sound therapy clinical trial (N=18) was conducted comparing the effectiveness of nature sounds with neutral broadband noise. Multiple experimental outcomes relating to tinnitus, emotion, attention and psychological state were measured at three time points: at sound fitting, 4 weeks after administration and 8 weeks after administration. Results: 1) The scoping review concluded personality traits to have a consistent association with the distress experienced by adult tinnitus help-seekers, and help-seekers were also more likely to experience anxiety and depression symptoms and/or disorders. Limitations present in current research were lack of appropriately controlled comparisons when assessing personality trait profiles of tinnitus sufferers and non-tinnitus individuals. 2) Tinnitus sufferers displayed higher levels of stress reaction, lower social closeness, lower self-control and higher alienation than the control group in the web-based survey. 3) In the behavioural emotion experiment, low valence (unpleasant) auditory stimuli led to higher subjective tinnitus loudness ratings in males and females and higher subjective distress ratings in males only. Visual emotional stimuli did not have an effect on tinnitus characteristics. 4) The narrative review provided theoretical support and indirect electrophysiological evidence for continuous prediction errors generated within the auditory system driving tinnitus perception and distress, as well as eliciting global disruptions to attention and working memory. 5) Both short-term Unpredictable and Predictable sound administration led to a decrease in tinnitus loudness in the adaptation experiment, however, only Unpredictable sound lowered tinnitus distress ratings. 6) A larger N1c waveform was elicited in the absence of any tone deviation within the left primary auditory cortex of tinnitus participants for the EEG study. Abnormal N1c waveform growth was present across levels of deviant conditions for the tinnitus group. There was limited evidence to support the Thalamocortical Dysrhythmia hypothesis of greater theta and gamma activity present among individuals with tinnitus. A role for attention and auditory scene analysis in driving tinnitus perception and salience was supported. No differences were present between groups for tone omissions. Different levels of activity between tinnitus and control groups were observed in regions corresponding to attentional as well as limbic networks. 7) The administration of sound therapy led to significant reduction in tinnitus impact over 8 weeks; this effect was largely due to BBN sound therapy which resulted in significantly greater reduction of tinnitus impact compared to nature sounds. The positive effect of sound on tinnitus was supported by secondary tinnitus and psychologicalrelated outcome measures, but not interviews. BBN sound resulted in an increase in loudness level matches needed to match tinnitus; there was minimal change in loudness level matches for nature sounds. There were indications of individual preferences and individual outcome effects observed. The presence of tinnitus subgroups was apparent in terms of which sound was most favoured, which sound had the most benefit, as well as in how sound-tinnitus interactions occurred as time progressed. Conclusions: Personality traits, emotion and prediction all play a significant role as residual factors under the ALT model to shape final tinnitus perception and experience as well as in influencing response of tinnitus to introduction of external sound introduction. Overall, tinnitus magnitude appears to increase with high stress reaction, low social closeness, low self-control and high alienation personality trait levels, as well as by the introduction of unpleasant auditory stimuli. In contrast, the presence of sound therapy stimuli decreases tinnitus magnitude and demonstrates psychological benefit over time. This thesis provides some empirical support for the ALT model of tinnitus. Further research is needed to examine attention as a weighting factor, develop clinically useful indicators of ideal sound therapy levels under the ALT framework, as well as customize therapeutic sound to tailor for individual residual levels, needs and preferences over time. Development of computational models based on the ALT which integrate residual factors, weighting factors and tinnitusexternal sound interactions may be useful for delineating subgroups and predicting how an individual might respond to potential treatments. The findings from this thesis can form a basic computational template to build-on.