Background to Training and Assessment Methods Use

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Proposed Tinnitus Generators Code for Silence?

Fowler (1939) asserted that even when exposed to a sound-treated room a ―high normal‖ ear may perceive sounds synonymous to ―myriads of insects in the distance‖ (Fowler, 1939) (page 1011). Fowler attributed this sensation to the findings of Fletcher (1929), describing the apparent perception of air molecules continuously colliding in the surrounding atmosphere. Heller and Bergman conducted their classic research involving a sound-treated chamber and 80 individuals with ―apparently‖ normal hearing thresholds, aged 18 to 60 years. Heller and Bergman (1953) were interested in learning more about the effects of subjecting individuals considered to have normal hearing, to surroundings with atypicallylow ambient noise. The research was driven by the observation that people lacking hearing impairment, and in good health, would occasionally report tinnitus-like sounds when environmental sound levels were limited to very soft intensities (Heller & Bergman, 1953).
After approximately 5 minutes in a low-sound setting thought to be between 15 dB and 18 dB (exact measures were unavailable due to sound-level meter limitations), 94% of normalhearing, adult participants reported tinnitus-like sounds with ―buzz‖, ―hum‖ and ―ring‖ described most often. The authors felt this indicated tinnitus is actually ever-present but normal ambient sound levels (generally above 35 dB) are adequate to mask it (Heller & Bergman, 1953). The Heller and Bergman (1953) study has been acknowledged as an important contribution but criticised as it is conceivable some of the presumably normalhearing participants may have had some detectable hearing loss, and were not formally assessed for this (Knobel & Sanchez, 2008). The Heller and Bergman (1953) study was also noted to lack gender and race-specific details (Tucker et al., 2005).
Tucker et al. (2005) essentially repeated a portion of the Heller and Bergman (2005) experiment with normal-hearing, young adults (N = 120, aged 18 to 30 years). Hearing was in this case, screened to confirm normal thresholds and participants were required to remain in a sound-treated booth for 20 minutes for a ―listening experiment‖ and provide a written account of any sounds heard. The booth was evaluated to ensure ear-level dB SPL was between 24 dB SPL (0.125 kHz) and 6 dB SPL (8 kHz). Results revealed that 64% reported tinnitus-like sounds. Findings were further broken down into gender specifics showing females and males were nearly equally matched for tinnitus emergence and race details revealing significantly more Caucasians (p<0.001) reported tinnitus-related sounds as compared to African American counterparts. The Tucker et al. (2005) study primarily highlighted significantly less sub-audible tinnitus as compared to Heller and Bergman (1953).
The findings were felt to argue against sub-audible tinnitus being considered a general feature, present for nearly all normal-hearing individuals in atypically quiet environs (Tucker et al., 2005).
A 2008 study again looked at silence and the emergence of tinnitus in individuals determined via assessment to have normal hearing (N = 66, aged 18 to 65 years) (Knobel & Sanchez, 2008). Knobel and Sanchez, in detailing the Tucker et al. (2005) study indicated the likelihood of auditory attention being activated by virtue of the experiment being described as a ―listening experiment‖ thereby priming those involved to attend for sound(s) (Knobel & Sanchez, 2008). Considering this, Knobel and Sanchez (2008) organised their methodology to account for different attentional domains (visual and auditory) and attentional load (problem-solving and non-problem solving). Three tasks were assigned: two which drew attention away from the auditory domain 1) problem-solving and 2) visual task, and one task which provoked auditory attention. The problem-solving task required participants to manipulate disks of varying sizes on a peg board in a particular order. The visual task had no problem-solving component but alerted participants that a change in lighting may, or may not, occur. The auditory task also lacked the problem-solving component but alerted participants 1 or more sounds may, or may not, be presented. Tasks were 5 minutes in duration, randomly presented to each participant, performed in a sound-treated booth, and required participants to report on any perception(s) (visual or auditory). It was hypothesised the emergence of tinnitus-like sounds in a low-ambient noise environment would be affected by auditory attention and expectancy. The tasks did reveal tinnitus-like sounds were perceived: by 19.7% of those who underwent the problem-solving task, by 45.5% engaged in the visual task, and by 68.2% for auditory task involvement. This study established the emergence of tinnitus-like sounds in situations with a lack of environmental sound but similar to Tucker et al. (2005), also confirmed significantly less sub-audible tinnitus compared to Heller and Bergman (1953).

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Spontaneous Activity

Eggermont (2000) concluded that with a normally-functioning auditory system the presence of spontaneous neural activity is a significant feature and remains essentially inaudible as we have habituated to it.
There has been some research supporting the theory tinnitus is the result of spontaneous firing rates (SFR), generated by auditory neural fibres (Evans, Wilson, & Borerwe, 1981). However, most research suggest tinnitus-related pathology is associated with a reduction in SFR (Kiang, Moxon, & Levine, 1970). This led to two theories: 1) that tinnitus may arise from the lack of SFR, 2) perhaps tinnitus occurs at the border of preserved and damaged hair cells, where SFR would vary greatly between regions (Kiang et al., 1970). It has been theorized that the drop in SFR, whether drug-induced or noise-induced, is likely related to a disparity in excitatory and inhibitory responses transmitted to, and impacting, the auditory cortex (Eggermont, 2010). It remains uncertain whether greater SFR corresponds to tinnitus perception (Eggermont & Roberts, 2004). Although there have been animal-based studies of tinnitus suggesting change in spontaneous firing in the auditory nerve there exists a paucity of findings establishing reliable generalisation of such findings to humans (Adjamian et al., 2009).

Chapter 1. Introduction
Chapter 2. Literature Review
2.1. Auditory System Anatomy and Physiology
2.2. Measuring Central Auditory Activity
2.3. Attention: Definition and Brief History
2.4. Attention Terminology and Techniques
2.5. Attention Models and Theories
2.6. Attention: Auditory and Visual Domains
2.7. Attention-related anatomy and networks
2.8. Limitations of Attention Research
2.9. Attention Treatments and Disordered Attention .
2.10. Tinnitus: Definition and Brief History
2.11. Tinnitus: Proposed Aetiologies and Sustaining Factors
2.12. Tinnitus: Underlying Pathophysiology .
2.13. Tinnitus: Assessment and Measurement
2.14. Tinnitus Treatments
2.15. Attention and Tinnitus
Chapter 3. Background to Training and Assessment Methods Use
3.1. Introduction
3.2. Studies informing the Main Study: Pilot or Small Studies?
3.3. Background to Attention Training and Tinnitus Assessment .
3.4. Assessment of Training Effects
3.5. Assessments
3.6. Summary
Chapter 4. Pilot Study A: CAB® Practise Effect(s)
4.1. Background and Aims .
2.2. Methods .
4.3. Results
4.4. Discussion
4.5. Conclusions .
Chapter 5. Pilot Study B: APT-IIm
Chapter 6. Pilot Study C: Computerised Auditory Attention Training
Chapter 7. Clinical Proof-of-Concept Trial of an Attention Training Game for Managing Tinnitus.
Chapter 8. Thesis Summary