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Blog Archive - February 2016

Tinnitus Blog - February 2016

Something old, something new, something borrowed, something blue: tinnitus adaptation level theory.

What is tinnitus adaptation level theory, and how did I come up with this idea?

Tinnitus adaptation level theory is a framework that myself and colleges developed to try and explain the relationship between psychoacoustic measures of tinnitus, loudness especially, and how it affects the person in terms of tinnitus severity or handicap. Adaptation is either an increase or decrease in the sensory or psychological response that can vary with time. Adaptation is a key feature of many of the therapy components on Tinnitus Tunes. I’ve written a couple of scientific papers about this and you can use this link to access a paper entitled “An adaptation level theory of tinnitus audibility" that was published in 2012. Currently some of my students are working on trying to test the adaptation model (prove or disprove its validity). So how does such an idea develop?

Lets start with the “something blue”

People often report that their tinnitus is loud and annoying, but when it is compared to external sounds it is quite quiet. How can that be? Part of this relates to the difference between magnitude and loudness. In real life we don’t usually consider sounds just in terms of intensity (what a sound level meter would show as dB) usually we’d also take into account other aspects of the sound including pitch, timbre and context. For example I might find a neighbors hip-hop music really loud at 3 am on a Sunday, but think my classic rock music, while I’m driving in my car, is just right – even though my music may be more dB This is because I am in control, I like the sound and its not 3 am when I want to be sleeping and my music seems less loud. Actually it’s because it is lower in magnitude - a mix of many things not just intensity. Tinnitus has high magnitude but low dB because of how the brain works. So if we are blue (sad or depressed) tinnitus can seem louder – because the brain makes it seem that way. If we feel better, control the context and background sound levels we can change the perceived magnitude of tinnitus.

Something borrowed

Is there anything new in science? I’m sure that there is, but it would also be fair to say that if we look at other scientific fields sometimes we can borrow ideas and apply them to tinnitus. This is certainly the case here, as it has been with most if not all tinnitus theories. Tinnitus adaptation level theory has taken ideas from existing tinnitus models, pain research, mental health studies (even marketing) and distilled those on the basis of what we know about tinnitus. Which reminds me I must return some overdue library books I borrowed.

Something old

I was researching an article, looking for something in the library I now can’t remember; when I rediscovered something I had learnt about in psychology. I had completely forgotten about this from undergraduate classes (sadly that happens a lot). This find was Helson’s 1964 book about adaptation level theory. In scientific terms the 1960s is old, but this is where the science of adaptation level theory began. The Adaptation Level Theory (ALT) was formulated by Helson (1964) to conceptualize the effect of context on sensory perception and psychophysics. The adaptation level (AL) is the body’s internal anchor or reference point. The theory says that incoming stimuli are not processed in isolation but are always compared to this reference for estimating sensory magnitude and making perceptual and discriminatory judgments.

It even has a mathematical formula: A = XpBqRr

  • A is the adaptation level (the reference point) components
  • X the focal stimuli (the stimuli in the forefront which are being attended to)
  • B the background or contextual stimuli (they provide the context within which focal cues operate), and
  • R is the sum of residual factors such as anxiety and emotion.

It is noteworthy that some of these components are internal to the person (who we are) and some are external and can be controlled (background). The weighting coefficients p, q and r establish the relative contribution of each component towards the final adaptation level (p+ q+ r =1). These weighting coefficients can be influenced by attention and related processes.

Something new

The “new” was applying Helson’s ideas to tinnitus. In this application to tinnitus: tinnitus is the focal component, any background noise or applied sound therapy are contextual stimuli and residuals are individual factors such as past experiences, emotion and personality. Attention is a weighting factor. Judgements of tinnitus magnitude can change over time as a result of context (presence/absence of other sounds), residual factors and weighting factors. For persistent tinnitus, a high internal AL is established – thus the tinnitus is perceived as being of high magnitude. This occurs when tinnitus is the focus of listening. In a similar manner, stress and negative emotions can increase tinnitus magnitude even if remains the same loudness.

In next months blog….what evidence is there for ALT applying to tinnitus?

 

Published by:

Dr Grant D Searchfield

Senior Lecturer Tinnitus and Hearing Technology Audiology

The University of Auckland New Zealand +64 9 923 6316