Sound Sensitivity and Auditory Gating Study
Marina Kliuchko of the Cognitive Brain Research Unit at the Institute of Behavioural Sciences (University of Helsinki, Findland) and colleagues sought to better understand and more specifically measure the neuralmechanisms related to noise sensitivity (NS). In their study noise sensitivity is described as both physiological and psychological states that increase an individual’s reactivity to noise. The authors note that NS is not synonymous with hyperacusis, tinnitus or neurologic disorders in which sound sensitivity is a symptom. In addition, the causes of NS are poorly understood, are often nonspecific to noise sources, and encompass a wide range of reactions to sound. The authors report that NS is estimated to disturb between 20-40 % in the general population, whereas high sensitivity to noise is estimated to be between 12-15%.
In this study, the authors describe NS as a factor that moderates noise and the reactivity that it induces, and they also point out that NS has negative impacts on physical and mental health.
Using a combined electro- and magnetoencephalography (EEG/MEG), the researchers presented 71 subjects with a multi-feature mismatch negativity (MMN) paradigm. In a typical oddball task a subject would be asked to identify a deviant stimulus (or deviant stimuli) in a series of repetitive stimuli. However, in this combined MMN paradigm, a deviant noise with increasing intensity was embedded within an auditory complex context (in this case music) along with 5 other deviant features (i.e. pitch, rhythm, location, and intensity). As the authors note, this paradigm has more ecological validity as it more closely resembles a typical noise environment relative to the oddball task’s repetitive tones.
The authors compared the automaticity of sound processing and the ability to discriminate the deviant sound feature within the more complex auditory context between High NS subjects and Low NS subjects. Results indicated that High NS individuals have more difficulty with general auditory encoding, as well as difficulty with auditory discrimination(particularly of noisy sounds). In addition, High NS individuals demonstrated higher nervous system arousal in the “noisy conditions” relative to the Low NS individuals.
Higher NS individuals also demonstrated attenuated auditory gating ability. Auditory gating refers to the way in which the central nervous system inhibits responsivity to repetitive stimuli (gating out) and increases responsivity to novel stimuli (gating in). More specifically, the researchers speculate that the difficulty in the High NS groups was due to gating out (or filtering out) novel stimuli within a stream of complex stimuli. The authors discuss the predictive coding framework, in which perceptual experiences are organized hierarchically based on prediction. They speculate that the High NS group may be unable to “build a precise top-down prediction of sensory input due to an inaccurate encoding of sound features”.
In addition to providing support that physiological and psychological over responsivity to noises is neurological in nature, the authors state that more research is needed to understand individual differences regarding negative reactivity to noise.