Comment on "Elucidating the relationship between noise sensitivity and personality" by Shepherd et al.

Sir,

I read with particular interest the paper of Shepherd et al.[1] Their work is commendable as a stand-alone research and I think that one of its strengths was demonstrating and raising the key issues about our tentative operationalization of noise sensitivity (NS) and the absence of knowledge of its nature and origins[1] on which I feel compelled to elaborate further. While I will do so in a full-length paper describing the theoretical justification, here I present my basic arguments on the matter and I would appreciate the kind response and comment of Dr. Shepherd and his colleagues.

One problem of our operationalization of NS is the lack of heuristically derived first-person data and the unreliability of the second-person data that we operate with, that is, “noise sensitivity … [is] one of those terms most of us think we understand, but do not explicitly define except by default of the way we measure it.”[2] What we label as NS is just a psychometric construct with unknown corresponding psychobiological counterparts. A limitation of most psychometric questionnaires is that they are hypothesized to assess psychological phenomena that we cannot observe directly. While in clinical medicine, for example, we can measure hearing impairment through audiometry, NS questionnaires have only face validity; furthermore, proving convergent/discriminant validity of these psychometric instruments by correlating them with others does not overcome the validity issue; that is a case that can be made and extended to psychiatric validity in general.[3]

Another insightful paper of Shepherd et al.[4] discusses some recent developments regarding the quest of overcoming these limitations by identifying the electrophysiological substrate of NS. They reviewed four studies of the electrophysiological correlates of NS and underscored the viability of new approaches to study NS, with studies focusing on brain dynamics being scant. Lee et al.[5] made a qualitative inquiry into noise annoyance and sensitivity by investigating the corresponding changes in alpha rhythms and found alpha desynchronization when the participants were exposed to extremely annoying sounds. Heinonen-Guzejev et al.[6] took a different approach suggesting that NS influenced mismatch negativity response. However, they did not recognize the quintessential limitation of NS as a construct, namely, its lack of objective validity. The best one could hope is to establish the underlying physiological substrate of this construct but whether the latter represents NS as it was operationalized would remain unclear. On the other hand, if we first make qualitative inquiries into the psychobiological processes underlying these neural response patterns and then cross-validate these qualitative first-person experiences with objective brain dynamics data, it is to be expected that the validity of a NS questionnaire developed on this basis will be superior to questionnaires currently in use. Functional neuroimaging and electroencephalography might help to individualize psychometrical diagnostics by integrating neurobiology and psychoacoustics. A neuroscientific program known as neurophenomenology[7] might be capable of addressing the conflicting findings about NS that Shepherd et al.[1] and others have observed and allow us to construct a “gold standard” NS questionnaire. The basic concept of incorporating phenomenological investigation into neurodynamical studies is to transcend the conceptual, epistemological, and methodological gaps between subjective experiences and neural activity. We could reveal the invariant structures within and across different experiences that would otherwise have been inconceivable. Thus, the interpretation of neurobiological data would be facilitated, accounting for the fluctuations of the subjective cognitive context.[78] The neurophenomenological approach could serve as a starting point to generate hypotheses that would then be used to construct NS questionnaires with high validity. According to it once we link the psychometric dimensions of NS to functional changes in the activation of specific brain regions, we will no longer need these costly technological procedures to monitor the effectiveness of various interventions aiming at assessing people's NS but will rather use the newly validated psychometric instruments.

Finally, previous research has not only paid little attention to the origins and true nature of NS as noted by Shepherd et al.[1] but has also failed to conceive it as a modifiable entity. The idea of attenuating the high NS of vulnerable individuals is very appealing. Increasing individual awareness of our own experiences by being trained in phenomenological inquiry might allow us to modify the nature of these experiences and to stabilize and reshape them.[7] For example, the awareness of pharmacologically resistant epileptic patients of their preseizure experiential symptoms allowed them to preemptively interrupt the process and to avoid the seizure through motor, sensory, vegetative and mental countermeasures adopted once the patients relived their seizure.[9] If people are trained to direct their attention inward to their own perception of noise, they might be able to self-modify their NS. Our target structures regarding NS might be in the limbic region, in particular the amygdala and the hippocampus that are involved in noise experiences and can modulate cortical plasticity and activity.[10] In animal experiments, based on the emotional or motivational state of the animal, a regulation of noise processing at an early stage of the ascending auditory pathway is possible via the thalamo-amygdala-collicular feedback circuit.[11] In humans, the degree of amygdalar activation could be voluntarily modified in both positive and negative directions using emotional regulation strategies (for a review, see[12]). As a result, we might be able to exploit our evolutionary adopted self-regulatory faculties for maintaining social, emotional, and physiological stabilities. Therefore, it is quite encouraging to see that researchers acknowledge the importance of understanding the nature of NS.[1]

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