Why Recoil at Unpleasant Noise Occurs
Unpleasant sounds such as fingernails down a chalkboard make us cringe. But, why do they make us cringe? Is it some special pitch of sound that produces this response, or is it something deeper?
In a study published today in the Journal of Neuroscience and funded by the Wellcome Trust, Newcastle University scientists investigated the interaction between the region of the brain that processes sound, the auditory cortex, and the amygdala, which is active in the processing of negative emotions when we hear unpleasant sounds. The responses were fairly surprising.
There is a hidden link between the emotional and auditory processing regions of the brain. When certain sounds occur,the link intensifies, and the activity shows up on fMRI. This means that emotional states are manipulatable by sound. That's an interesting discovery for many fields, and immersion in a virtual environment is certainly one of a great many possible applications.
"It appears there is something very primitive kicking in," stated Dr Sukhbinder Kumar, the paperís author from Newcastle University. "Itís a possible distress signal from the amygdala to the auditory cortex."
The researchers discovered that the activity of the amygdala and the auditory cortex varied in direct relation to the ratings of perceived unpleasantness given by the subjects. The emotional part of the brain, the amygdala, in effect takes charge and modulates the activity of the auditory part of the brain so that our perception of a highly unpleasant sound, such as a knife on a bottle, is heightened as compared to a soothing sound, such as bubbling water.Further experimentation has revealed a sound frequency range which triggers this unpleasant reaction. Literally any sound broadcast in the frequency range of 2,000 to 5,000 Hz triggered the same reaction. This opens up the possibility of embedding high-frequency sounds in otherwise normal sound files and dynamic sound creation systems to add a subconscious edge of unease to a given environment.
The researchers of course, did not have VR in mind when they conducted the study, and see medical applications for the same work.
Professor Tim Griffiths from Newcastle University, who led the study, stated: "This work sheds new light on the interaction of the amygdala and the auditory cortex. This might be a new inroad into emotional disorders and disorders like tinnitus and migraine in which there seems to be heightened perception of the unpleasant aspects of sounds."