Researchers have found that introverts actually process their worlds differently, which may explain why they respond differently to stimuli.
About twenty percent of people are born with this "highly sensitive" trait, which may also manifest itself as inhibitedness, or even neuroticism. The trait can be seen in some children who are "slow to warm up" in a situation but eventually join in, need little punishment, cry easily, ask unusual questions or have especially deep thoughts.
While such traits are relatively familiar because they are easy to observe, the researchers, have found evidence that for those with this innate trait, the actual underlying difference is in the brain's attention to details.
The study was conducted by Jadzia Jagiellowicz, Xiaomeng Xu, Arthur Aron, and Elaine Aron at Stony Brook University, along with Guikang Cao and Tingyong Feng of Southwest University, China and Xuchu Weng of the Chinese Academy of Sciences, Beijing, China.
The research, designed to validate the fundamental role of deeper processing of information, was published in Social Cognitive and Affective Neuroscience.
Sensory perception sensitivity (SPS), a personality trait characterized by sensitivity to internal and external stimuli, including social and emotional ones, is found in over one hundred other species, from fruit flies and fish to canines and primates. Biologists are beginning to agree that within one species there can be two equally successful "personalities." The sensitive type, always a minority, chooses to observe longer before acting, as if doing their exploring with their brains rather than their limbs. The other type "boldly goes where no one has gone before." The sensitive's strategy, sometimes called reactive or responsive, is better when danger is present, opportunities are similar and hard to choose between, or a clever approach is needed. It is not an advantage when resources are plentiful or quick, aggressive action is required.
Perhaps because those studying human personality have not focused on genetics and evolution until recently, these two fundamental innate styles in humans have been largely overlooked.
Stony Brook researchers Elaine and Arthur Aron had already found that those with a highly sensitive temperament are, compared to others, more bothered by noise and crowds, more affected by caffeine, and more easily startled. That is, the trait is about sensitivity. Further, they proposed that this is all part of a "sensory processing sensitivity." In other words, the simple sensory sensitivity to noise, pain, or caffeine is a side effect of an inborn preference to pay more attention to experiences.
Hints of this processing sensitivity were found in the observation that, compared to the majority of people, the sensitive ones among us tend to prefer to take longer to make decisions, are more conscientious, need more time to themselves in order to reflect, and are more easily bored with small talk. However, the theory that what created the difference was processing rather than mere sensitivity needed to be validated.
The research team used a questionnaire already known to separate the sensitive from the non-sensitive. Then the team used functional magnetic resonance imaging (fMRI) methods to compare the activity of the brains of sensitive and non-sensitive participants while they were in the process of looking for small differences in pictures.
The Stony Brook team proposed that differences in neuroticism and introversion are often due to something more fundamental, i.e. differences in the attention given to the processing of sensory information.