Research into the Sensitive Personality

A growing body of research supports the notion that certain types of people are predisposed toward extraordinary sensitivity. These findings approach sensitivity from two equally valid perspectives:

  1. As a reaction to minute changes in a person’s internal state; and
  2. As responsiveness to changing conditions outside the individual.

This look at the science and psychology of sensitivity begins with the nature of sense perception itself.

Inborn Sensory Differences

“No two people live in the same sensory world,” observes Paul Breslin, a neuroscientist at the Monell Chemical Senses Center in Philadelphia. “The world you see, the food you taste, the odors you smell – all are perceived in a way unique to you.” Testing at the Monell Center demonstrates, for example, that a bitter chemical known as PTC (phenylthiocarbamide) can be tasted by some people at the vanishingly small concentration of 18 parts per billion. But if the concentration is high enough – say, 360 parts per million – everyone can taste it. In the realm of scent, there’s a similar finding: some people with cystic fibrosis can detect certain smells at levels ten thousand times weaker than the norm

The implications of this research are profound. When one considers that virtually everything we know about ourselves and the world is based on information obtained through the senses, the fact that objective differences exist between people suggests that our ‘consensus’ reality may encompass a far wider spectrum than previously appreciated.

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High Sensitivity

Elaine Aron, a clinical psychologist, has written extensively about Highly Sensitive Persons (HSPs), a term she coined based on interviews or consultations with thousands of individuals. Aron describes HSPs as: “born with a tendency to notice more in their environment and deeply reflect on everything before acting…They are also more easily overwhelmed by ‘high volume’ or large quantities of input arriving at once.”

While some HSPs report having at least one sense that is very keen, their entire bodies process information more thoroughly than other people. HSPs are thus more affected by pain and various medications, and have more reactive immune systems and more allergies.

HSPs are also highly empathetic, feeling their own emotions and paying heed to others’ most intensively. They tend to have rich inner lives, with complex, vivid dreams. They can come across as highly perceptive, creative and intuitive when able to surmount what often is a natural inclination toward shyness, fearfulness, stress, and withdrawal.

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High and Low Reactors

Two Harvard University psychologists, Jerome Kagan and Nancy Snidman, have done much to document that people fall naturally into one of these two categories. In their book The Long Shadow of Temperament, Kagan and Snidman note that approximately one-fifth of the young children they’ve studied are ‘high reactors’ who demonstrate high levels of discomfort or distress at novel stimuli or situations. The 40% who are ‘low reactors,’ in contrast, welcome and adapt to new experience. This pattern typically extends into adolescence and beyond.

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Sensory Defensiveness

Psychologist Sharon Heller expounds on what she terms ‘sensory defensiveness’ in her book Too Loud, Too Bright, Too Fast, Too Tight. The individuals she points to have been unusually sensitive as long as they can remember. Their parents will often recall that, as infants, they may not have liked being cuddled, or that they had an exaggerated reaction to sounds, tastes or smells.

However, writes Heller, “any trauma that disrupts the nervous system at any age can generate sensory defensiveness," including head injury and psychological abuse. Such severe or long-standing trauma can “alter brain chemistry and literally rewire the brain."

Sensory overload, however acquired, can increase stress as well as vulnerability to illness. Heller implicates the body's fight-or-flight system. In people who are sensory defensive, she says, this system is constantly in operation. Environmental stimuli that wouldn’t trigger a stressful reaction in other people cause a chronic stress response in these individuals.

Once the immune system is depleted and the body succumbs, the stage is set for a variety of ailments, including:

  1. chronic fatigue
  2. sleep difficulties
  3. decreased ability to concentrate
  4. high blood pressure
  5. headaches
  6. irritable bowel syndrome
  7. ulcers and gastrointestinal problems
  8. allergies and skin disorders
  9. aching muscles
  10. chronic pain
  11. depression
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Sensory Processing Disorder

This condition was first described by an occupational therapist, the late Dr. Jean Ayres, as revolving around difficulty handling information coming through the senses. She likened SPD to a “traffic jam in the brain,” whereby the individual fails to recognize where a given sensation is coming from and whether that sensation is important or trivial, dangerous or benign. Children, whose nervous systems are still developing, are especially affected.

Two senses, beyond the usual five, appear to be affected: the proprioceptive and vestibular systems. These indicate, respectively, where our limbs are in relation to the rest of our body and how our body is oriented in space. Examples of difficulties with these senses include:

  1. Having shaky balance or difficulty maintaining an upright position
  2. Not using the left and right sides of one’s body in a coordinated manner
  3. Being unsure how to carry out new or unfamiliar movements
  4. Bumping into people and things and being generally clumsy

In addition, children with SPD may have extreme reactions to sensory stimuli that their peers take for granted. (In this respect, the condition overlaps with High Sensitivity and Sensory Defensiveness.)

Such children will feel overwhelmed, confused, and/or tormented on an ongoing basis. Their frustration, in turn, frequently translates into problematic behavior: irritability, jumpiness, full-blown tantrums. To parents, teachers, and peers, this behavior occurs for no apparent reason and is interpreted as moodiness, stubbornness, spaciness, or just plain disrespect. Children with SPD become ostracized and labeled as discipline problems or as learning disabled.

Some kids with SPD report anomalous perceptions. Allergies and other immune issues crop up as well.

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Thin Boundaries

The personality construct of Boundaries was developed by Ernest Hartmann, a psychiatrist and sleep disorder researcher. He asserts that each person can be characterized on a spectrum of boundaries from thick to thin.

Thick boundary people “strike[s] us as very solid and well organized; they keep everything in its place. They are well defended. They seem rigid, even armored; we sometimes speak of them as thick-skinned.” At the other end of the spectrum, thin boundary individuals are “especially sensitive, open, or vulnerable. In their minds, things are relatively fluid.”

Other characteristics of the thin boundary personality type are:

Thin boundary individuals, Hartmann proposes, are unusually sensitive from an early age, so they react more intensively to the usual traumas and difficulties of childhood. They are easily hurt, with intensely emotional memories carried into adulthood.

At least 5,000 people have taken the Boundary Questionnaire and more than 100 papers reference this robust concept. Hartmann believes it is not just a useful way to describe salient psychological differences but will be shown to reflect actual variations in neural and somatic functioning.

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Rather than assume that physical sensitivities predate or condition the psychological consequences, perhaps an individual's highly-charged psychological issues can be transmuted into physical symptoms such as asthma and other forms of allergy, chronic pain and fatigue, and sleep disorders.

This is the approach taken by Ian Wickramasekera, a psychologist intrigued by the psychosomatic nature of certain illnesses. "Put simply," he writes, "the [individual] is being…made sick by distressing secret perceptions, memories, or moods that [he/she] blocks from consciousness." The affected person can become hypersensitive and/or absorbed in the problems of others to such an extent that somatic symptoms develop out of his/her 'surplus empathy.' This process he terms Somatization.

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Kazimierz Dabrowski (1902-1980), a Polish physician interested in personality development, studied 'gifted' individuals and noted five recurring traits. These he termed ‘over-excitabilities’:

'Over-excitability,' the translation of Drabowski's concept into English, is meant to convey the sheer abundance of energy possessed by gifted individuals and manifested in these areas. He believed that, by virtue of such energy, they not only think differently from their peers, they also register perceptions more intensively and feel things more deeply.

Interestingly, profoundly gifted children (e.g., prodigies) are known to relate accounts of what appear to be ‘past lives.’ These children – particularly between the ages of 3 and 5 – may speak of their “other mothers” from “before” when they lived someplace else. They may (often with intense feeling) identify places they supposedly frequented and things they supposedly did. They may also tell of seeing or speaking to relatives or friends who have died, and insist that the interactions are real.

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The thin boundary trait of immersing oneself in something is termed 'absorption.' As articulated by psychologists Auke Tellegen and Gilbert Atkinson in 1974, it is “a disposition for having episodes of total attention… result[ing] in a heightened sense of reality of the attentional object, imperviousness to distracting events, and an altered sense of reality in general." Some statements conveying this capacity are the following:

Absorption is closely related to both hypnotic susceptibility and dissociation (the sense of being distant from oneself, numb, or on automatic pilot). Lines between what is manifestly real and what is imaginary become blurred as the person becomes immersed in some reverie or experience. Such deep experiences are sometimes perceived as mystical or transcendent.

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Psychologists Sheryl Wilson and Theodore Barber in 1983 profiled what they called the ‘fantasy-prone personality’ based on a study of 52 female subjects. These women engaged in vivid fantasy much of the time, and experienced what they imagined “as real as real.”

Their capacity for fantasy was often evident from an early age, and appeared to be built on a profound involvement with sensory experience. A fantasy-prone person will, for example, while "watching a bird or looking at a tree…suddenly lose the sense of their body and feel they are the bird or the tree." Or they will 'see,' 'hear,' 'smell' and 'feel' what is being described during a conversation – an ability remarkably close to synesthesia. Imaginary companions, imaginary worlds, and imaginary sensations may be conjured up and experienced as if they are the real thing. The experience is akin to a full-fledged hallucination.

To a great extent, fantasy-prone persons see themselves as psychic and report many anomalous perceptions, such as telepathy, precognition, being out-of-body, seeing or hearing apparitions, and having an anomalous influence on electrical appliances.

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The idea that certain people have an exceptionally fluid ‘connectedness within’ has a distinguished history. An early exponent was psychologist William James, who, along with many of colleagues, was much taken with ‘subliminal consciousness.’ Today the concept is advanced by Australian researcher Michael Thalbourne, who has updated and refreshed it.

Thalbourne defines transliminality as “the tendency for psychological material to cross thresholds in or out of consciousness.” Persons who are highly transliminal, he says, would be expected to have mystical, creative, and psychic experiences based on material bubbling up from the preconscious. Such perceptions would rarely occur to individuals low in transliminality. Studies done by Thalbourne and his colleagues disclose nine aspects of this personality trait:

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Context Induced Experiences

A key question that arises with regard to both fantasy-proneness and high transliminality is: What, exactly, is crossing into awareness? To what extent is the imagery or perception an accurate representation of what’s in the external environment, versus a reflection of one’s internal feelings or preoccupations? Put another way, how likely is it that this type of individual is so empathetic and so suggestible that legitimate external stimuli prompt his/her internal imagery machine to manufacture an experience that’s mistaken for real?

Apparitions can certainly be provoked by an intense need for something: think of island castaways conjuring up a realistic rescue ship or parched nomads visualizing an oasis in the desert. And some people can easily be tricked into ‘sensing’ that which does not exist. This was memorably demonstrated one April Fools on BBC Television, when viewers were told by a respected professor that it was now possible to broadcast smells – and that the aromas of onion and coffee could be perceived by anyone doing enough concentrating on his/her end of the television. Hundreds of viewers wrote in to say that they had, indeed, picked up those particular scents (along with a few others not mentioned).

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Genetic Basis for Sensitivity

One of the key results of the Environmental Sensitivity Survey (PDF, 10pp, 240KB) is that ‘sensitive’ respondents were more than twice as likely as controls to indicate that an immediate family member was affected by the same physical, mental, or emotional conditions as they themselves checked on the survey. This suggests that anomalous perception itself may have a genetic basis.

Several pieces of recent research stand out. Carla Shatz, a neurobiologist at Stanford University, has shown that a particular protein molecule – previously thought to be solely a part of the immune system – plays a critical role in early brain wiring. While her discovery was made in mice, the same might be found to apply to humans. In fact, Shatz notes that the gene associated with this protein in humans is located on a chromosome segment that has been implicated in a number of neurological disorders, including dyslexia. "It is time for people to think out of the box," she remarks. "All bets are off when it comes to how these immune molecules are functioning in the brain."

A relationship between dyslexia, migraine headache and allergies had been postulated by the late Norman Geschwind, a predecessor of Schatz’ at Harvard. In this context, it may be noteworthy that 14% of the respondents to the Environmental Sensitivity Survey indicated they were dyslexic – versus none of the controls.

Another researcher, Lisa Boulanger of the University of California – San Diego, is exploring whether the seeds of autism might be planted in babies whose mothers are affected by viral infection during a particular juncture in their pregnancy. Could it be that an over-stimulated immune system affects the baby’s developing brain? Boulanger points out, as others have, that autism is often accompanied by sensory overload, and sees this as a clue: perhaps the children of mothers who had challenges to their immune system during pregnancy lack the ability to filter out extraneous sensory information. “All of these things are just correlated in a very interesting way,” she observes.

Speaking of interesting, a remarkable inherited difference has been found for – of all things – dancing. An Israeli study of 85 dancers and advanced dancing students found that they have variants of two particular genes whose expression is linked to spiritual experience as well as social communication. This suggests that certain people literally “born to dance,” according to researcher Richard Ebstein. “The genes we studied are…related to the emotional side of dancing – the need and ability to communicate with other people and a spiritual side to their natures that not only enables them to feel the music but to communicate the feeling to others via dance.”

Memory, too – or at least certain forms of it – appears to have a genetic basis. Persons with a particular gene variant have been found to be twice as good at remembering emotionally charged events as individuals with the more common version of the gene. Given that individuals with ‘thin boundaries’ retain vivid childhood memories – particularly of perceived trauma – the implications for sensitivity are obvious.

It’s likewise been found that people with variations in a particular stress-related gene appear to have been affected more strongly by abuse at an early age than comparable individuals without this particular genetic variation. The terrible legacy may persist into adulthood in the form of Post Traumatic Stress Disorder (PTSD). If such a susceptibility is inherited, it’s fair to wonder if anomalous experience – which the sensitivity survey links to childhood trauma – has a genetic basis as well.

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