Highly sensitive person
A highly sensitive person (HSP) is a person having the innate trait of high sensitivity (or innate sensitiveness as Carl Gustav Jung originally coined it). According to Elaine N. Aron and colleagues as well as other researchers, highly sensitive people, which would represent about a fifth of the population, process sensory data much more deeply and thoroughly due to a biological difference in their nervous systems.  This is a specific trait with key consequences that in the past has often been confused with innate shyness, inhibitedness, innate fearfulness, introversion, and so on.  The existence of the trait of innate sensitivity was demonstrated using a test that was shown to have both internal and external validity. Although the term is primarily used to describe humans, the trait is present in nearly all higher animals.
The term highly sensitive person was coined by Dr. Elaine N. Aron in 1996, and the name is gaining popularity because it presents the trait in a positive light, as it posits shyness, inhibitedness, fearfulness as negative traits that may or may not be acquired by highly sensitive people and animals, depending on environmental challenges. Yet other names used to describe the trait in literature include 'introverted emotional temperament', 'chronic cortical/cortisol arousal', 'hypervigilance', and 'innate shyness'.
Dr. Aron describes the opposite end of the spectrum, "the opposite of a Highly Sensitive Person (HSP) is a person who takes many risks, that is acts without reflecting very much. An HSP who is an HSS (High Sensation Seeker) also will find ways to have lots of new experiences, but won't take a lot of unreflected-upon risks."  She also cites studies involving other animals ranging from mammals to houseflies and goldfish.

# Epistemological considerations
The approach adopted by Aron and colleagues questions the role of notions such as "shyness" in explaining basic differences in behaviour that are encountered in many species, including humans. 
As opposed to shyness, which is constructed as a negative trait, a genetic weakness that can be worsened by circumstances, the trait of high sensitivity is considered a basic, evolutionarily conserved trait with survival advantages in itself. Zoologists observed the existence of a shy-bold continuum in animal species:
... in sunfish a "shy-bold continuum" has been identified, in which "bold" individuals differ from "shy" ones in their propensity to approach novel objects (including minnow traps), eat certain food items, and acclimate to laboratory environments. The "shy-bold continuum" has also been observed in humans and several other mammals.
Zoologists are aware that notions of shyness and boldness are anthropomorphic (as exemplified by the use of quotation marks, above; "personality" is another term used with quotation marks). Some animals and even insects were shown to get survival advantages (avoidance of dangers) and even, as a consequence, reproductive advantages (availability for "exuberant" courtships behaviours)" from being "shy".
Faced with this apparent misnaming of a basic survival strategy, Aron and colleagues developed the notion of high sensitivity, expanding on Jung's suggestion of the trait innate sensitiveness, which he distinguished from his own notion of introversion. In support of this distinction, Aron showed that the Highly Sensitive Person Scale identified a sizable proportion of extraverted sensitive persons (30%). In addition, Aron provides evidence supporting that highly sensitive persons can also be highly sensitive to favourable social cues and respond with traits of extraversion.

# Research
The research on sensory-processing sensitivity, however, builds on Eysenck's views on introversion and arousal and Gray's work on the inhibition system. This research in turn builds on Pavlov's work on sensory response to both physical and mental overstimulation, and work by Jung and his contemporaries differentiating extroverted and introverted cognitive senstitivity types.  This research shows that about 15-20% of humans and higher animals have a nervous system that is more sensitive to subtleties. This means that regular sensory information is processed and analyzed to a greater extent, which contributes to creativity, intuition, sensing implications and attention to detail, but which may also cause quick overstimulation and overarousal.
This temperament may also have some correlation with continuously high cortisol levels, which may cause hypervigilance and susceptibility to trauma, or the same traumas may encourage hypervigilance, which in turn may contribute to high cortisol. Being highly sensitive may amplify or create psychological issues when overarousal occurs. The ability to unconsciously or semi-consciously process environmental subtleties often contributes to an HSP seeming 'gifted' or possessing a 'sixth sense'. Sensitiveness is often confused with shyness, but 30% of HSPs have extroverted personalities. Another common misconception is that only females can be HSPs - there are roughly the same number of male HSPs as female. The percentage appears to hold true for all animals possessing this trait."

# Attributes and characteristics
HSP students work differently than others. They pick up on the subtle things, learning better this way than when overaroused. If an HSP student is not contributing much to a discussion, it does not necessarily mean they do not understand or are too shy. HSPs often process things better in their heads or they may be overaroused. This can be the reason for their not contributing. HSPs are usually very conscientious but underperform when being watched. This also applies to work situations; HSPs can be great employees  good with details, thoughtful and loyal, but they do tend to work best when conditions are quiet and calm. Because HSPs perform less well when being watched, they may be overlooked for a promotion. HSPs tend to socialize less with others, often preferring to process experiences quietly by themselves.  

# Contrast with Dabrowski's overexcitability
Readers interested in HSP may want to compare and contrast Aron's approach with Dabrowski's concept of overexcitability in his theory of Positive Disintegration.

# Criticism
As explained above, many writers on HSP propose a positive, accepting attitude towards (being an) HSP. However, this is not the general consensus in the professional psychological community. E.g. Jeffrey E. Young, founder of the increasingly applied Schema Therapy, although never having been critical of HSP writers or writings, links high sensitivity, or as he calls it, the 'highly empathic temperament', with the Self Sacrifice Schema (Young, 2003, p. 246-251), which in turn is almost always related to the Emotional Deprivation Schema. In his opinion, these persons (patients) need to learn to focus on themselves instead of others and to learn to get their own needs met, needs they typically are not aware of. As such, HSP can be seen not as a positive personality trait, but as a psychopathological condition that can be treated with experiential, cognitive, behavioral and limited-reparenting strategies.

# Rebuttal of the criticism
That naturally sensitive individuals tend to be more empathic, unselfish and self-sacrificing is probably a correct, neutral observation. However, whether these traits are positive or negative depends on the situation and what one does with them.
Self-sacrificing can go too far and become self-destructive, but the opposite - to be uncaring and selfish - is usually not considered particularly desirable either. Those at the extreme ends of the spectrum both need to learn to balance the needs of others vs the needs of self into a healthy mean. So, just because it is common among sensitive people to be overly self-sacrificing, it does not make sensitivity and empathy negative traits in themselves.
There is also a difference between emotional/psychological sensibility and sensory sensibility. Emotional sensibility and being overempathic/overly self-sacrificing may well be modified to a degree with therapy. Well, not the empathic ability in itself, of course, but rather the sometimes unhealthy attitude towards self and others that comes with it. Cognitive behavioral therapy or CBT is probably excellent for this purpose.
However, sensory sensibility is usually an inherited biological trait that just means one has more delicate and finely tuned senses; e.g., hearing, touch, taste (more taste-buds on the tongue), colour vision (more cones in the eye), etc. Extreme cases of sensory sensitivity can also occur as a result of illness, environmental illness, drug use, spiritual development or sensory integration difficulties. Neither is "treatable" with CBT or psychotherapy, nor is it always desirable.

# Sources and notes
-  Ketay, S., Hedden, T., Aron, A., Aron, E., Markus, H., & Gabrieli, G. (2007, January). The personality/temperament trait of high sensitivity: fMRI evidence for independence of cultural context in attentional processing. Poster presented at the annual meeting of the Society for Personality and Social Psychology, Memphis, TN. Summary by Aron (2006): "A functional study comparing brain activation in Asians recently arrived in the United States to European-Americans found that in the nonsensitive, different areas were activated according to culture during a difficult discrimination task known to be affected by culture, but culture had no impact on the activated areas for highly sensitive subjects, as if they were able to view the stimuli without cultural influence."
-  Brodt, S., Zimbardo, P. "Modifying Shyness-Related Social Behavior Through Symptom Misattribution" Journal of Personality and Society Psychology 41 (1981): 437-49.
-  Jump up to: 3.0 3.1 Aron, E.N. The Clinical Implications of Jungs Concept of Sensitiveness , Journal of Jungian Theory and Practice, 8,2006, 11-43.
-   WebMD Live Events Transcript The Highly Sensitive Person In Love with Elaine Aron
-  Jump up to: 5.0 5.1 5.2 5.3  
Aron, Elaine. 1996. The Highly Sensitive Person. ISBN 0-553-06218-2.
Aron, Elaine and Aron, Arthur. 1997. Sensory-Processing Sensitivity and Its Relation to Introversion and Emotionality, Journal of Personality and Social Psychology. Aug. 1997 Vol. 73, No. 2, pp. 345-368.
- Aron, Elaine. 1996. The Highly Sensitive Person. ISBN 0-553-06218-2.
- Aron, Elaine and Aron, Arthur. 1997. Sensory-Processing Sensitivity and Its Relation to Introversion and Emotionality, Journal of Personality and Social Psychology. Aug. 1997 Vol. 73, No. 2, pp. 345-368.
-  Kagan, J. 1994 Galens prophecy. NewYork: Basic Books.
-  Wilson, DS; Clark, AB; Coleman, K; Dearstyne, T. (1994) "Shyness and boldness in humans and other animals." Trends in Ecology & Evolution Vol. 9, no. 11, pp. 442-446.
-  Jump up to: 8.0 8.1 Hedrick AV (2000). "Crickets with extravagant mating songs compensate for predation risk with extra caution". Proc. Biol. Sci. 267 (1444): 6715. doi:10.1098/rspb.2000.1054. PMID 10821611. |access-date= requires |url= (help).mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
-  Jump up to: 9.0 9.1 Aron, E. N. (2004). "Revisiting Jung's Concept of Innate Sensitiveness." Journal of Analytical Psychology, 49, 337-367.
-   sensitiveperson.com Attributes and Characteristics of Being Highly Sensitive by Thomas Eldridge

# Further reading
- Bruch, M., Gorsky, J., Cullins, T., & Berger, P. (1989). "Shyness and Sociability Reexamined: A Multicomponent Analysis"  Journal of Personality and Social Psychology, 57: 904-15.
- Deo, P. & Singh, A. (1973). "Some Personality Correlates without Awareness" Behaviorometric, 3: 11-21.
- Gough, H., & Thorne, A., "Positive, Negative, and Balanced Shyness: Self-Definitions and the Reations of Others" in Shyness: Perspectives on Research and Treatment ISBN 0-306-42033-3.
- Higley, J., & Suomi, S. "Temperamental Reactivity in Non-Human Primates" in Temperament in Childhood ed. Kohnstramm, G., Bates, J., and Rothbart, M. (New York: Wiley, 1989), 153-67.
- Kagan, J., Reznick, J., & Snidman, N. (1988). "Biological Bases of Childhood Shyness" Science, 240:167-71.
- Thorne, A. (1989). "The Press of Personality: A Study of Conversations Between Introverts and Extraverts" Journal of Personality and Social Psychology, 53: 713-26.
- Raleigh, M., & McGuire, M. (1984). "Social and Environmental Influences on Blood Serotonin and Concentrations in Monkeys" Archives of General Psychiatry, 41: 181-90.
- Revelle, W., Humphreys, M. Simon, L., & Gillian, K. (1980). "Interactive Effect of Personality, Time of Day, and Caffeine: A Test of the Arousal Model" Journal of Experimental Psychology General, 109: 1-13.
- Zumbo, B., & Taylor, S. (1993). "The Construct Validity of the Extraversion Subscales of the Meyers-Briggs Type Indicator" Canadian Journal of Behavioral Science, 25: 590-604.
- Aron, Elaine. 1999. The Highly Sensitive Person's Workbook. ISBN 0-7679-0337-4.
- Aron, Elaine. 2000. The Highly Sensitive Person in Love. ISBN 0-7679-0336-6.
- Aron, Elaine. 2002. The Highly Sensitive Child. ISBN 0-7679-0872-4.
- ed. Bates, J. and Wachs, T. Temperamented: Individual Differences in the Biological Aspects of Temperament. ISBN 1-55798-222-8.
- Mesich, Kyra. 2000. The Sensitive Person's Survival Guide. ISBN 0-595-09800-2.
- Mandel, Debra. 2003. Healing the Sensitive Heart. ISBN 1-58062-708-0.
- Jaeger, Barrie. 2004. Making Work Work for the Highly Sensitive Person. ISBN 0-07-140810-X.
- ed. Wachs, T., and King, B. Behavioral Research in the Brave New World of Neuroscience and Temperament. ISBN 1-55798-222-8.
- Zeff, Ted. 2004. The Highly Sensitive Person's Survival Guide. ISBN 1-57224-396-1.
- Young, Jeffrey E. et.al. 2003. Schema Therapy: a practitioner's guide ISBN 1-57230-838-9
- PDF Research paper Jawer, Mr. Michael (2005) Environmental Sensitivity: A Neurobiological Phenomenon?. Seminars in Integrative Medicine 3(3):pp. 104-109.
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