Jung (1915) suggested that certain people possessed ‘innate sensitiveness’ of both a sensory and emotional nature and a trait of high sensitivity. He argued that such innate sensitiveness predisposed some people to be especially impacted by negative or traumatic childhood experiences. Jung also noted positive aspects of being highly sensitive, however, resulting in ‘an enrichment of the personality’ under better circumstances.
This trait was subsequently linked with various other theoretical concepts including introversion (e.g. Eysenck, 1981), inhibitedness in children (e.g. Kagan, 1994), reactivity
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(e.g. Rothbart, 1989), innate shyness (e.g. Daniels & Plomin, 1985) and has also been referred to as ‘behavioural inhibition to the unfamiliar’ (Kagan et al., 1984).
Aron and Aron (1997) coined the term ‘Sensory Processing Sensitivity’ (SPS) to describe this temperamental trait. They developed the Highly Sensitive Person Scale via large-scale interviewing to identify people displaying these attributes. This scale,
containing 27 items, has shown good content validity, reliability, convergent validity, and discriminant validity (Smolewska, McCabe, & Woody, 2006). Questions probing to ascertain sensitivity to sensory data using a seven-point Likert Scale include ‘Do you seem to be aware of subtleties in your environment?’ and ‘Are you easily overwhelmed by things like bright lights, strong smells, coarse fabrics, or sirens close by?’
Pluess et al. (2018) subsequently developed a 12-item Highly Sensitive Child (HSC) scale for use with children and adolescents. Lionetti, Aron, Aron, Klein, & Pluess, (2019) have more recently developed an observer-rated instrument; the Highly Sensitive Child-Rating System (HSC-RS), to capture different levels of sensitivity to the
environment in children aged 3 – 5 years.
Evidence from observations, questionnaires, cross-over interactions, functional Magnetic Resonance Imaging (fMRI) and genotype studies provide support for SPS as an innate personality trait possessed by circa 15-20% of the population, equally distributed across genders and cultures (Aron, Aron, & Jagiellowicz, 2012). Non-human research has also discovered similar traits including enhanced environmental sensitivity in up to 20% of the population of at least 100 other species, ranging from sunfish (Wilson, Coleman, Clark, & Biederman, 1993) to primates (Suomi, 1997) supporting the argument that this trait serves an important evolutionary function.
According to Wilson et al. (1993) this significant minority sub-group, within most species, observe and think carefully before acting, with the benefit of a more sensitive nervous system designed to detect subtle differences. The remaining 80% are bolder and prone to act without complete information. Two different, but complementary inherited traits are considered to advantage the species, which could be important for survival when faced with environmental challenges.
Whilst Aron & Aron (1997) considered SPS to be a single unitary construct, others, such Smolewska et al., (2006), identified three: low sensory threshold (sensitivity to
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sensory stimuli), ease of excitation (becoming emotionally overwhelmed by internal and external demands) and aesthetic awareness and appreciation, the latter being considered a positive consequence of noticing and experiencing more deeply than others.
SPS is reported to be valued more in certain cultures than others, such as China (Chen et al., 1992), Thailand and, to a certain extent, Denmark (Zeff, 2010). In his clinical interviews of 30 highly sensitive males, Zeff (2010) reported that in Western society, particularly USA and Canada, reflection and sensitivity is considered a particularly negative trait in men, however.
Correlational evidence has associated SPS and negative childhood experiences with anxiety, including social phobia and depression (Neal, Edelmann, and Glachan, 2002). According to Boterberg & Warreyn (2016) children with high SPS are also more likely to complain of medically unexplained physical symptoms (MUPS), eating and sleeping problems compared to children with average or low SPS. Neuroimaging studies have also found that both reward and fear areas of the brain are more easily activated in ‘inhibited’ adolescents (e.g. Bar-Haim et al., 2009).
Aron (2002) reported that many people with SPS intuitively adapt their
environments and participate in activities which aid their self-regulation, but this is not always the case, placing them at risk of stress and symptoms of ill health (Benham, 2006). In a recent study by Brindle, Moulding, Bakker, & Nedeljkovic, (2015) it was suggested that the relationship between SPS and negative affect may be mediated by emotional regulation. Brindle et al. (2015) added that a lack of access to effective emotional
regulation strategies could lead to a level of learnt helplessness, potentially impacting more widely on the person’s subsequent use of emotional regulation strategies. The argument of Dean et al. (2018) that individuals benefit from being taught to notice their response to sensory stimuli and to actively plan socially acceptable self-regulation strategies is likely to be very relevant in this respect.
The investigation of SPS has a rapidly growing interdisciplinary and international evidence-base, encompassing, amongst others, the fields of Developmental Psychology (e.g. Pluess et al., 2018), Personality and Individual Differences (e.g. Boterberg &
Warreyn, 2016), and Neuropsychology and Pathology (e.g. Ellis et al., 2011). It has yet to make a discernible impact in the field of Educational Psychology, however. Several books for the general public have been published by clinical psychologists and lay researchers,
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based on clinical interviews and personal experience, offering advice on adult life,
parenting and schooling, nevertheless (e.g. Aron, 2002; Zeff, 2010; Davenport, 2015). The importance of positive home and school experiences and the implications of negative experiences for mental health are emphasised in such publications. Anecdotal evidence from clinical interviews and personal experience are not considered methodologically sound, however, on the grounds of potential investigator bias (Yin, 2009).