For better and for worse: Examining Environmental Sensitivity in adolescence at multiple levels of analysis and across development.

Children and adolescents differ in their ability to perceive and process information about their environment, that is in their environmental sensitivity (Pluess et al., 2018). Approximately 20 to 30% of individuals appear generally more sensitive than others, which means that they are more susceptible to characteristics of their developmental context (Pluess, 2015), such as the quality of parenting (Slagt et al., 2016). The overarching aim of this doctoral dissertation was to gain more insight into environmental sensitivity as an individual difference variable by applying an integrative approach including multiple age groups (i.e., preschool phase, middle childhood, early to late adolescence). Two main objectives were addressed.

Objective 1 was about the assessment of environmental sensitivity at phenotypic level. In Chapter 2 we evaluated the psychometric properties of a questionnaire to assess individual differences in environmental sensitivity in children, HSC-12 scale (Pluess et al., 2018), across developmental stage (i.e., early versus middle to late adolescence), gender, and country (i.e., Belgium and the UK). Based on the results of Chapter 2, we developed new items and improved the HSC-scale (HSC-21) (Chapter 3). The psychometric properties of the HSC-21 scale were tested across developmental stage (i.e., children and adolescents), gender, countries (i.e., Belgium and The Netherlands), and informants (i.e., self and mother reports). The scale seems to function well across these groups, with some reservations for criterium validity. In Chapter 5 the psychometric properties of an observer-rated measure (HSC-RS) of environmental sensitivity in preschoolers were validated.

Objective 2 was to get more insight in the characterization of individual differences in environmental sensitivity at multiple levels of analyses (i.e., phenotypic, physiological, and genetic level). In Chapter 4, we examined whether individual differences in environmental sensitivity at phenotypic level (as measured with the HSC-21) were related to individual differences in environmental sensitivity at physiological level (in terms of heightened physiological stress reactivity in response to a laboratory social stress task). We found evidence for a positive association between a heightened sensitivity at phenotypic level and perceived stress, but not for an association with the biological stress response (i.e., autonomic nervous system and endocrine stress reaction). In Chapter 5 we examined how we can characterize observer-rated sensitivity at behavioral, genetic, and physiological level in preschoolers. Meaningful associations were found between observer-rated sensitivity and temperament traits, and some suggestive evidence for an association between observer-rated sensitivity and a cumulative polygenic score. No associations between observer-rated sensitivity and cortisol nor EEG asymmetry were found.

 To summarize, this doctoral dissertation extended the existing literature by providing more insight in the assessment of individual differences in environmental sensitivity and among the characterization of environmental sensitivity across multiple levels of analysis. Across all chapters, outstanding issues, avenues for further research, clinical and societal implications, and strengths and limitations were discussed (Chapter 6).