is often conceptualized as an adaptive characteristic, there may be individual differences in the adaptiveness of high levels of self‐regulation in fear‐based temperamental styles such as shyness (Eisenberg et al., 1995; Graziano et al., 2007; Gross & Munoz, 1995; Ponitz et al., 2009). Similarly, although shyness is often conceptualized as avoidance in novel social contexts, our results suggest that not all shy children display reluctance to engage in social situations, and some of this heterogeneity may depend on children’s temperamental self‐regulation (Kagan et al., 1987, 1988).
Self‐Regulation and Adaptive Shyness Subtypes
In addition to functioning as an important moderator between shyness and socioemotional outcomes, self‐regulation can also inform our understanding of different subtypes of shyness (e.g., positive and nonpositive expressions of shyness). As highlighted previously, individuals who display positive affect in conjunction with shy‐related behaviors (i.e., positive shyness) are thought to be distinct from individuals who display primarily negative or neutral affect in conjunction with shy‐related behaviors (i.e., nonpositive shyness).
In infancy, positive shyness has been most commonly identified through infants’ expressions of a coy smile (Colonnesi et al., 2013; Reddy, 2000). Behaviorally, coy smiles include the presence of a smile paired with gaze and/or head aversion that occurs before or during the decline of the peak of the smile (Colonnesi et al., 2013). In infants, coy smiles are most often observed in the presence of a stranger (Colonnesi et al., 2013) and the presence of positive and negative shyness (i.e., nonpositive shyness) continues to be distinguishable during toddlerhood (Colonnesi et al., 2014) and childhood (Poole & Schmidt, 2019a). As well, the degree to which children engage in each type of expression of shyness appears to be associated with different socioemotional outcomes. As highlighted previously, positive shyness is associated with more positive outcomes when compared to nonpositive expressions of shyness. In both toddlerhood and childhood, positive shyness is associated with more sociability and less anxiety, while nonpositive shyness is associated with less sociability, more social anxiety, and greater behavioral manifestations of fear during self‐presentation tasks (Colonnesi et al., 2014; Poole & Schmidt, 2019a). Taken together, these studies suggest that: (1) different subtypes of shyness are distinguishable as early as infancy; (2) children who display more positive shy expressions may experience reduced risk for socioemotional difficulties; and (3) children who engage in relatively high levels of positive shy expressions may be indistinguishable from non‐shy children in some respects (Poole & Schmidt, 2019a).
One proposed explanation for why these distinct subtypes of shyness are associated with different outcomes is self‐regulation. It has been suggested that displays of positive affect in conjunction with avoidance related behaviors may function to regulate an individual’s arousal levels in novel social situations such that displays of positive affect may allow for modulation of arousal while children remain oriented toward novel social stimuli (Colonnesi et al., 2014; Poole & Schmidt, 2019a; Sroufe & Waters, 1976). In support of this notion, Asendorpf (1990) noted that within a coy smile, gaze aversion tends to occur during the most communicative part of the smile, suggesting that the smile may act as a regulatory mechanism by modulating one’s internal milieu. Moving forward, it would be helpful to determine whether positive and nonpositive shyness are in fact differentially related to level of self‐regulation, and whether individual differences in temperamental self‐regulation influence the development and maintenance of positive and nonpositive expressions of shyness.
Taken one step further, it would be interesting to determine whether different aspects of self‐regulation (e.g., inhibitory control, attentional shifting) work to moderate the association between positive and nonpositive shyness and social behavior or clinical outcomes similarly to when shyness is treated as a homogenous construct. Finally, using evolutionary frameworks such as differential susceptibility to guide future studies and analyses may provide us with valuable information about the multiple contexts that may support adaptive functioning in both positive and nonpositive expressions of shyness (Belsky & Pluess, 2009; see also Schmidt & Miskovic, 2013).
How Are These Self‐Regulatory Mechanisms Instantiated in the Brain in Adaptive Shyness?
Although the origins of shyness are multifaceted, interest in the neurobiological foundations of shyness has received considerable attention over the past several decades (see, e.g., Fox et al., 2001, 2005; Kagan et al., 1987, 1988; Schmidt & Schulkin, 1999, Schmidt & Miskovic, 2013, 2014, for reviews). This has been fostered by the availability of theoretical frameworks for understanding nonhuman animal and human brain‐behavior relations as well as advancements in technologies that have allowed for the relatively noninvasive collection of electrical brain activity such as electroencephalography (EEG). This combination has positioned researchers well to study the neural substrates underlying shyness, and how these neural processes may mediate adaptive and nonadaptive behaviors associated with shyness.
Frontal Brain Asymmetry and Shyness
One of the most widely studied neural correlates of shyness and related phenomena is frontal brain EEG alpha asymmetry. This work is rooted in motivational models of frontal brain activation, which have described resting state frontal brain alpha asymmetry as a trait‐like measure (i.e., a biological diathesis) that is stable across time and context (see Coan & Allen, 2004; Davidson, 2000; Fox, 1991, 1994; Reznik & Allen, 2018, for reviews). According to this framework, greater relative activity in the left frontal brain region is presumed to facilitate approach‐related motivations and emotions such as sociability and happiness, whereas greater relative activity in the right frontal region has been implicated in avoidance‐related motivations and emotions such as shyness and fear (Reznik & Allen, 2018).
Researchers have used EEG‐based data to derive asymmetries of frontal brain activity and the frontal activation motivational model as a theoretical platform to test hypotheses related to individual differences in temperament (including shyness and related constructs) and affective style across development (see Schmidt & Miskovic, 2014, for a review). Typically, these studies examined frontal asymmetry as the difference in EEG alpha power in the right frontal hemisphere minus EEG alpha power in the left frontal hemisphere. Because EEG alpha power is inversely related to cortical activity, negative scores reflect greater relative right frontal brain activity (Tomarken et al., 1992).
During different developmental periods, researchers have provided support for the relation between right frontal asymmetry and social avoidance‐related tendencies. For example, in infants and children, resting right frontal asymmetry has been associated with behavioral inhibition and emotional reactivity (Calkins et al., 1996; Davidson & Fox, 1989; Fox & Davidson, 1987; McManis et al., 2002), which are the temperamental antecedents of shyness. In preschool children, those described as socially inhibited and withdrawn during interactions with peers show right frontal asymmetry at rest (Fox et al., 1996), as do temperamentally shy children (Poole et al., 2018, 2019; Theall‐Honey & Schmidt, 2006). In adults, higher levels of behavioral inhibition, shyness, and social anxiety also have been linked to right frontal asymmetry at rest (Moscovitch et al., 2011; Schmidt, 1999; Sutton & Davidson, 1997) and increases in right frontal brain activity in responses to social stress in adults (Davidson, et al., 2000) and children (Schmidt et al., 1999).
Adaptive Subtypes of Shyness in the Brain
An additional line of our research has been to examine the neural substrates of different subtypes of shyness in children that are presumed to have different adaptive functions. As mentioned earlier in the first section, we have been particularly interested in different subtypes of shyness that share conceptual overlap, such as fearful/nonpositive shyness and self‐conscious/positive shyness, as they appear to have different adaptive functions. We have recently explored each of these two different conceptualizations of shyness in two separate studies to determine whether we could distinguish them on resting brain‐based measures.
In Study 1, we classified children with early‐developing (fearful)