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. Author manuscript; available in PMC: 2022 Aug 1.
Published in final edited form as: Infant Behav Dev. 2021 Jun 10;64:101597. doi: 10.1016/j.infbeh.2021.101597

Cardiac Physiological Regulation Across Early Infancy: The Roles of Infant Surgency and Parental Involvement with Mothers and Fathers

Mary Richter 1, Diane M Lickenbrock 1
PMCID: PMC8384679  NIHMSID: NIHMS1714093  PMID: 34119740

Abstract

High baseline respiratory sinus arrhythmia (RSA) and infant temperament are associated with a child’s ability to self-regulate, but moderators of this association have not been thoroughly examined in the literature. Parents who are more involved might have more opportunities to interact with and soothe their children. The current study examined whether parental involvement moderated the association between infant temperament and baseline RSA with mothers and fathers across early infancy. Participants included families (n=91) assessed at 4 and 8 months of age. Infant temperamental surgency and parental involvement were measured via parent-report when infants were 4 months old, and infant baseline RSA was measured at 4 and 8 months of age. Results revealed differences in mother versus father predictors of infant baseline RSA. A significant Infant Surgency X Maternal Play interaction was revealed; infants of mothers who were low involvement increased in their baseline RSA as their surgency increased. A significant main effect of father care was found; infants with highly involved fathers had higher baseline RSA. In conclusion, mothers and fathers may differentially influence their infant’s cardiac physiological regulation based on their specific type of involvement.

Keywords: parental involvement, temperament, physiological regulation, infancy, fathers

Cardiac physiological regulation is a vital tool that allows an individual to maintain homeostasis during periods of stress (Porges, 1995). As an infant undergoes changes in his or her level of environmental stress, his or her heart rate changes in response to this stress (Porges, 2007). However, individual differences in temperament are an important factor to consider when evaluating cardiac physiological regulation (Dale et al., 2011). Infant surgency, in particular, might dictate how he/she physiologically responds to his/her environment (Shiner et al., 2012; Stifter, Dollar, & Cipriano, 2011). In addition, parents may provide necessary soothing strategies to help an infant regulate their physiology (Blandon, Calkins, Keane, & O’Brien, 2010; Stifter & Rovine, 2015; Taipale, 2016). The current study examined the associations between infant temperament and parental involvement on infant cardiac physiological regulation.

Cardiac Physiology

The parasympathetic nervous system (PNS) is the division of the human nervous system that acts to calm the body down after a stress response or maintains a homeostatic state (Beauchaine, 2001; Holzman & Bridgett, 2017; Porges, 1995). The PNS acts on the heart by decreasing heart rate after a threat has been encountered. As threats increase, this control over the heart decreases. In other words, the PNS’s control over the heart can be thought of as a brake that gets released when a threat is encountered. This brake remains released as additional threats are encountered (Porges, 2007).

One way to assess the effects of the PNS is through respiratory sinus arrhythmia (RSA), which measures the variability in a person’s heart rate as it corresponds to the respiratory cycle (Porges, 2007). When the PNS exerts a strong brake on heart rate, RSA is high; when the brake is weak, RSA is low (Porges, 2007). Baseline RSA describes the potential of an individual to respond to changes in the environment (Stifter & Corey, 2001). Higher levels of baseline, or resting, RSA in children typically are associated with better attentional control, positive expressions of emotion, the ability to moderate negative moods (Healy, 2013), better emotion regulation, and higher social competence in children (Li, Deater-Deckard, Calkins, & Bell, 2017). Lower levels of baseline in children, has been linked to aggressive behavior across child age groups (Li et al., 2017), weaker emotion regulation, more extreme emotional reactions (Buss, Goldsmith, & Davidson, 2005), attentiveness/vigilance for potential threats (Viana et al., 2017), and coping less effectively to environmental demands (Healy, 2013; Viana et al., 2017).

However, compared to the child and adult nervous system, the infant nervous system is immature and still developing. Infant heart rate is often higher, there is less heart rate variability, and RSA is typically lower in young infants than adults (Porter & Dyer, 2017). Research on the developmental stability of the PNS has shown little to no developmental stability in early infancy (e.g., Porter, Bryan, & Hsu, 1995). Other studies have shown age differences the developmental stability of RSA (Patriquin, Lorenzi, Scarpa, Calkins, & Bell, 2015; Porter & Dyer, 2017). For example, research has shown that RSA values become increasingly stable beginning at 12 months of age (Patriquin et al., 2015; Porter & Dyer, 2017). The maturation of the PNS is closely linked to infants’ abilities to regulate their physiological states and emotions (Blandon et al., 2010) and subsequent positive developmental outcomes, such as better academic and social skills (Buss, Davis, Ram, & Coccia, 2018).

Even though the infant physiological system is still developing during early infancy, it is important to study RSA in young infants to gain an understanding of how different factors may affect infant physiological functioning (Burgess, Marshall, Rubin, & Fox, 2003). A recent meta-analysis by Holzman and Bridgett (2017) reported stronger relations between heart rate variability in adults compared to weak to nonsignificant associations in younger samples. Higher baseline RSA in early infancy is also associated with environmental engagement (Beuchaine, 2001) and is correlated with infant behavioral and temperamental reactivity (Porges, Doussard-Roosevelt, Portales, & Suess, 1994). These findings indicate that infancy might be a prime time to examine early moderators of physiological regulation, because the physiological system is still malleable and might be susceptible to environmental influences.

Infant Temperament

Individual differences in temperament are associated with a child’s ability to self-regulate, including physiological regulation (Dale et al., 2011). Temperament has been defined as relatively stable characteristics of an individual that arise early in life and contribute to affectivity, activity level, regulation, and attention (Shiner et al., 2012). Though it was once believed that temperament was stable across the lifespan, later research showed that as biological systems mature, and new skills are acquired to inhibit behavior, the expression of an infant’s affect and his or her emotional reactivity may change (Rothbart, 2011). Evidence also shows that the environment is influential on temperament. Therefore, both genetic and environmental factors affect an individual’s temperament throughout the lifespan (Rothbart, 2011).

One component of temperament is surgency, which describes how likely a child is to experience high levels of positive emotionality and actively engages with and explores his or her environment (Blandon et al., 2010). Children who are rated high in surgency often display characteristics such as high activity level, tendency to approach novel items, and positive affect (Hong et al., 2015). These children often prefer to engage with toys that provide high-intensity pleasure, such as toys that light up or make noise, and they are generally social and may be highly vocal (Putnam, Rothbart, & Gartstein, 2008).

Studies have found both positive and negative developmental outcomes related to children high in surgency (Blandon et al., 2010; Stifter, Putnam, & Jahromi, 2008). The ability to actively engage the environment as well as the tendency towards positive affect may be beneficial developmentally; however, the tendency to approach novel items has been linked to frustration and aggression particularly when children’s goals are blocked (Blandon et al., 2010). In addition, evidence has shown a link between surgency and self-regulation. Infants who display greater approach tendencies and higher levels of positive affect are more likely to have a lower inhibitory control later in life (Blandon et al., 2010). This is related to the fact that children rated high in surgency are also rated high in impulsivity (Putnam et al., 2008). If children cannot regulate their high approach tendencies and high-intensity positive emotions, they may be at risk for disruptions in social interactions and behavior problems (Blandon et al., 2010). These children may also be at risk for internalizing and externalizing symptoms (Stifter et al., 2008).

In contrast to children high in surgency, children low in surgency display low approach tendencies to novel items and people. Rather, they are cautious around new people and events and may even be apprehensive (Bassett et al., 2017) which can lead to the development of anxiety particularly in social contexts (Hipson & Sequin, 2015). Children low in surgency are shy, socially withdrawn, and tend to observe new people from a distance (Bassett et al., 2017). Developmentally, these can lead to overly vigilant behaviors and a heightened responsivity to socializes’ behaviors (Bassett et al., 2017). They may also be at a higher risk for internalizing problems (Dollar & Stifter, 2012).

Surgency is an important factor to assess because it might be associated with an individual’s physiological functioning, such as RSA (Li et al., 2017). However, research is greatly lacking in this area (Blandon et al., 2010; Holzman & Bridgett, 2017; Stifter et al. 2011). Research has found that surgency early in life interacted with RSA to predict surgency several years later (Blandon et al., 2010; Li et al., 2017). For children with large increases in baseline RSA across time points, surgency was highly stable. On the other hand, for children with small increases or decreases in baseline RSA, surgency was only moderately stable (Li et al., 2017). In addition, children who were high in baseline RSA at two years of age were more likely to have high levels of surgency at seven years old (Blandon et al., 2010). Therefore, this research suggests that there is a link between surgency and cardiac physiological regulation in young children with RSA a possible index of surgency (Liu et al., 2017). However, more research needs to be done on potential moderators of this relationship during early infancy, which the current study attempted to examine.

Parental Involvement

Parental involvement is essential for infant development with greater levels of involvement leading to increased positive child socioemotional and cognitive outcomes (Pleck, 2010). For example, children with more involved parents tend to have an internal locus of control later in life and perform better academically (Williams & Radin, 1999). Furthermore, early parental involvement may influence later parent-child relationships, including attachment (Lickenbrock & Braungart-Rieker, 2015; Planalp, Braungart-Rieker, Lickenbrock, & Zentall, 2013), as well as a child’s physiological regulation (Blandon et al., 2010). Young children’s physiological regulation during challenging situations may be influenced by parenting behaviors (Blandon et al., 2010). Studying how child temperament and parent involvement contribute to changes in an infant’s cardiac physiological regulation may give insight into factors that may aid or inhibit an individual’s development of cardiac physiological regulation (Blandon et al., 2010).

Although mothers and fathers each contribute to a child’s development in important ways, mothers and fathers interact differently with infants (Lickenbrock & Braungart-Rieker, 2015; Planalp et al., 2013) and infants might be gaining additional experiences with physiological regulation in these interactions (e.g., Moore, 2009). Mothers are more likely to engage in caregiving activities, such as feeding and bathing, whereas fathers are more likely to engage in play activities, such as rough-and-tumble activities (Lewis & Lamb, 2003). Research has suggested that father’s rough-and-tumble play styles may contribute to a healthy development of emotion regulation in young infants (Pleck, 2007). On the other hand, because the types of activities fathers engage in typically require greater motor skills, fathers tend to be more involved with older children (Mehall, Spinrad, Eisenberg, & Gaertner, 2009). Due to this difference in parental involvement types between the two parents, both mothers and fathers were examined in the current study.

Despite these known differences in mother and father involvement, the examination of how each parent’s involvement interacts with infant surgency to produce different child outcomes has not been well studied (Blandon et al., 2010) especially during early infancy. Therefore, the current study bridged this gap in the literature by examining the interaction between infant surgency and maternal/paternal involvement, and whether this interaction is associated with infant cardiac physiological regulation.

Current Study

The current study evaluated the relationship between infant temperament and parent involvement and its impact on infant physiological regulation. Temperament has been found to be associated with physiological regulation (e.g., RSA; Li et al., 2017). Of all the factors of temperament, surgency has been one of the least studied (Blandon et al., 2010). Although temperament has been linked to RSA (Blandon et al., 2010; Li et al., 2017), moderators of this relationship have not been highly examined. This study attempted to remedy that gap by examining parental involvement as a potential moderator. Parenting has also been linked to infant cardiac physiological regulation (Conradt & Ablow, 2010). However, fathers have been underrepresented in parenting research (Doyle, Weller, Daniel, Mayfield, & Goldston, 2016); therefore, the present study included both maternal and paternal involvement to examine potential differences in infant physiological regulation in mother-infant and father infant dyads. Research evaluating factors that may influence infant physiological regulation is vital due to the positive outcomes, including social and emotional outcomes (Smith, Hastings, Henderson, & Rubin, 2019).

In the current study, the association between infant temperament and parental involvement on infant cardiac physiological regulation was examined in mother-infant and father-infant dyads when infants were 4 and 8 months of age. These ages were chosen because they are some of the earliest known ages at which RSA can be measured accurately in infants due to their developing cardiac systems (Porter & Dyer, 2017). Infant baseline RSA was measured at both the 4- and 8-month time periods (i.e., autoregressive design). This allows for the adjustment of between person differences in physiological maturation as well as the measurement of the developmental mechanisms of baseline RSA change. Overall, there were 2 hypotheses for the current study, please see them outlined below.

Hypothesis 1: Parental Involvement as a Moderator.

The first hypothesis was that parental involvement would act as a moderator between infant surgency at 4 months and infant baseline RSA at 8 months.

Hypothesis 1A.

First, it was expected that infants who are high in surgency and have parents high in parental involvement at 4 months would show high change in baseline RSA at 8 months of age. High surgent children can exhibit not only highly positive behavior, but also high activity level, impulsivity and anger (Blandon et al., 2010; Stifter et al., 2008). As a result, these children might benefit from high parental involvement in which parents provide necessary stimulation but also control and soothing (Blandon et al., 2010; McDoniel & Buss, 2018). High parental involvement might foster high baseline RSA in these highly surgent infants.

Hypothesis 1B.

Second, it was predicted that infants who are high in surgency and parents are low in parental involvement at 4 months would have lower change in baseline RSA at 8 months of age. Because the parents are not involved and around their infants as much, those infants do not have as many opportunities to interact with their parents and receive needed stimulation and/or soothing from their parents (Blandon et al., 2010). Thus, their baseline RSA would remain lower.

Hypothesis 1C.

Similar to Hypothesis 1A (infants high in surgency/parents highly involved), it was predicted that infants who are low in surgency and have parents who are high in parental involvement at 4 months would show a high change in baseline RSA at 8 months of age. Because their parents are highly involved, these infants were expected to benefit from the increased interactions with their mothers and fathers (Planalp & Braungart-Rieker, 2015).

However, these infants were expected to be lower in RSA at both time-points compared to the highly surgent infants.

Hypothesis 1D.

Fourth, it was predicted that infants who are low in surgency and have parents who are low in parental involvement at 4 months would show a lower change in baseline RSA at 8 months. Because the parents are not as involved, these children would not have many opportunities for receiving soothing that would increase baseline RSA (Blandon et al., 2010).

Hypothesis 2: Parent Differences.

The second hypothesis is that there would be differences in the expected results with maternal and paternal involvement. Mothers and fathers interact differently with children (Lickenbrock & Braungart-Rieker, 2015; Planalp et al., 2013), and fathers typically do not become highly involved until children are older (Mehall, Sprinrad, Eisenberg, & Gaertner, 2009). Therefore, due to these differences in maternal and paternal involvement, the moderation effect of parental involvement on surgency and infant cardiac physiological regulation may be different between the two parents. However, this hypothesis was exploratory.

Method

Participants

Families were recruited as part of a larger longitudinal study involving 4, 6, and 8-month-old infants with a sample size of 91 families (mother, father, infant). Due to the overarching research question and study hypotheses, only data from the 4 and 8-month visits were used in this study. The majority of infants were male (59.3%). The study occurred at a large state university campus located in a mid-sized, Southeastern city. Recruitment occurs through flyers, tabling at family events, and through mailing letters to families who publish their birth announcements in the local newspaper. The larger longitudinal study received Institutional Review Board approval. All families who participated received $20 in compensation at each visit.

To be included in this study, infants met the age criteria of 4, 6, and 8 months (+/− 14 days). Both parents were able to participate in the study at all time points, and they both must read and understand English. The mother must have had a healthy pregnancy and delivery with no birth complications, and the infant must have been full-term (gestational age ≥ 37 weeks; birth weight ≥ 5.5lbs). In addition, the family did not plan to move out of the area in the next six months.

The majority of parents were European American (mothers: 91.2%; fathers: 89%). Mothers were on average 30.44 years of age (SD = 5.26; range = 19 to 44). Fathers were on average 32.14 years of age (SD = 6.35; range = 19 to 55). The majority of parents (95.7% of mothers and 86.9% of fathers) reported finishing at least some college. The distribution of the remaining education levels completed are as follows: 3.3% of fathers completed some high school, 3.3% of mothers and 8.8% of fathers completed high school, and 1.1% of mothers and 1.1% of fathers completed trade school. The majority of parents worked a full-time job (51.6% of mothers and 86.8% of fathers). The distribution of the remaining employment levels are as follows: 15.4% of mothers and 6.6% of fathers worked part-time, 24.2% of mothers and 3.3% of fathers were unemployed, and 7.7% of mothers and 3.3% of fathers reported other employment circumstances. The majority of families were middle class (62.7% reported an income of $45,000-$104,999). The distribution of the remaining income levels is as follows: 4.4% reported less than $15,000, 6.6% reported $15,000-$29,999, 11% reported $30,000-$44,999, 6.6% reported $105,000-$119,999, and 8.8% reported an income greater than $120,000. The living arrangement of families were as follows: 91.2% married and living together, 7.7% unmarried and living together, and 1.1% of families were single.

Attrition was moderate (18.7%) from the first time point (4 months) to the last time point (8 months). Statistical comparisons between the families that had completed the study (n = 74) from the total sample (n = 91) along different demographic variables revealed no significant differences between the families that completed the study and the families who dropped out of the study. Of the 74 families who completed the study, 56 mother-infant and 55 father-infant dyads had complete data on all study variables at 4 and 8 months. Reasons for missing data included incomplete questionnaire data at 4 months (Families: n = 3; Mother only: n =1, Father only: n =2), incomplete laboratory visits months and/or technological issues during cardiac recording at 4 or 8 months (Families: n =17).

Procedure

Informed consent was obtained at the commencement of the first visit with both parents signing the consent forms and one parent provided consent for the infant to participate. Prior to each lab visit, mothers and fathers were mailed a packet of questionnaires assessing infant temperament and parental involvement that they were told to complete and bring with them to each laboratory visit. In addition, at the beginning of each laboratory visit, mothers and fathers answered questions related to demographic information. During the laboratory visit, mothers and fathers also completed another packet of questionnaires that further assess parental involvement. Each laboratory visit lasted two hours on average.

Mothers and fathers individually participated with his/her infant, and the parent that went first with his/her infant was randomly assigned (% fathers who participated in laboratory visits who went first: 51.8% at 4 months; 33.8% at 8 months). Cardiac data was obtained from the parent and infant using a Bionex 2-slot chassis assembly with impedance module (Mindware Technologies, Gahanna, OH), which measures both heart rate variability and impedance. Seven electrodes were placed on the mother, father, and infant. Two electrodes were placed on the right and left side clavicle, one electrode was placed in the middle of the torso by the diaphragm, two were placed above each hip bone, and two were placed on the back of the body by the neck and small of the back. The first parent entered the observation room with his/her infant and was instructed by the primary experimenter to be seated and to sit quietly with the infant on his/her lap while cardiac physiology was acquired for three-minutes. During this period, parents were allowed to engage in face-to-face contact with the child. The primary experimenter left the room and watched in an adjacent room through a one-way mirror with the secondary experimenter. The parent then completed the Still-Face Paradigm (SFP; Tronick, Als, Adamson, Wise, & Brazelton, 1978) and participated in a 3-minute recovery task. After the first series of baseline, SFP, and recovery tasks were completed and the infant was in a calm/neutral state, the second parent repeated the same series with the infant.

Measures

Infant Behavior Questionnaire- Revised

(IBQ-R; Gartstein & Rothbart, 2003). The IBQ-R was used to assess infant temperament. Both mothers and fathers independently completed this assessment, which consists of 191 items focusing on the emotional and behavioral responses of infants to different situations. In total, 14 dimensions of infant temperament are assessed including approach, vocal reactivity, high intensity pleasure, smile and laughter, activity level, perceptual sensitivity, sadness, distress to limitations, fear, falling reactivity, low intensity pleasure, cuddliness, duration of orienting, and soothability (Perry, Dollar, Calkins, & Bell, 2018). Responses were recorded on a 7-point Likert scale ranging from 1 (never) to 7 (always) with an eighth option for does not apply. The scales on the IBQ-R measure three different dimensions of temperament: negative affectivity, surgency, and orienting (Li et al., 2017). For the current study, only the subscales comprising surgency were used (activity level, high-intensity pleasure, perceptual sensitivity, positive anticipation, smiling and laughter, and vocal reactivity; Putnam et al, 2008).

Since its development, the IBQ-R has demonstrated reliability and validity, which is supported by the results from numerous research studies (Bridgett et al., 2009). For the current study, only the infant surgency factor score was used (Mother-report α = .73; Father-report α = .75). Mother- and father-report of infant surgency was moderately correlated (r = .30, p < .05), therefore, the scores were averaged. Other studies have also reported that mother and father reports of temperament were moderately correlated and averaged the scores together to create a more comprehensive measure of temperament (i.e., Jessee, Mangelsdorf, Shigeto, & Wong, 2011). Higher scores mean higher infant surgency.

What I Did with My Baby Checklist

(Lickenbrock & Braungart-Rieker, 2015; Planalp, Braungart-Rieker, Lickenbrock, & Zentall, 2013). Parental involvement was measured using a diary-like checklist known as the What I Did with My Baby Checklist. This self-report questionnaire was completed by each parent to measure parental involvement. The survey assesses the amount of time each parent was available, playing with, or otherwise caring for their infant within a 24-hour period. Fathers and mothers chose a day that reflected their typical schedule/routine and checked off different childcare and play/interaction events with their infant. Two sets of behaviors were included in this checklist, care (six items) and play (four items). The care items included changing diapers, feeding, bathing, soothing, and waking up for the infant at night. The play items included active or calm playing, teaching, and going on outings. Proportion scores were created for each set of behaviors (care/play) separately for mothers and fathers. Higher proportion scores indicate more care or play behaviors. Reliability scores cannot be calculated since this is a checklist and not all items are checked by each parent (Planalp et al., 2013).

Infant Cardiac Physiology.

Respiratory sinus arrhythmia (RSA) was measured using electrocardiography data during the baseline. Similar to previous studies, trained research assistants manually inspected the data files for artifacts using MindWare Heart Rate Variability (HRV version 3.0.25) software (Buss et al., 2018). This software calculated RSA values for each of the six 30-second segments. Those values were averaged over the six segments to get one RSA value per infant.

Coders were trained to edit HRV data files until they achieved sufficient reliability (intraclass correlations (ICCs) ≥ .80). To avoid bias, coders were not allowed to edit infant data from both parents in one age group. Coders overlapped by coding 28% of the overall 4-month data and 30% of the 8-month data. Average ICC was .97 for 4-month infant baseline RSA with mothers, .98 for 4-month infant baseline RSA with fathers, .98 for 8-month infant baseline RSA with mothers, and .97 for infant baseline RSA with fathers. There was a small amount of data that could not be edited due to extreme noise due to dry electrodes or technological issues during data collection (4 mos. Infant with Mother: n = 1, 4 mos. Infant with Father: n =1; 8 mos. Infant with Father: n =2). Infant baseline RSA values were highly correlated between ratings with mothers and infant RSA ratings with fathers at both the 4-month (r = .57, p < .05) and 8-month (r = .64, p < .05) time points, therefore the infant’s RSA baseline scores with mothers and fathers were averaged. Higher baseline scores indicate a stronger capacity to respond to the environment when environmental challenges are encountered.

Results

Preliminary Analyses

Means, standard deviations, skewness, and kurtosis of the study variables are presented in Table 1. All variables were normally distributed. Analyses were run with the raw data to test the extent to which the study variables were related to demographic variables (infant gender, mother/father age, mother/father education, mother/father ethnicity, parity, parent order, family income, and marital status). A total of 66 analysis of variance (ANOVA), chi-square, correlations, t-tests were run with the raw data (depended on the scaling of the demographic variables). Four significant effects emerged, which is roughly expected due to chance (.06). Therefore, no demographic covariates were included in subsequent analyses. Little’s MCAR X2 (29) = 26.91, p = .58, indicating that the missing data were most likely missing completely at random. Missing data was imputed in SPSS 27 using the expectation-maximization (EM) algorithm for 88 out of the overall 91 families. Three families were excluded prior to imputing the data due to not having any data for the variables of interest.

Table 1.

Descriptive Statistics

n Min Max M SD Skewness Kurtosis
Surgency 84 3.15 5.55 4.18 .53 .14 −.21
Father Care 81 .00 1.00 .52 .19 −.45 .41
Father Play 82 .00 1.00 .55 .27 −.31 −.55
Mother Care 83 .33 1.00 .72 .14 −.09 −.29
Mother Play 83 .25 1.00 .70 .21 −.08 −.80
Infant RSA4 81 .50 4.98 3.06 .90 −.48 .55
Infant RSA8 63 1.91 5.70 3.57 .77 .29 .19
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Note: Surgency: Infant Surgency at 4 months Averaged Across Mothers and Fathers; Father Care: Father Care at 4 months ; Father Play: Father Play at 4 months; Mother Care: Mother Care at 4 months; Mother Play: Mother Play at 4 months; Infant RSA4: Infant Baseline RSA at 4-Months Averaged Across Mothers and Fathers; Infant RSA8: Infant Baseline RSA at 8-Months Averaged Across Mothers and Fathers. Numbers reported are non-imputed, raw data.

Zero-order correlations among variables are presented in Table 2. Infant surgency was significantly correlated with infant baseline RSA at 8-months with highly surgent infants being higher in baseline RSA. Father care involvement at 4-months was significantly correlated with infant baseline RSA at 8-months with more highly involved fathers having infants with higher baseline RSA. Father play involvement was significantly correlated with infant baseline RSA at 4-months with fathers who were highly involved in play having infants with higher baseline RSA. Correlations for mother involvement measures were non-significant.

Table 2.

Correlations Among Variables (n= 88)

1. 2. 3. 4. 5. 6. 7.
1. Surgency 1.00
2. Father Care .08 1.00
3. Father Play .21t .29** 1.00
4. Mother Care .12 .09 .14 1.00
5. Mother Play .15 .03 .13 .21t 1.00
6. Infant RSA4 −.06 .04 .22* .13 .08 1.00
7. Infant RSA8 .21* .36** .02 .02 −.14 .16 1.00
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Note: Surgency: Infant Surgency at 4 months Averaged Across Mothers and Fathers; Father Care: Father Care at 4 months; Father Play: Father Play at 4 months; Mother Care: Mother Care at 4 months; Mother Play: Mother Play at 4 months; Infant RSA4: Infant Baseline RSA at 4 months Averaged Across Mothers and Fathers; Infant RSA8: Infant Baseline RSA at 8 months Averaged Across Mothers and Fathers;

t

p < .10

*

p < .05

**

p < .01

Paired t-tests revealed differences between maternal and paternal involvement for both play and care. Mothers were involved more in play activities compared to fathers (t (87) = −4.41; p < .001; Mother Play: M = .70, SD = .21; Father Play: M = .55, SD = .26. Mothers were also more involved in care activities compared to fathers (t (87) = −8.49; p < .001; Mother Care: M= .72, SD = .14; Father Care: M = .52, SD = .19).

Parental Involvement as a Moderator

The first hypothesis states that parental involvement would act as a moderator between infant temperament and infant physiological regulation. To test this hypothesis, a hierarchical multiple regression model was conducted with infant surgency, parental involvement, and infant baseline RSA at 4 months as the predictors and infant baseline RSA at 8 months as the outcome. Due to a small sample size, mother and father analyses were kept separate, which is similar to previous studies with comparable sample sizes (Jessee et al., 2011; Lickenbrock & Braungart-Rieker, 2015). The first step included the main effects of infant surgency, parental involvement (mother involvement, father involvement), and baseline RSA at 4-months. The second step included the main effects and the 2-way interactions between infant surgency and parental involvement (surgency X maternal involvement, surgency X paternal involvement). The variables were mean centered to help with interpreting results, and any significant interactions were examined one standard deviation above and below the mean (Aiken & West, 1991). The simple slopes results were graphed using online resources from http://www.jeremydawson.co.uk/slopes.htm (Dawson, 2014).

The second (exploratory) hypothesis states that there would be differences in the effect of parental involvement on infant temperament between maternal and paternal involvement. This hypothesis was explored by running separate multiple regression models for maternal versus paternal data.

Infant Surgency - Maternal Involvement.

As can be seen in Table 3, results from the set of regression models including infant surgency and mother play involvement revealed a significant two-way interaction between infant surgency and mother play involvement (See Figure 1), 95% CI [−2.64, −.17]. Simple slopes analyses were run to probe this interaction one standard deviation above and below the mean and revealed a significant effect for mothers who were low in play involvement. More specifically, results revealed that infants who were high in surgency and had mothers low in play involvement at 4 months had higher change in baseline RSA at 8 months (B = .61, SE = .18, β = .46, p = .001) than those low in surgency. The simple slope tests for mothers who were high in play involvement was nonsignificant (B = .03, SE = .19, β = .02, p = .90). The models including mother care involvement were nonsignificant.

Table 3.

Infant Surgency and Maternal Involvement at 4-months Predicting Infant Baseline RSA at 8-months (n=88)

Model Variables Mothers: 4 Months→8 Months
Play B(SE) β p df F R 2 ΔR2
I. .02 3 3.39 .11
Surgency .32 (.14) .25 .02
Mother Play −.63 (.34) −.19 .07
Infant RSA4 .14 (.08) .19 .08
II. .01 4 3.95 .16 .05
Surgency .32 (.13) .24 .02
Mother Play −.64 (.33) −.20 .06
Infant RSA4 .15 (.08) .19 .06
Surg. X Play −1.41 (.62) −.23 .03
Care
I. .10 3 2.20 .07
Surgency .29 (.14) .22 .04
Mother Care −.15 (.51) −.03 .77
Infant RSA4 .13 (.08) .17 .11
II. .17 4 1.65 .07 .001
Surgency .29 (.14) .23 .04
Mother Care −.13 (.52) −.03 .80
Infant RSA4 .13 (.08) .17 .12
Surg. X Care −.27 (.89) −.03 .76
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Note: Surgency: Infant Surgency at 4 months Averaged Across Mothers and Fathers; Mother Care: Mother Care at 4 months; Mother Play: Mother Play at 4 months; Infant RSA4: Infant Baseline RSA at 4-Months Averaged Across Mothers and Fathers

Figure 1.

Figure 1.

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Graph of mother play involvement by infant surgency interaction.

Infant Surgency - Paternal Involvement.

As can be seen in Table 4, the results from the set of regression models including infant surgency and father care involvement revealed a significant main effect of father care involvement in the first step. Fathers who were higher in care involvement at 4 months had infants who had higher change in baseline RSA at 8 months. Similar to the mother play models, a marginal effect of infant surgency was revealed. Because the second step also revealed similar findings to the first step and the infant surgency and father care involvement interaction was nonsignificant, these findings were not interpreted. The set of regression models including father play involvement were nonsignificant.

Table 4.

Infant Surgency and Paternal Involvement at 4-months Predicting Infant Baseline RSA at 8-months (n=88)

Model Variables Fathers: 4 Months→8 Months
Play B(SE) β p df F R 2 ΔR2
I. .08 3 2.33 .08
Surgency .31 (.14) .24 .03
Father Play −.19 (.28) −.08 .50
Infant RSA4 .14 (.08) .19 .09
II. .15 4 1.73 .08 .00
Surgency .31 (.14) .24 .03
Father Play −.19 (.29) −.07 .51
Infant RSA4 .14 (.09) .18 .12
Surg. X Play .07 (.61) .01 .91
Care
I. .001 3 6.33 .18
Surgency .25 (.13) .19 .06
Father Care 1.22 (.36) .34 .001
Infant RSA4 .12 (.08) .16 .12
II. <.001 4 5.79 .22 .03
Surgency .27 (.13) .21 .04
Father Care 1.23 (.35) .34 .001
Infant RSA4 .14 (.08) .18 .07
Surg. X Care −1.51 (.79) −.19 .06
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Note: Surgency: Infant Surgency at 4 months Averaged Across Mothers and Fathers; Father Care: Father Care at 4 months; Father Play: Father Play at 4 months; Infant RSA4: Infant Baseline RSA at 4-Months Averaged Across Mothers and Fathers

Discussion

The current study sought to examine how infant temperament and parental involvement influence infant cardiac physiological regulation. The current study’s main contribution is the examination of the role both mothers and fathers play in their infant’s cardiac physiological regulation. Although fathers are increasingly being studied in developmental literature, a general lack of paternal presence in the infant development literature still exists (Cabrera, Volling, & Barr, 2018). In addition, there is a lack of studies regarding surgency in infant temperament literature (Planalp & Braungart-Rieker, 2015), therefore this study attempted to fill this gap. Hierarchical multiple regression analyses were conducted to test the hypotheses that 1) parental involvement would act as a moderator between infant temperament and infant baseline RSA and 2) there would be differences seen between maternal and paternal involvement. A significant interaction was found between infant surgency and maternal play involvement such that infants who were higher in surgency and had mothers who were low in play involvement at 4 months had higher change in baseline RSA at 8 months. A significant main effect was found for paternal care involvement such that fathers who were higher in care involvement at 4 months had infants with higher change in baseline RSA at 8 months.

RSA Correlation

One particularly interesting finding regarding the correlations is lack of a significant correlation between baseline RSA at 4 months and baseline RSA at 8 months. A lack of correlation between infant RSA at 4 months and infant RSA at 8 months may be explained by fluctuations in the cardiac system in infants of this age (e.g., Porter & Dyer, 2017). Other studies have also found low to moderate correlations between earlier baseline RSA values and later baseline RSA values such that baseline RSA at 5 months was only moderately correlated with baseline RSA at 10 months (r = .30; Perry et al., 2018). Yet another study found no correlation between 6 month and 12-month baseline RSA (r = .03; Putnam & Stifter, 2002). Therefore, the lack of a significant correlation between baseline RSA at 4 months and baseline RSA at 8 months has been found in other studies.

Infant Surgency X Maternal Play Interaction

The significant interaction between surgency and maternal play involvement is counter to the study’s hypothesis. It was hypothesized that infants who were high in surgency and had mothers who were low in involvement at 4 months would have lower change in baseline RSA at 8 months. These infants might not have as many opportunities to engage with their mothers who might provide the necessary stimulation, control, and soothing that these infants require (Blandon et al., 2010; McDoniel & Buss, 2018). In light of the findings, high surgency in children could act as an enhancing factor when paired with low maternal play involvement as these children had a high potential to respond to changes in the environment, and other groups of children did not. High surgent children are high in activity level and positive affect (Hong et al, 2015), which could mean that they are better able to engage their environments on their own without maternal play support (Blandon et al., 2010). Therefore, it is possible that these infants with mothers who were low in play might have more opportunities for more internally driven regulation (e.g., physiological regulation) compared to the infants of high play mothers.

This finding also supports the differential susceptibility theory (Ellis et al., 2011), which states that some individuals are more susceptible than others to both negative as well as positive environments (Ellis et al., 2011). Infants who are high in surgency might react to a low maternal play environment differently than other children. In addition, children who are very high or very low in surgency react differently to stressful situations than children who have moderate levels of surgency (Blandon et al., 2010). Yet another study found that children who were more emotionally reactive, such as those who are high in surgency, did not seem to be susceptible to differences in parenting (Slagt, Dubas, Ellis, van Aken, & Dekovic, 2019). However, surgency is also comprised of impulsivity, which is known to also put these children at risk for maladaptive developmental outcomes (Stifter et al. 2008).

Of the studies that have examined surgency, there are discrepancies in findings. Some studies have found surgency to be adaptive, as surgency reflects a preference towards positivity (e.g., Blandon et al., 2010). Other studies have found surgency to be related to externalizing problems, because surgency was examined in relation to high approach or low impulsivity levels (Stifter et al., 2008). By combining multiple components of surgency together, researchers cannot examine which specific aspects of surgency may be driving the association between surgency and infant outcomes (e.g., RSA). Future studies should examine surgency on a fine-grained level. For example, future research should probe the interaction between surgency and parent involvement further to disentangle these complex associations.

These results are in opposition to a previous study that found that infants who were high in surgency had mothers who played more with them (Planalp et al., 2013). This study also found that infants low in surgency had mothers who exhibited high care involvement, whereas the current study did not find any significant relationship between infant surgency and maternal care. It is interesting to note that both the current study and the Planalp et al. (2013) study used the IBQ-R and the What I Did with My Baby Checklist to measure infant temperament and parental involvement. However, Planalp and colleagues only had mothers report on infant temperament, and the present study had both parents report. In addition, Planalp et al. studied infants from 3 months of age through 20 months of age, whereas the current study only assessed families when infants were 4 and 8 months old. Perhaps important changes occur somewhere between 8 and 20 months. In addition, play was controlled for in care analyses and care was controlled for in play analyses (Planalp et al., 2013), which the current study did not do. Both the current study and the Planalp et al. study had samples with highly educated parents, which might lead to counterintuitive or even inverted associations due to limited variance. Due to these discrepancies, additional studies are needed to examine the interaction between surgency and maternal involvement at different ages and diverse sample characteristics.

One shortcoming of the current study is that maternal sensitivity/intrusiveness was not taken into account. These parenting quality components could also interact with temperament to affect infant regulation (Planalp et al., 2013). Sensitivity is a rating of the parent’s awareness to the infant’s emotions and ability to adapt to changes in the infant’s emotions (Lickenbrock & Braungart-Rieker, 2015). Research has shown that mothers display greater sensitivity to infants who are low in surgency (Planalp et al., 2013). In contrast to sensitivity, intrusiveness is an exertion of control over the infant (Perry et al., 2018). For example, perhaps low maternal play involvement could also be an indicator of too little play or insensitive parenting. Similarly, high maternal play involvement could be an indicator of play that is too intense, which could become intrusive (Perry et al., 2018). Future studies should include parental sensitivity and intrusiveness in order to examine how those aspects of parenting may interact with infant temperament to affect infant cardiac physiological regulation.

Paternal Involvement Findings

The main effect of paternal care on infant cardiac physiological regulation is in agreement with previous studies that have found more highly involved parents have more opportunities to help their children regulate (Blandon et al., 2010). Past research has also highlighted this positive effect of father care (Lewis & Lamb, 2003). Fathers who are high in care involvement with infants have children who do better in school and are more successful in spousal relationships later in life (Lewis & Lamb, 2003). However, other studies have not found this main effect of paternal care (Planalp et al., 2013).

Regression results revealed nonsignificant effects of father play, which is surprising giving the extensive literature on paternal play involvement (Lewis & Lamb, 2003; Mehall et al., 2009; Planalp et al., 2013). However, a lack of a significant finding with father play could be because fathers are not typically as involved in play activities until children are older due to the restrictions in infant motor development (Mehall et al., 2009; Planalp et al., 2013). Future studies should focus more on specific paternal involvement activities. Care and play activities could be broken down further into individual tasks to gauge if there is a particular activity that enhances infant physiological regulation. For example, future studies could include typical parenting behaviors for fathers as well, such as stimulating or rough-and-tumble play (Majdandžić et al., 2016; StGeorge et al., 2018), physical touch, singing, or reading to the infant (StGeorge et al., 2018).

Even though findings revealed that mothers exhibited more care and play involvement than fathers, perhaps fathers who are more involved with their infants play more with their infants than mothers (Lewis & Lamb, 2003). Alternatively, given the findings that father play was positively correlated with infant RSA at 4 months and father care was positively associated with infant RSA at 8 months, perhaps infants who are higher in baseline RSA and highly surgent might evoke more involvement from their fathers. Future research should further explore these possibilities by examining parental involvement in mothers and fathers within the context of the family.

It is important to acknowledge that this study is not able to disentangle the extent to which both genetics and environment are associated with infant physiological regulation. Parents with high baseline RSA might also be better caregivers due to their greater ability to respond to potential challenges in the environment (Stifter & Corey, 2001). This physiological advantage might be passed on genetically to their offspring and might explain the main effect seen between paternal care involvement and infant baseline RSA. However, it could also be the case that parenting behaviors serve as a direct environmental influence on infant physiological regulation (Moore, 2009). Future research should account for different environmental factors, such as parent anger (Moore, 2009), that could affect infant physiological regulation.

Limitations, Future Directions, and Implications

This study has several limitations that must be noted. One limitation of this study is the small sample size. Due to the modest sample, mother and father involvement data were kept in separate models, and as a result hypothesis two (comparing mothers and fathers results) was not statistically examined. Different patterns in outcomes between parents do not necessarily indicate the ability to make direct comparisons between mothers and fathers. Future studies should aim to have larger sample sizes to increase statistical power and should also consider taking family systems perspective when examining infant cardiac physiological regulation. Examining the development of infant cardiac physiological regulation within the context of the family, such as parenting concordance and/or compensatory mechanisms, would allow for researchers to make further conclusions about transactional developmental processes of the infant physiological system beyond the parent-infant dyad. Generalizability of the results is also an issue as the majority of parents were married and living together. This study did not account for differences in involvement levels between single-parent and two-parent households. For fathers who are the primary caregiver, their involvement level may differ considerably from mothers (Lewis et al., 2009).

Even though the study was multi-method due to inclusion of both questionnaires and the laboratory assessment of physiology, response bias when utilizing questionnaires is a potential limitation. It is important to note that the present study had both parents independently rate their infant’s temperament, the scores were moderately correlated, and the alphas were acceptable. Future studies could also combine questionnaire data with observational forms of temperament to achieve higher validity in ratings of infant temperament. Parental involvement could also be measured using methods that assess involvement beyond just a one-day rating. Interviews could be conducted from multiple family members about the average involvement of a parent over time (Williams & Radin, 1999). Even though the checklist included items about the hours the parent was available to the infant over the course of the day, it did not include items about how many times a day a parent engaged in those specific parenting activities. It also did not cover the full range of possible care and play activities. Therefore, a more complete, comprehensive measure may be needed in order to more fully access parental involvement.

The current study also examined infant RSA during the context of a baseline task with mothers and fathers. Due to the underlying research question pertaining to infant cardiac physiology, it is important to note that infant arousal/affective state during this task was not taken into consideration in analyses. Future research could also include ratings of infant arousal and affective state in conjunction with physiological measures. Moreover, previous reviews have stressed the importance of taking into consideration the context in which cardiac physiology is measured when interpreting findings (see Dennis, Buss, & Hastings, 2012 for a comprehensive review). Future studies should try to replicate these findings with infant RSA measured during challenging tasks, such as a frustration task. It is possible that research examining infant RSA suppression from baseline to a stress-inducing state might find different results.

Researching how infant temperament and parental involvement interact could further understanding of how parents can influence their child’s development. Previous research has shown that different temperament styles in infants might require parents to interact with their infants in different ways to best support their infant’s temperament style (Planalp et al., 2013). Findings from the current study could inform the development of further interventions with both mothers and fathers that increase their awareness of how not only their actions but also their infant’s temperament might affect infant regulation. This study also adds to the literature regarding the link between infant temperament and cardiac physiology.

Conclusions

Overall, this study extends the literature on the link between children’s temperament and physiological regulation by focusing on the possible moderator of parental involvement. This study showed that infants who are high in surgency and have low maternal play involvement may have an enhanced potential to respond to environmental challenges as they have higher baseline RSA than other groups of children. In addition, fathers who engage in more care activities have infants who have a greater potential to respond to challenges in their environments than infants with fathers low in care involvement. Findings suggest that the PNS is still very flexible in young infancy. Taken together, these results underscore the importance of evaluating the associations between parenting, infant surgency, and cardiac physiological regulation across early infancy.

Highlights.

  • Longitudinal predictors of infant cardiac physiological regulation were examined from 4 to 8 months.

  • The study examined infant cardiac physiology with mothers and fathers.

  • The association between infant surgency and cardiac physiology depended on mother play.

  • Father care was associated with infant cardiac physiology.

Acknowledgements

This research was supported by NIGMS (8P0GM103436, P20GM103436), a WKU RCAP Level 1 grant, and a WKU Ogden College of Science & Engineering QTAG grant awarded to the second author. We would like to thank the families who participated in the study, as well as our research assistants.

Footnotes

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