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Behavioral development of infant holding and its laterality

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Contents lists available atScienceDirect

Infant Behavior and Development

Behavioral development of infant holding and its laterality in relation

to mothers’ handedness and child-care attitude

K. Negayama

a,

, M. Kawai

b

, H. Yamamoto

c

, K. Tomiwa

d

, Y. Sakakihara

e

,

Japan Children’s Study Group

aFaculty of Human Sciences, Waseda University, Japan

bInstitute for Education, Mukogawa Women’s University, Japan

cClinical Research Institute, Mie-chuo Medical Center, National Hospital Organization, Japan

dGraduate School of Medicine, Kyoto University, Japan

eDepartment of Child Care and Education, Ochanomizu University, Japan

a r t i c l e i n f o

Article history:

Received 2 October 2008

Received in revised form 28 June 2009 Accepted 17 November 2009

Keywords: Holding Infants Laterality Handedness Parenting stress

a b s t r a c t

The holding of 465 Japanese infants by their mothers was longitudinally observed at 4 and 9 months with several checkups and questionnaires of physical and psychological develop- ment and child-care attitude in a larger longitudinal study of mother–child relationships. A left side bias in holding was significant for the 4-month-old infants. The infants’ increased autonomy in their ability to adopt a posture at 9 months weakened the holding bias. The mothers’ handedness was related to different right/left hand contact patterns, but it was significant only for holding on the left side. The infants’ reflexes relating to posture did not correlate with the holding bias at 4 months. The meaning and possible determinants of holding laterality are discussed.

© 2009 Elsevier Inc. All rights reserved.

1. Introduction

Holding is essential for young infants as it enables caregivers to transport, nurse, protect, and love them. However, in spite of its importance, little is known about the behavior or how it develops. Holding is a caregivers’ behavior directed to infants, but it is also more than that. Infants actively participate in holding by clinging to the holders, changing their own postures, or even by rejecting it (Saijo, 2002a,b; Saijo & Negayama, 2001). It is actually a joint engagement of holder and infant in dynamic and mutual bodily communication. Although touch from parent to infant has been regarded as an important intervention (Field, 1995, 2001), our standpoint emphasizes the mutuality between parent and infant.

There have been short reports on the development of holding (Rheingold & Keene, 1965; Saijo, 2002a,b; Saijo & Negayama, 2001), but the present study is the first attempt to describe the behavior and its development with a large sample size. In order to describe its development, movements of the mothers’ hands and of the infants’ hands and legs, and the holding position, were focused on in particular.

Corresponding author. Tel.: +81 4 2947 6739; fax: +81 4 2924 3789. E-mail address:negayama@waseda.jp(K. Negayama).

0163-6383/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.infbeh.2009.11.001

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1.1. Laterality

Left-side preference in holding has been demonstrated repeatedly (e.g.,Alvarez, 1990; Bundy, 1979; de Château, 1983; Salk, 1960, 1973). Salk was inspired by a rhesus monkey mother showing a left-side bias in her holding. The same bias was also found in caged great apes (Manning & Chamberlain, 1990). Left-side preference is present even among nulliparous human females (Saling & Tyson, 1981) and in children as young as 3 years old (Souza-Godeli, 1996). This might suggest a genetic component in the holding of infants to the left (de Château, 1987; de Château & Andersson, 1976), although a cultural variation has also been noted (Nakamichi, 1996).

Although the left-side bias was initially assumed to be related to the sound of the heartbeat (Alvarez, 1990; Salk, 1960, 1973), it was then found that a mother with her heart on the right side still held her infant to the left (Todd & Butterworth, 1998). Left-side bias has also been attributed to hemispheric dominance (Alvarez, 1990; Harris, Almerigi, Carbary, & Fogel, 2001; Manning & Chamberlain, 1991). The right hemisphere is known as a center of emotion, and holding an infant on the left side enables both caregivers and infants to send social stimuli from their own left side and to receive the partners’ social stimuli via their own left side receptors.

Left-holding bias may be good for a child’s language development (Sieratzki & Woll, 1996). However, right-side holders speak with higher pitch and amplitude compared to left-side holders (Reissland, 2000). Furthermore, according toTurnbull and Bryson (2001), lateral ear preference for perception of emotion by hearing is not significantly associated with lateral holding bias, and they propose the possibility of the contribution of several sense modalities, including the tactile.

Matheson and Turnbull (1998)failed to prove the hypothesis that, if perception of the infant via the left eye is important in stimulating the leftward bias, occlusion of the left eye might reduce the leftward holding. Thus lateral visual information was not proved to be a primary determinant of the left-side bias.Lucas, Turnbull, and Kaplan-Solms (1993)reported that leftward holders did not show higher left visual field scores of perception of facial emotion than rightward holders. Again they proposed the possibility of the contribution of perceptual modalities other than vision, including the tactile.

1.2. Holding as tactile behavior

Laterality of holding may be connected with the tactile modality. It should be emphasized that communication mediated by contact in general is unique (Negayama, 2002): it is always simultaneously bilateral; it is also personal and the experience is not shared by a third other; and it can be directed to/from any part of the body. Holding is also special in involving prolonged contact. Such characteristics are favorable for conveying affection between caregivers and infants.

Handedness might also be involved.Van der Meer and Husby (2006)demonstrated a positive relationship between handedness and the side of doll-holding in participants from 4 to 86 years. Right-handed parents showed a consistent left- side preference in holding, which declined slightly as the infants grew older (Dagenbach, Harris, & Fitzgerald, 1988). In another study, right-handers reported significant imaginary left-side bias in holding, whereas left-handers did not (Harris, Almerigi, & Kirsch, 2000).Vauclair and Donnot (2005)also demonstrated that right-handers exhibited a left-side bias in a doll-holding task, while left-handers did not show such bias. On the other hand, handedness has been reported to have little or no influence on holding behavior (Bogren, 1984; de Château et al., 1978). Thus the relationship between maternal handedness and holding bias has been controversial and open to further examination.

Infants may be held on the arm or on the shoulder. Arm-holders showed a left-side bias, whereas shoulder-holders did not (Vauclair & Donnot, 2005). Visual feedback is richer when infants are held on the arm than on the shoulder, and this suggests that arm position is also related to side preference. The arm-holders also showed a left visual field preference whereas the shoulder-holders did not. When choosing a happier face, the participants showed a left visual field bias. Thus, in spite of the absence of a simple effect of handedness, an interaction between handedness and hand use could still be postulated. Hence there is a need to scrutinize what the right and left hands actually do when an infant is being held. The present study is the first to carefully analyze the behavior of mothers’ right and left hands in holding.

1.3. Holding as communication

Laterality of holding is in fact determined by many factors (Sieratzki & Woll, 1996), and more attention should be paid to its communicative function. Holding is not only a physical behavior, but is also strongly connected with the emotional quality of caregiver–infant relationship. A detailed analysis of holding recorded in home movies showed that behavioral interactions between mother and infant in holding were important cues to understand the quality of the relationship (Massie, 1975, 1977, 1978).

Weatherill et al. (2004)demonstrated right-side preference in depressed mothers of 1-year-olds. The mothers holding their newborn to the left side had stronger concerns about pregnancy, delivery and child health at birth (Bogren, 1984), had more contact with the district nurses and Health Centers, and showed a greater need for support and more anxiety about their children during the 3-year follow-up period (de Château, 1987). These reports suggest a possible link between the mothers’ holding side preference and the later quality of relationship with their infant from a very early stage of development, but it is still not clear when the left-side preference produces a positive childcare attitude, or vice versa. In this context, it is important to relate maternal handedness to the behavioral interaction with the infant during holding.

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Table 1

Participants’ details.

Mie Osaka

n Mean SD % n Mean SD %

Participant age at 4 months 185 129.4 4.3 280 139.0 11.5

Participant age at 9 months 184 281.7 3.4 264 283.6 13.0

Gestation (d) 275.4 9.8 275.0 13.8

Birth weight (g) 2972.0 370.0 2980.3 443.0

Birth body (cm) 49.4 1.8 48.9 2.8

Body weight (g) 6760.6 779.9

Number of siblings 1.6 0.7 1.5 0.7

Birth order 1.6 0.7 1.5 0.7

Sex

Boys 92 50.0 128 48.7

Girls 92 50.0 135 51.3

Twin

Twin 6 3.3 6 2.3

Singleton 176 96.7 257 97.7

Delivery

Cesarean section 29 13.2 42 13.6

Vaginal delivery 150 68.2 215 69.6

Forceps delivery 1 0.5 2 0.6

Vacuum extraction 11 5.0 8 2.6

Cesarean section 29 13.2 42 13.6

Final education of mother

Junior high-school 5 2.8 7 2.7

Senior high-school 43 24.4 58 22.5

University 126 71.6 189 73.3

Graduate school 2 1.1 4 1.6

Feeding style at 4 months

Breast feeding 47 56.0 52 54.2

Formula feeding 12 14.3 15 15.6

Mixed feeding 25 29.8 29 30.2

Working style at 4 months

Full-time 63 84.0 41 54.7

Part-time 5 6.7 13 17.3

Self-employed 7 9.3 21 28.0

Donnot, Vauclair, and Bréjard (2008)found that breast-feeding reduces left-side bias for holding newborns, as well as reducing depressive symptoms. Thus, analysis of the effect of feeding style (breast-feeding or formula feeding) and holding laterality on parenting stress was also included in the present study.

1.4. Summary of aims

The major purposes of the present study were twofold: firstly, to clarify the longitudinal development of holding as a behavior by observing the same mother–infant dyads at both 4 and 9 months, referring especially to hand use and laterality of holding; and secondly, to specify the meanings of laterality in terms of the mother–infant relationship by examining the links between laterality and some psycho-physical parameters, including the mothers’ handedness and selected data obtained from medical checkups, as detailed below.

2. Method

2.1. Participants and procedure of examination

The present study was part of a larger longitudinal cohort study from 4 months to 3 years of age examining early determinants of later social development. Of 465 Japanese children living in the two western sites of Mie (N = 185) and Osaka (N = 280) Prefectures, 92 (50.0%) and 128 (48.7%) infants were boys, 95 (51.3%) and 151 (53.9%) were first-borns, and 6 (3.3%) and 6 (2.3%) infants were twins, respectively (Table 1). Both sites started the study at roughly the same age, but the Mie infants were slightly younger and the difference was significant. In the Osaka samples some information was lacking, and hence in some of the following analyses only the Mie data were analyzed.

The mothers who agreed to participate in the study, in response to our written request, visited hospitals with their infants at 4, 9, 18, and 36 months of age. The study was carried out in a specially built 5.4 m × 5.4 m × 2.5 m test booth with

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a one-way mirror, and according to a predetermined procedure. The booth was equipped with 6 remote-controlled video cameras and a microphone that enabled us to record behavior of the dyads from different directions. The present study focused on 4- and 9-month-old infants only (seeTable 1for detail of background information of the Mie and the Osaka participants).

The present study consisted of several different tests and experimental situations to check infant health and development and mother–infant relations. Medical checkups were done to test neurological, motor, cognitive, and social development. The medical examinations employed in the present study were those routinely performed at the well-baby clinic by the physi- cians. These neurological examinations can detect the subtle deviations of muscle tone and reflexes indicating the presence of neurological disorders, especially cerebral palsy. In the present study, to check a relationship with the development of holding, examinations of Landau reflex, grasping reflex, muscle tonus, and postural development of infants were focused on. The Landau reflex is a straightening of legs and back while trying to lift up the head when the infant is held horizontally and face down. This test is sensitive to hypo- and hyper-tonicity of the trunk and extremities. Development of postural reflexes and other relevant motor responses were further examined in the Mie sample by observing head-lifting while being pulled up, head-raising when placed in a prone position, and reaching and grasping objects. The total examination procedure took about 40 min.

Mothers were asked to complete about 500 questions originally developed by JCS research Group covering basic demo- graphic information perinatal conditions, family, APGAR, SES, parenting stress, parents’ physical and mental health (GHQ, General Health Questionnaire), child-rearing attitude, life habits, and child sleeping pattern at 4 and/or 9 months. Infor- mation on motor, manipulative, language, social, and feeding development was also collected by KIDS-A (Kinder Infant Developmental Scale Type A,Miyake, Ohmura, Takashima, Yamauchi, & Hashimoto, 1989). The questions were sent to the parents two weeks before observation and the answers were collected at the hospital visit.

Out of the diverse questions above designed for the full large cohort study, a Parenting Stress Scale was devised for the present study to produce a psychological index of the mother’s child-care attitude. This was a sum of the scores of 10 questions about possible stresses in child-care with 4-point rating scales. The questions were “I do not know how I should treat my child.”, “I do not know how I should rear my child.”, “I get angry with my child.”, “I regret my child-rearing.”, “I want to push away my child”, “I think that a fault in my child is due to me.”, “My husband does not care for my child.”, “I am confused by the flood of information about child-care”, “I have little time to be in contact with my child.”, “Child-rearing is a burden to my husband.”

The mothers were also administered the H.N. Handedness Inventory (Hatta & Kawakami, 1995) to check their handedness. The inventory consists of 10 unimanual tasks: use of an eraser, a match, a pair of scissors, a pin, a knife, a screwdriver, a hammer, a razor, a toothbrush, and a ball. The mothers were asked to mark one of three alternatives: left hand, right hand, or both hands. Normally, those with more than 4 choices of left hand are interpreted as left-handed, and more than 8 choices of right hand as right-handed. But there has been a strong pressure for left-handers to be ‘corrected’ into right-handers in Japan, and sufficient left-handers were not obtained by this procedure in the present study. Hence an Index of right-handedness was calculated instead, by subtracting the number of left-hand choices in the above 10 tasks from that of right-hand choices, ranging from −10 to 10.

2.2. Procedure of observation

A mother and infant pair was led to the booth where a medical staff person was present. The instructions were given to the mother by that person. The mother was first asked to put the infant down on the floor and pick him/her up again immediately. Then she was invited to walk around in the booth with the infant in her arms, which enabled us to record the holding from different directions. Thereafter the mother was prompted to place the infant in a baby chair for other experiments not reported here. The mother and infant were videotaped 3-dimensionally by the cameras on the booth walls and ceiling. The total length of the observation of putting down, picking-up and holding was normally about 2 or 3 min. The observation was skipped when the infants were in a state of low arousal or ill temper.

The episodes of holding were saved in HDD, and then cut-up into clips for analysis with ‘Mivurix’, a free program for video analysis developed byArakawa (2005). Each clip was analyzed with a focus on the side-bias of holding, i.e., the position of the infant’s head in relation to the mother’s body (left, center, or right); the behaviors of the mother’s and the infant’s right and left hands; the infant’s legs; and the positions (front or side of mother’s body) and postures (vertical, diagonal, horizontal) of the held infant (seeFig. 1). Contact by the mother’s hands was analyzed in particular detail. For the infant’s hands, only the presence or absence of contact with the mothers’ body was analyzed, in order to examine the infant’s own participation in posture maintenance. The infant’s legs sometimes clutched the mother’s body to keep their own posture stable. Holding behaviors changed dynamically during the observation, and hence we analyzed only the holding pattern at the end of walking around, as it was relatively stable.

The behaviors were coded by a well-trained coder. An index of inter-coder concordance was calculated by the agreement and disagreement of coding, A/(A + D), based on 20% of the episodes of observation. Indices of concordance for mother’s right and left hands, infant’s right and left hands, infant’s clutching mother with legs, holding position, and laterality of holding were 0.93, 0.89, 0.98, 0.87, 0.98, 0.96, and 0.89 at 4 months and 0.96, 0.96, 0.90, 0.90, 0.87, 0.90, and 0.87 at 9 months, respectively.

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Fig. 1. Illustrations of some major holding patterns/positions. A: Holding on the left in a vertical posture. Left hand, the hand of the same side as holding, is on the upper body (Embracing armpit and back) and the right hand, the hand of the opposite side to holding, is on the lower body (Embracing leg and buttocks). Infant’s legs do not clutch mother. B: Holding on the left in a vertical posture. Left hand, the hand of the same side as holding, is on the lower body (Embracing leg and buttocks) and the right hand, the hand of the opposite side to holding, is on the upper body (Embracing neck and back). Infant’s legs clutch mother. C: Holding on the right in a vertical posture. Right and left hands are on lower body (Joining both hands under buttocks). D: Holding at the center in a vertical posture. Left hand is on lower body (Hooking crotch) and right hand on the upper body (Embracing abdomen). Infant’s hands are not on mother (0H-on). E: Holding on the left in a diagonal posture. Left hand is on the upper body (Embracing shoulder and back) and the right hand is on the lower body (Embracing leg and buttocks).

3. Results 3.1. Laterality

52.2% and 35.8% of the mothers showed left- and right-side preferences in holding at 4 months, respectively. The bias of left-side holding vs. right-side holding was significant at 4 months, 2(1, N = 263) = 4.61, p = .003. However, the difference was not significant at 9 months (47.6% and 41.1% for left and right sides, respectively), 2(1, N = 371) = .83, p = .361. Among 4-month-olds, those with left-side holding mothers were significantly younger, by 2 days in average, than those of the right-side holders, F (1, 276) = 4.33, p = .038, i.e., the younger infants tended to be held on the left. The consistency of holding bias is shown inTable 2.

The infants held on the right- and the left-sides at 4 months were compared in the reflexes, muscle tonus, and pos- tures in the Mie samples, and no significant differences in any of the tests between the two groups was found. Mothers’ report by KIDS also showed no significant relationship between side preference and any aspect of motor development at 4 months.

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Table 2

Holding position at 4 and 9 months.

Position at 4 months Position at 9 months Number of dyads (%)

Left Left 83 (31.6)

Center 14 (5.3)

Right 37(14.1)

134 (51.0)

Center Left 10 (3.8)

Center 5(1.9)

Right 18 (6.8)

33 (12.5)

Right Left 30(11.4)

Center 10 (3.8)

Right 56 (21.3)

96 (36.5)

Total 263 (100.0)

How mothers made contact with the infant with their right and left hands during holding was analyzed in the Mie sample at 4 and 9 months. As shown inTable 3, mothers frequently placed their hands on the infant’s upper back, embraced the leg and buttocks, or placed them under the buttocks at 4 months. A certain proportion of mothers showed holding with both hands joined together under the buttocks. The latter pattern increased and became the most prominent contact pattern at 9 months (from 9.2% at 4 months to 44.2% at 9 months). Body weight increased from 6761 g at 4 months to 8413 g at 9 months in average, and this seemed to be a significant cause of the change in holding.

The position of the held infants was also diverse, with holding against the mothers’ front the most frequent posi- tion at both ages. Holding to the side, however, significantly increased from 4 to 9 months. Infants’ clutching mothers with their legs also increased from 4 to 9 months, and the infants’ hands contacted the mothers’ body less at 9 months (Table 4).

The holding bias was produced by a combination of right and left hand contact by the mothers.Fig. 2shows correspon- dence analysis of different behaviors of mothers’ right and left hands, infants’ hand contacts and infants’ leg clutching in the Mie group at 4 months. In order to simplify, mothers’ hand behaviors were compiled into 5 categories: (1) On back/chest consists of Place on upper back, Embrace armpit and back, and Embrace neck/shoulder and back; (2) On buttocks/hips consists of Embrace leg and buttocks, Place under buttocks, and Place on hips; (3) On armpit consists of Grab armpit and Place on armpit; (4) Under buttocks is Joining both hands under buttocks; (5) Hooking crotch. For infant behaviors, 0H-, 1H-, and 2H-on mean no hand, 1 hand, and 2 hands on mother; and Clutching and Non-clutching are Clutching mother with legs or not.

From the analysis, four clusters emerged. Cluster 1 was holding with both hands under the buttocks. Clusters 2 and 3 were symmetrical in that one hand is at the lower body and the other at the upper body. Interestingly, clutching with the legs occurred together with weight support by the right hand (Cluster 2). Conversely, the infants’ legs were relaxed and their hand(s) were on their mothers when the mothers’ right hand was on the upper area (Cluster 3), suggesting that the infants were more interactive with the mother when their right hand was free. Hooking crotch (Cluster 4) was holding without hand contact by the infant, which was partly because of directing the infants forward as illustrated inFig. 1.

Table 3

Patterns of contact with infant by mother’s right and left hands at 4 and 9 months.

4 months old 9 months old

Right hand Left hand Right hand Left hand

N % N % N % N %

Place on upper back 32 22.7 19 13.5 6 3.8 3 1.9

Embrace armpit and back 6 4.3 8 5.7 8 5.1 9 5.8

Embrace neck/shoulder and back 3 2.1 2 1.4 1 0.6 0 0.0

Grab armpit 4 2.8 3 2.1 4 2.6 2 1.3

Place on armpit 7 5.0 12 8.5 0 0.0 8 5.1

Embrace leg and buttocks 37 26.2 48 34.0 27 17.3 31 19.9

Place under buttocks 12 8.5 19 13.5 5 3.2 10 6.4

Place on hips 5 3.5 0 0.0 20 12.8 9 5.8

Join both hands under buttocks 13 9.2 13 9.2 69 44.2 69 44.2

Hook crotch 6 4.3 5 3.5 6 3.8 6 3.8

Others 13 9.2 10 7.1 10 6.4 9 5.8

Unknown 3 2.1 2 1.4 0 0.0 0 0.0

141 100.0 141 100.0 156 100.0 156 100.0

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Table 4

Holding positions and infant’s hand and leg behaviors at 4 and 9 months.

At 4 months At 9 months P

Mother’s hands Upper and Lowerc Lower and Lowerd

Upper and Lowerc 37 66 .000a

Lower and Lowerd 7 15

Held position Front of mother Side of mother

Front of mother 263 43 .000a

Side of mother 2 1

Clutching mother with legs Yes No

Yes 3 3 .000a

No 42 266

Infant’s hands Both hands on mother One hand on mother Both hands off mother

Both hands on mother 79 65 20 .002b

One hand on mother 33 36 14

Both hands off mother 9 11 9

a McNemar test.

b McNemar–Bowker test.

cOne hand on infant’s upper body and the other hand on infants lower body.

dBoth hands on infant’s lower body.

The combinations of right- and left-hand contacts while holding on the right- or left-side were classified into three different patterns from the Mie and Osaka data: (1) the hand of the holding side was under the buttocks and the opposite hand on the upper body, i.e., infant body weight was supported mainly by the hand of the holding side; (2) the hand of the holding side was on the upper body and the opposite hand under the buttocks, i.e., infant weight was supported mainly by the hand of the opposite side; and (3) both hands were under the buttocks. The distribution of the 3 patterns was 69 (42.1%), 51 (31.1%), and 44 (26.8%) dyads on the left, and 50 (43.5%), 40 (34.8%), and 25 (21.7%) dyads on the right, respectively. The distributions of the 3 patterns for the left-side and right-side holdings were both significant (2(2, N = 164) = 6.09, p = .048 for the left-side holding; 2(2, N = 115) = 8.26, p = .016 for the right-side holding, respectively). Thus the hand of the holding side tended to be used to support the infant’s weight.

3.2. Handedness and side preference

When the handedness of the mothers was taken into consideration, the result turned out to be more complex.Fig. 3 shows the patterns of contact with the right and left hands while holding on the left or the right side at 4 months, based on the 241 dyads of the Mie and Osaka samples whose handedness was reported.

Fig. 2. Correspondence analysis of different behaviors in mothers’ right and left hands, infants’ right and left hand contacts and clutching with legs of the Mie group at 4 months. R and L in parentheses stand for right and left hands, respectively.

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Fig. 3. Index of right handedness, hand contact positions, and laterality at 4 months old. RH and LH stand for right hand and left hand, and ‘upper’ and

‘lower’ stand for ‘on the upper body’ and ‘on the lower body’.

Table 5

Relationship between breast-feeding/holding side bias and Parenting Stress Score.

Feeding Holding side

Exclusive breast-feeding Others ANOVA Left Right ANOVA

Mean 17.83 19.78

F (1,49) = 5.48, p = .023 18.18 19.93 F (1,49) = 3.92, p = .053

SD 4.04 3.81 4.10 3.65

Main effects of laterality (left and right holding) or hand contact patterns (RH upper and LH lower, RH lower and LH upper, and RH lower and LH lower) on scores of Index of right handedness were not significant: F (1, 235) = .004, n.s. for laterality, and F (2, 235) = .290, n.s. for hand contact pattern, respectively. However, an interaction of laterality × hand contact pattern was significant, F (2, 235) = 3.86, p = .023. When holding on the left-side, the right handedness was significantly weaker when the right hand was on the infant’s lower body and the left hand was on the upper body (RH lower and LH upper) than in the two other hand patterns (p’s = .019 and .027 by LSD test for the differences from RH upper and LH lower and from RH lower and LH lower, respectively). RH upper and LH lower was not significantly different from RH lower and LH lower. In other words, when holding on the left side, the mothers with a relatively stronger left-handed tendency preferred to contact the upper body area with the left hand (LH upper) and to support the infant with the right hand (RH lower). However, when holding on the right side, the preferred hand tended to be used to support the infant on the lower body area instead of contacting the upper body area, although the difference across the 3 hand contact patterns did not reach a significant level, F (2, 96) = 1.48, p = .234.

3.3. Feeding style, holding side and parenting stress

Finally, the effects of mothers’ feeding style (exclusive breast-feeding or other) and preference in holding side (right or left) on the score on the Parenting Stress Scale were examined by two-way ANOVA for the Mie participants at 4 months. Although the sample size was not large, main effect of feeding style was significant, and that of holding side was nearly significant, F’s (1, 88) = 5.48 and 3.92, p’s = .023 and .053, respectively. The exclusively breast-feeding mothers were less stressed in child-rearing than those giving formula, and the left-side holders tended to be less stressed than the right- holders at 4 months (Table 5). However, exclusive breast-feeders were not significantly biased towards left-holding, 2(1, N = 52) = .25, n.s.

4. Discussion

The present study attempts to describe mother–infant holding as a behavioral interaction and to describe its longitudinal development at 4 and 9 months of infants’ age. It also attempts to relate the behavioral characteristics of holding to physical as well as psychological parameters of mothers and infants. Laterality of holding and handedness of the mothers were especially focused on.

Detailed analyses of holding demonstrated that holding is a complex combination of right and left hands of both mothers and infants, and the infant’s legs. Position and posture of the infants were diverse, too. The mothers’ hand behavior was dynamically afforded by the infant’s body, and similarly, the infant’s hand and leg behaviors were afforded by the mother’s body.

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The results indicate that a preference for left-side holding is evident at 4 months, which is consistent with the findings of previous studies. However, this left-side bias disappears by 9 months, and even among 4-month-olds those held on the left-side are significantly younger than those on the right-side.Donnot and Vauclair (2007)demonstrated the existence of a left-side holding bias among mothers of newborns, which indicates that the left-side bias is evident from immediately after birth but disappears as infants develop. The present results suggest that the bias and its disappearance are related to some developmental parameter(s) of infants and their mothers.

Two major holding patterns were revealed, one hand under the buttocks with the other hand on the upper body, and both hands joined under the buttocks. Together with an increase of the latter pattern at 9 months, hands-off mother, clutching mother with legs, and being held on the lateral rather than the frontal position increased in infants. The change then made it easier for the infants to rotate the upper body and look around to explore the booth when mothers walked around. It was a sign of an increase in autonomy of infant behavior at 9 months. The mothers gave more freedom to the infants to move by joining both hands under the buttocks without holding the upper body. This increased autonomy and curiosity toward the environment among infants is a cause of the reduction in the mothers’ left-side holding at 9 months.

Holding is certainly a joint activity of mothers and infants in which the infant actively participates, and laterality of holding is obviously linked with the infants’ development. In spite of that, the lateral bias of holding was not related to any of the parameters of the infants’ physical development (reflexes, muscle tonus, posture and mothers’ everyday observation) at 4 months. A general absence of any links between the lateral bias of holding at 4 months and concurrent physical development may suggest that, at this age, the infants’ neurological maturation is not a major determinant of the appearance of a side bias of holding. However,Ginsburg, Fling, Hope, Musgrove, and Andrews (1979)demonstrated a relationship between holding bias and head-turning in neonates, and the relationship between side bias of holding and infants’ physical parameters should be further explored with younger infants.

Infants were more autonomous in keeping an upright posture with clutching mothers with the legs when the body was supported by the mother’s right hand, whereas they contacted mothers manually without leg clutching and were seemingly more interactive with the mothers when supported by the left hand. It was also found in the present study that the left-side and the right-side holders were not symmetrical in their hand contact patterns.Van der Meer and Husby (2006)demonstrated a clear tendency to hold a doll infant by the non-dominant arm, leaving the dominant hand available for other tasks (giving a dummy to the doll in their procedure). It is plausible that left-side holding is advantageous for right-handers for interacting with infants with the preferred hand, including bottle-feeding (Donnot et al., 2008).

In fact, a significant interaction was found between the side of holding and the hand contact patterns with respect to the right-handed tendency: the right handedness was significantly weaker when infants were held on the left side with the mothers’ right hand on the infants’ lower body and the left hand on the upper body than in the two other hand contact patterns. In other words, mothers with relatively stronger left-handedness tended to support the infants with the right hand and interact with them with the left hand when holding them on the left side.

This result is compatible with a hemispheric laterality hypothesis that the left side is more sensitive for affection, and hence the dominant hand was used for interaction with infant. It could be postulated that the left hand works to send and receive tactile sensations to/from the right hemisphere, and the mothers with a tendency to left-handedness might also have a stronger inclination to place the infants on the left side.

However, this tendency was reversed when the infant was held on the right side. It might be that, when on the right side, the tendency of the dominant hand to interact with infant is weakened and the hand is used to support the infant weight instead. Mothers of newborns show the left-side bias but without a clear relationship between hemispheric special- ization and holding bias (Donnot & Vauclair, 2007). It might rather be hypothesized from the present findings that initial lateral preference of holding is based on the combination of the mothers’ handedness and hemispheric dominance. Further examination is obviously needed on this point.

Infant holding has mostly been studied for neonates or dolls, which do not actively participate in holding, with the exception of the studies done at 1 year byWeatherill et al. (2004)andTodd and Butterworth (1998)at 40 days. Infants in the present study affected the mothers’ holding behavior with their own active participation and with their curiosity about their surroundings.

Infants’ spontaneous arm movements and reaching show a fluctuation in lateral biases during the first year in spite of the presence of rightward predominance (Corbetta & Thelen, 1999). Using an ultrasound technique, Hepper et al. demonstrated a right-hand preference among fetuses (Hepper, McCartney, & Shannon, 1998; Hepper, Shahidullah, & White, 1991). The right-hand preference in fetuses is actually connected with right handedness in the postnatal period, although the reason of the preference is not clear (Hepper, Wells, & Lynch, 2005). However, as handedness appears to be more or less fixed by the age of 3 years, and the degree of lateralization develops until age 7 (McManus et al., 1988), it seems difficult to explain the present result of holding bias by the infants’ handedness in a straightforward way. Obviously the fetal preference of a particular hand does not directly link with the position of holding as later motor development is also involved. Conversely, it is possible that left holding bias induces the infants’ later rightward hand predominance. It is worth investigating further how the handedness of infants is developmentally related to the holding bias. The complex co-development of handedness and posture is an interesting question to answer from a dynamic systems approach, asCorbetta and Thelen (1999)have suggested.

In a study byWeland and Sperber (1970), patients with anxiety tended to hold a small rubber ball against the left-side of the chest which may suggest that a function of left-side holding is to reduce anxiety of both mothers and infants and hence

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provide a secure base on which an intimate relationship is gradually built. Holding bias observed at 4 days old byde Château (1987)was related to anxiety and the need for child-care support over the following 3 years. The present study also found a tendency that the left-side holders felt less stress about child-rearing at 4 months, which is in accordance with the result of Weatherill et al. (2004). At the same time, exclusively breast-feeding mothers were less stressed by child-care. This result is compatible with that ofDonnot et al. (2008). Thus, holding as a tactile experience for both mother and infant could help to foster the relationship between them later on.

Acknowledgements

This research has been supported by RISTEX, JST (Japan Science and Technology Agency). The authors are grateful to Ayumu Arakawa, Noriko Yamakawa, Tadahiko Maeda, Yoko Anji, Kumiko Namba, Yuko Yato, Shunya Sogon, Megumi Sasaki, and Kumi Takata for collecting and analyzing data, and to the mothers and infants whose cooperation made the work possible.

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Fig. 1. Illustrations of some major holding patterns/positions. A: Holding on the left in a vertical posture
Fig. 2. Correspondence analysis of different behaviors in mothers’ right and left hands, infants’ right and left hand contacts and clutching with legs of the Mie group at 4 months
Fig. 3. Index of right handedness, hand contact positions, and laterality at 4 months old

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