Cold pressor stress reduces left cradling preference in nulliparous human females

The left cradling preference refers to the finding that women hold their infants more frequently on the left side of their own bodies. Several observational studies showed reduced left cradling during stressful circumstances, such as mother-infant separation, or domestic violence. However, until now no experimental study was conducted to investigate the immediate impact of stress on cradling behaviour. Half of the 64 female subjects participating were randomly assigned to a stressful bilateral cold pressor test. The remaining subjects performed a non-stressful control procedure. Before and after this intervention, cradling behaviour was assessed using a baby-like doll. Subjects showed a left cradling preference prior to the intervention. The cold pressor test increased blood pressure and heart rate significantly. A repeated ANOVA revealed an interaction of intervention (cold pressor vs. control) X assessment period (pre- vs. post-intervention), indicating that cold pressor stress reduces left cradling behaviour in female volunteers. Our data indicate that stress influences cradling preference. This may be of relevance for caregiver-infant interactions.     

Cradling side preference is associated with lateralized processing of baby facial expressions in females

Women’s cradling side preference has been related to contralateral hemispheric specialization of processing emotional signals; but not of processing baby’s facial expression. Therefore, 46 nulliparous female volunteers were characterized as left or non-left holders (HG) during a doll holding task. During a signal detection task they were then asked to detect the emotional baby faces in a series of baby portraits with neutral and emotional facial expressions, presented either to the left or the right visual field (VFP). ANOVA revealed a significant HG × VFP interaction on response bias data (p < .05). Response bias was lowest when emotional baby faces were presented in the visual field of cradling side preference, suggesting that women’s cradling side preference may have evolved to save cognitive resources during monitoring emotional baby face signals.     

The Leftward Cradling Bias and Prosody: An Investigation of Cradling Preferences in the Deaf Community

Popular theory on the tendency to cradle an infant to the left side points to the specialization of the right hemisphere for the perception and expression of emotion. J. S. Sieratzki and B. Woll (1996) recently suggested that more emphasis be placed on the auditory modality, specifically focusing on the role of prosodic information. In this study, the direction of the lateral cradling bias in a group of profoundly deaf children, a group of deaf adults, and a control group of adults with no hearing impairment was investigated. The authors found a strong leftward cradling bias in all groups, a bias that was, if anything, stronger in the deaf participants. Given that people who are profoundly deaf, especially those who have been deaf from birth, have not been exposed to auditory prosody, the data do not support the suggestion that such prosodic information is the basis for the leftward cradling bias.     

Differential effect of ill-being and chronic stress on cradling behavior of first and multi-time parents

A preference for cradling infants on the left side has been demonstrated in women, as has a relation of reduced left-cradling and stress/negative affect. This relation has not yet been investigated in male participants. Due to less left-cradling in non-fathers compared to fathers it was suggested that fatherhood might have an influence on cradling behavior. The present study investigated the cradling preference of first- and multi-time parents before and after birth, and its relation to ill-being and stress. Results revealed that cradling behavior of first-time fathers was not different before and after the birth of the infant. Thus, fatherhood does not seem to have an acute influence on cradling behavior. Furthermore, cradling behavior of first- and multi-time parents was differentially influenced by ill-being and stress.These results present new information about the course of cradling preference from pregnancy to postpartum and indicate that the relation of cradling and ill-being/stress is more complex for parents than for non-parents.     

The leftward cradling bias and prosody: an investigation of cradling preferences in the deaf community.

Popular theory on the tendency to cradle an infant to the left side points to the specialization of the right hemisphere for the perception and expression of emotion. J. S. Sieratzki and B. Woll (1996) recently suggested that more emphasis be placed on the auditory modality, specifically focusing on the role of prosodic information. In this study, the direction of the lateral cradling bias in a group of profoundly deaf children, a group of deaf adults, and a control group of adults with no hearing impairment was investigated. The authors found a strong leftward cradling bias in all groups, a bias that was, if anything, stronger in the deaf participants. Given that people who are profoundly deaf, especially those who have been deaf from birth, have not been exposed to auditory prosody, the data do not support the suggestion that such prosodic information is the basis for the leftward cradling bias.     

Lateral asymmetry and tactile sensitivity

Weinstein found in 1963 that the left female breast is more sensitive to tactile stimulation than the right breast. Saling and Cooke in 1984 hypothesized that this asymmetry in breast sensitivity underlies the well-documented leftward bias in maternal cradling behaviour, which is independent of manual specialization. Our interest in the Saling and Cooke hypothesis led to an attempt to replicate Weinstein's 1963 study. His findings were not supported. Further, a review of the literature on the lateral distribution of cutaneous thresholds showed that there is little experimental support for the widely held belief that the left side of the body is uniformly more sensitive than the right.     

Cell-mediated immune hypersensitivity is stronger in the left side of the body than the right in healthy young subjects.

More frequent appearance of herpes zoster infection on the left side of the body has been noted. In women, breast cancer occurs more frequently on the left side. It has been suggested that the left neocortex is involved in neuroimmunomodulation via the dopaminergic system. In this study, our purpose was to investigate the possible difference in cell-mediated hypersensitivity between right and left body sides using the tuberculin test with 22 male and 36 female healthy high school students. In the present study, the cell-mediated hypersensitivity was higher in the left side of the body than the right. This difference was slightly more apparent in the girls and may be related to brain asymmetry in neuroimmunomodulation.     

Comparative analysis of proprioception in left and right arms

Using the “kinaesthetic memory for the target” technique, differences in the accuracy of pointing to a target with the right and left arms are analysed. The effect of rotation of the head to left and right upon this process is also studied.

With the head normally orientated, it was found that pointing with the right arm is significantly better than with the left. Accuracy of pointing is greater with the target directly in front of the body than when it lies to either left or right side.

When the head is rotated, the direction of the pointing error is inversely related to the direction of rotation.

The study suggests that the precision of control over arm (in the absence of vision) is related to the varying ability of individual subjects to correlate limb movements with the prevailing orientation of the body, especially of the head and neck. This is additional to the influences of genetically-determined handedness and of the sensory input from the moving limb.     

Human left-sided cradling preferences for dogs

Photographs of men and women holding dogs were analyzed for side-holding preferences. A significant majority of women in dog-themed magazines held dogs on their left sides, similar to reports of women holding infants. Men did not show the same left-sided preference, which is also consistent with other studies. The implications of these results for various hypotheses about infant cradling behavior were discussed.     

The ideologically objectionable premise model: Predicting biased political judgments on the left and right

This paper introduces the ideologically objectionable premise model (IOPM), which predicts that biased political judgments will emerge on both the political left and right, but only when the premise of a judgment is not ideologically objectionable to the perceiver. The IOPM generates three hypothesized patterns of bias: biases among both those on the left and right, bias only among those on the right, and bias only among those on the left. These hypotheses were tested within the context of the dual process motivational model of ideological attitudes (DPM; Duckitt, 2001), which posits that right-wing authoritarianism (RWA) and social dominance orientation (SDO) are related but distinct ideological attitudes. Across two studies, all three IOPM hypotheses were tested and supported on the RWA ideological attitude dimension, and two of the three IOPM hypotheses were tested and supported on the SDO dimension. These findings indicate that the context of the judgment is an important determinant of whether biases emerge in political judgment.     

Infant-holding bias variations in mother–child relationships: A longitudinal study

This longitudinal study examined the associations between maternal depressive symptoms and infant holding bias in a sample of N = 43 women during three prospective sessions: during pregnancy, two months after childbirth, and when the child was 19 months of age. The majority of mothers (65.8% on average) held their children on the left side of their body at all three sessions; approximately 30% demonstrated a change in their preference, in particular between the pre- and first post-natal session. Examination of reciprocal associations between holding bias and depression revealed that prior and concurrent depression did not predict changes in holding-side biases, whereas women's holding preferences when their infant was two months old predicted change in pre- to postnatal depressive symptoms; women favouring a right-sided holding bias were significantly more likely to report increased depressive symptoms across the perinatal period, whereas a left-sided holding bias was associated with decreased depressive symptomatology.     

Maternal cradling bias in baboons: The first environmental factor affecting early infant handedness development?

The most emblematic behavioral manifestation of human brain asymmetries is handedness. While the precise mechanisms behind the development of handedness are still widely debated, empirical evidences highlight that besides genetic factors, environmental factors may play a crucial role. As one of these factors, maternal cradling behavior may play a key role in the emergence of early handedness in the offspring. In the present study we followed 41 Papio anubis infants living in social groups with their mother for which direction (e.g., left- or right-arm) and degree of maternal cradling-side bias were available from a previous published study. We assessed hand preferences for an unimanual grasping task at three developmental stages: (A) 0–4, (B) 4—6, and (C) 9–10 months of age. We found that individual hand preferences for grasping exist as soon as the first months of age, with a population-level left-handedness predominance, being stable until 6 months; to wit the period during which juveniles are mainly carried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed later in the development, once juveniles are no longer carried (i.e., from 9 to 10 months of age), are less dependent from the maternal cradling bias and less consistent with the earlier developmental stages, especially in infants initially cradled on the right maternal side. Our findings suggest that the ontogenetic dynamics of the infant's hand preference and its changes might ultimately rely on the degree of infant dependence from the mother across development.     

Her heart is in the right place: an investigation of the ‘heartbeat hypothesis’ as an explanation of the left side cradling preference in a mother with dextrocardia

A majority of mothers, whether right- or left-handed, exhibit a preference to hold their babies to the left of the body midline. One of the earliest explanations for this finding proposed that babies were being held close to the mother's heart [Salk, L. (1960). World Mental Health, 12 , 168–175]. Salk suggested that the foetus becomes imprinted on the sound of the maternal heartbeat in utero. This paper reports a left holding preference in a mother who has the heart positioned on the right rather than the normal left side of the body. Salk's ‘heartbeat hypothesis’ is not supported by the holding preference of the dextrocardiac mother, nor by the detailed patterns of holding in the control group. © 1998 John Wiley & Sons, Ltd.     

Hemifacial preferences for the perception of emotion and attractiveness differ with the gender of the one beheld

Though the left cheek appears more emotive, perceptions of attractiveness vary with gender. For the first time, this study assessed the relationship between perceptions of emotion (happiness) and attractiveness in naturalistic photographic portraits. One hundred ninety-two participants (63 male; 129 female) viewed pairs of left and right cheek poses, and made a forced-choice decision indicating which image appeared (a) more emotive and (b) more attractive (order counterbalanced). Half the images were mirror-reversed to control for perceptual biases. Results indicated a striking gender difference: for males, the left cheek appears both more emotive and more attractive; for females, preferences are subject to stronger perceptual influences, with the right cheek bias for emotion and attractiveness reversing to a left cheek bias when images are mirror-reversed. These findings suggest that if you want to show the world your “best side”, men should lead with the left but for women, the right cheek is right.     

Hemifacial preferences for the perception of emotion and attractiveness differ with the gender of the one beheld

Though the left cheek appears more emotive, perceptions of attractiveness vary with gender. For the first time, this study assessed the relationship between perceptions of emotion (happiness) and attractiveness in naturalistic photographic portraits. One hundred ninety-two participants (63 male; 129 female) viewed pairs of left and right cheek poses, and made a forced-choice decision indicating which image appeared (a) more emotive and (b) more attractive (order counterbalanced). Half the images were mirror-reversed to control for perceptual biases. Results indicated a striking gender difference: for males, the left cheek appears both more emotive and more attractive; for females, preferences are subject to stronger perceptual influences, with the right cheek bias for emotion and attractiveness reversing to a left cheek bias when images are mirror-reversed. These findings suggest that if you want to show the world your "best side", men should lead with the left but for women, the right cheek is right.     

Children reorient using the left/right sense of coloured landmarks at 18-24 months

In previous studies, children disoriented in small enclosures used room shape, but not wall colours, to find hidden objects. Their reorientation was said to depend solely on a "geometric module" informationally encapsulated with respect to colour. We argue that previous studies did not fully evaluate children's use of colour owing to a bias in the enclosures' design. In this study, disoriented 18-24 month olds searched for toys in small square enclosures with two blue and two white walls. Children successfully reoriented using wall colour. This shows that they can make location judgments based on the left/right sense of the colours of adjoining landmarks. Performance was no different when symmetric colourful shapes were added to walls, but improved with asymmetric shapes which could be used without left/right judgments. The relatively poor use of colour in previous studies may be explained partly by a bias in their design, and partly by children's limited ability to discriminate the left/right sense of nongeometric features.     

Consistent left gaze bias in processing different facial cues

While viewing faces, humans often demonstrate a natural gaze bias towards the left visual field, that is, the right side of the viewee’s face is often inspected first and for longer periods. Previous studies have suggested that this gaze asymmetry is a part of the gaze pattern associated with face exploration, but its relation with perceptual processing of facial cues is unclear. In this study we recorded participants’ saccadic eye movements while exploring face images under different task instructions (free viewing, judging familiarity and judging facial expression). We observed a consistent left gaze bias in face viewing irrespective of task demands. The probability of the first fixation and the proportion of overall fixations directed at the left hemiface were indistinguishable across different task instructions or across different facial expressions. It seems that the left gaze bias is an automatic reflection of hemispheric lateralisation in face processing, and is not necessarily correlated with the perceptual processing of a specific type of facial information.     

Left to right: representational biases for numbers and the effect of visuomotor adaptation

Adaptation to right-shifting prisms improves left neglect for mental number line bisection. This study examined whether adaptation affects the mental number line in normal participants. Thirty-six participants completed a mental number line task before and after adaptation to either: left-shifting prisms, right-shifting prisms or control spectacles that did not shift the visual scene. Participants viewed number triplets (e.g. 16, 36, 55) and determined whether the numerical distance was greater on the left or right side of the inner number. Participants demonstrated a leftward bias (i.e. overestimated the length occupied by numbers located on the left side of the number line) that was consistent with the effect of pseudoneglect. The leftward bias was corrected by a short period of visuomotor adaptation to left-shifting prisms, but remained unaffected by adaptation to right-shifting prisms and control spectacles. The findings demonstrate that a simple visuomotor task alters the representation of space on the mental number line in normal participants.     

Visual exploration of reaching space during left and right arm movements in 6-month-old infants

Infant's manual laterality and eye-hand coordination emerge during the second part of the first year of life with the development of reaching. Nevertheless, little is known about the potential asymmetric characteristics of this coordination. The aim of this study was to describe visuo-spatial exploration in 6-month-old infants during reaching, according to the hand used. More specifically, we examined if the use of the left or the right hand was linked to a specific type of visual exploration. Gaze direction during goal-directed reaching towards an object placed on the table was measured with a remote ASL 504 eye tracker (Bedford MA). Twelve babies aged 6 months were observed during six reaching sessions, alterning three sessions with an object on the left side of the subject and three with an object on the right side. Gaze direction and some hand variables (hand activity, hand opening and hand position from the body) were coded with The Observer software. Results showed that babies visually explore their reaching space differently according to the hand used: they look more at the object when they use their right hand and more around the object when they use their left hand; they also look more often at their left hand than at their right one. These results suggest that an asymmetric visuo-manual coordination exists as early as 6 months: vision seems to support (1) left hand during reaching for evaluate distances from object to baby by means of visual feedbacks and (2) right hand for identify what sort of object is. Results are discussed in light of manual specialization and specific hemispheric skills at this age.     

Speech and music draw attention to the right ear in stereophonic listening

This study investigated whether right-handed subjects would prefer the right ear for normal speech and the left ear for musical stimuli. Right-handed college students (9 women and 2 men) were presented two stereophonic tape recordings, one of normal speech, the other of nonlyrical, orchestral music. Subjects used an attenuator to match the intensity of signals in the left and right earphones. The subjects consistently favored the right side in both conditions. These findings are inconsistent with those of other researchers, such as Segalowitz and Plantery. However, the findings support the 1980 research of Porac, Coren, and Duncan, offering perceptual evidence of a general right-ear bias in right-handed subjects.