Atypical maternal cradling laterality in an impoverished South African population

Asymmetries run deep: the interplay between cradling bias, face recognition, autistic traits, and personality

Personality traits are linked to a variety of cognitive and socio-emotional factors, including lateralization patterns. Autism, prosopagnosia, and atypical cradling have been associated with altered lateralization and socio-emotional processing. This study explores how autism traits, cradling-side preferences, and face recognition abilities relate to individual personality differences. Three-hundred neurotypical adults (150 males) completed an online survey including the imaged cradling preference and three validated questionnaires: the Autism spectrum Quotient (AQ), Prosopagnosia Index-20 (PI-20), and the Big Five Personality Questionnaire (BFQ). Results showed a strong left-cradling bias (LCB) unaffected by sex, handedness, parental status, autism traits, or face recognition abilities. AQ negatively predicted Extraversion, Agreeableness, Emotional Stability, and Openness. LCB correlated with higher Agreeableness and moderated the negative association between AQ and Extraversion. These findings suggest a potential link between cradling preferences, autism traits, and personality, possibly reflecting reduced right-hemisphere specialization in emotional processing and social behaviour.

Handedness as a major determinant of lateral bias in human functional cradling

Studies examining infant cradling have almost uniformly concluded with a general human left-side bias for cradling, indicating that people prefer to hold an infant to the left of their body. Explanations for the notion of the left-side cradling bias have traditionally been searched for in a variety of factors, for example, in terms of maternal heartbeat, genetic factors, in the form of an ear asymmetry where auditory information is perceived faster through the left ear, as a result of a right hemispheric functional specialization for perception of emotions and faces, and in identifying a motor bias of the infant, such as the tendency of newborn infants to lie with the face to the right when placed supine. Interestingly, handedness is generally considered an inadequate explanation for the lateralized cradling bias, despite it being an intuitively plausible one. In this brief review, I put forward the cradler's handedness as the most convincing and elegant determinant of the cradling bias. This explanation is consistent with a developmental cascades' framework where the cradling bias can be understood as the result of a multitude of factors across a range of levels and systems.

The Intricate Web of Asymmetric Processing of Social Stimuli in Humans

Although the population-level preference for the use of the right hand is the clearest example of behavioral lateralization, it represents only the best-known instance of a variety of functional asymmetries observable in humans. What is interesting is that many of such asymmetries emerge during the processing of social stimuli, as often occurs in the case of human bodies, faces and voices. In the present paper, after reviewing previous literature about human functional asymmetries for social and emotional stimuli, we suggest some possible links among them and stress the necessity of a comprehensive account (in both ontogenetic and phylogenetic terms) for these not yet fully explained phenomena. In particular, we propose that the advantages of lateralization for emotion processing should be considered in light of previous suggestions that (i) functional hemispheric specialization enhances cognitive capacity and efficiency, and (ii) the alignment (at the population level) of the direction of behavioral asymmetries emerges, under social pressures, as an evolutionary stable strategy.

Social touch in the age of computational ethology: Embracing as a multidimensional and complex behaviour

Social affective touch is an important aspect of close relationships in humans. It has been also observed in many non-human primate species. Despite the high relevance of behaviours like embraces for personal wellbeing and mental health, they remain vastly under-investigated in psychology. This may be because psychology often relies on a limited repertoire of behavioural measurements such as error rates and reaction time measurements. These are, however, insufficient to capture the multidimensional complexity of highly interactive dyadic behaviours like embraces. Based on recent advances in computational ethology in animal models, the rapidly emerging field of human computational ethology utilizes an accessible repertoire of machine learning methods to track and quantify complex natural behaviours. We highlight how such techniques can be utilized to investigate social touch and which preliminary conditions, motor aspects and higher-level interactions need to be considered. Ultimately, integration of computational ethology with mobile neuroscience techniques such as ultraportable EEG systems will allow for an ecologically valid investigation of social affective touch in humans that will advance psychological research of emotions.

Maternal cradling bias: A marker of the nature of the mother-infant relationship

The tendency of mothers to cradle their infant on their left side was first demonstrated by Salk back in 1960, but has been the subject of renewed interest in recent years. In this paper, I examine the different aspects of this tendency, making a short detour to explore this behavioral bias in other mammals and in nonhuman primates. The left cradling bias has been investigated not only in mothers, but also in fathers, children and students, as well as in different cultures. Moreover, the origins and causes of this behavior have been explored by examining its links to hemispheric specialization and to other motor asymmetries in mothers and infants. In recent years, researchers have also explored divergent patterns of cradling in groups of mothers exhibiting stress, anxiety, or depressive symptoms during pregnancy and after delivery, as well as in children with atypical development (e.g., autism spectrum disorder). The findings reported in the past 20 years open up promising avenues for anticipating potential difficulties in the relationship between mother and child, for given that a left cradling bias has been found in about 75% of the samples tested, cradling patterns could constitute natural behavioral markers of the socio-emotional harmony between cradler and cradled.

Keep a Left Profile, Baby! The Left-Cradling Bias Is Associated with a Preference for Left-Facing Profiles of Human Babies

The left-cradling bias (LCB) refers to the (typically female) preference to hold an infant on the left side of one’s own body. Among the three main accounts proposed for such a phenomenon, namely the “handedness”, “heartbeat” and “hemispheric asymmetry” hypotheses, the latter has met with the greatest empirical success. Accordingly, the LCB would facilitate the communication of socio-emotional information through the right hemisphere of both the cradled and the cradling individual, and should emerge mainly in face-to-face interactions. In this regard, it should be noticed that when the infant’s body is oriented toward the cradler, the left or right side of their face is relatively more visible to left- and right-cradlers, respectively. Therefore, we hypothesized that the LCB might also be associated with a preference for left-facing profiles (i.e., those showing the left, and more expressive, hemiface/cheek) of human babies. In order to test our hypothesis, we assessed the cradling-side preferences of female participants, as well as their preference for the left- or right-facing profile of a human infant depicted in a drawing. Left-cradlers exhibited a significantly larger preference for the left-facing version of the drawing compared with right-cradlers, a finding further corroborating the right-hemisphere hypothesis.

Received Cradling Bias During the First Year of Life: A Retrospective Study on Children With Typical and Atypical Development

A population-level left cradling bias exists whereby 60-90% of mothers hold their infants on the left side. This left biased positioning appears to be mutually beneficial to both the mother and the baby's brain organization for processing of socio-emotional stimuli. Previous research connected cradling asymmetries and Autism Spectrum Disorders (ASD), entailing impairment in socio-communicative relationships and characterized by an early hypo-lateralization of brain functions. In this explorative study, we aimed to provide a contribution to the retrospective investigations by looking for early behavioral markers of neurodevelopmental disorders such as ASD. We hypothesized that an atypical trajectory in maternal cradling might be one of the possible signs of an interference in mother-infant socio-emotional communication, and thus of potential neurodevelopmental dysfunctions. To this aim, we examined photos depicting mother-child early cradling interactions by consulting family albums of 27 children later diagnosed with ASD and 63 typically developing children. As regards the first half of the first year of life, no differences were shown between maternal cradling-side preferences in typical and ASD groups, both exhibiting the left-cradling bias in the 0-3 months period, but not in the 3-6 months period. However, our results show dissimilar patterns of cradling preferences during the second half of the first year of life. In particular, the absence of left-cradling shown in typical mothers was not observed in ASD mothers, who exhibited a significant left-cradling bias in the 6-12 months age group. This difference might reflect the fact that mother-infant relationship involving children later diagnosed with ASD might remain "basic" because mothers experience a lack of social activity in such children. Alternatively, it may reflect the overstimulation in which mothers try to engage infants in response to their lack of responsiveness and social initiative. However, further investigations are needed both to distinguish between these two possibilities and to define the role of early typical and reversed cradling experiences on neurodevelopment.

The left-cradling bias and its relationship with empathy and depression

Women usually cradle their infants to the left of their body midline. Research showed that the left cradling could be altered by affective symptoms in mothers, so that right cradling might be associated with a reduced ability to become emotionally involved with the infant. In this study, we assessed cradling-side bias (using family photo inspection and an imagination task), as well as depression and empathy, in 50 healthy mothers of 0-3 years old children. The main finding was that the strength of the left-cradling bias was negatively related with participants' depression scores and slightly positively related with their empathy scores. Our results thus provide further evidence that cradling-side preferences can represent an evolutionary proxy of mother's affective state, influencing the early development of the infant social brain and behaviour.