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.

Baboon (Papio anubis) chimeric face processing by human (Homo sapiens) judges: Influence of stimuli complexity on the perception of oro-facial asymmetries.

Two methodologies have traditionally been used to measure hemispheric specialization for perception and expression of emotions in human and nonhuman primates. The first refers to objective measures, that is, measures of area and length of facial features, and the second concerns subjective "measures," that is, assessment of chimeric faces by human judges. We proposed a refined approach to the subjective assessment of hemispheric specializations, which aims at delimiting methodological issues in the study of orofacial asymmetries. The study focused on a baboon threat orofacial expression, which has led to discordant results according to the methodology used (Wallez & Vauclair, 2011, 2013). We presented human participants with two sets of chimeric stimuli varying the regions of the face likely to be processed. The whole face set was composed of classical chimeric faces, and the upper face set was made of chimeric faces for which the lower part was blurred. The purpose of this new procedure was to shed light on the perception process of baboon faces by human participants during a free-viewing chimeric task. Results showed a concomitant influence of the chimera structure depending on the order of the presentation of the set, revealing a training effect in our human judges. These factors combined together allowed the appearance of an overall left-left chimeric choice by human judges (i.e., which indicates a right hemisphere involvement in baboon threat expression). These findings bring novel insights into the study of orofacial asymmetries in nonhuman primates by human judgments. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Hand preferences for unimanual and bimanual coordinated actions in olive baboons (Papio anubis): Consistency over time and across populations.

The reliability of handedness data in nonhuman primates and variations of sample size across studies are critical issues for exploring their potential continuity with humans concerning hemispheric specialization. In this study, we investigated the consistency of handedness for unimanual and bimanual tasks in olive baboons (Papio anubis). For both tasks, we found a consistency of hand preferences over time among subjects retested 5 years later and a consistency of population-level handedness between 2 independent populations. Altogether, when combining the 2 samples, bimanual (N = 260) but not unimanual task (N = 220) elicited right-handedness predominance. These findings demonstrate the reliability and robustness of predominance of right-handedness in olive baboons for bimanual coordinated behaviors. (PsycINFO Database Record

Verbal cues effectively orient children's auditory attention in a CV-syllable dichotic listening paradigm.

In their groundbreaking work featuring verbal dichotic listening tasks, Mondor and Bryden showed that tone cues do not enhance children's attentional orienting, in contrast to adults. The magnitude of the children's right-ear advantage was not attenuated when their attention was directed to the left ear. Verbal cues did, however, appear to favour the orientation of attention at around 10 years, although stimulus-onset asynchronies (SOAs), which ranged between 450 and 750 ms, were not rigorously controlled. The aim of our study was therefore to investigate the role of both types of cues in a typical CV-syllable dichotic listening task administered to 8- to 10-year-olds, applying a protocol as similar as possible to that used by Mondor and Bryden, but controlling for SOA as well as for cued ear. Results confirmed that verbal cues are more effective than tone cues in orienting children's attention. However, in contrast to adults, no effect of SOA was observed. We discuss the relative difficulty young children have processing CV syllables, as well as the role of top-down processes in attentional orienting abilities.

Auditory orienting of attention: Effects of cues and verbal workload with children and adults.

The use of tone cues has an improving effect on the auditory orienting of attention for children as for adults. Verbal cues, on the contrary, do not seem to orient attention as efficiently before the age of 9 years. However, several studies have reported inconsistent effects of orienting attention on ear asymmetries. Multiple factors are questioned, such as the role of verbal workload. Indeed, the semantic nature of the dichotic pairs and their load of processing may explain orienting of attention performance. Thus, by controlling for the role of verbal workload, the present experiment aimed to evaluate the development of capacities for the auditory orienting of attention. Right-handed, 6- to 12-year-olds and adults were recruited to complete either a tone cue or a verbal cue dichotic listening task in the identification of familiar words or nonsense words. A factorial design analysis of variance showed a significant right-ear advantage for all the participants and for all the types of stimuli. A major developmental effect was observed in which verbal cues played an important role: they allowed the 6- to 8-year-olds to improve their performance of identification in the left ear. These effects were taken as evidence of the implication of top-down processes in cognitive flexibility across development.

Hand preferences in preschool children: Reaching, pointing and symbolic gestures.

Manual asymmetries emerge very early in development and several researchers have reported a significant right-hand bias in toddlers although this bias fluctuates depending on the nature of the activity being performed. However, little is known about the further development of asymmetries in preschoolers. In this study, patterns of hand preference were assessed in 50 children aged 3-5 years for different activities, including reaching movements, pointing gestures and symbolic gestures. Contrary to what has been reported in children before 3 years of age, we did not observe any difference in the mean handedness indices obtained in each task. Moreover, the asymmetry of reaching was found to correlate with that of pointing gestures, but not with that of symbolic gestures. In relation to the results reported in infants and adults, this study may help deciphering the mechanisms controlling the development of handedness by providing measures of manual asymmetries in an age range that has been so far rather neglected.

Training experience in gestures affects the display of social gaze in baboons' communication with a human.

Gaze behaviour, notably the alternation of gaze between distal objects and social partners that accompanies primates' gestural communication is considered a standard indicator of intentionality. However, the developmental precursors of gaze behaviour in primates' communication are not well understood. Here, we capitalized on the training in gestures dispensed to olive baboons (Papio anubis) as a way of manipulating individual communicative experience with humans. We aimed to delineate the effects of such a training experience on gaze behaviour displayed by the monkeys in relation with gestural requests. Using a food-requesting paradigm, we compared subjects trained in requesting gestures (i.e. trained subjects) to naïve subjects (i.e. control subjects) for their occurrences of (1) gaze behaviour, (2) requesting gestures and (3) temporal combination of gaze alternation with gestures. We found that training did not affect the frequencies of looking at the human's face, looking at food or alternating gaze. Hence, social gaze behaviour occurs independently from the amount of communicative experience with humans. However, trained baboons-gesturing more than control subjects-exhibited most gaze alternation combined with gestures, whereas control baboons did not. By reinforcing the display of gaze alternation along with gestures, we suggest that training may have served to enhance the communicative function of hand gestures. Finally, this study brings the first quantitative report of monkeys producing requesting gestures without explicit training by humans (controls). These results may open a window on the developmental mechanisms (i.e. incidental learning vs. training) underpinning gestural intentional communication in primates.

Evolution of the central sulcus morphology in primates.

The central sulcus (CS) divides the pre- and postcentral gyri along the dorsal-ventral plane of which all motor and sensory functions are topographically organized. The motor-hand area of the precentral gyrus or KNOB has been described as the anatomical substrate of the hand in humans. Given the importance of the hand in primate evolution, here we examine the evolution of the motor-hand area by comparing the relative size and pattern of cortical folding of the CS surface area from magnetic resonance images in 131 primates, including Old World monkeys, apes and humans. We found that humans and great apes have a well-formed motor-hand area that can be seen in the variation in depth of the CS along the dorsal-ventral plane. We further found that great apes have relatively large CS surface areas compared to Old World monkeys. However, relative to great apes, humans have a small motor-hand area in terms of both adjusted and absolute surface areas.

Morphological differences between imperative and declarative pointing: hand shape, arm extension, and body posture.

The authors used frame-by-frame video analyses to describe the features of imperative and declarative pointing gestures produced by young children, in comparison to reaching actions. First, the results showed that imperative pointing shared common features with reaching actions (hand shape, arm extension), but body posture observed in reaching differed from the one observed in pointing, both in imperative and declarative contexts. Second, hand shape was influenced by precision constraints: imperative gestures shifted from whole-hand pointing to index-finger pointing when the target was surrounded by distractors. This study is the first of its kind to highlight the effect of several variables on morphological features of pointing using quantitative measures and may provide insights into the nature of imperative and declarative pointing.

Deictic gestures and symbolic gestures produced by adults in an experimental context: hand shapes and hand preferences.

The objective of this study was to gain new insights into the processes underlying gestural communication in adults by examining hand shapes and hand preference patterns associated with different types of gestures. Several communicative situations eliciting pointing gestures and symbolic gestures were presented to 81 participants in an experimental context. Results have highlighted some differences in hand shapes depending on the function of pointing: contrary to results reported in children, the proportion of index-finger gestures was higher in imperative situations than in declarative situations. The distance between the gesturer and the referent was also found to influence hand shapes, proximal pointing being more frequently associated with index-finger gestures than distal pointing. The comparison of hand preferences revealed a greater right-sided asymmetry for declarative pointing than for non-communicative activities, whereas there was no difference between imperative pointing and non-communicative activities, or between symbolic gestures and non-communicative activities. The present study thus sheds some light on the features and the roles of communicative gestures in adults. Results are discussed in relation to the ontogenetic and phylogenetic origins of communication.

Children below 9 years use both verbal cues and lateralized cues to orient their attention in an emotional dichotic listening task.

The current study aimed to demonstrate that children below 9 years of age efficiently orient their auditory attention with both verbal cues and lateralized cues to identify emotional stimuli. The use of emotional stimuli is an optimal condition according to the assumption that a multi-component task calling on different resources from the two cerebral hemispheres is easier than a multi-component task requiring resources from the same hemisphere. A sample of 103 right-handed children from 7 to 12 years of age was required to identify emotional speech made up of pseudowords preceded by a binaural verbal cue or by a lateralized tone cue. As expected, we observed better performance for the skilled ear (i.e., the left ear for emotional processing) and an improving effect of verbal cues. According to our success criterion (mean correct report rates significantly different from chance), an efficient control of orienting attention was observed in all groups of children. This means that children from 7 to 8 years of age were able to efficiently orient their attention to identify emotional stimuli. Results are discussed in relation to the hemispheric lateralization of emotions.

Hand preferences on unimanual and bimanual tasks in Tonkean macaques (Macaca tonkeana).

This is the first study to examine hand preferences in Tonkean macaques on a bimanual task. One of our objectives was to continue the move toward greater task standardization, in order to facilitate comparisons between species and studies on handedness. The main aim was to test and determine task robustness, by varying intra-task complexity. To this end, we administered several different tasks to the subjects: two unimanual tasks (grasping task featuring items of different sizes) and three coordinated bimanual tasks (tube task involving different materials, weights, and diameters). Although we found no significant hand preference in either task at the group level, the macaques were more strongly lateralized for small items than for large ones in the unimanual grasping task. Moreover, the absence of a correlation between these two versions of the unimanual task confirmed the weakness of this grasping task for assessing handedness. Regarding the bimanual tube task, no difference was found between the three versions in either the direction or the strength of hand preference. Moreover, the highly correlated hand preferences between these three versions suggest that the tube task provides a more robust means of measuring manual preferences.

On the origins of human handedness and language: a comparative review of hand preferences for bimanual coordinated actions and gestural communication in nonhuman primates.

Within the evolutionary framework about the origin of human handedness and hemispheric specialization for language, the question of expression of population-level manual biases in nonhuman primates and their potential continuities with humans remains controversial. Nevertheless, there is a growing body of evidence showing consistent population-level handedness particularly for complex manual behaviors in both monkeys and apes. In the present article, within a large comparative approach among primates, we will review our contribution to the field and the handedness literature related to two particular sophisticated manual behaviors regarding their potential and specific implications for the origins of hemispheric specialization in humans: bimanual coordinated actions and gestural communication. Whereas bimanual coordinated actions seem to elicit predominance of left-handedness in arboreal primates and of right-handedness in terrestrial primates, all handedness studies that have investigated gestural communication in several primate species have reported stronger degree of population-level right-handedness compared to noncommunicative actions. Communicative gestures and bimanual actions seem to affect differently manual asymmetries in both human and nonhuman primates and to be related to different lateralized brain substrates. We will discuss (1) how the data of hand preferences for bimanual coordinated actions highlight the role of ecological factors in the evolution of handedness and provide additional support the postural origin theory of handedness proposed by MacNeilage [MacNeilage [2007]. Present status of the postural origins theory. In W. D. Hopkins (Ed.), The evolution of hemispheric specialization in primates (pp. 59-91). London: Elsevier/Academic Press] and (2) the hypothesis that the emergence of gestural communication might have affected lateralization in our ancestor and may constitute the precursors of the hemispheric specialization for language.

Baboons' hand preference resists to spatial factors for a communicative gesture but not for a simple manipulative action.

Olive baboons (Papio anubis) do acquire and use intentional requesting gestures in experimental contexts. Individual's hand preference for these gestures is consistent with that observed for typical communicative gestures, but not for manipulative actions. Here, we examine whether the strength of hand preference may also be a good marker of hemispheric specialization for communicative gestures, hence differing from the strength of hand preference for manipulative actions. We compared the consistency of individuals' hand preference with regard to the variation in space of either (i) a communicative partner or (ii) a food item to grasp using a controlled set-up. We report more consistent hand preference for communicative gestures than for grasping actions. Established hand preference in the midline was stronger for gesturing than for grasping and allowed to predict the consistency of hand preference across positions. We found no significant relation between the direction of hand preference and the task.

Patterns of hemispheric specialization for a communicative gesture in different primate species.

We review four studies investigating hand preferences for grasping versus pointing to objects at several spatial positions in human infants and three species of nonhuman primates using the same experimental setup. We expected that human infants and nonhuman primates present a comparable difference in their pattern of laterality according to tasks. We tested 6 capuchins, 6 macaques, 12 baboons, and 10 human infants. Those studies are the first of their kind to examine both human infants and nonhuman primate species with the same communicative task. Our results show remarkable convergence in the distribution of hand biases of human infants, baboons and macaques on the two kinds of tasks and an interesting divergence between capuchins' and other species' hand preferences in the pointing task. They support the hypothesis that left-lateralized language may be derived from a gestural communication system that was present in the common ancestor of macaques, baboons and humans.

Tonkean macaques communicate with their right hand.

There are two conflicting hypotheses to explain the origins of language. Vocal origin theory states that language results from the gradual evolution of animals' vocal communication, but gestural origin theory considers that language evolved from gestures, with the initial left-hemispheric control of manual gestures gradually encompassing vocalizations. To contribute to this debate, we investigated functional hemispheric specialization related to hand biases when grasping or showing an object through manual gesture in Tonkean macaques. The results of this study, the first quantitative study on Tonkean macaques' handedness, showed a remarkable convergence of the Tonkean macaques' handedness patterns with those of baboons and human infants, with hand preferences for manual communicative gestures significantly favoring the use of the right hand. Our findings support the hypothesis that left hemispheric lateralization for language is derived from a gestural communication system that was present in the common ancestor of macaques, baboons and humans.

Human (Homo sapiens) and baboon (Papio papio) chimeric face processing: right-hemisphere involvement.

[Correction Notice: An Erratum for this article was reported in Vol 127(3) of Journal of Comparative Psychology (see record 2013-30238-001). In the article, the link to the supplemental material was not included. Supplemental material for this article is available at: http://dx.doi.org/10.1037/a0031494.supp.] The perception and production of facial expressions have traditionally been used to infer hemispheric specialization for emotions in both human and nonhuman primates. The authors examined orofacial asymmetries in Olive baboons using 2 methodologies. First, objective measures were used to assess hemimouth length and area for screeching and eyebrow-raising. Right-hemisphere specialization was found only for screeching. Second, subjective measures were acquired via a human judgment of the emotional intensity of baboons' chimeric faces for the 2 previous emotional behaviors plus a neutral expression. They also addressed the question of hemispheric lateralization for emotions in human judges by using a chimeric task with human faces. The left-composite chimeric faces of baboons and the human chimeric faces were judged to be emotionally stronger than the right ones for the emotional behaviors, and no preference was found for the neutral non emotional category. Human participants, especially those who displayed a left-hemisphere specialization for processing emotions, demonstrated higher ability to distinguish the most emotionally communicative signals in baboons' facial expressions than right-hemispheric dominant participants. These results are discussed within the theoretical framework of the human and the nonhuman primate literature on hemispheric specialization for perception and production of facial expressions of emotions.

Hand preference for pointing and language development in toddlers.

The aim of this study was to investigate the relationship between hand preference for communicative gestures and language during development. Hand preference for pointing gestures and level of language were assessed in 46 toddlers between 12 and 30 months of age. Results showed a right-hand preference for pointing and the use of a developmental quotient (DQ) for language revealed a significant correlation between the degree of hand preference and DQ for language in children with a quotient above 100. Thus, these children were more right-handed for pointing gestures as DQ increased. These results highlight the close association between the development of hand preference for pointing and the speed of language development, suggesting a new direction for studies of language-gesture links in toddlers.

Contrast of hemispheric lateralization for oro-facial movements between learned attention-getting sounds and species-typical vocalizations in chimpanzees: extension in a second colony.

Studies involving oro-facial asymmetries in nonhuman primates have largely demonstrated a right hemispheric dominance for communicative signals and conveyance of emotional information. A recent study on chimpanzee reported the first evidence of significant left-hemispheric dominance when using attention-getting sounds and rightward bias for species-typical vocalizations (Losin, Russell, Freeman, Meguerditchian, Hopkins & Fitch, 2008). The current study sought to extend the findings from Losin et al. (2008) with additional oro-facial assessment in a new colony of chimpanzees. When combining the two populations, the results indicated a consistent leftward bias for attention-getting sounds and a right lateralization for species-typical vocalizations. Collectively, the results suggest that both voluntary-controlled oro-facial and gestural communication might share the same left-hemispheric specialization and might have coevolved into a single integrated system present in a common hominid ancestor.