Masako Myowa-Yamakoshi

Contagious yawning in chimpanzees

Six adult female chimpanzees were shown video scenes of chimpanzees repeatedly yawning or of chimpanzees showing open–mouth facial expressions that were not yawns. Two out of the six females showed significantly higher frequencies of yawning in response to yawn videos; no chimpanzees showed the inverse. Three infant chimpanzees that accompanied their mothers did not yawn at all. These data are highly reminiscent of the contagious yawning effects reported for humans. Contagious yawning is thought to be based on the capacity for empathy. Contagious yawning in chimpanzees provides further evidence that these apes may possess advanced self–awareness and empathic abilities.

Factors influencing imitation of manipulatory actions in chimpanzees (Pan troglodytes).

The purpose of the study was to investigate what kind of factors determine the degree of difficulty for chimpanzees (Pan troglodytes) when they imitate actions. Five adult chimpanzees were instructed to perform 48 arbitrary manipulatory actions consisting of different bodily motor patterns and object directionality. Results showed that actions in which an object is directed toward another external location (another object and ones own body) were easier to perform than those that involved manipulating a single object alone. Actions involving unfamiliar motor patterns were more difficult to perform than those involving familiar motor patterns that were already present in the subjects repertoire. Error responses were characterized as perseverative repetition of previously instructed actions. These findings suggest that chimpanzees find the directionality of manipulated objects a more salient cue than details of the demonstrators body movements performing the manipulation.

Group differences in the mutual gaze of chimpanzees (Pan troglodytes).

A comparative developmental framework was used to determine whether mutual gaze is unique to humans and, if not, whether common mechanisms support the development of mutual gaze in chimpanzees and humans. Mother-infant chimpanzees engaged in approximately 17 instances of mutual gaze per hour. Mutual gaze occurred in positive, nonagonistic contexts. Mother-infant chimpanzees at a Japanese center exhibited significantly more mutual gaze than those at a center in the United States. Cradling and motor stimulation varied across groups. Time spent cradling infants was inversely related to mutual gaze. It is suggested that in primates, mutual engagement is supported via an interchangeability of tactile and visual modalities. The importance of mutual gaze is best understood within a perspective that embraces both cross-species and cross-cultural data.

Preference for human direct gaze in infant chimpanzees (Pan troglodytes)

We studied gaze perception in three infant chimpanzees (Pan troglodytes), aged 10-32 weeks, using a two-choice preferential-looking paradigm. The infants were presented with two photographs of a human face: (a) with the eyes open or closed, and (b) with a direct or an averted gaze. We found that the chimpanzees preferred looking at the direct-gaze face. However, in the context of scrambled faces, the infants showed no difference in gaze discrimination between direct and averted gazes. These findings suggest that gaze perception by chimpanzees may be influenced by the surrounding facial context. The relationship between gaze perception, face processing, and the adaptive significance of gaze perception are discussed from an evolutionary perspective.

New observations of ant-dipping techniques in wild chimpanzees at Bossou, Guinea.

Ant-dipping behavior is often cited as a clear example of chimpanzee culture, since different populations have apparently different dipping techniques (the one-handed method used by chimpanzees in Bossou, Guinea and Taï, Côte d’Ivoire, and the two-handed method used in Gombe, Tanzania). Here we report a new observation of ant-dipping behavior from Bossou using the two-handed method, in addition to the first detailed description of the one-handed method. Although the main dipping pattern was the one-handed method in Bossou, one adult male was observed dipping for ants using the two-handed method, while other chimpanzees employed the conventional one-handed method in the same episode. The two-handed method was also sporadically observed in a juvenile and in adolescents, who were still immature in dipping techniques and hence prone to suffer from ant attacks. Cross-population comparisons of dipping techniques suggest that there are two sub-types of the one-handed method, and the Bossou one-handed technique may be substantially different from that of Taï. In terms of overall behavioral repertoire in ant dipping, the Bossou pattern appears more similar to that of Gombe than Taï. This may be explained by the difference in target ant species.

Development of face recognition in an infant gibbon (Hylobates agilis)

The development of the ability to recognize faces was studied in a nursery-reared male infant gibbon (Hylobates agilis). We used traditional and modified head-turning procedures that measured the infant’s eye- and head- tracking of moving stimuli. In Experiment 1, the infant was presented with face-like and nonface-like drawings. He showed a preference for face-like stimuli. Experiment 2a tested the infant’s recognition of photographs of familiar and unfamiliar faces; by 4 weeks of age, the infant preferred looking at a familiar human face to unfamiliar faces. Experiment 2b investigated the infant’s sensitivity in acquiring a preference for faces. The infant was more sensitive to the characteristics of a familiar human face than to those of unfamiliar faces. These findings suggest that there may be similarities between the early face recognition ability of humans and gibbons.

Broad cortical activation in response to tactile stimulation in newborns.

Tactile sensation, which is one of the earliest developing sensory systems, is very important in the perception of an individual’s body and the surrounding physical environment, especially in newborns. However, currently, only little is known about the response of a newborn’s brain to tactile sensation. The objective of the present study was to determine the response of a newborn’s brain to tactile sensation and to compare the brain responses to various sensory stimuli. Ten healthy newborns, 2–9 days after birth, were enrolled. A multichannel near-infrared spectroscopy system was used to measure brain responses. The probe array covered broad cortical areas, including the parietal, temporal, and occipital areas. We measured cortical hemodynamic changes in response to three different types of stimuli: tactile, auditory, and visual. Activated areas were analyzed by t-tests, and the number of activated channels among the three different stimuli was compared by &khgr;2-tests. The results showed that when the brain responded to each type of stimulation, the corresponding primary sensory area was activated, and tactile stimuli induced broader areas of brain activation than the other two types of stimuli (auditory or visual). Thus, broad brain areas, including the temporal and parietal areas, were activated by tactile stimuli in early newborn periods. These results suggest that there are differences in newborns’ reactions to various types of sensory stimuli, which may reflect the importance of tactile sensation in the early newborn period.

Infants prefer the faces of strangers or mothers to morphed faces: an uncanny valley between social novelty and familiarity

The ‘uncanny valley’ response is a phenomenon involving the elicitation of a negative feeling and subsequent avoidant behaviour in human adults and infants as a result of viewing very realistic human-like robots or computer avatars. It is hypothesized that this uncanny feeling occurs because the realistic synthetic characters elicit the concept of ‘human’ but fail to satisfy it. Such violations of our normal expectations regarding social signals generate a feeling of unease. This conflict-induced uncanny valley between mutually exclusive categories (human and synthetic agent) raises a new question: could an uncanny feeling be elicited by other mutually exclusive categories, such as familiarity and novelty? Given that infants prefer both familiarity and novelty in social objects, we address this question as well as the associated developmental profile. Using the morphing technique and a preferential-looking paradigm, we demonstrated uncanny valley responses of infants to faces of mothers (i.e. familiarity) and strangers (i.e. novelty). Furthermore, this effect strengthened with the infants age. We excluded the possibility that infants detect and avoid traces of morphing. This conclusion follows from our finding that the infants equally preferred strangers’ faces and the morphed faces of two strangers. These results indicate that an uncanny valley between familiarity and novelty may accentuate the categorical perception of familiar and novel objects.

Preterm birth is associated with an increased fundamental frequency of spontaneous crying in human infants at term-equivalent age

Human infant crying has been researched as a non-invasive tool for assessing neurophysiological states at an early developmental stage. Little is known about the acoustic features of spontaneous cries in preterm infants, although their pain-induced cries are at a higher fundamental frequency (F0) before term-equivalent age. In this study, we investigated the effects of gestational age, body size at recording and intrauterine growth retardation (IUGR) on the F0 of spontaneous cries in healthy preterm and full-term infants at term-equivalent age. We found that shorter gestational age was significantly associated with higher F0, although neither smaller body size at recording nor IUGR was related to increased F0 in preterm infants. These findings suggest that the increased F0 of spontaneous cries is not caused by their smaller body size, but instead might be caused by more complicated neurophysiological states owing to their different intrauterine and extrauterine experiences.

Infant's action skill dynamically modulates parental action demonstration in the dyadic interaction.

When interacting with infants, human adults modify their behaviours in an exaggerated manner. Previous studies have demonstrated that infant-directed modification affects the infants behaviour. However, little is known about how infant-directed modification is elicited during infant-parent interaction. We investigated whether and how the infants behaviour affects the mothers action during an interaction. We recorded three-dimensional information of cup movements while mothers demonstrated a cup-nesting task during interaction with their infants aged 11 to 13 months. Analyses revealed that spatial characteristics of the mothers task demonstration clearly changed depending on the infants object manipulation. In particular, the variance in the distance that the cup was moved decreased after the infants cup nesting and increased after the infants task-irrelevant manipulation (e.g. cup banging). This pattern was not observed for mothers with 6- to 8-month-olds, who do not have the fine motor skill to perform the action. These results indicate that the infants action skill dynamically affects the infant-directed action and suggest that the mother is sensitive to the infants potential to learn a novel action. A video abstract of this article can be viewed at: https://www.youtube.com/watch?v=VNS2IHwLIhg&feature=youtu.be.