For infants who have not yet acquired linguistic competence, physical contact is one of the essential aspects of communication with others. Therefore, I have been studying parent-infant games involving physical contact, in particular tickling play, and the development of their interactions. In this article, I will explain some important findings from my study.

Characteristics of physical contact

Physical contact, i.e., touching each other, literally brings about a bilateral and simultaneous experience of "touch" and "being touched." A sensation of touch between a caregiver and his/her baby will be shared simultaneously. In addition, physical contact can have various meanings according to motor patterns, touching parts, and context-based interactions. Physical contact triggers strong emotions, either positive (loving) or negative (dislike). Based on these characteristics, Negayama (2002) pointed out that physical contact is "a vivid communication channel to share realistic intention with others."

Meanwhile, physical contact is also a sense of being aware of a "boundary" from others. For example, psychologists Philippe Rochat and Susan J. Hespos (1997) conducted a study targeting newborns. They observed the frequency of babies' rooting response to the two types of stimulation: when the experimenter stroked the baby's cheeks and when the baby spontaneously brought one hand to his/her face and touched a cheek.^[*1] The results revealed that these babies showed a rooting response to the touch of the experimenter more frequently than the touch of themselves in the same facial region. This result indicates that newborn babies differentiate their self from others through physical contact. Physical contact can provide opportunities for rudimentary differentiation between self and others.

Tickling play

Tickling play involves interesting interactions stemming from such characteristics of physical contact. This mother-infant physical play occurs naturally in everyday life. It seems to cause heartwarming and pleasant feelings.

However, when we carefully observe tickling play, certain "unpleasant" elements will be seen. For example, intensive tickling in body areas rarely touched by other people (e.g., the armpits or the ribs) may elicit unpleasant sensations and avoidance reactions such as bodily tension and pushing back the hands. No matter how enjoyable tickling play looks, an initially pleasurable tickle may end up with an aversive reaction if the tickling is forceful and continuous. Therefore, tickling play requires a delicate balance between pleasure and displeasure. Because of this difficulty, enjoyment is enhanced when a good balance is achieved between the mother and infant.

"Ticklishness," the goal of tickling play, is a unique body sensation. We cannot tickle ourselves; we need to be tickled by someone else to feel the sensation. Therefore, children's positive response to tickling indicates development of their intuitive self-other differentiation.

The development of tickling play: "Delayed Tickling" and anticipation

When do infants feel ticklish? Newborn babies rarely feel ticklish in response to being tickled. Strong ticklishness is said to occur after around six months of age (Negayama & Yamaguchi, 2005).

More precisely, what kind of interaction occurs between mother and infant? We closely examined mother-infant interactions in tickling play, targeting babies of around six months when they start showing ticklishness (Ishijima & Negayama, 2013). As a result, two types of mothers' tickling became apparent. One is actual touch with straightforward finger movements. The other is "delayed" (virtual) tickling with tickling-like finger movements in the air before actual touch. Babies started responding to such "delayed" tickling at six months or later.

Next, we conducted a microanalysis of mother-infant interactions, focusing on "delayed" tickling play.^[*2] As a result, it was confirmed that mothers showed a gradual raise in the vocal pitch during their "delayed" tickling while infants gazed at the tickling mother's face and hands. Furthermore, infants showed an anticipatory ticklishness before the actual touch. Finally, when the actual touch occurred, the tickling mother's vocal pitch became highest, and the infant sometimes gazed at the mother's face while showing ticklishness.

It is quite interesting to observe the infant gazing at the tickling mother's face because their ticklish expression includes a component of avoidance reaction. The tickling play seems to have interactions between the passive role (ticklee) and the active role (tickler). However, infants in the part of ticklee actively and multimodally participate in interactions, using their tactile, visual, and auditory sensations. ^[*3]

Co-creation of musicality and climax in multimodal tickling play

Malloch and Trevarthen discussed the concept of "Communicative Musicality" (Malloch & Trevarthen, 2009/2018). According to their theory, there are typical "musical" rules in mother-infant communications, whereby they share a certain rhythm and tempo and sensitively attune themselves to melodic narrative-based interactions. The same can apply to tickling play. Mothers and infants multimodally attune their own behavior based on the rhythm and tempo of saying "tickle tickle," and together create the climax of their interaction (for more information, please see Ishijima, 2020)

In addition to the "delayed" tickling, there is another type of tickling using songs, such as the Japanese nursery rhyme "Ippon bashi kochokocho [Tickling Bridges]". These techniques enable infants to predict a "climax" tickling in the next moment. Such tickling behavior styles were defined as "narrative tickling". Our study confirmed that more mothers with babies of seven months have mother-infant interactions using narrative tickling than mothers with five-month-old babies (Ishijima & Negayama, 2017).

Sharing of laughter and resonance of body sensation in tickling play

It was further observed that in cases where infants expressed ticklishness in tickling play, significantly more mothers were likely to laugh compared to the mothers of those who did not show ticklishness (Ishijima & Negayama, 2017). This indicates that mothers and infants share laughter in tickling play. It may sound like nothing special, but sharing laughter is critical when thinking about "humanness."

Tickling play can be observed in chimpanzees, our closest evolutionary neighbor. However, their mode of tickling play is somewhat different from humans. According to Matsusaka, the sharing of laughter does not occur among chimpanzees through play (Matsusaka, 2008). Chimpanzees do not sensitively interpret others' psychological states (pleasure) and hence, do not try to increase the pleasure of others. Therefore, there should be no room for the behavior styleof "delayed" tickling (Matsusaka, 2017).

In contrast, human mothers think about "how and where to tickle to make him/her feel ticklish" in tickling play based on their own body sensations. Mothers flexibly attune their behavior by observing the baby's response (and, at the same time, anticipating their ticklishness and laughter). Therefore, when the infant shows ticklishness, the sharing of laughter and a strong feeling of togetherness, understanding, and enjoyment between mother and infant is significant.

I am currently conducting a longitudinal study focusing on parent (mother/father)-infant interactions in tickling play. In the questionnaire survey, I asked the participants how they felt during tickling play with their baby. Some answered they felt "a bit of ticklishness" during the play, although they are in the role of tickler. This finding indicates that human caregivers (mothers/fathers) feel a broad sense of unity and a high level of empathy based on inter-body relationship when their child shows ticklishness and they share laughter.

Developmental significance and functions in mothers' delayed tickling and infants' anticipation

In tickling play, infants sometimes show an anticipatory ticklishness before the actual touch. This anticipation of the mother's tickling may indicate that infants are developing the ability to understand others' intentions in their daily interactions.

Developmental psychologists have argued such ability of intention-reading as "Joint Attention" within the domain of a triadic relationship (i.e., self-other-object). Joint attention means the sharing of a common focus on something with someone by following the direction of the other party's gaze and looking at the target object. It is said that joint attention provides a developmental foundation for understanding others' psychological state, such as their intentions and emotions. As joint attention typically emerges in infants after nine months, it is called the "nine-month revolution" (Tomasello, 1999). In contrast, in the case of chimpanzees, we rarely see the establishment of complicated mutual negotiations under a triadic (self-other-object) relationship (Tomonaga, 2006). In addition, chimpanzees do not exchange things in turn through play under a triadic relationship (Myowa, 2009).

When considering the development of infants' social behavior, tickling play provides important clues. Basically, tickling play is a dyadic relationship between the mother and infant. However, when their attention is directed to the tickling/tickled body (i.e., body sensation and ticklishness), the state of tickling play becomes like a triadic relationship. Since the sharing of body sensation occurs under such a relationship, the infant anticipates and actively responds to the mother's intention and behavior, which enhancesthe mother's enjoyment, achieving the climax of their tickling play. We consider this process as a "proto-triadic relationship," which is experienced before the genuine triadic relationship, based on the resonance of body sensations (Negayama, 2011; Ishijima & Negayama, 2013).

Narrative tickling, such as delayed tickling and tickling with a song, is often shown in mother and infant pairs around seven months old. We consider the possibility of such tickling play, having a fundamental role in developing infants' cognitive abilities based on body sensation, which may allow infants to communicate with others at a higher cognitive level including narrative understanding, leading to anticipation, intention-reading and the understanding of others' minds. Tickling might have a natural function of promoting the infants' development of social cognition. This merits further examination.

*This article was prepared based on Dr. Konomi Ishijima's journal article "Interactions Through Body and Mind: Development of Mother-Infant Tickling Play," published in 2020 (Parenting Newsletter No. 159, The Association of Breastfeeding Your Child: The Oketani Method).

• [*1] A newborn reflex by turning the head towards the stimulation with mouth open and tonguing, which is triggered by touching the corner of the baby's mouth.
• [*2] Microanalysis is the method of analyzing the microscopic elements of behavioral changes in chronological order by using recording devices such as a video camera. This method enables the observation of a behavioral state (such as a slight movement of someone's eyes) at intervals of every second or less, which cannot be achieved in real-time observations (Okamoto, 2000).
• [*3] Multimodal involves multiple sensory stimulations, such as visual, auditory, and tactile sensations.

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Cited References

• • Ishijima, K. (2020). "Section 1, Chapter 5: Significance of multimodal interaction in mother-infant tactile". Imagawa, K. (ed.) Reasons why we have music: Interdisciplinary inquiry in music. Ongaku No Tomo Sha, Corp. 65-80.
• • Ishijima, K. & Negayama, K. (2013). Mother-infant interaction in tickling play: Intention reading based on narrative sharing. The Japanese journal of developmental psychology, 24 (3), 326-336.
• • Ishijima, K. & Negayama, K. (2017). Development of mother-infant interaction in tickling play: The relationship between infants' ticklishness and social behaviors. Infant Behavior & Development, 49, 161-167.
• • Malloch, S. & Trevarthen, C. (2009). Communicative Musicality :Exploring the basis of human companionship. Oxford University Press. (Japanese translation: Malloch & Trevarthen (eds.), Negayama & Imagawa, et al. (supv.) (2018) Ongaku No Tomo Sha, Corp.)•
• • Matsusaka, T. (2008). Origins and evolution of laughter. Japanese Psychological Review, 51（3）, 43.
• • Matsusaka, T. (2017). Relationship between the environment and the diversity of play in wild chimpanzees. Child Science, (5), 206-222.
• • Myowa, M. (2009). What is human-like play? - Emotional development and evolution when observing the play of human and chimpanzee. Kamei, N. (ed.). Introduction to Anthropology through play: "Children" encountered in fieldworks. Showado. 135-164.
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• • Rochat, P., & Hespos, S. J. (1997). Differential rooting response by neonates: Evidence for an early sense of self. Early Development & Parenting, 6, 105-112.
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• • Rochat, P., & Hespos, S. J. (1997). Differential rooting response by neonates: Evidence for an early sense of self. Early Development & Parenting, 6, 105-112.
• • Negayama, K. & Yamaguchi, H. (2005). Development of mother-infant tickling play and infant's ticklishness. Journal of Child Health, 64, 451-460.
• • Negayama, K. & Imagawa, K. et al. (2018). (supv.) Communicative musicality : exploring the basis of human companionship. Ongaku No Tomo Sha, Corp.
• • Okamoto, Y. (2000). Micro-Analysis. Tajima, N. & Nishino, Y. (eds.) Techniques of Developmental Research. pp.175-179. Fukumura-Shuppan (Tokyo).
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