IEEE TRANSACTIONS ON AUTONOMOUS MENTAL DEVELOPMENT, VOL. 4, NO. 1, MARCH 2012 17 A Model to Explain the Emergence of Imitation Development Based on Predictability Preference Takashi Minato, Dale Thomas, Yuichiro Yoshikawa, and Hiroshi Ishiguro, Member, IEEE Abstract—Imitation is a very complicated function which requires a body mapping (a mapping from observed body mo- tions to motor commands) that can discriminate between self motions and those of others. The developmental mechanism of this sophisticated capability, and the order in which the required abilities arise, is poorly understood. In this paper, we present a mechanism for the development of imitation through a simulation of infant–caregiver interaction. A model was created to acquire a body mapping, which is necessary for successful mutual imitation in infant–caregiver interaction, while discriminating self-motion from the motion of the other. The ability to predict motions and the time delay between performing a motion and observing any correlated motion provides clues to assist the development of the body mapping. The simulation results show that the development of imitation capabilities depends on a predictability preference (a function of how an agent feels regarding its options of “what to imitate,” given its ability to predict motions). In addition, the simulated infants in our system are able to develop the components of a healthy body mapping in order, that is, relating self motion first, followed by an understanding of others’ motions. This order of development emerges spontaneously without the need for any explicit mechanism or any partitioning of the interaction. These results suggest that this predictability preference is an important factor in infant development. Index Terms—Body mapping, imitation, infant development, predictability preference, self-other distinction. I. INTRODUCTION I MITATION is a very important function in human infant development, especially for the development of our ability to understand and communicate with others. For example, sim- ulation theory has suggested that the capacity to understand others’ internal state relies on a process which matches the ob- served behavior with the action of the observer, that is, imita- tion by the observer [1]. According to Piaget’s developmental theory [2], infants’ imitative behaviors (shown in Table I) are observed while the infants learn to coordinate their senses and motor skills in the first two years. Before infants come to be able to imitate other persons in stage 3, they show repetitive behav- iors (it seems they are mainly attentive to their own bodies) in stage 2. This process (from stage 2 to 3) has also been observed Manuscript received February 28, 2010; revised September 11, 2010; ac- cepted April 26, 2011. Date of publication May 31, 2011; date of current version March 13, 2012. T. Minato is with Asada Project, ERATO, Japan Science and Technology Agency, Osaka, Japan,, and also with the Graduate School of Engineering, Osaka University, Osaka, Japan (e-mail: minato@atr.jp). D. Thomas is with Asada Project, ERATO, Japan Science and Technology Agency, Osaka, Japan (e-mail: dale_thomas@hotmail.com). Y. Yoshikawa and H. Ishiguro are with the Graduate School of Engi- neering Science, Osaka University, Osaka, Japan (e-mail: yoshikawa@sys.es. osaka-u.ac.jp; ishiguro@sys.es.osaka-u.ac.jp). Digital Object Identifier 10.1109/TAMD.2011.2158098 TABLE I INFANT BEHAVIORS IN PIAGET’S STAGES OF COGNITIVE DEVELOPMENT in other studies [4]. It is suggested that infants develop a sense of “self” after birth [4], that is, the self-knowledge of infants is formed during the developmental process. It may be that infants are unable to distinguish self-produced motions from motions produced by others within their perception in the early develop- mental process. However, infants come to repeat their own mo- tions in advance of imitating others even though they are fre- quently in the presence of other people (caregivers) and they may observe not only self-produced motions but also move- ments produced by others. In primary circular reactions, infants may be unable to recognize “their body” motions but just re- spond to interesting events, however, it is considered that these reactions work as self-imitation for the development of infant’s sensorimotor coordination [5]. We infer that the infant acquires the ability to distinguish self from others during this process (the transition from self to mutual imitation). This developmental process is considered to be essential for imitation development. However, not many studies have focused on this mechanism. This paper focuses on the mechanism of the transition from self to mutual imitation in the process of acquiring a body mapping. Imitation requires a body mapping that associates an ob- served motion with the corresponding motor commands needed to perform the same action. Although some studies have sug- gested that infants have an innate body mapping, and there have been some examples of neonates imitating their parents in some manner (e.g., [6]), we consider a neonate’s body mapping to be not sufficiently innate and that it is acquired, at least in part, through sensorimotor experiences after birth (e.g., [7]). Self-imitation requires a mapping that associates 1943-0604/$26.00 © 2011 IEEE