You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Interpersonal Synchrony: A Survey of Evaluation Methods across Disciplines 
Chapter Title:  Prospects in Social Robots and Embodied Conversational Agents 
1. Abstract of Cited Paper (BIB001):  Human social behavior is rhythmic, and synchrony plays an important role in coordinating and regulating our interactions. We are developing technology that allows the robot Keepon to perceive and behave rhythmically, and to synchronize its dancing behaviors to music or to children's movement as perceived using pressure sensors. We present two experiments in which Keepon dances with children to music, and in which the robot's rhythmic attention and role of leader or follower are manipulated in order to examine the effects on engagement and rhythmic synchrony. We found that children can assume the roles of leader or follower in a rhythmic interaction, that followers indeed tend to synchronize with the robot's movements, and that the role of follower causes the children to more closely follow a musical rhythm.

Literature Review:
Gratch et al. evaluated the importance of contingency, a prerequisite of synchrony, on various settings involving human-human and human-virtual agent interactions BIB001 . They compared the participants' feeling of rapport when facing a responsive or noncontingent virtual agent listener. The responsive behavior corresponded to nonverbal productions (nodding, shaking, mirroring) when specific vocal and motion behaviors from the human were recognized. In the noncontingent behavior, the human was presented with a virtual agent with a prerecorded behavior sequence. The researchers found evidence that the contingency of agent feedbacks influenced the behavior of the human participant and was involved in the creation of virtual rapport. Similarly, in the field of social robotics, equipping a machine with social abilities, such as synchrony and turntaking, represents a great challenge in the design of socially accepted interfaces  . Michalowski et al. designed the robot, Keepon, to engage in synchronous interactions with children BIB002 . Keepon is programmed to dance by performing periodic movements that smoothly and dynamically change tempo according to perceived rhythms. The rhythms can be extracted from various sensors according to the conditions being tested (vision, audio, pressure sensors, accelerometers, etc.). They studied the effect of synchronized movements on engagement under several conditions with the robot following the rhythm of a song or the movement of the child. Kozima et al. also performed a longitudinal observation of autistic children interacting with Keepon  . Keepon was introduced as a toy in a daycare center for children with pervasive developmental disorders over a three-year period. They observed the emergence of interactions between the children and the robot. Some children engaged in imitation play with the robot. For other children, the robot acted as a pivot for "sharing and exchanging pleasure and surprise with the caregivers." The authors claimed that the predictable and simple behavior of the robot facilitated the emergence of social behaviors.