## 2 Related Work  
Embodied pedagogical agents are virtual characters that have a body and can interact and communicate using voice, gestures, and facial expressions for instructional purposes [18]. In general, the embodied pedagogical agents are distinguished from simple software agents that have autonomy but do not possess a virtual body and lack in communication means and mediums. Embodied agents may be particularly suitable for virtual environments. The main type of virtual agent concerns the virtual embodied pedagogical agents, which constitute a predominant type utilized in virtual reality educational environments. Embodied pedagogical agents have been used in various ways to deliver educational content as part of a vision that a virtual agent can advantageously influence learning [19; 20].  
In recent years, the examination of the effectiveness of embodied pedagogical agents has attracted the increasing attention of researchers. In the literature, there is significant research interest and many works study the effectiveness of virtual agents. In most cases, research works point out that virtual characters, even in cases when they possess minimal expressiveness, can have a positive influence on the learning experience of students, a phenomenon that is often called persona effect [14].  
The integration of virtual characters in various pedagogical settings in virtual reality environments can enhance the learning experience [13] by providing additional incentives for interaction and thus, engagement [21]. However, studies have pointed out that the interaction necessitates the active coordination and cooperation of at least two intelligent parties, which can be limited due to the absence of social intelligence [13]. Other works point out that learners experience more positive situations and emotions during interaction with a virtual agent that provides positive instead of negative feedback [22], and also that they can perform better in problem-solving procedures after having participated in educational games with polite instead of impolite agents [23; 24].  
The exact impact of the embodied pedagogical agents on learning outcomes is, however, inconclusive in the literature [18]. Reports also show that students who participated in educational games about plants did not perform better on attitudinal measures and knowledge recall when they were engaged with agents compared to situations that did not include additional support from agents [25]. Past empirical work has indicated that the way a virtual agent is introduced to the virtual world and the students may affect the learning outcomes [18].  
The aim of the present study is to thoroughly examine and deeply understand the effect that embodied agents have on the learning outcomes of students as well as on their learning experience, engagement, and performance. Although the virtual agents constitute a vital part of virtual environments their exact impact is yet to be addressed and examined [18]. Therefore, the main contribution of the present study concerns the examination of the following three hypotheses:  
H1: Embodied pedagogical agents improve students' learning experience in virtual world educational environments.  
H2: Embodied pedagogical agents improve students' performance and comprehension in virtual world educational environments.  
H3: Embodied pedagogical agents enhance students' engagement and their cooperation and communication with peers.  
The study aims to shed light on these hypotheses and examine the functionality of the embodied pedagogical agents in the AVARES virtual reality educational environment that was used. In the next sections, we present the environment, analyze the learning activities it offers to students, and examine the impact that pedagogical agents have on students' learning.