Pedagogical Agents on the Web

Erin Shaw, W. Lewis Johnson, and Rajaram Ganeshan

Center for Advanced Research in Technology for Education
USC Information Sciences Institute
4676 Admiralty Way, Marina del Rey, CA 902-6695 USA

{shaw, johnson, rajaram}


Animated pedagogical agents are lifelike animated characters that facilitate the learning process. This paper describes Adele, a pedagogical agent that is designed to work with Web-based educational simulations. The Adele architecture implements key pedagogical functions: presentation, student monitoring and feedback, probing questions, hints, and explanations. These capabilities are coupled with an animated persona that supports continuous multi-modal interaction with a student. The architecture supports client-side execution in a Web browser environment, and is able to inter-operate with simulations created by off-the-shelf authoring tools.

Keywords Pedagogical agent, intelligent tutor, architecture.

  2. Animated pedagogical agents are animated characters that facilitate learning in computer-based learning environments. These agents have animated personas that respond to user actions. In addition, they have enough understanding of the learning context and subject matter that they are able to perform useful roles in learning scenarios.

    Although pedagogical agents build upon previous research on intelligent tutoring systems (Wenger 1987), they bring a fresh perspective to the problem of facilitating on-line learning, and address issues that previous intelligent tutoring work has largely ignored. Because pedagogical agents are autonomous agents, they inherit many of the same concerns that autonomous agents in general must address. (Johnson and Hayes-Roth 1998) argue that practical autonomous agents must in general manage complexity. They must exhibit robust behavior in rich, unpredictable environments; they must coordinate their behavior with that of other agents, and must manage their own behavior in a coherent fashion, arbitrating between alternative actions and responding to a multitude of environmental stimuli. In the case of pedagogical agents, their environment includes both the students and the learning context in which the agents are situated. Student behavior is by nature unpredictable, since students may exhibit a variety of aptitudes, levels of proficiency, and learning styles.

    Our goal is to create agents that have life-like personas, that are able to interact with students on an ongoing basis. This contrasts with other pedagogical agent work (e.g., Ritter 1997) that ignores personas. Animated personas can cause learners to feel that on-line educational material is less difficult (André et al 1998). They can increase student motivation and attention (Lester et al 1997). But most fundamentally, animated pedagogical agents make it possible to more accurately model the kinds of dialogs and interactions that occur during apprenticeship learning and one-on-one tutoring. Factors such as gaze, eye contact, body language, and emotional expression can be modeled and exploited for instructional purposes.

    This paper focuses on a particular pedagogical agent developed at USC: Adele (Agent for Distance Education - Light Edition). Adele shares many capabilities with our other pedagogical agent, Steve, who was described at previous Autonomous Agents conferences and elsewhere (Johnson et al 1998, Johnson and Rickel 1998, Rickel and Johnson 1998, Rickel and Johnson 1997). Adele extends the pedagogical capabilities of Steve, and applies them to a wider range of educational problems. But whereas Steve was originally designed to operate in immersive virtual environments, Adele is designed to operate over the Web. Web-based delivery both constrains the available modalities of interaction with the user and imposes strong requirements on the implementation. This paper describes Adele's capabilities and discusses issues relating to hosting such agents in a Web-based learning environment.

  4. Adele is designed to support students working through problem-solving exercises that are integrated into instructional materials delivered over the World Wide Web. Adele supports both single-user, single-system tutoring and multi-user, multi-system collaborative exercises.

    Figure 1 shows a typical case-based diagnosis exercise in which students are presented with a simulated patient in a clinical setting. In the role of physicians, students are able to perform a variety of actions on the simulated patient; they may ask questions about medical history, perform a physical examination, order


    Figure 1. Adele explains the importance of abdomen palpation. Figure 2. Adele advises in a critical care scenario.

    diagnostic tests, and make diagnoses. Adele monitors the student's actions and provides feedback accordingly. Depending upon the instructional goals, Adele may highlight aspects of the case, suggest correct actions, provide hints and rationales for particular actions, reference relevant background material, and provide contextual assessment, to test a student's understanding.

    In the time-critical trauma care exercise, shown in Figure 2, the patient's state changes over time. Adele monitors the patient's state as it changes, as well as the student's actions, and alerts the student if she detects an instability in the patient's condition to which the student does not promptly react. The trauma care exercise is designed to be collaborative, as is typically the case in an emergency room, and currently supports the roles of physician and nurse.

    1. Agent-Oriented Approach

    Adele's design was based on an autonomous agent paradigm instead of an intelligent tutoring system paradigm. The design was based heavily upon earlier work on Steve. In the case of Steve, the distinction with conventional tutoring systems is fairly clear. Each Steve agent is able to operate in a dynamic environment incorporating multiple students and multiple other Steve agents. Steve can manipulate objects in the virtual environment, in order to demonstrate how to perform tasks, or in order to collaborate with students. Steve can sense where the student is and what he or she is looking at, and can adapt instructionally. He can use gaze, body position, and gesture to engage the student in multi-modal dialog.

    Because Adele is confined to a conventional desktop GUI interface, she has fewer options for interacting with students. Nevertheless, the agent-based approach offers advantages, even with the more limited interface. Adele's use of gaze and gesture, and her ability to react to student actions, makes her appear lifelike and aware of the user, and her use of facial expressions can have a motivating influence on a student. Adele was designed modularly and can be integrated with Web-based exercises and simulations that are authored with off-the-shelf tools that support an external programming interface.

  6. Adele's system, shown in Figure 3, consists of four main components: the pedagogical agent, the simulation, the client-server, and the server store. The pedagogical agent consists further of two sub-components, the animated persona and the reasoning engine. A fifth component, the session manager (not shown), is employed when the system is run in multiple-user mode. The central server is used to maintain a database of student progress and when appropriate, to provide synchronization for collaborative exercises being carried out by multiple students on multiple computers.

    The reasoning engine performs all monitoring and decision making. Its decisions are based on a student model, a case task plan, and an initial state, which are downloaded from the server when a case is chosen, and on the agent's current mental state, which is updated as a student works through a case. Upon completion, a record of the student's actions is saved to the server where it is used to assess the level of the student's expertise and determine how Adele will interact with the student in future cases.

    The animated persona is simply a Java applet that can be used alone with a Web page-based JavaScript interface or incorporated into larger applications, such as the simulation-based exercises we describe here. We chose to create our own animated agent instead of using an off-the-shelf persona like Microsoft Agent, to ensure platform independence and extensibility. The persona applet allows animation frames to be easily added and exchanged to support a choice of personas.

    The simulation can be authored using the language or authoring tool of one's choice. For example, the simulation for the clinical diagnosis application was built in Java while that for a trauma care application was built using Emultek's RAPID, a rapid-prototyping tool whose simulations can run in a Web browser inside a plug-in. All simulations communicate with the agent via a common application programming interface (API) that supports event and state change notifications as defined by the simulation logic.

    Figure 3. Architectural overview of the single-user system. In the multi-user system, the Reasoning Engine is server-based, as is a fifth component, the Session Manager (not shown).

    The integrated system is downloaded to and run on the client's side for execution efficiency. This is in contrast to the architecture of most other Web-based Intelligent Tutoring Systems where the intelligent tutor sits on the server side, resulting in increased latency in tutor response to student actions (e.g., Brusilovsky et. al 1997). Reducing latency is especially critical when one considers animating an agent's response to a student's action, in order to achieve the perception of awareness in a shared workspace.

  8. The representation scheme used in Adele was designed to be simple and general, yet enable Adele to provide useful feedback to students. Simplicity is essential in order for the agent reasoning engine to run efficiently on the client side. It is also essential in order to support knowledge acquisition and authoring; we want domain experts to be able to specify domain knowledge for Adele with a minimum of intervention by knowledge engineers. Generality is important so that Adele can be applied to as wide a range of courses as possible. Her current task representation can support not only, for example, a wide range of educational science courses, but is also appropriate for many kinds of skill training.

    Adele's knowledge representation focuses on the steps that the student should take in the task, the dependencies between them, and their rationales. The task steps and their dependencies are represented in a task plan. Each task plan is described in a general enough fashion to allow students to perform actions in whatever order they wish, as long as critical ordering constraints are satisfied. The task plan framework can be applied to a wide range of procedural skills. The rationales typically refer to underlying domain knowledge such as disease properties. In order to ensure simplicity, Adele's knowledge is specialized for each case. This allows us to avoid formalizing extensive amounts of background knowledge in Adele. Instead, this knowledge is provided informally in the rationale texts associated with each task plan step, and in supporting Web-based reference materials.

    1. Task Plan
    2. Diagnosis and treatment are examples of canonical tasks in the health science settings in which Adele is deployed. Depending on the context, a task can be a simple sequence of steps or it can be a complex and non-linear partial ordering on a set of steps. Adele represents all procedural tasks using a standard hierarchical plan (Russell & Norvig, 1995). A plan hierarchy is comprised of steps, each of which is either a primitive action (e.g. corresponds to a simulation event) or a complex action (e.g. is itself a plan). Adele's plan representation is based on Steve's, except that where Steve's plans are converted into Soar productions and processed by Soar (Laird et. al, 1987), Adele's plans are read as objected-oriented data structures and processed by Adele's Java-based reasoning engine.

      (step palpate-axillary

      :effect ((palpate-axillary-done = T)

      (set palpate-axillary-value))

      :phrase "palpate" "palpating" "the axillary nodes")

      Figure 4. A primitive step in a task plan hierarchy.

      (step examine-lymphnodes

      :precond (examine-lesion)

      :steps (and palpate-axillary-nodes



      :hint "Is Lymphadenopathy indicated?"

      :rationale "Lymphadenopathy would occur in infect-

      ious diseases such as TB, viral, fungal, and

      some bacterial infections, and in cancer."

      :verbose "The distribution of the nodes involved

      gives a clue based on their drainage."

      :context "lymphnodes"

      :role physician)

      Figure 5. A complex step (bottom) in a task plan hierarchy.

      Figures 4 and 5 show two steps in a task plan hierarchy. The top step, palpate-axillary-nodes, is a primitive action and is shown with its effects and dialogue hints. Below it is the complex action, examine-lymphnodes, which consists of three required steps, as denoted by the Boolean and, as well as a precondition, hint, rationale, verbose rationale, context and role. A step's end conditions are implicitly defined by its sub-steps and effects, but may be described explicitly as well.

      Preconditions and end conditions are represented by Boolean expressions in conjunctive normal form. They can also be steps as in Figure 5, where the step examine-lesion is a precondition of the step palpate-lymphnodes. Steps are supported as goals by sub-classing the expression tree to include a new type of Boolean, a step expression, which, like Boolean constants, logical expressions, and comparative expressions, evaluates to true or false. Evaluating a step expression is equivalent to evaluating a step's end conditions, which is done recursively in the case of complex plans. This extension makes it possible to support the creation of both goal- and task-based plans.

      The plan hierarchy is evaluated at each step to account for the dynamic nature of a simulation and the unpredictability of a student's actions. Actions whose goals become 'undone' are automatically re-executed while those whose goals are implicitly satisfied are skipped. In this way, Adele's task plan is dynamically updated.

    3. Feedback

    The reasoning engine can be run in three modes. In its most restrictive mode, it will simply block actions whose preconditions are unsatisfied. Adele uses this opportunity to provide unsolicited feedback about what should be done to satisfy the desired step's preconditions. The persona displays a Hint button so that a student may also ask for hints directly, before guessing or taking an incorrect action. (Similarly, the persona has a Why? button, that allows a student to ask for a rationale.) In practice mode, the engine does not block - the student can make mistakes - and Adele does not provide unsolicited feedback, but still allows a student to ask for hints. In exam mode, Adele is not available. The modes are analogous to those of the SICULE tutor (Alexe & Gecsei, 1996)

    Adele uses authored hints when they are available. Using a focus stack, she proceeds from the top-most relevant point in the plan hierarchy, which is found by working upwards from the desired action to the root of the tree until an unsatisfied node, i.e. sub-plan, is found. If the hint for the sub-plan has already been given then the search continues down to the sub-sub-plans and ultimately to the unsatisfied task itself. As a rule, the higher the sub-plan, the more general its hints will be. For example, for the hierarchical task path diagnosis-rootðgive-physicalðexamine-lymphnodes-ðpalpate-clavicular-node, the hints might be 'Proceed as would in a clinical setting', 'Have you examined the patient?', 'Is Lymphadenopathy indicated?', and 'Are the clavicular nodes well drained?', respectively. Adele will follow the path from general to specific when giving feedback.

    Authored hints are only given once, to avoid unwarranted repetition, and may not be given at all. For example, asking "Have you examined the patient?" does not make sense if, for example, a student tries to palpate the lymphnodes before examining the lesion (a precondition of palpate-lymphnodes). In this case, Adele skips right to the hint for examining the lesion and invalidates all the general hints above it in the hierarchy. When no authored hints exist, Adele will automatically generate a suggestion using the phrase hints associated with a step.

  9. Situation-Based Reasoning
  10. While the task plan representation described above is adequate for diagnostic tasks, it does not extend well to dynamic settings like trauma or critical care where unforeseen complications may arise. For example, in one exercise, the patient's oxygenation level goes below 30, which is indicative of a breathing problem. If the problem is not corrected immediately the patient's life is at risk. Adele must have the knowledge to guide a student through these complications as they arise.

    We have borrowed the notion of a situation from Marsella and Schmidt (1990, Marsella & Johnson, 1998) to structure this kind of knowledge in Adele. Marsella and Schmidt introduce the Situation Space as a means of structuring the space of states associated with a domain so that it can be used to guide planning activity in dynamic domains. A situation is defined by a name, world state, goal expression, priority, and set of transitions. The world state and goal expressions are partial state descriptions. Priority is used to order situations when more than one is appropriate. Transitions describe possible situations that can result from this situation whenever the associated conditions become true in the world state.

    Figure 6. Transition from a current to a priority situation.

    Typically, when a situation is entered, a situation-appropriate sub-plan is instantiated to achieve the goal expression. Because the tutoring domain allows us to 'know' all possible situations a priori, there is no need to generate a plan in real time for each situation. Instead, all situational plans are pre-authored, taking into account potential negative interactions, for example, that of a newly-added step undoing the effects of a previously-executed step, or conflicting with the effects of an existing step that is required to satisfy another goal. Thus, what remains for Adele's reasoning engine is a situation-monitoring task.

    There is always a current situation defined in Adele's reasoning engine, which monitors the world state for changes that may cause a transition to another situation. The current plan that forms the basis for tutoring changes with the situation. In Figure 6, Normal Trauma is the primary situation, and remains current until the value of oxygen becomes less than or equal to thirty. The value change triggers a transition to a new situation, Breathing Problem, which then invokes a higher-priority plan to solve the breathing problem and reduce the value of oxygen, triggering a transition back to the original situation.

    Figure 7. Adele instructs a student to answer a quiz when the student selects a urine dipstick test.

  12. Adele has been extended to support some additional instructional capabilities that Steve presently lacks. Using knowledge about both the student and the context she can intervene to present quizzes, provide pointers to relevant reference materials, and help motivate students by commenting on their progress.

    1. Opportunistic Learning
    2. Situation-based reasoning can also be applied to the problem of recognizing pedagogical opportunities as a student works through a given task. For example, when a student orders a diagnostic test, a situation might provide Adele an opportunity to ask the student questions about the results of the test, as shown in Figure 7. Questions can be adapted to reflect a student's current understanding. Unlike domain-specific situations like the breathing-problem described above, there is no need for a plan to deal with these types of pedagogical opportunities.

      However, by maintaining an awareness of the situation the agent can undertake situationally-appropriate interactions with the student, for example, allowing the student one or more chances to answer a question or asking follow-up questions. In this way situations are used to represent the knowledge that allows the pedagogical agent to react to changes in the state of the simulated world, not only for dealing with domain-specific conditions but also for exploiting pedagogical opportunities.

      A situation object and a reference action are shown in Figure 8. The situation, showFNAReference, becomes current when its conditions are true. This occurs when the student schedules the patient for a fine needle aspiration (FNA), and it is the case that the student has not been told about the video on the FNA procedure. This type of situation is called a momentary situation because it simply triggers an event, unlike a quiz situation, below, which requires processing. Here, it triggers a refer action named FNAVideo that causes Adele tell the student about a video that is available in the reference library. If a URL is specified, a refer action will also enable the agent persona's Show button that, when selected by the student, will bring up a Web page from which the video can be accessed.

      (situation showFNAReference

      :type momentary

      :condition (and (schedule-fna-done == T)

      (knowsAboutFNAVideo == false))

      :actions (:refer FNAVideo))

      (refer FNAVideo

      :comment "Did you know that there is a video that

      describes how to do a fine needle aspiration

      in the reference library?"

      :effects ((knowsAboutFNAVideo = true))

      :url videos/fna.avi)

      Figure 8. A situation that triggers a reference action.

      Giving a quiz is another example of how situation-based reasoning can be used for opportunistic learning. When the quiz situation askUrinalysisQuiz in Figure 9 is current, Adele will invoke a quiz named urinalysisQuiz and guide the student through it; she will introduce it, answer questions about it, and finally, give feedback on the answers chosen. A quiz action is more complex than a refer action, but it is described similarly.

      (situation askUrinalysisQuiz

      :type quiz

      :condition (and (order-urinalysis-done == T)

      (knowsAboutUrinalysis == false))

      :actions (:quiz urinalysisQuiz)

      :hint "Two of these options are appropriate."

      :rationale "The quiz tests your understanding.")

      Figure 9. A situation that triggers a quiz action.

    3. Contextual References
    4. Because Adele is part of an instructional system, we must support course authors who wish to provide references to materials that are relevant to the instructional goals. The materials are made available as part of a Web-based reference library and may range from documents and images to videos and animations. In a typical library setting, a user who wishes to find a particular document initiates a search from the library's home page. While we cannot yet read a student's mind, we, or at least Adele, can infer the topic of the search based on the current context. For example, when a student begins to examine a patient, Adele knows that the context is the physical examination. If the student references the library at this time, he will find himself on a page that contains topics related to performing a physical examination. This is accomplished by a context tag in the task plan, and a map from context to Web page.

    5. Student Assessment

    Adele continuously monitors and records a student's interaction with a simulation. During a procedural task, Adele verifies that the task steps are done in the correct order and gives feedback as described above. She also tracks the student's responses to quizzes and referrals. We use a standard overlay model to track the data and feed it back into the processing. Our model is similar to one used in previous tutoring work in the medical domain (Eliot & Woolf, 1995).

    When a task is finished, Adele's assessment module analyzes the student's record and provides domain-appropriate feedback. For example, in a clinical domain, Adele provides three types of post-task assessment: 1) An evaluation of the diagnosis; 2) an evaluation of the diagnostic costs incurred, and 3) an evaluation of the steps taken. See Figure 10. The diagnosis assessment uses information about differential diagnoses, such as their confirmatory diagnostic tests, to comment on the correct diagnosis, or to compare an incorrect diagnosis to the correct one. Different domains will require different assessment modules, and Adele's feedback will differ accordingly.

  14. To facilitate Web-based delivery, Adele is implemented in Java, making it possible to download Adele-enhanced course modules over the Web. This approach offers long-term advantages, although in the near term, incompatibilities between Java virtual machines make portability somewhat difficult. High quality text-to-speech synthesis is platform-dependent, so variants of Adele are provided to take advantage of the text-to-speech synthesis capabilities available on each platform.

    On the persona side, Adele has a repertoire of facial expressions and body postures that represent emotions, such as surprise and disappointment. These permit Adele to respond in a more lifelike fashion to student actions. On the instructional side, we have developed ways of building more instructional guidance into Adele's interactions with the student. Based on a student's action, Adele may choose to intervene, offering advice about what to do instead, e.g., "before you order a chest X-ray you should examine the condition of the lesion." Alternatively, based on the context or action history, Adele can ask the student a 'pop quiz' question that must be answered before proceeding.

    Adele's animations are produced from two-dimensional drawings. This makes it possible to run Adele on a variety of desktops, without relying upon specialized 3D graphics capability. The main drawback of 2D imagery is that it is difficult to compose behaviors, e.g., frown while looking to one side. We are experimenting with VRML browsers as a way of providing articulated human figures on a desktop setting. However, since adding a VRML browser adds complexity to the software installation, there will still be applications where 2D animations are preferable.

    1. Simulation Interface

    Another implementation issue that influenced the design was the need to interface to externally authored simulations. Simulation authoring tools such as VIVIDS (Munro et. al, 1996) and Emultek's RAPID are frequently used both to author simulation behavior and the simulation interface at the same time. For this reason, Adele was designed to run in a separate window, communicating with educational simulations using an interprocess communication link. We then developed behaviors for Adele to give the impression that she is integrated with the other displays running on the desktop, even though she runs in a separate window. When the student clicks on a button in the simulation window, Adele turns her head to look toward where the student clicked. She has a pointer that she can use to point to objects in other windows, similar to the pointer used by André's PPP Persona (André et al. 1998). These behaviors partially compensate for her inability to manipulate objects directly.

  16. Over the past year, we have worked closely with the medical faculty and students at the USC Medical School to create two course modules: one for clinical diagnosis problem solving and one for emergency room trauma care training. We acquired the necessary knowledge for the tasks using script-style forms that contain detailed descriptions of each step of a procedure. Our implementation progress was monitored at many intervals. In-house usability experts and medical students on research rotations evaluated the system's usability and pedagogy, and comments from physicians have been solicited during demonstrations.

    The first formative evaluation of the Adele system was undertaken in November, 1998. The system was evaluated by a class of over one hundred unmonitored second year medical students. Two face-to-face evaluations were also conducted. For this evaluation, physicians in the Department of Family Medicine authored a new case on Lung Cancer that the students had covered in class.

    The questions on the evaluation addressed both specific elements of the tutoring system, such as the interface and the rationales, and the general reaction of the students to Adele and the concept of the system. A short pre-evaluation was given in order assess the students level of computer literacy. The final form contained thirty questions in six categories: system use, system components, rationales, Adele, and learning. Each answer was scored using a Likert scale of 0-4. The analysis is discussed in detail in Shaw et. al, 1998. We provide a summary of the findings here.


    Figure 10. Two views of an evaluation. The evaluation on the left lists all unnecessary tests and their costs. The evaluation of the diagnosis on the right hand side compares the incorrect diagnosis to the correct one.

    Most students were able to use the system easily, however, there was no help for those that did have problems, and we plan to add system knowledge, in addition to task knowledge, to Adele so that she can provide mechanical help at the system level.

    Students found Adele's hints helpful and liked her rationales. They had mixed feelings, though, about when they wanted to hear the rationales given. We noticed during a one-on-one session that the student was not asking "Why?", and thus not accessing much of the authored knowledge, so we decided to have Adele give some of the rationales automatically, whether a student asks for them or not. We implemented three variations: give a rationale only when asked, give it automatically after a hint, and give it automatically after a user takes a step, and then asked the students which variation they preferred. Most said they preferred to hear a rationale only when they asked for it, although our experience suggests that they would not ask at all if given a choice. We are devising further tests in order to explore this issue further.

    Finding the right level of realism has been difficult. Viewers accept Adele's persona and we have found no clear advantage of 3D over 2D as far as user acceptance is concerned, however, students did not think that Adele was believable as an attending physician and we need to find out why. Though students were not disturbed by the lack of lip-synchronization in the animation, text-to-speech synthesis quality is not ideal, and we continue to experiment with different speech synthesis systems in order to arrive at an acceptable solution

  18. We are currently developing three new cases for the medical domain; one is an extension of our new unit on Lung Cancer, which we plan to evaluate again in March, 1999, and the others are differential cases for our original learning unit on Myeloma. We are also adding support for multiple skill levels, so that Adele can be used both by all grades of medical students.

    We are also modifying Adele's task representation to include knowledge about hypotheses modified by the steps. For example, suppose a student asks the patient if a lesion hurts and the patient responds that it does not. This finding would reduce the possibility of a hypothesis of infection and increase it for a hypothesis of cancer. As a student works through a case, Adele can keep track of the likelihood of various hypotheses and use this information to provide hints that guide the student towards likely hypotheses. We are also building an interface that allows a student to state her own hypotheses and link them to relevant findings which allows Adele compare the student's reasoning to her own and provide appropriate feedback to the student.

    Meanwhile, we have initiated a new project in collaboration with the USC's School of Gerontology to create additional problem-solving exercises for other life science courses, all centered on health care for aging populations. The first of these courses, to be deployed in the Fall, will address clinical problem solving in geriatric dentistry and will be ready for a student trial in March.

  20. Adele and other pedagogical agents like her have lessons to offer regarding autonomous agent design. Researchers in believable agents argue that the audience's perception of an agent's competence is more important than the competence itself (Sengers 1998), and that competence is but one of many factors that agent authors should take into account (Reilly 1997). A key question is to what extent these claims are true for pedagogical agents. User feedback from Adele does indeed suggest that agent design must take the student's perspective into account. Behaviors such as gaze shifting are essential in order to give students the impression that these agents are aware of them and understand them. Presentation details such as body posture, facial expression, and tone of voice have at least some impact on students' impressions of these agents, although we have yet to demonstrate how much.

    However, students differ from the typical "audiences" for believable agents in that they can engage agents in instructional dialogs. Giving students the ability to probe an agents' knowledge requires a certain depth of knowledge on the part of the agent. The main lessons to be learned are: 1) Pedagogical agents need enough domain knowledge to support the anticipated instructional dialogs; 2) An agent's behavior and appearance enhance the perception of expertise in the agent; 3) Users can react to agents in unexpected ways, so prototyping and experimentation are essential.

  22. CARTE staff members Kate Labore and Dr. Jeff Rickel, 'A' Team members Ami Adler, Andrew Marshal, Anna Romero, and medical researcher Michael Hassler all contributed to the work presented here. Our collaborating organizations provided indispensable assistance, Drs. Allan Abbott, Demetrio Demetriatis, William La, Wesley Naritoku, Sidney Ontai, and Beverly Wood at the USC School of Medicine, and Carol Horwitz and Craig Hall at Air Force Research Laboratory. This work was supported by an internal research and development grant from the USC Information Sciences Institute.


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