Modeling Theory of Mind and Cognitive Appraisal With Decision-Theoretic Agents
Agent-based simulation of human social behavior has become increasingly important as a basic research tool to further our understanding of social behavior, as well as to create virtual social worlds used to both entertain and educate. A key factor in human social interaction is our beliefs about others as intentional agents, a Theory of Mind. How we act depends not only on the immediate effect of our actions but also on how we believe others will react. In this paper, we discuss PsychSim, an implemented multiagent-based simulation tool for modeling social interaction and influence. While typical approaches to such modeling have used first-order logic, PsychSim agents have their own decision-theoretic models of the world, including beliefs about their environment and recursive models of other agents. Using these quantitative models of uncertainty and preferences, we have translated existing psychological theories into a decision-theoretic semantics that allow the agents to reason about degrees of believability in a novel way. We demonstrate the expressiveness of PsychSim's decision-theoretic implementation of Theory of Mind by presenting its use as the foundation for a domain-independent model of appraisal theory, the leading psychological theory of emotion. The model of appraisal within PsychSim demonstrates the key role of a Theory of Mind capacity in appraisal and social emotions, as well as arguing for a uniform process for emotion and cognition.
Modeling Theory of Mind and Cognitive Appraisal with
David V. Pynadath
, Mei Si
, and Stacy C. Marsella
Institute for Creative Technologies, University of Southern California
12015 Waterfront Drive, Playa Vista, CA 90094-2536 USA
Cognitive Science Department, Rensselaer Polytechnic Institute
110 8th Street, Troy, NY 12180 USA
firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
April 7, 2011
Agent-based simulation of human social behavior has become increasingly important as a basic research tool to
further our understanding of social behavior, as well as to create virtual social worlds used to both entertain and
educate. A key factor in human social interaction is our beliefs about others as intentional agents, a Theory of Mind.
How we act depends not only on the immediate effect of our actions but also on how we believe others will react. In
this paper, we discuss PsychSim, an implemented multiagent-based simulation tool for modeling social interaction
and inﬂuence. While typical approaches to such modeling have used ﬁrst-order logic, PsychSim agents have their
own decision-theoretic models of the world, including beliefs about their environment and recursive models of other
agents. Using these quantitative models of uncertainty and preferences, we have translated existing psychological
theories into a decision-theoretic semantics that allow the agents to reason about degrees of believability in a novel
way. We demonstrate the expressiveness of PsychSim’s decision-theoretic implementation of Theory of Mind by
presenting its use as the foundation for a domain-independent model of appraisal theory, the leading psychological
theory of emotion. The model of appraisal within PsychSim demonstrates the key role of a Theory of Mind capacity
in appraisal and social emotions, as well as arguing for a uniform process for emotion and cognition.
Computational models of social interaction have become increasingly important in both basic research on human social
behavior and a range of applications. For example, computational models of psychological or sociological theories
promise to transform how theories of human behavior are formulated and evaluated . In addition, computational
models of human social interaction have also become increasingly important as a means to create simulated social
environments used in a variety of training and entertainment applications . For example, many serious games have
used models of social interaction as the basis for virtual (typically embodied) autonomous characters [2, 24, 33, 44, 46].
We argue that such models of social interaction must address the fact that people interact within a complex social
framework. A central factor in social interaction is the beliefs we have about each other, a Theory of Mind .
Our choice of action is inﬂuenced by how we believe others will feel and react. Whether we believe what we are
told depends not only on the content of the communication but also on our model of the communicator. How we
emotionally react to another’s action is inﬂuenced by our beliefs as well, for example whether we believe he or she
intended to cause harm . The central goal of our research is to bring such Theory of Mind capacities to the design
of computational models of social interaction both as a basic research tool and as a framework for virtual character
Unfortunately, traditional artiﬁcial intelligence techniques are ill-suited for modeling Theory of Mind. Representa-
tions using ﬁrst-order logic are often insensitive to the distinctions among conﬂicting goals that people must balance in
a social interaction. For example, psychological research has identiﬁed a range of goals that motivate classroom bullies
(e.g., peer approval, sadism, tangible rewards) . Different bullies may share the same goals, but the relative priori-
ties that they place on them will lead to variations in their behavior. Resolving the ambiguity among equally possible,
but unequally plausible or preferred, options requires a quantitative model of uncertainty and preference. Unfortu-
nately, more quantitative frameworks, like decision theory and game theory, face their own difﬁculties in modeling
human psychology. Game-theoretic frameworks typically rely on concepts of equilibria that people rarely achieve
in an unstructured social setting like a classroom. Decision-theoretic frameworks typically rely on assumptions of
rationality that people violate.
We have developed a social simulation framework, PsychSim [20, 27], that operationalizes existing psychological
theories as boundedly rational computations to generate more plausibly human behavior. PsychSim allows a user to
quickly construct a social scenario where a diverse set of entities, groups or individuals, interact and communicate.
Each entity has its own preferences, relationships (e.g., friendship, hostility, authority) with other entities, private
beliefs, and mental models about other entities. The simulation tool generates the behavior for these entities and
provides explanations of the result in terms of each entity’s preferences and beliefs. The richness of the entity models
allows one to explore the potential consequences of minor variations on the scenario.
A central aspect of the PsychSim design is that agents have fully speciﬁed decision-theoretic models of others.
Such quantitative recursive models give PsychSim a powerful mechanism to model a range of factors in a principled
way. For instance, we exploit this recursive modeling to allow agents to form complex attributions about others,
send messages that include the beliefs and preferences of others, and use their observations of another’s behavior to
inﬂuence their model of that other.
In operationalizing psychological theories within PsychSim, we have taken a strong architectural stance. We
assume that decision-theoretic agents that incorporate a Theory of Mind provide a uniform, sufﬁcient computational
core for modeling the factors relevant to human social interaction. While the sufﬁciency of our framework remains an
open question, such a strong stance yields the beneﬁt of uniform processes and representations that cover a range of
phenomena. Our stance thus provides subsequent computational beneﬁts, such as optimization and reuse of the core
algorithms that provide the agent’s decision-making and belief revision capacities.
More signiﬁcantly, this uniformity begins to reveal common elements across apparently disparate psychological
phenomena that typically have different methodological histories. To illustrate such common elements, we have
demonstrated how a range of human psychological and social phenomena can be modeled within our framework,
including wishful thinking , inﬂuence factors , childhood aggression  and emotion .
In this article, we discuss two of those models. First, we use a model of childhood aggression to motivate the
discussion of the overall framework as well as to demonstrate its expressiveness. Second, in keeping with the theme
of this volume, we go into considerable detail on how PsychSim’s decision-theoretic agents with a Theory of Mind
provide a particularly effective basis for a computational model of emotion.
Computational models of emotion have largely been based on appraisal theory [5, 7, 18, 22, 6, 23, 28, 47], a leading
psychological theory of emotion. Appraisal theory argues that a person’s subjective assessment of their relationship
to the environment determines his or her emotional responses [8, 13, 14, 23, 29, 30, 41, 42]. This assessment occurs
along several dimensions, such as motivational congruence, accountability, novelty and control. For example, an
event that leads to a bad outcome for a person (motivationally incongruent) and is believed to be caused by others
(accountability) is likely to elicit an anger response. On the other hand, if the event is believed to be caused by the
person himself/herself, he/she is more likely to feel guilt or regret .
We approach the task of incorporating appraisal into the existing PsychSim multiagent framework as a form of
thought experiment: Can we leverage the existing processes and representations in PsychSim to model appraisal? The
motivations for this thought experiment are three-fold. First, we seek to demonstrate overlap between the theoretical
model of appraisal theory and decision-theoretic, social agents of PsychSim. Speciﬁcally, we are interested in whether
appraisal offers a possible blueprint, or requirements speciﬁcation, for intelligent social agents by showing that an
existing framework not predesigned with emotion or appraisal in mind has, in fact, appraisal-like processes already
Conversely, we seek to illustrate the critical role that subjective beliefs about others plays in allowing agents to
model social emotions. Because the agent’s representations and decision-making processes are rooted in a Theory
of Mind capacity, incorporating and maintaining beliefs about others, the appraisal process inherits this social frame,
allowing the agent to appraise events from its own perspective as well as others. Thus, in keeping with the tenets of
social appraisal , the behaviors, thoughts and emotions of the other can also be appraised and thereby inﬂuence
Finally, we seek a design that is elegant, by reusing architectural features to realize new capabilities such as emo-
tion. Alternative approaches for creating embodied conversational agents and virtual agents often integrate separate
modules for emotion, decision-making, dialogue, etc., which leads to sophisticated but complex architectures .
The work here is an alternative minimalist agenda for agent design. In particular, based on the core theory of mind
reasoning processes, appraisal can be derived with few extensions.
We begin the paper with a demonstration of PsychSim’s application to a childhood aggression scenario. We then
discuss how PsychSim can represent appraisal theory and present a preliminary assessment of its implementation.
2 The Agent Models
This section describes PsychSim’s underlying architecture, using a school bully scenario for illustration. The agents
represent different people and groups in the school setting. The user can analyze the simulated behavior of the students
to explore the causes and cures for school violence. One agent represents a bully, and another represents the student
who is the target of the bully’s violence. A third agent represents the group of onlookers, who encourage the bully’s
exploits by, for example, laughing at the victim as he is beaten up. A ﬁnal agent represents the class’s teacher trying
to maintain control of the classroom, for example by doling out punishment in response to the violence. We embed
PsychSim’s agents within a decision-theoretic framework for quantitative modeling of multiple agents. Each agent
maintains its independent beliefs about the world, has its own goals and it owns policies for achieving those goals.
2.1 Model of the World
Each agent model starts with a representation of its current state and the Markovian process by which that state evolves
over time in response to the actions performed.
Each agent model includes several features representing its “true” state. This state consists of objective facts about
the world, some of which may be hidden from the agent itself. For our example bully domain, we included such
state features as power(agent), to represent the strength of an agent. trust(truster,trustee) represents
the degree of trust that the agent truster has in another agent trustee’s messages. support(supporter,
supportee) is the strength of support that an agent supporter has for another agent supportee. We represent
the state as a vector, ~s
, where each component corresponds to one of these state features and has a value in the range
Agents have a set of actions that they can choose to change the world. An action consists of an action type (e.g.,
punish), an agent performing the action (i.e., the actor), and possibly another agent who is the object of the action.
For example, the action laugh(onlooker, victim) represents the laughter of the onlooker directed at the
2.1.3 World Dynamics
The state of the world changes in response to the actions performed by the agents. We model these dynamics using a
transition probability function, T (~s
), to capture the possibly uncertain effects of these actions on the subsequent
= ~a) = T (~s
For example, the bully’s attack on the victim impacts the power of the bully, the power of the victim, etc. The
distribution over the bully’s and victim’s changes in power is a function of the relative powers of the two—e.g., the
larger the power gap that the bully enjoys over the victim, the more likely the victim is to suffer a big loss in power.
PsychSim’s decision-theoretic framework represents an agent’s incentives for behavior as a reward function that maps
the state of the world into a real-valued evaluation of beneﬁt for the agent. We separate components of this reward
function into two types of subgoals. A goal of Minimize/maximize feature(agent) corresponds to a nega-
tive/positive reward proportional to the value of the given state feature. For example, an agent can have the goal of
maximizing its own power. A goal of Minimize/maximize action(actor, object) corresponds to a nega-
tive/positive reward proportional to the number of matching actions performed. For example, the teacher may have
the goal of minimizing the number of times any student teases any other.
We can represent the overall preferences of an agent, as well as the relative priority among them, as a vector of
weights, ~g, so that the product, ~g · ~s
, quantiﬁes the degree of satisfaction that the agent receives from the world, as
represented by the state vector, ~s
. For example, in the school violence simulation, the bully’s reward function consists
of goals of maximizing power(bully), minimizing power(victim), and maximizing laugh(onlookers,
victim). By modifying the weights on the different goals, we can alter the motivation of the agent and, thus, its
behavior in the simulation.
2.3 Beliefs about Others
As described by Sections 2.1 and 2.2, the overall decision problem facing a single agent maps easily into a partially
observable Markov decision problem (POMDP) . Software agents can solve such a decision problem using ex-
isting algorithms to form their beliefs and then determine the action that maximizes their reward given those beliefs.
However, we do not expect people to conform to such optimality in their behavior. Thus, we have taken the POMDP
algorithms as our starting point and modiﬁed them in a psychologically motivated manner to capture more human-like
behavior. This “bounded rationality” better captures the reasoning of people in the real-world, as well as providing the
additional beneﬁt of avoiding the computational complexity incurred by an assumption of perfect rationality.
2.3.1 Nested Beliefs
The agents have only a subjective view of the world, where they form beliefs,
, about what they think is the state of
the world, ~s
. Agent A’s beliefs about agent B have the same structure as the real agent B. Thus, our agent belief
models follow a recursive structure, similar to previous work on game-theoretic agents . Of course, the nesting
of these agent models is potentially unbounded. However, although inﬁnite nesting is required for modeling optimal
behavior, people rarely use such deep models . In our school violence scenario, we found that 2-level nesting was
sufﬁciently rich to generate the desired behavior. Thus, the agents model each other as 1-level agents, who, in turn,
model each other as 0-level agents, who do not have any beliefs. Thus, there is an inherent loss of precision (but with
a gain in computational efﬁciency) as we move deeper into the belief structure.
For example, an agent’s beliefs may include its subjective view on states of the world: “The bully believes that the
teacher is weak”, “The onlookers believe that the teacher supports the victim”, or “The bully believes that he/she is
powerful.” These beliefs may also include its subjective view on beliefs of other agents: “The teacher believes that the
bully believes the teacher to be weak.” An agent may also have a subjective view of the preferences of other agents:
“The teacher believes that the bully has a goal to increase his power.” It is important to note that we also separate an
agent’s subjective view of itself from the real agent. We can thus represent errors that the agent has in its view of itself
(e.g., the bully believes himself to be stronger than he actually is).
Actions affect the beliefs of agents in several ways. For example, the bully’s attack may alter the beliefs that agents
have about the state of the world—such as beliefs about the bully’s power. Each agent updates its beliefs according to
its subjective beliefs about the world dynamics. It may also alter the beliefs about the bully’s preferences and policy.
We discuss the procedure of belief update in Section 2.4.
2.3.2 Policies of Behavior
Each agent’s policy is a function, π(
b), that represents the process by which it selects an action or message based on
its beliefs. An agent’s policy allows us to model critical psychological distinctions such as reactive vs. deliberative
behavior. We model each agent’s real policy as a bounded lookahead procedure that seeks to maximize expected reward
simulating the behavior of the other agents and the dynamics of the world in response to the selected action/message.
Each agent i computes a quantitative value, V
), of each possible action, a, given its beliefs,
, a, ~π
) = max
The agent computes the posterior probability of subsequent belief states (Pr(
)) by using the transition function, T ,
to project the immediate effect of the action, a, on its beliefs. It then projects another N steps into the future, weighing
each state against its goals, ~g. At the ﬁrst step, agent i uses its model of the policies of all of the other agents, π
and, in subsequent steps, it uses its model of the policies of all agents, including itself, π. Thus, the agent is seeking
to maximize the expected reward of its behavior as in a POMDP. However, PsychSim’s agents are only boundedly
rational, given that they are constrained, both by the ﬁnite horizon, N, of their lookahead and the possible error in
their belief state,
b. By varying N for different agents, we can model entities who display different degrees of reactive
vs. deliberative behavior in their thinking.
2.3.3 Stereotypical Mental Models
If we applied this full lookahead policy within the nested models of the other agents, the computational complexity
of the top-level lookahead would quickly become infeasible as the number of agents grew. To simplify the agents’
reasoning, these mental models are realized as simpliﬁed stereotypes of the richer lookahead behavior models of the
agents themselves. For our simulation model of a bullying scenario, we have implemented mental models correspond-
ing to attention-seeking, sadistic, dominance-seeking, etc. For example, a model of an attention-seeking bully speciﬁes
a high priority on increasing the approval (i.e., support) that the other agents have for it, a dominance-seeking bully
speciﬁes a high priority on increasing its power as paramount, and a bully agent speciﬁes a high priority on hurting
These simpliﬁed mental models also include potentially erroneous beliefs about the policies of other agents. Al-
though the real agents use lookahead exclusively when choosing their own actions (as described in Section 2.3.2),
the agents believe that the other agents follow much more reactive policies as part of their mental models of each
other. PsychSim models reactive policies as a table of “Condition⇒Action” rules. The left-hand side conditions may
trigger on an observation of some action or a belief of some agent (e.g., the bully believing himself as powerful). The
conditions may also be more complicated combinations of these basic triggers (e.g., a conjunction of conditions that
matches when each and every individual condition matches).
The use of these more reactive policies in the mental models that agents have of each other achieves two desirable
results. First, from a human modeling perspective, the agents perform a shallower reasoning that provides a more
accurate model of the real-world entities they represent. Second, from a computational perspective, the direct action
rules are cheap to execute, so the agents gain signiﬁcant efﬁciency in their reasoning.
2.4 Modeling Inﬂuence and Belief Change
Messages are attempts by one agent to inﬂuence the beliefs of another. Messages have four components: source,
recipients, subject, and content. For example, the teacher (source) could tell the bully (recipient) that the principal
(subject of the message) will punish violence by the bully (content). Messages can refer to beliefs, preferences,
policies, or any other aspect of other agents. Thus, a message may make a claim about a state feature of the subject
(“the principal is powerful”), the beliefs of the subject (“the principal believes that he is powerful”), the preferences of
the subject (“the bully wants to increase his power”), the policy of the subject (“if the bully thinks the victim is weak,
he will pick on him”), or the stereotypical model of the subject (“the bully is selﬁsh”).
2.4.2 Inﬂuence Factors
A challenge in creating a social simulation is addressing how groups or individuals inﬂuence each other, how they
update their beliefs and alter behavior based on any partial observation of, as well as messages from, others. Although
many psychological results and theories must inform the modeling of such inﬂuence (e.g., [1, 3, 25]) they often suffer
from two shortcomings from a computational perspective. First, they identify factors that affect inﬂuence but do not
operationalize those factors. Second, they are rarely comprehensive and do not address the details of how various
factors relate to each other or can be composed. To provide a sufﬁcient basis for our computational models, our
approach has been to distill key psychological factors and map those factors into our simulation framework. Here, our
decision-theoretic models are helpful in quantifying the impact of factors in such a way that they can be composed.
Speciﬁcally, a survey of the social psychology literature identiﬁed the following key factors:
Consistency: People expect, prefer, and are driven to maintain consistency, and avoid cognitive dissonance, be-
tween beliefs and behaviors.
Self-interest: The inferences we draw are biased by self-interest (e.g., motivated inference) and how deeply we
analyze information in general is biased by self-interest.
Speaker’s Self-interest: If the sender of a message beneﬁts greatly if the recipient believes it, there is often a
tendency to be more critical and for inﬂuence to fail.
Trust, Likability, Afﬁnity: The relation to the source of the message, whether we trust, like or have some group
afﬁnity for him, all impact whether we are inﬂuenced by the message.
2.4.3 Computational Model of Inﬂuence
To model such factors in the simulation, one could specify them exogenously and make them explicit, user-speciﬁed
factors for a message. This tactic is often employed in social simulations where massive numbers of simpler, often
identical, agents are used to explore emergent social properties. However, providing each agent with quantitative
models of itself and, more importantly, of other agents gives us a powerful mechanism to model this range of factors
in a principled way. We model these factors by a few simple mechanisms in the simulation: consistency, self-interest,
and bias. We can render each as a quantitative function of beliefs that allows an agent to compare alternate candidate
belief states (e.g., an agent’s original
b vs. the
implied by a message).
Consistency is an evaluation of the degree to which a potential belief agreed with prior observations. In effect,
the agent asks itself, “If this belief holds, would it better explain the past better than my current beliefs?”. We use a
Bayesian deﬁnition of consistency based on the relative likelihood of past observations given the two candidate sets
of beliefs (e.g., my current beliefs with and without believing the message). An agent assesses the quality of the
competing explanations by a re-simulation of the past history. In other words, it starts at time 0 with the two worlds
implied by the two candidate sets of beliefs, projects each world forward up to the current point of time, and computes
the probability of the observation it received. The higher the value, the more likely that agent is to have chosen the
observed action, and, thus, the higher the degree of consistency.
In previous work, we have investigated multiple methods of converting such action values into a degree of con-
sistency . For the purposes of the current work, we use only one of those methods, deﬁning the consistency of a
sequence of observations, ω
, . . ., with a given belief state,
b, as follows:
, . . . , ω
) = Pr
, . . . , ω
The algorithm ﬁrst ranks the utilities of the actor’s alternative actions in reversed order (rank(v)). The value function,
V , computed is with respect to the agent performing the action at time τ . Thus, the higher the rank of the likelihood
of the observation, the more consistent it is with the candidate belief state.
Self-interest is similar to consistency, in that the agent compares two sets of beliefs, one which accepts the message
and one which rejects it. However, while consistency evaluates the past, we compute self-interest by evaluating
the future using Equation 3. An agent can perform an analogous computation using its beliefs about the sender’s
preferences to compute the sender’s self-interest in sending the message.
Bias factors represent subjective views of the message sender that inﬂuence the receiver’s acceptance/rejection of
the message. We treat support (or afﬁnity) and trust as such a bias on message acceptance. Agents compute their
support and trust levels as a running history of their past interactions. In particular, one agent increases (decreases) its
trust in another, when the second sends a message that the ﬁrst decides to accept (reject). Similarly, an agent increases
(decreases) its support for another, when the second selects an action that has a high (low) reward, with respect to the
preferences of the ﬁrst. In other words, if an agent selects an action a, then the other agents modify their support level
for that agent by a value proportional to ~g ·
b, where ~g corresponds to the goals and
b the new beliefs of the agent
modifying its support.
Upon receiving any information (whether message or observation), an agent must consider all of these various
factors in deciding whether to accept it and how to alter its beliefs (including its mental models of the other agents).
For a message, the agent determines acceptance using a weighted sum of the ﬁve components: consistency, self-
interest, speaker self-interest, trust and support. Whenever an agent observes an action by another, it checks whether
the observation is consistent with its current beliefs (including mental models). If so, no belief change is necessary. If
not, the agent evaluates alternate mental models as possible new beliefs to adopt in light of this inconsistent behavior.
Agents evaluate these possible belief changes using the same weighted sum as for messages.
Each agent’s decision-making procedure is sensitive to these changes that its actions may trigger in the beliefs of
others. Each agent accounts for the others’ belief update when doing its lookahead, as Equations 2 and 3 project the
future beliefs of the other agents in response to an agent’s selected action. Similar to work by  this mechanism
provides PsychSim agents with a potential incentive to deceive, if doing so leads the other agents to perform actions
that lead to a better state for the deceiving agent.
We see the computation of these factors as a toolkit for the user to explore the system’s behavior under existing
theories, which we can encode in PsychSim. For example, the elaboration likelihood model (ELM)  argues that
the way messages are processed differs according to the relevance of the message to the receiver. High relevance or
importance would lead to a deeper assessment of the message, which is consistent with the self-interest calculations
our model performs. PsychSim’s linear combination of factors is roughly in keeping with ELM because self-interest
values of high magnitude would tend to dominate.
3 Childhood Aggression Model
The research literature on childhood aggression provides interesting insight into the role that Theory of Mind plays
in human behavior. Investigations of bullying and victimization  have identiﬁed four types of children; we focus
here on nonvictimized aggressors, those who display proactive aggression due to positive outcome expectancies for
aggression. Children develop expectations on the likely outcomes of aggression based on past experiences (e.g., did
past acts of aggression lead to rewards or punishment). This section describes the results of our exploration of the
space of different nonvictimized aggressors and the effectiveness of possible intervention strategies in dealing with
3.1 Scenario Setup
The user sets up a simulation in PsychSim by selecting generic agent models that will play the roles of the various
groups or individuals to be simulated and specializing those models as needed. In our bullying scenario, we constructed
generic bully models that compute outcome expectancies as the expected value of actions (V
from Equation 2). Thus,
when considering possible aggression, the agents consider the immediate effect of an act of violence, as well as the
possible consequences, including the change in the beliefs of the other agents. In our example scenario, a bully has
three subgoals that provide incentives to perform an act of aggression: (1) to change the power dynamic in the class
by making himself stronger, (2) to change the power dynamic by weakening his victim, and (3) to earn the approval
of his peers (as demonstrated by their response of laughter at the victim). Our bully agent models the ﬁrst incentive as
a goal of maximizing power(bully) and the second as minimizing power(victim), both coupled with a belief
that an act of aggression will increase the former and decrease the latter. The third incentive seeks to maximize the
laugh actions directed at the victim, so it must consider the actions that the other agents may take in response.
For example, a bully motivated by the approval of his classmates would use his mental model of them to predict
whether they would laugh along with him. We implemented two possible mental models of the bully’s classmates:
encouraging, where the students will laugh at the victim, and scared, where the students will laugh only if the teacher
did not punish them for laughing last time. Similarly, the bully would use his mental model of the teacher to predict
whether he will be punished or not. We provide the bully with three possible mental models of the teacher: normal,
where the teacher will punish the bully in response to an act of violence; severe, where the teacher will more harshly
punish the bully than in the normal model; and weak, where the teacher never punishes the bully.
The relative priorities of these subgoals within the bully’s overall reward function provide a large space of possible
behavior. When creating a model of a speciﬁc bully, PsychSim uses a ﬁtting algorithm to automatically determine the
appropriate weights for these goals to match observed behavior. For example, if the user wants the bully to initially
attack a victim and the teacher to threaten the bully with punishment, then the user speciﬁes those behaviors and the
model parameters are ﬁtted accordingly . This degree of automation signiﬁcantly simpliﬁes simulation setup. In
this experiment, we selected three speciﬁc bully models from the overall space: (1) dominance-seeking, (2) sadistic,
and (3) attention-seeking, each corresponding to a goal weighting that favors the corresponding subgoal.
3.2 Experimental Results
PsychSim allows one to explore multiple tactics for dealing with a social issue and see the potential consequences.
Here, we examine a decision point for the teacher after the bully has attacked the victim, followed by laughter by the
rest of the class. At this point, the teacher can punish the bully, punish the whole class (including the victim), or do
nothing. We explore the impact of different types of proactive aggression by varying the type of the bully, the teacher’s
decision to punish the bully, the whole class, or no one, and the mental models that the bully has of the other students
and the teacher.
A successful outcome is when the bully does not choose to act out violently toward the victim the next time around.
Bully Punish Model of Model of Success?
Type Whom? Students Teacher
Sadistic bully * ¬severe N
class scared * N
encouraging ¬severe N
no one * ¬severe N
Attention Seeking bully * * N
class scared weak N
encouraging * N
no one * * N
Dominance Seeking * * weak N
Table 1: Outcomes of intervention strategies
By examining the outcomes under these combinations, we can see the effects of intervention over the space of possible
classroom settings. Table 1 shows all of the outcomes, where we use the “*” wildcard symbol to collapse rows where
the outcome was the same. Similarly, a row with “¬severe” in the Teacher row spans the cases where the bully’s
mental model of the teacher is either normal or weak.
We ﬁrst see that the PsychSim bully agent meets our intuitive expectations. For example, we see from Table 1 that
if the bully thinks that the teacher is too weak to ever punish, then no immediate action by the teacher will change the
bully from picking on the victim. Thus, it is critical for the teacher to avoid behavior that leads the bully to form such
mental models. Similarly, if the bully is of the attention-seeking variety, then punishment directed at solely himself
will not dissuade him, as he will still expect to gain peer approval. In such cases, the teacher is better off punishing the
We can see more interesting cases as we delve deeper. For example, if we look at the case of a sadistic bully when
the teacher punishes the whole class, we see that bully can be dissuaded only if he thinks that the other students will
approve of his act of violence. This outcome may seem counter-intuitive at ﬁrst, but the sadistic bully is primarily
concerned with causing suffering for the victim, and thus does not mind being punished if the victim is punished as
well. However, if the bully thinks that the rest of the class is encouraging, then the teacher’s punishment of the whole
class costs him peer approval. On the other hand, if the bully thinks that the rest of the class is already scared, so that
they will not approve of his violence, then he has no peer approval to lose.
Such exploration can offer the user an understanding of the potential pitfalls in implementing an intervention
strategy. Rather than providing a simple prediction of whether a strategy will succeed or not, PsychSim maps out
the key conditions, in terms of the bully’s preferences and beliefs, on which a strategy’s success depends. PsychSim
provides a rich space of possible models that we can systematically explore to understand the social behavior that arises
out of different conﬁgurations of student psychologies. We are continuing to investigate more class conﬁgurations and
the effects of possible interventions as we expand our models to cover all of the factors in school aggression identiﬁed
in the literature.
4 A Model of Appraisal
To further illustrate the capacity of these decision-theoretic agents to model social interaction, we also used them to
implement a computational model of emotion, largely based on Smith and Lazarus’s theory of cognitive appraisal .
As noted in Section 1, our implementation was driven by a thought experiment: Can we leverage the existing processes
and representations in PsychSim to model appraisal? The motivations for this thought experiment are three-fold. First,
we seek to demonstrate an intrinsic coupling between the theoretical model of appraisal and decision-theoretic social
reasoning. Speciﬁcally, we wish to show that an existing social framework with no explicit emotion or appraisal
capabilities has, in fact, appraisal-like processes already present as part of its decision-making processes. Second, we
also seek to illustrate the critical role that subjective beliefs about others play in modeling social emotions. Finally, we
seek a minimalist design that elegantly reuses architectural features to model new social phenomena, like emotion.
This work on modeling appraisal is in the spirit of EMA [10, 19] (see also Chapter X), which deﬁnes appraisal
processes as operations over a plan-based representation (a causal interpretation) of the agent’s goals and how events
impact those goals. The agent’s existing cognitive processes maintain the causal interpretation, which appraisal-
speciﬁc processes leverage. Thus, in EMA, the cognitive processes for constructing the person-environment relation
representation are distinct from appraisal itself, which is reduced to simple and fast pattern matching over the plan
We seek to eliminate this distinction by demonstrating how the cognitive processes for decision-making can also
generate appraisals. While EMA uses a uniform representation across cognition and appraisal, we seek to additionally
establish uniformity over the algorithms underlying both cognition and appraisal. In so doing, we can identify that
appraisal itself is already an integral part of the cognitive processes that a social agent must perform to maintain its
beliefs about others and to inform its decision-making in a multiagent social context.
Speciﬁcally, we treat appraisal as leveraging component algorithms already present in a PsychSim agent by de-
riving key appraisal variables from the outputs of these algorithms. Furthermore, the appraisal process inherits the
intrinsic social nature of these algorithms, allowing the agent to appraise events from another’s perspective, as well as
from its own. Thus, in keeping with Manstead and Fischer’s concept of social appraisal, the behaviors, thoughts and
emotions of the other can also be appraised and thereby inﬂuence the agent.
We have modeled ﬁve appraisal dimensions so far: motivational relevance, motivational congruence, account-
ability, control and novelty. We adapted Smith and Lazarus’s  deﬁnitions for modeling motivational relevance,
motivational congruence and accountability. Our model of control is roughly equivalent to Smith and Lazarus’s 
deﬁnition of problem-focused coping potential. It is closer to Scherer’s  deﬁnition of control, because it accounts
for the overall changeability of the situation and not an individual agent’s power to make a change. Finally, we modeled
novelty based on Leventhal and Scherer’s [15, 30] deﬁnition of predictability-based novelty, as there is no equivalent
concept in Smith and Lazarus.
The model of appraisal is built within Thespian [33, 34, 35, 36, 37, 38, 39], which extends PsychSim for modeling
and simulating computer-aided interactive narratives. This computational model of appraisal is one of Thespian’s
extensions. We demonstrate the application of the appraisal model in three different scenarios: a simple conversation
between two people, a ﬁring-squad scenario as modeled in , and a fairy tale, “The Little Red Riding Hood”. The
last scenario will be described in detail in the next section as it will be used as an example to motivate the discussion
of our appraisal model. The details of the other two scenarios are given in Section 5.
4.1 Little Red Riding Hood Domain
The story contains four main characters, Little Red Riding Hood (Red), Granny, the hunter and the wolf. The story
starts as Red and the wolf meet each other on the outskirts of a forest while Red is on her way to Granny’s house. The
wolf wants to eat Red, but it dares not because there is a wood-cutter close by. At this point, the wolf and Red can
either have a conversation or go their separate ways. The wolf may have future chances to eat Red if he ﬁnds her alone
at another location. Moreover, if the wolf hears about Granny from Red, it can even go to Granny’s house and eat her
as well. Meanwhile, the hunter is searching for the wolf to kill it. Once the wolf is killed, all of the wolf’s previous
victims can escape. Our model of this story builds upon the base PsychSim representation, as described in Section 2.
4.2 Modeling Appraisal in Thespian
Appraisal is a continuous process . People constantly reevaluate their situations and cope with unfavorable situa-
tions, forming a “appraisal-coping-reappraisal” loop. In this section we illustrate how we can model this phenomenon
and derive appraisal dimensions by leveraging algorithms and information within a PsychSim agent’s belief revision
and decision-making processes.
During decision making, the lookahead process generates the agent’s expectations about possible future events so
that it can choose the action with the most favorable outcome. Figure 1 is an example of one-step lookahead while
assuming that the other characters will also perform a one-step lookahead. Bold shapes denote the actions with the
highest expected utility based on the actor’s mental models. When no shapes are in bold, there are multiple actions
with the same expected utility, and the actor has no speciﬁc preference over which action will be picked. Finally, this
example is a simpliﬁed version of our actual implementation, where the agents simulated more steps of lookahead and
had more actions to choose from.
The agent remembers the expectations generated in its last two lookahead processes, because the evaluations of
some appraisal dimensions (e.g. accountability) need to trace back more than one step. Note that these expectations
contain not only the agent’s expectations about its own and the other agents’ future actions, but also the expected
states/utilities of all possible action choices of each of the agents. These state/utility traces serve as required input for
the explanation algorithms that provide the user with the agent’s motivations for making its observed choices.
Upon observing a new event (an action performed by an agent or the user), each agent updates its beliefs and
appraises the new situation. The calculation of motivational relevance, motivational congruence, novelty and account-
ability depends on only the agent’s beliefs about the other agents’ and its own utility values in the current and previous
steps, which therefore can be derived immediately (see Section 4.3). Our calculation of control occurs only after the
agent has made its own decision in response to the observed event. In fact, at this time the agent could potentially
reevaluate every appraisal dimension as it computes updated information about expected states/utilities.
The mental models that Thespian agents have of each other enable them to not only have emotional responses to
the environment but also form expectations of other agents’ emotions. To simulate another agent’s appraisal processes,
the observing agent’s beliefs about the other agent are used for deriving appraisal dimensions. For instance, the wolf
can use its beliefs about Red to evaluate the motivational relevance and novelty of an event to her, which will most
likely be totally different from the wolf’s own evaluations of those dimensions. In our current implementation, if
the observing agent has multiple mental models of other agents, currently it uses only the most likely mental models
(rather than the entire distribution of likelihoods) to simulate their appraisals.
4.3 Appraisal Dimensions
This section illustrates how the agents can evaluate ﬁve appraisal dimensions (motivational relevance, motivation
congruence or incongruence, accountability, control and novelty) using states/utilities calculated during the agents’
belief revision and decision-making processes.
Figure 1: Red’s lookahead process
4.3.1 Motivational Relevance & Motivational Congruence or Incongruence
Motivational relevance evaluates the extent to which an encounter touches upon personal goals. Motivational congru-
ence or incongruence measures the extent to which the encounter thwarts or facilitates personal goals .
Algorithm 1 Motivational Relevance & Motivation Congruence
# preUtility: utility before the event happens
# curUtility: utility after the event happens
Motivational Relevance =
Motivational Congruence =
We model these appraisal dimensions as a product of the agent’s utility calculations which are integral to the agent’s
decision-theoretic reasoning. We use the ratio of the relative utility change and the direction of the utility change to
model these two appraisal dimensions. The rationale behind this is that the same amount of utility change will result
in different subjective experiences depending on the agent’s current utility. For instance, if eating a person increases
the wolf’s utility by 10, it will be 10 times more motivationally relevant and congruent when the wolf’s original utility
is 1 (very hungry) than when the wolf’s original utility is 10 (less hungry).
Algorithm 1 evaluates motivational relevance and motivational congruence/incongruence. preUtility denotes the
agent’s expected utility before the other agent takes an action. For agents who perform at least one step of lookahead,
this value is evaluated by the agents’ previous decision-making process. Taking Figure 1 as an example, Red’s expected
utility is the sum of her utility over this sequence of actions: Red chats with the wolf, the wolf chats with Red and Red
chats with the wolf again. This follows Red’s expectations of the interaction. curUtility denotes the agent’s updated
expected utility, reﬂecting the effect of the other agent’s action. Note that this value is also pre-computed when the
agent generated its expectations about the other agent’s possible actions. For example, if the wolf chooses the action
as Red has expected, then curUtility is the same as preUtility for Red. If the wolf instead chooses to walk away, then
Red’s expectation about future events changes. In this case, she would expect herself to walk away too and curUtility
would be the sum of Red’s utilities over this alternate sequence of actions: Red chats with the wolf, the wolf walks
away and Red walks away too. If an agent does not perform any lookahead (i.e., it cares about only its immediate
reward and not the responses of the other agents), the value of curUtility will not be calculated by the agent’s previous
decision-making process. It will be calculated when the agent updates its beliefs to compute its immediate reward in
the next time step, and the evaluation of the appraisal dimensions will happen at that time.
The sign of Motivational Congruence indicates whether the event is motivationally congruent or incongruent to
the agent. When the value is negative, the event is motivationally incongruent to the extent of Motivational Relevance,
and otherwise the event is motivationally congruent to the agent.
Agents can also have goals to help or hinder other agents in the pursuit of their own goals. If an action helps ad-
vance a Thespian agent’s self-centered goals but hurts a friend’s goals (where a friend is someone whom the agent has
a goal to help), then the agent’s overall utility is diminished, subsequently muting the action’s motivational congruence
and relevance. For example, while Red will derive a self-centered satisfaction from eating the cake, that satisfaction
will be offset by the negative impact on Granny, who has been deprived of the cake’s beneﬁt.
Accountability determines who deserves credit or blame for a given event . Various theories have been proposed
for assigning blame/credit, e.g. [32, 48]. The reasoning usually considers factors such as who caused the event, did
the person foresee the result, was the person coerced to cause the event, etc.
Just as the appraisal of motivational relevance and motivation congruence can be performed as part of the existing
Thespian/PsychSim decision-making and belief update processes, we argue here that accountability can be treated as
an extension to Thespian/PsychSim’s existing approach to support/afﬁnity relationships between agents.
Figure 2 illustrates how an agent can determine accountability for an event’s outcome. Our algorithm ﬁrst looks
at the agent whose action directly causes the harm/beneﬁt and judges to what degree it should be held accountable.
The algorithm uses the function IfCoerced() to determine whether that agent was coerced into performing the given
action. If the direct actor was not coerced, it is held fully accountable for the result and the reasoning proceeds no
further. Otherwise, any agents that coerced the direct actor are also held partially accountable. The algorithm judges
each such coercer on whether it, too, was coerced by somebody else, with any such coercers sharing accountability
as well. This process could potentially continue cascading indeﬁnitely, but we instead limit the number of steps for
which accountability extends back through the history. In the current investigation, we assume that the observing agent
expects others to foresee the effects of their actions. While this assumption is not always true, people do often assume
that others will project into the future to the same depth as they will themselves.
Algorithm 2 contains pseudocode for determining whether an agent was coerced, and Algorithm 3 determines who
coerced the agent. Currently, we use a qualitative model to judge coercion based on the agent’s utility gain/loss. If
the agent’s chosen action has a strictly greater utility than its other options, then we view the agent’s choice as being
coerced, in that its decision was driven by its circumstances. If an alternate action would not have decrease the agent’s
utility, then we view the agent as not being coerced, in that it was free to make a different choice without sacriﬁcing
its own utility.
We use a qualitative rather than quantitative method to decide coercion. If all other action options lead to less
Algorithm 2 IfCoerced(actor, pact)
# actor: the agent being studied
# pact: the action performed by actor
# preUtility: actor’s utility before doing pact
for action ∈ actor.actionOptions() do
if action 6= pact then
# if there exists another action which does not hurt actor’s own utility
if EU (action) ≥ preUtility then
Figure 2: Accountability
utility than its chosen action, then we view the agent as justiﬁed in its choice and must look back further to ﬁnd the
accountable agent. In the special case when the agent’s chosen action is its best choice but still results in a utility drop,
the agent is regarded as not being coerced. In such cases, because the agent is going to be punished regardless of what
it does, we treat it as having the freedom to pick actions which will not hurt the other agent’s utility.
In Algorithm 2, preUtility is deﬁned as in Algorithm 1, with the important distinction that preUtility now refers to
the beliefs of the observer (the agent who performs appraisal) about the actor’s expected utility. Similarly, EU(action)
denotes the observer’s belief about the actor’s utility of alternative option.
To decide who coerced an agent, we consider each agent that acted between the coerced agent’s current and last
actions. For each potential coercer, if the coerced agent would not have been coerced (as deﬁned by Algorithm 2) if
the potential coercer had made a different choice, then the potential coercer is judged as being a true coercer. This
process is illustrated in Algorithm 3.
Algorithm 3 Is Coercer For(agent, actor, agent pact, actor pact)
# agent pact: the action performed by agent
# actor pact: the action performed by actor
for action ∈ agent.actionOptions() do
if action 6= agent pact then
Simulate action agent pact
if not IfCoerced(actor, actor pact) then
The appraisal of control evaluates the extent to which an event or its outcome can be inﬂuenced or controlled by
people . It captures not only the individual’s own ability to control the situation but also the potential for seeking
instrumental social support from other people. Unlike the evaluations of motivational relevance, motivational con-
gruence and accountability in which the most probable mental models of other agents are used for reasoning, here
we factor in the probabilities of the mental models because the degree of control is affected by the estimation of how
likely certain events will happen in the future.
Algorithm 4 Control(preUtility)
# preUtility: utility before the event happens
control ← 0
∈ mental models about agent1 do
∈ mental models about agent2 do
∈ mental models about self do
# project limited steps into the future using this set of mental models
# curUtility: utility after the lookahead process
if curUtility ≥ preUtility then
control ← control + p(m
) ∗ p(m
) ∗ p(m
Algorithm 4 gives the pseudocode for evaluating control. This algorithm ﬁrst simulates future steps of the interac-
tion using each possible combination of mental models of self and others, and checks whether the utility drop will be
recovered. The algorithm then considers the likelihood of the given mental model combination. For example, assume
Granny has two mental models of the wolf. In the ﬁrst mental model, the wolf will always die after being shot by the
hunter. In the second mental model, the wolf will never die even after being shot. Granny believes that there is a 60%
possibility that the ﬁrst mental model is correct. Next assume Granny has two mental models regarding the hunter.
One mental model indicates that the hunter is close by and this mental model has a 50% chance to be correct. The
other mental model indicates that the hunter is far away. After Granny is eaten by the wolf, the only event that can
help her is the wolf being killed by the hunter. In this case, her sense of control is: 60% · 50% = 30%.
Algorithm 4 contains pseudocode for a three-agent interaction, but it is straightforward to conﬁgure the algorithm
for any number of agents. In this algorithm, preUtility is deﬁned as in Algorithm 1, but curUtility denotes the agent’s
utility associated with its state after the lookahead projection.
In this work, we adapt Leventhal and Scherer’s deﬁnition of “novelty at the conceptual level”, i.e., whether the event
is expected from the agent’s past beliefs
[15, 30]. In our model, novelty appraisal is treated as a byproduct of an
agent’s belief maintenance. Speciﬁcally, in a multiagent context the novelty of an agent’s behavior is viewed as the
opposite of the agent’s motivational consistency, i.e. the more consistent the event is with the agent’s motivations, the
less novel. Of course, this evaluation is performed from the observing agent’s perspective and using the observing
agent’s beliefs, and there can be discrepancies between what the observing agent feels and what the agent who did the
action feels. Computationally, we deﬁne novelty as 1 − consistency, where consistency is calculated as described
in Section 2.4.3. The less consistent an action is with the observing agent’s expectation about the actor, the higher the
novelty if that action happens. For example, if from Red’s perspective the wolf did an action which has the second
highest utility among the wolf’s ﬁve alternative actions, the amount of novelty Red will feel if seeing that action is
5 Appraisal Model in Action
All the previous examples of our new appraisal model are derived from a Thespian implementation of the Little Red
Riding Hood story. In this section we provide two additional scenarios to illustrate the usage of our computational
model of appraisal in modeling social interactions. In particular, in Section 5.1 we demonstrate the tight relationship
between emotion and cognitive decision-making by showing how appraisal is affected by the depth of reasoning in
decision-making. In Section 5.2 we provide a complex situation for accountability reasoning and show that the result
of our model is consistent with another validated computational model of social attribution.
Leventhal and Scherer have also deﬁned novelty at the sensory-motor level and schematic level. We did not model them because they are
mainly related to people’s low level perceptual processes rather than cognitive processes.
Step Action Perspective Lookahead Steps Motivational
1 A greets B B 1 0
B 2 100
2 B greets A A 1 0
A 2 0.99
3 A asks B a question B 1 0
B 2 0.99
4 B answers the question A 1 0
A 2 0.49
Table 2: Small talk between two persons
5.1 Small Talk
To reveal the tight relationship between cognitive processes and emotion in our model, we implemented an abstract
domain of two persons (A and B) taking turns talking to each other. Both of them have these goals: to be talkative
and to obey social norms. In fact, just the norm-following behavior itself is an incentive to them — they will be
rewarded whenever they do an action that is consistent with social norms. Table 2 contains the two persons’ appraisals
of motivational relevance regarding each other’s actions. We did not include results of other appraisal dimensions as
they are less interesting in this scenario.
In PsychSim, we explicitly model the depth of reasoning in agents as the number of steps they project into the
future. In this example we provide a comparison of appraisal results when the person’s previous reasoning process
takes a different number of steps. It can be observed in Table 2 that different depths of reasoning lead to different
appraisals. A person appraises another person’s initiatives as irrelevant when performing shallow reasoning (lookahead
steps = 1). In this case, even though the person has predicted the other person’s action, because the action does not
bring him/her immediate reward, the person cannot see the relevance of the action. Once the person reasons one step
further, he/she ﬁnds out that by opening up a topic the other person provides him/her a chance to engage in further
conversation and perform a norm following action, the person will then appraise the other person’s action as relevant.
We implemented the Firing-squad scenario from  to illustrate accountability reasoning in which agents are coerced
and have only partial responsibility. The scenario goes like this:
In a ﬁring-squad, the commander orders the marksmen to shoot a prisoner. The marksmen refuse the order. The
commander insists that the marksmen shoot. They shoot the prisoner and he dies.
We modeled the commander as an agent with an explicit goal of killing the prisoner, and the marksmen as having
Appraisal Dimension Existing PsychSim Processes
Motivational Relevance Decision-Making (exploit utility calculations based on single mental model)
Motivational Congruence Decision-Making (exploit utility calculations based on single mental model)
Accountability Belief (Mental Model) update (Support Relationship)
Control Decision-Making (exploit utility calculations based on alternative mental models)
Novelty Belief (Mental Model) update
Table 3: Appraisal tightly coupled with decision making
no goals related to the prisoner, but they will be punished if they do not obey the commander’s order. Using our
appraisal model, from the prisoner’s perspective, the marksmen hold responsibility for his/her death because they are
the persons who directly perform the action. Further, the prisoner can simulate the decision-making process of the
marksmen which will lead him/her to ﬁnd out that the marksmen are coerced because their utilities will be hurt if they
do anything else other than shooting. The commander acts right before the marksmen in the scenario and therefore
is identiﬁed as a potential coercer for the marksmen. Using Algorithm 3 , we can predict that the prisoner can see if
the commander chose a different action, the marksmen would not be coerced to shoot. Assuming the prisoner does
not ﬁnd a coercer for the commander, he/she will now believe that the commander holds full responsibility for his/her
death. This prediction is consistent with the prediction from Mao’s model of social attribution and the data collected
from human subjects to validate that model .
6 Discussion of Appraisal Model
In PsychSim, comparison among expected utilities plays the central role in decision-making and mental model up-
date. Comparison of expected utilities also plays a central role for deriving appraisal dimensions. Our algorithms
for deriving appraisal dimensions demonstrate that no additional calculation of utilities or states other than what has
already been performed in the Thespian agent’s existing decision-making and belief revision processes is required for
appraisal. Table 6 summarizes the relationship between PsychSim’s existing processes and the evaluation of appraisal
Compared to other computational models of appraisal, the main advantage of this model is that the agents explicitly
model other agents’ goals, states and beliefs (Theory of Mind). Modeling Theory of Mind makes this model partic-
ularly suitable for simulating emotions in social interactions in two ways. First, appraisals are strongly embedded in
the social context. For example, novelty is not simply evaluated as whether the physical stimulus is unexpected, but
whether the other agents behave as expected. Second, appraisals that are explicitly relevant to social interaction and
derivation of social emotion (e.g., accountability) have to leverage Theory of Mind.
Further, the fact that Thespian agents have a Theory of Mind capability enables them to simulate the emotions of
others. This ability allows us to simulate an agent’s potential mis-expectations about other agents’ emotional states.
For example, if Granny believes that the hunter can always kill the wolf successfully and the hunter believes that he
can only kill the wolf successfully 60% of the time, Granny’s control when being eaten by the wolf will be evaluated
differently from Granny’s and the hunter’s perspectives.
The appraisal model can not only simulate ego-centric emotions, but also can simulate emotions that take social
relationships into account. Thespian agents can have goals regarding other agents’ utilities and emotions (emotion
can be modeled as a feature of an agent’s state). Therefore, an agent’s emotion can be related to other agents’ utility
changes and emotions. For example, we can simulate an agent having goals of facilitating another agent’s goals, or
even more speciﬁcally having goals of making the other agent feel happy. This agent will act deliberately to help the
other agent, and “feel” bad if it hurts the other agent’s utility or emotional state.
Finally, the underlying PsychSim framework allows us to explicitly model the depth of reasoning in agents. As
shown in Section 5.1, different depths of reasoning lead to different appraisals. Though we have only demonstrated
this effect using one appraisal dimension (motivational relevance), this effect is general. Different steps of projection
lead to different expectations of future events, and an agent’s expectations affect its reasoning about whether an event
is novel, whether the effect of the event is changeable and who caused the event.
In terms of future work, one of the extensions we are considering concerns social appraisal , which argues
that another’s behaviors, thoughts or feelings can inﬂuence an agent’s own appraisals. In the current framework, the
capacity of the agent to appraise from another’s perspectives provides a way for the agent to infer another agent’s
appraisals. It therefore provides a framework for exploring the various ways those appraisals can inﬂuence the agent’s
We have discussed PsychSim, an environment for multiagent simulation of human social interaction that employs
a formal decision-theoretic approach using recursive models. This approach allows us to model phenomena rarely
addressed in simulated worlds. We have exploited the recursive models to provide a psychologically motivated com-
putational model of how agents inﬂuence each other’s beliefs. We have also developed a range of technology to
simplify the task of setting up PsychSim models, exploring the simulation and analyzing results. Discussion of these
algorithms is beyond the scope of this paper, but they provide users with automated algorithms for ﬁtting simulation
parameters to observed behavior, reporting sensitivities in the results, and suggesting potentially interesting perturba-
tions to the scenario . We believe PsychSim has a range of innovative applications, including computational social
science and the modeling of social training environments.
As an illustration of such applications, and PsychSim’s expressiveness, we provide a computational model of
appraisal for POMDP-based agents, implemented in the Thespian framework for interactive narrative. The focus is
on ﬁve key appraisal dimensions for virtual agents: motivational relevance, motivational congruence, accountability,
control and novelty. The approach argues that appraisal is an integral part of a social agent’s cognitive processes.
All of these capabilities of the appraisal model derive from the basic PsychSim cognitive components as laid out
in Section 2. We were thus able to leverage the decision-theoretic Theory of Mind as implemented in our agents to
realize appraisal theory, even though modeling appraisal was not an original intention of the agents’ design. The reuse
of architectural features therefore provides, not only a novel computational model of emotion, but also a demonstration
of a tight relationship between emotion and cognition, suggesting a uniform cognitive structure for emotion and cog-
nition. In addition, by demonstrating how a Theory of Mind capacity is critical to deriving appraisals, and in particular
modeling appraisals critical to social emotions like anger, this work argues for the critical role for Theory of Mind in
modeling social interaction generally.
This work was sponsored by the U.S. Army Research, Development, and Engineering Command (RDECOM), and the
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