the opinions and desires of a non-player character (actors), it is
possible to devise a cost-benefit calculation to decide what they are
likely to do. This is a common problem in Game AI and much good work
has already been done on this. But this supposes a fixed set of
opinions (beliefs) in the actors. We would like to allow the actors to
evolve and change their opinions over time, just as real people do. We
also want to replicate the fact that while the opinions people hold are
often understandable, they are not always rational. In this paper we
introduce a methodology to do just this.
opinion flow is a big topic. People’s opinions are understandably
multi-faceted and complex. Here we are saying dash to this complexity
and reducing the decisions on one particular issue (the topic at hand)
to one simple number. At the end of the day in our game universe, one
supports King John, supports King Richard, or doesn’t particularly support anyone. If the bulk of the population supports King John, then his troops will receive more resources – and that is an effect that can be felt by King Richard1.
perform our calculation, we are borrowing concepts from the Boids
algorithm and from Social Network Analysis. This technique makes
possible new types of conflict, such as a Public Relations battle, and
can make concrete the ‘battle for hearts and minds.’
opinions are influenced by events, but also by what they perceive to be
the opinions of the people around them — people tend to believe what
the people around them believe. The central analogy of this paper is
that just as birds, fish, and other animals move their bodies in
groups, humans move their opinions in groups2. Animals flock with their bodies. People flock in their opinions.
A bird that strays from the flock
will change its course to move
back toward the flock, even as the
flock may begin to veer toward it.
Most people feel uncomfortable if
their thinking is too far unaligned
from that of the group, and will try
(either by trying to change the
group or their own thinking) to
minimize that distance.
technique can be applied to large populations or small populations. A
large population example could be an entire population of a country and
their support of a particular armed militia group. (If the player can
reduce public support for the militia, its resources will decrease.) A
small population example could be the actors around a key decision
maker. (If the player can locate and change the opinions of the people
around the decision maker, it will be possible to influence the
decision maker.) Both examples will be explored here.
Brief Explanation of Boids algorithm
with only a few simple parameters, accurately replicates the movement
of flocks of birds and schools of fishes. The movement appears so
realistic that it won an Academy Award in 1987 in the movie “Batman
Highly complex behavior can be explained
by the simple reactions of many independent agents all working with
incomplete information. The movement of an opinion in a society may
also appear to be incredibly complex, but it also the result of many
independent agents making straightforward calculations with incomplete
In Table 1 is a mapping of the Boids Effect, and the effect on thought as modeled here.
Effect on Thought
Birds steer in the general direction of the group.
tend to give credence to an idea shared by many people. They build
their picture of what the ‘group’ thinks based on information from
their news sources.
Birds move toward their near by flock mates.
People tend toward the ideas of the people they respect.
Birds maintain a safe distance from their flock mates.
People maintain a distance from ideas held by people for whom they have contempt.
Table 1 . Boids Effect vs. Effect on Human Thought
In a sense we are applying Newton’s second law of motion (Force = mass * acceleration)
to ‘ideas’ which have no mass. Ideas do, however, have a velocity. Sometimes ideas move fast – such as 'my Internet stock isn’t worth as much as I thought it was. I better sell.’ Sometimes ideas move slowly – such as ‘women should have the right to vote.’ Although universal suffrage may now seem like common sense to most of us, it was an idea that took centuries to become accepted.
is a physical model and the Boids effects create forces, which
influence the movement of the animal. For example, a bird seeing that
it is falling behind will begin to accelerate until it catches up with
Our forces will provide a propensity for
the opinion of an individual to move in a particular direction. If
there are people close to me that hold a particular opinion, then I
will be likely to hold that same opinion. If I hold a different
opinion, I will have to mentally justify it to myself in some way (such
as thinking I have information that they don’t have.) The brain is a
muscle, and mental justifications don’t come free. So the easy thing,
and the typical thing, is to just give in and accept the ‘conventional
wisdom’ and to fly with the rest of the flock.
is a separate, and quite important, consideration in the Boids
algorithm. The birds only have information regarding the other birds in
their field of vision. We will model this by providing all of the
members of our virtual society a connectivity score to all of the other
members. This type of approach is common in social network analysis,
and is explained further in the next section.