Who Needs Emotions? The Brain Meets the Robot

286 robots
and emotion-related process is modeled as a different type of specialist that
is specifically tailored for its role in the overall system architecture.
Each specialist receives messages from those connected to its inputs,
performs some sort of specific computation based on these messages, and
then sends the results to those elements connected to its outputs. Its activation
level, A, is computed by the following equation:
n
A = wi j j b
j
⎛ ⎞
⎜
⎝⎜
⎠⎟
+ ∑
= 1
for integer values of inputs i j, weights w j, and bias b over the number of
inputs n. The weights can be either positive or negative; a positive weight
corresponds to an excitatory connection, and a negative weight corresponds
to an inhibitory connection. Each process is responsible for computing its
own activation level. The process is active when its activation level exceeds
an activation threshold. When active, the process can send activation energy
to other nodes to favor their activation. It may also perform some
special computation, send output messages to connected processes, and/
or express itself through motor acts by sending outputs to actuators. Hence,
although the specialists differ in function, they all follow this basic activation
scheme.
Units are connected to form networks of interacting processes that allow
for more complex computation. This involves connecting the output(s) of one
unit to the input(s) of another unit(s). When a unit is active, besides passing
messages to the units connected to it, it can also pass some of its activation
energy. This is called spreading activation and is a mechanism by which units
can influence the activation or suppression of other units. This mechanism
was originally conceptualized by Lorenz (1973) in his hydraulic model of
behavior. Minsky (1986) uses a similar scheme in his ideas of memory formation
using K-lines. Popular architectures of Brooks (1986) and Maes (1991)
are similar in spirit. However, ours is heavily inspired by ethological models
and, hence, is most similar to that of Blumberg, Todd, and Maes (1996).
Ethology, comparative psychology, and neuroscience have shown that
observable behavior is influenced by internal factors (i.e., motivations, past
experience, etc.) and by external factors (i.e., perception). This demands that
different types of systems be able to communicate and influence each other
despite their different functions and modes of computation. This has led
ethologists such as McFarland and Bosser (1993) and Lorenz (1973) to propose
that there must be a common currency to the perceptual, motivational,
and behavioral systems. Furthermore, as the system becomes more complex,
it is possible that some components conflict with others (e.g., competing for
shared resources such as motor or perceptual abilities of the creature). In this