In this paper I will show how reactive agents can solve relatively
complex tasks without requiring any internal state and I will demonstrate
that this is due to their ability to coordinate perception and action. By
acting (i.e. by modifying their position with respect to the external
environment and/or the external environment itself), agents partially
determine the sensory patterns they receive from the environment. As I
will show, agents can take advantage of this ability to: (1) select
sensory patterns that are not affected by the aliasing problem and
avoiding those that are; (2) select sensory patterns in which groups of
patterns requiring different answers do not strongly overlap; (3) exploit
the fact that, given a certain behavior, sensory states might indirectly
encode information about useful features of the environment; (4) exploit
emergent behaviors resulting from a sequence of sensory-motor loops and
from the interaction between the robot and the environment. Finally I
will discuss the relation between pure reactive agents and pure
representational agents and I will argue that a large variety of
intermediate cases between these two extremes exists. In particular I
will discuss the case of agents which encode in their internal states
what they did in the previous portion of their lifetime which, given a
certain behavior, might indirectly encode information about the external
environment.
