POWER AND THE LIMITS OF REACTIVE AGENTS

                                Stefano Nolfi
             Institute of Psychology, National Research Council
                    Viale Marx 15, 00137, Roma, Italy
                  Voice:++39-06-86090231, Fax:++39-06-824737
                         e-mail:nolfi@ip.rm.cnr.it
                       http://gral.ip.rm.cnr.it/nolfi


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.