Reactive agents are generally believed to be incapable of coping with perceptual ambiguity (i.e., identical sensory states that require different responses). However, a recent finding suggests that reactive agents can cope with perceptual ambiguity in a simple model (Nolfi, 2002). This paper investigates to what extent reactive and nonreactive agents can cope with perceptual ambiguity, and which strategies are employed when doing so. A model of active categorical perception (called Acp) is introduced. In Acp, situated agents with different types of neurocontrollers are optimized to categorize objects by adaptively coordinating action and perception. Our experiments show that both nonreactive and reactive agents can cope with perceptual ambiguity. An analysis of the behavior reveals that nonreactive agents use their internal memory to cope with perceptual ambiguity, while reactive agents use the environment as an external memory to compensate for their lack of an internal memory. We conclude that reactive agents can cope with perceptual ambiguity in the context of active categorical perception, and that they can organize their behavior according to stimuli that are no longer present, especially when they incorporate a nonlinear sensorimotor mapping. Moreover, we may conclude that sensory state-transition diagrams provide insight into the strategies employed by reactive agents to deal with perceptual ambiguity, and their use of the environment as an external memory.