Perceptual symbol systems provide a welcome alternative to amodal encapsulated means of cognitive processing. However, the relations between perceived reality and internal mentation require a more differentiated approach, reflecting both developmental differences between infant and adult experience and qualitative differences between consciously perceived and mentally represented contents. Neurological evidence suggests a developmental trajectory from initial perceptual states in infancy to a more differentiated consciousness from two years of age on. Children's processing of and verbal expressions regarding motion events provides an example of the changing capacity for mental experience.