Synonyms for Perceivable (same or very similar meaning)
WordNet sense 1 (capable of being perceived by the mind or senses):
perceptibleWordNet sense 2 (capable of being apprehended or understood):
graspable, intelligible, understandable, apprehensibleWordNet sense 3 (capable of being comprehended or understood):
comprehensible, comprehendibleFrom the ODE community, based on WordNetadd/edit