How might we evaluate the sensory abilities of animals, given that they cannot tell us whether they can or cannot make a particular perceptual distinction?

Aristotle discusses the faculties supposedly possessed by the souls/minds of various types of animal. In particular, he posits that all animals possess sensory abilities, though not all possess every possible sense. In addition, he suggests that some “higher” animals possess imagination. Aristotle, of course, comes at the very beginning of the scientific study of the world, and today’s evidentiary standards are much higher. How might we evaluate the sensory abilities of animals, given that they cannot tell us whether they can or cannot make a particular perceptual distinction? And how might we try to evaluate whether an animal possesses the ability to imagine that which is not present?