What Do We Perceive?

"What do we perceive?" is a question which comes from the thinking about illusions. If material things are the objects of our perception, why we do perceive some qualities that are not belong to the associated material things? In illusions, what on earth do we perceive?Ayer insists: 'What we directly perceive are sense-data', and furthermore, he produces the incorrigible foundations for the empirical knowledge. Austin analyses Ayer's sense-data theory and his principles of Empirical Foundationalism deeply.Austin argue: To explain the illusion cases need not suppose a kind of immaterial objects of perception as the intermediaries. In fact, our perceptions involve recognition and understanding, what is wrong in illusions is our understanding and recognition.When we answer the question 'what do you perceive?' , we are giving the knowledge of perceptions rather than only objects of perceptions. We could perceive or describe the objects as different things. Ayer takes material things and sense-data as the only two choices, which is to take "what do you perceive" as strictly asking for the objects of perceptions.