The central thesis of disjunctivism is that while a perceptual experience in a case of illusion or hallucination may perhaps involve an awareness of something like sense-data or adverbial contents, the only object of experience in a case of veridical perception is a mind-independent material object.
If the subject in a case of vision and the subject in a case of illusion are equally justified, that will be trouble for approaches that give justifying privilege to the states of seeing that \(a\) is \(F\) or seeing \(a\)'s \(F\ ness.
A further question to be asked in this context is whether the disjunctivist should treat all cases of illusion as equivalent to cases of partial hallucination.
Now, given the proposed account of the case of illusion, that case cannot be distinguished from the case of delusion by appeal to the fact that, in the former, an environmental feature is experienced while, in the latter, there is no suitable environmental feature to be experienced.
If the flash-beep illusion is indeed a case of a visual percept induced by an auditory stimulus, the question remains as to how in the brain this might occur, particularly in the timeframe available.
Extrapolating from the current results, we believe that the illusion would show resistance also in a case of false feedback training, when observers are incorrectly informed about 'correct' response in illusion trials.
In cases of perceptual error, we form a false belief on the basis of an experience, as when an uninformed subject concludes there is motion below (to get the effect, let your eyes drift over the image): Figure 3. "Rotating snakes"[3] This is a paradigm case of an illusion, where you do see a scene, but misperceive what the scene is like.
Williamson himself would opt for (i): 'If perceptual evidence in the case of illusions consists of true propositions, what are they?
First, he exploits the role of judgmental acumen in perceptual judgment in order to provide an alternative explanation of cases of illusion (or more generally of things looking ways that they are not).
(i) There are cases of illusion in which we have a sensory experience as of seeing something of some sort with specific features but in which nothing has those specific features.
The veil of ideas objection also has controversial ramifications for cases of illusion or hallucination.
