Tim Crane has a number of his essays available online, and I read through ‘Is Perception a Propositional Attitude?’ Here’s my rough gloss on it:
To show that perception is a propositional attitude, the perceptual experience would need to have propositional content and would thus need to have truth-conditions. This seems obvious, since, for example, my experience of ‘the cat on the mat’ has as its content the proposition that ‘the cat is on the mat’, which has a truth-condition – it is either true or false. Thus, the content of experience would be roughly the same as the content of belief.
However, granting that experience can be accurate or inaccurate, it doesn’t follow that the contents of experience have truth conditions. What follows, given that accuracy is a matter of degree, is that experiences can have greater or lesser degrees of accuracy – not that they are true or false.
Thus, experiences are either accurate or inaccurate, not true or false, and therefore don’t have truth conditions, and therefore don’t have propositional content, and therefore are not propositional attitudes.