I 've read a few books of R. Gregory, with pleasure and learning much in the meantime. This book however is not what it promisses: a clear classification of illusions. Alas, the ideas in the book jump from subject to subject, it seems to me a haphazard collection of what is already present in his other books. It looks to me as a hasty try to deliver yet another book. Essentialy, the book is about his classification of illusions (blindness, ambiguity, paradox, etc.) But this classification is not at all worked out. In each category, the writer presents a few or a lot of observations with generally too little detailing, with sometimes a minimum of explanations and an unequilibrated discussion. Do not expect any new illustration; in fact there are not so many and not so originally (easily found in other books). I was disappointed - after the reading you cannot use this classification because of its being unclear. The writer pretends to present us 'The Periodic Table' of illusions, but this is a vast overstatement.
I know all this is not said in the title of the book, but then the title is not accurate (although not lying: it really is about the cognitive brain making sense out of the sensations.)
Many topics in the book are interesting, but the systematic treat is lacking. So, if this is the first book you read on illusions, it will give you the appetite for more. You will also be confused. If this would be your 5th book on illusions... skip it!