This book is really just a meditation on something that we can never know because "what we see when we read" is as individual as each human and each reading experience. Readers may think very little about the reading experience as it is an ethereal and ever-evolving notion. Mendelsund tries to recreate the experience in the format of his book that reads likes a philosophic treatise that has been smoking up in an alley.
He looks at concepts like character and setting and tends to focus a lot of his consideration on a few classic texts like Finnegan's Wake, Anna Karenina and Moby Dick. Readers who have read those texts would gain an additional layer of insight but is not 100% necessary. I followed his thoughts and assertions despite not having read Tolstoy. Considering Nancy Pearl's doorways, this book is firmly behind the language door as it reads lyrically and with profound humour and humanity. (Am I gushing?)
Ultimately, Mendelsund suggested that reduction is what we see and that reduction is the currency of human experience. We can never take in everything, so we take in what we can or want to see. Reading is a sum of our own experience, knowledge and education and no one reads a book in the same way. The book celebrates our own individuality and paints a cast landscape in the books we read which can never be fully known.
I suggest this book for every readers' advisor to understand the reading experience from a completely new perspective.