As shown in his first book, The Structure of Behavior, and this extension of that piece, Merleau-Ponty was a philosopher who was way ahead of his time.
While Husserl was off sputtering abstractly about phenomenology and 'essences', Merleau-Ponty planted himself squarely into the concrete, thick, world of lived experience: this book is a detailed phenomenological description of of attention, memory, space-perception, free will, and other psychological/phenomenological categories. M-P claims that simply by paying attention to this lifeworld, we see that previous philosophical systems have overlooked ineliminable dimensions of what it is like to be a person, and that this oversight has led to radically incomplete philosophical accounts of things like memory, perception, etc..
The book is so rich, original, and nuanced that it is hard to do it justice in a short review here. Not saddling himself with narrow academic techniques or fields, he draws on any resources he can to come to make sense of human experience. He cites not only philosophers such as Heidegger and Sarte, but draws equally heavily upon the Gestalt psychologists and neuroscientists of his day. He discusses phantom limbs, experiments on spatial perception, and psychophysical results from the Gestalt psychologists.
Many ideas that are popular in modern analytic philosophy and psychology can be found in this book: the view that 'sense data' are simply theoretical constructs, the view that attention focuses on objects not abstract spatial locations, and the claim that our original concepts cannot be understood independently of the embodied interactions with the world where we first come to use them.
I fear that Merleau-Ponty's nuanced philosophical psychology will fall through the cracks, being ignored by continental philosophers who focus on other things nowadays, and also by English speaking philosophers who dismiss Merleau-Ponty because he is a continental philosopher.
If you consider yourself a philosopher of mind, epistemologist, or a continental philosopher, please read this book. Twice.