The first two chapters of this well-received book is a well written, standard account of the most basic mechanism of vision, and includes a historical perspective. Here the text is sometimes very elementary, for example in its detailed explanation of the refraction of light and how a lens works.

The third chapter concerns our perception of bodily space. The author describes the stretch receptors in the muscle spindles and the Golgi tendon organs and explains their basic functioning. Then she goes on to a detailed account of neural signalling and the generation of the action potential. So far this chapter is also fairly standard, but the text is now much more difficult, and I wonder whether those who are able to follow the reasoning in the third chapter really had a need of the elementary stuff in the two first.

My first objection as to the content concerns the role of the stretch receptors. The basic message of the third chapter, as I interpret it (together with some passages in Chapter 7), is that our knowledge of the position and orientation of our body and its parts is mainly derived from current signals from these receptors, with some help from different kinds of touch receptors and sometimes from vision. However, this cannot be so since the information from the stretch receptors is much too incomplete and imprecise to serve this purpose. A more plausible (and fairly common) view is that the integration over time with information from corollary discharge (efference copies) supplies the needed precision. Surprisingly, the author does not seem to count with any important role for corollary discharge in shaping our knowledge about our body – except in the case of movement of the eyes. Here she fully acknowledges the existence and importance of corollary discharge, but argues that eye movements are an exception. Her argument (in Chapter 7) is that these movements are unique in that they are never hindered by external obstacles, which means that the efference copies are reliable estimates of next eye position. I find this argument for uniqueness wholly unconvincing. Surely, all that is needed for efference copies to be reliable is that it is improbable that the movement in question will be hindered, and this is very often the case for movements of the neck and the arms. And there surely is abundant information from physiological studies that corollary discharge is ubiquitous in the animal world.

Chapter four is about the processing of visual information from the retina to the visual cortex, and is on the whole well written and informative. The same holds for the first part of Chapter six, where the corresponding neural mechanisms are detailed. However, these sections are also conspicious by their lack of references to other traditions in visual perception theory than the mainstream one, i.e. the computational bottom-up approach. So, Gestalt psychology is not given any credit and J.J. Gibson’s name is not mentioned. More about this later.

Chapter five deals with auditory perception and is the best part of the book, together with its continuation in the second part of Chapter six. This is probably so because auditory mechanisms have been a main focus of the author’s own research.

Chapters seven and eight deal with navigation in space and how the brain integrates information from vision, hearing and balance to make this navigation possible. Again I sense the absence of J.J. Gibson. The author conveys a picture of the brain as tackling, at every moment, the task of integrating immense amounts of current information from different sensory sources. A main message of the Gibsonian school (although Gibson would never formulate it thus) is that we sometimes need very little current information in order to navigate properly. The “time-to-contact” mechanism is a beautiful case in point, that I think no account of perception should fail to mention. Another one is the fact that if you are going on a straight path, then you are going towards the unique unmoving point in the optic flow from which it flows. So you can disregard the rest of the flow, if all you want is to know where you are going (or where you will land). The comment (p. 185) that the optic flow “contributes to our sense of our own movements” is a glaring understatement!

Chapter nine is named Space and Memory. Among other things it contains a brief account of recent (and not-so-recent) discoveries about the role of hippocampus in spatial navigation. The chapter is well written and well worth reading.

Chapter ten, finally, is about thinking and emphasises the connections between sensory and cognitive processes. Arguing from familiar facts about co-localization and interference between sensation and cognition, the author goes one to speculate about further similarities between the domains. I found the chapter interesting but was startled by the author’s comment, “The theory that thought might involve simulating the activity patterns in our sensory and motor areas of the brain is called grounded or embodied cognition” (p. 205). OK, maybe some people have called the simulation theory of cognition “embodied cognition”, but then what has not been called by that heavily overused name?

My overall judgment is that this is an uneven book, especially when it comes to the very varying difficulty of reading its different parts, but to some extent with respect to the quality of its content. What also bothers me is that the light, not to say cheerful, style it is written in tends to convey an impression that everything that is said is uncontroversial – except, of course, in the cases when the author explicitly refers to a controversy. For the mentioned reasons I cannot wholeheartedly recommend the book.

© 2015 Helge Malmgren

Helge Malmgren, Dept. of Medicine, Sahlgrenska Academy, University of Gothenburg