Susan Berry's Fixing My Gaze, is part autobiography, part pop-sci account of the development of binocular perception in humans, and part defense of the practices of vision therapy. Some might be familiar with her story from Olivar Sack's piece in the New Yorker a few back, "Stereo Sue" (Sacks 2006).

Susan Berry's eyes crossed when she was two months old. By the time she was nine, she had had three corrective surgeries which made her eyes look straight, but had failed to align them properly. Instead of using both eyes to see, her brain only processed information from one of her eyes. As a result, she became one of the 10% of people who cannot use their eyes in coordination to see in depth. Berry was stereoblind – her brain could not process the information from both eyes simultaneously, an important source of depth-information. She had difficulty perceiving the spaces between objects. When she watched a snowfall, for example, it looked just like on a TV screen: a single, flat plane of falling dots.

The first few chapters of the book go over the fundamentals of the human visual system and explain how our brain uses information from two eyes to help see in depth. The writing is not too technical and is perfect for the casual reader or someone who is not too familiar with vision science or the cognitive science of perception. However, the depth of explanation is not always consistent; there are some sections that are more technical than necessarily and others that are a little skimpy.

Only when she took a college course on perception did Berry learn that her perception of the world was not the same as everybody else's. She also learned, as is taught in most modern textbooks, that there is a critical period for perceptual development. If the brain does not receive binocular information early on, then cells that process that information do not develop. In her forties, Berry's vision worsened and her optometrist suggested that she see a vision therapist.

Through a series of exercises for her eyes that Berry did daily over the span of many months, she was able to learn how to turn her eyes inward and outward, something that most people do naturally. Eventually, she was able to perform the exercises perfectly, even the ones that required binocular vision. She writes that gradually objects in the world began to "pop out." A chandelier would appear to drop from the ceiling and suddenly take up space in the room. Her performance on the exercises and the reports of her experience suggest that she fully gained depth perception almost forty years past the supposed critical period. She brings forward many case-studies and personal communications with others who underwent visual therapy and regained their stereovision.

This is a great book for anyone who knows someone who lacks stereovision or for someone that lacks it themselves. It gives a very compelling account of what the world looks like to a person who sees it only through one eye. It gives a fairly good account of how stereovision works, why it might fail and what hope someone might have of regaining or attaining for the first time, binocular perception.

However, I have some reservations about the book for someone who is looking for more than a pop-sci take. Although there is a copious amount of anecdotal evidence of people who have regained their vision, vision therapy is highly contentious practice and some claims from vision therapists are greatly disputed. From a scientific standpoint, Berry's apparently unequivocal support of vision therapy seems unjustified. While many agree that vision therapy can be used to regain binocular vision, its use in treat dyslexia, for example, is under dispute. As with many pop-sci books, I find this to be misleading for the casual reader who might be unfamiliar with other research. Furthermore, this is not a book for anyone interested in the details of the processes of binocular perception. While there is some rudimentary detail in the earlier chapters, there is a lack of depth (no pun intended) in the intricacies of both the neuroscience and the optics of binocular vision. A final complaint: there are no footnote numbers even though there are many pages of notes. Sometimes these are just paper citations, but often times they are interesting elaborations on the text. It is a tremendous pain to have to flip back and forth to see if you have come upon a part of the text that is commented.

Overall, this is a compellingly written, pop-sci account of Berry's journey through vision therapy in gaining binocular vision. It is also an anecdotal defense of vision therapy. This is the book for anyone interested in learning some of the basics of how we see in depth in an easy-to-understand and interesting format. 

Sacks, Oliver, A Neurologist's Notebook, "Stereo Sue," The New Yorker, June 19, 2006, p. 64

© 2010 Gennady Erlikhman

Gennady Erlikhman is a graduate student in the psychology department at UCLA studying human perception. He received his BA from University of Pennsylvania in Cognitive Science and in Philosophy.