Martha Farah published her influential volume Visual Agnosia in 1990. As she notes in the Preface to the second edition of this book, she undertook the project in the interest of “reviewing and systematizing the case literature and posing some basic questions that could, in principle, be answered by such cases.” The first edition of Visual Agnosia accomplished her objectives. From the extraordinarily rich but often confusing body of neuropsychological data, Dr. Farah developed a comprehensive account of visual processing disorders that was both true to the clinical phenomena and informed by then-current accounts of normal vision. Her short monograph quickly gained a wide audience and has become a standard reference. It has occupied a readily accessible spot on my bookshelf for years.
In the 15 years since the publication of Visual Agnosia, substantial progress has been made in the understanding of visual cognition, some of it attributable to the work of Dr. Farah and her collaborators. The second edition of Visual Agnosia incorporates these insights. For example, new sources of information have been incorporated. Functional imaging of vision was in its infancy at the time of the first edition; in the intervening years, functional magnetic resonance imaging in particular has made substantial contributions to the understanding of early visual processing, visual attention, motion perception, and several other topics. Although the second edition of Visual Agnosia remains true to its roots—the emphasis remains on disorders of visual processing in patients with brain lesions—the data from functional imaging studies inform and constrain the interpretation of the neuropsychological data. Additionally, while remaining approximately the same length, the accumulation of new information has led to changes in the emphasis accorded different topics. For example, reflecting the considerable investigations of normal and abnormal face processing, the discussion of prosopagnosia has been expanded to accommodate the wealth of new information. Additionally, a new chapter on the topic of semantic knowledge has been added. At the time of the first edition, this topic received relatively little attention. In the intervening years, however, there has been an explosion of interest in the topic. Reflecting this change, the second edition includes a concise and insightful chapter devoted to this controversial topic.
Finally, there has been a welcome change in the organizational structure of the volume. Whereas the first volume contained separate chapters on the phenomenology and interpretation of the “apperceptive” and “associative” agnosias, the second volume devotes chapters to specific subtypes of these disorders. For example, the second edition includes chapters on Visual Form Agnosia, Dorsal Simultanagnosia, Ventral Simultanagnosia and Pure Alexia, and Perceptual Categorization Deficit and Disorders of Orientation. The topic- or syndrome-based approach permits a more natural and seamless integration of the relevant clinical, neuropsychological, and theoretical issues.
Dr. Farah has once again performed a great service for those of us interested in the topic of disorders of visual processing and what their implications are for normal vision. By incorporating new data from investigations of patients with brain lesions as well as insights from functional imaging and connectionist modeling, she has generated a lucid and up-to-date monograph that, like its predecessor, is likely to be a classic for years to come.
