In 1988, when I was a first year graduate student, I heard Dr. Farah give a talk on the neuroscience of visual imagery. After listening to her scintillating discussion of the brain, imagery and visual agnosia, I was amazed at both the subtleties of the human brain and the skill of Dr. Farah to reveal these subtleties. Nearly twenty years later, Dr. Farah's second edition of Visual Agnosia is no different. One is left with a sense of how remarkable the human brain is, both with respect to its strange deficits when damaged and the power of scientists like Martha Farah to uncover these mysteries. Visual Agnosia is a fascinating book about a fascinating topic, the disorders of visual perception following brain damage.
Farah is fair and balanced when it comes to arguments and disputes within her field. With respect to debates, disagreements and unresolved issues, Farah is quick to point out both the weaknesses in her own conclusions and the strength of rival views. In several cases, she presents an initially bewildering array of alternative explanations for a finding, such as her discussion of optic aphasia. However, she then carefully untangles the issues, outlines each explanation, its strengths and weaknesses, and ultimately leads us to an understanding of the issues, its specifics and its generalities. In the end, one is left understanding both the phenomenon and its theoretical implications.
Visual Agnosia, 2nd edition, is an update of a book that Farah published in 1990. True to the original, Farah focuses on brain-based disorders of visual perception, commonly known as agnosias. The updated version of Visual Agnosia integrates the past 15 years of research on agnosia and visual perception into a new classification system and some new theories of visual agnosia. Classic neuropsychology is a field that proceeds slowly, completely dependent on the whimsy and fury of nature to deliver appropriate patients. However, the last 15 years has seen an increase in the careful cognitive experimentation on neuropsychological patients, allowing for hypothesis testing not seen in an earlier era. Farah seamlessly integrates the old and new research on agnosia.
Agnosias range from the 'apperceptive agnosias,' which involve distorted perception, to the 'associative agnosias', which involve impaired connections between perceptual representations and semantic representations. Farah frequently reminds us, however, that the reality of the brain and damage to the brain is a more complicated equation. These labels, for Farah, do not describe the entire patient. As anyone who has ever examined a neuropsychological patient knows, the neat classifications that we learn about in textbooks have little bearing on individuals and their examination. However, Farah argues that they do correspond to psychological reality, and that the dissociations seen between visual functions tell us something about how visual cognition occurs.
Despite the obvious strengths of Visual Agnosia, I found one aspect of it disappointing. Early on, Farah promises to relate the neuropsychology of visual agnosia to the burgeoning field of functional neuroimaging. Indeed, Farah writes 'It has recently become possible to combine imaging and patient-based research in a powerful new way, by imaging patients while they engage in the process of interest' (p. 10). I found this prospect to be intriguing and important; however, on this one, Farah did not deliver the goods. Whereas there was ample discussion of behavioural data on patients, there was precious little concerning neuroimaging of either patients or intact participants. Given the obvious importance, relevance and current popularity of neuroimaging, I found this lack disappointing.
Each chapter contains one or more sections entitled the 'Neuropathology of . . . ' These sections briefly summarize the literature concerning the locus of brain damage for a given syndrome. Unfortunately, these neuroanatomy sections are not integrated with the functional issues discussed