In Visual Agnosia (second edition), Martha
J. Farah provides an updated overview of the empirical evidence that has been
collected to describe a diverse array of neurological disorders involving
visual object recognition and the theoretical assumptions that have been
proposed to account for their existence. 
Each of the disorders is clearly described in reference to its
anatomical locus, and its unique cluster of disrupted and intact
perceptual/cognitive functions. The author heavily relies on empirical evidence
gathered from functional neuroimaging studies and in-depth analyses of subjects
whose neurological disorders involve disruptions of different aspects of visual
object recognition.  The evidence is
used to argue that the cluster of impaired and intact functions unique to each
disorder provides an insight into how visual information is processed by the
human brain at different levels of analysis.  

The
multitude of disorders that involve visual object recognition is neatly
organized in chapters.  In each chapter,
empirical evidence is carefully and methodically examined as if the author were
a forensic examiner who is dissecting an object from a criminal investigation
in an attempt to reconstruct a complex array of events leading to and
explaining the crime.  Unquestionably,
it is the author’s reliance on evidence that makes the narrative powerfully
grounded.  Indeed, at every turn, data
from in-depth analyses of subjects with disorders of visual object recognition
are coupled with functional neuroimaging data of unimpaired subjects to produce
a core set of "facts" about the disorders. Then, theoretical
accounts, which involve assumptions about brain functioning, are cautiously
submitted to the reader as the possible organizing principles for the facts that
the author has painstakingly collected. 

At
first glance, the second edition of Visual
Agnosia does not appear to introduce many new "facts" about
impairments of visual object recognition, nor does it constitute a great
departure in substance from the first edition. 
However, a more careful examination of its content confirms that the
second edition does indeed extend the range and depth of coverage of the
disorders previously discussed by the author. 
For instance, it includes a comprehensive description of impairments of
semantic memory and topographic recognition, which had been neglected in the
earlier edition.  It also reinforces the
notion that every bit of new evidence and theoretical reorganization of the
"facts" about these impairments can go a long way in enhancing our
understanding of not only such impairments but also intact functioning. For the
interested reader, the reference section is undoubtedly a great source of
additional information regarding both domains.

One of
the most interesting sections of the book is the last chapter in which the
author draws upon the up-to-date knowledge of impairments of visual object
recognition that she has espoused in the earlier chapters to make the case that
such knowledge can help researchers to understand intact visual object
recognition.  It is in this chapter that
the author’s narrative abilities could come to life to produce insightful
assumptions about normal visual object recognition. Unfortunately, the shortness
of the chapter immediately reveals a missed opportunity. The author claims that
she "would be disappointed if the book were read only as a review of
clinical syndromes", and that "the ultimate goal of this book is to
present the insights about normal visual object recognition that come to us
from the study of agnostic patients." However, the author devotes a total
of 7 pages to this goal of her work and, to make things even more puzzling, she
adopts a checklist format for the chapter. Both of these choices contradict her
claim.  If the main goal of the book is
indeed to describe how knowledge about unimpaired processing can come from the
examination of its disruptions, why would the author devote so little thought
to this issue and in such a schematic format? 
This chapter is likely not only to befuddle readers but also to leave
them grasping for more while feeling dissatisfied.  Fortunately, the shortcomings of the last chapter are not too
disturbing when readers reflect on what they have read on earlier pages.  Indeed, in these chapters, an abundance of
information is neatly packed and narrated with wit, and theoretical accounts
appear to be born naturally from the raw data. 
In each chapter, the author illustrates how a canonical adherence to
scientific principles of evidence collection and interpretation can enhance our
understanding of neurological disorders. At the same time, she also conveys the
cautionary message that such an understanding may shift as more evidence is
collected and new interpretations are forced to come into play.

Visual Agnosia is a book not only for
students of cognitive neuroscience but also for individuals who simply want to
know about impairments of visual object recognition. It is undeniable, however,
that, at times, the narrative may become a bit too technical for some
readers.  In these instances, readers
can choose to skip the sections that describe in fine details a subject’s
impaired and intact processing abilities (see pp. 10-11) and focus on the
summary that usually follows. 
Consequently, readers from all walks of life, even though they may lack
a solid background in cognitive neuroscience, can come to appreciate the story
that the author tells about impairments of visual object recognition.
Unquestionably, Visual Agnosia is a
great read for everybody with some curiosity about this heterogeneous category
of impairments.

© 2004 Maura Pilotti

Maura Pilotti,
Ph.D., Department of Psychology, Dowling College, New York.

Categories: Psychology