Perceptual Learning; Manfred Fahle and Tomaso Poggio, Editors. The MIT Press, Cambridge, MA, 2003. ISBN: 0-262-06221-6. $68.00 Scope: This is a multi-authored book consisting of chapters written by scientists in perceptual learning. It intends to be a comprehensive presentation of advances made in the past decade in the understanding of perceptual learning. The editors define perceptual learning as "any relatively permanent and consistent change in the perception of a stimulus array following practice or experience...[that is] relatively independent from conscious experience...[and that] seems to directly modify the neuronal pathways active during processing of the task..." Thus, a purely sensory experience that modifies neuronal pathways and leads to an alteration in perception and implicit memory. The information presented deals with changes in primary sensory cortices as a result of perceptual learning in the adult. Modern studies of perceptual learning have expanded the concept of cortical plasticity from what was thought to be an early-in-life phenomenon to a process that continues after birth. The "classical view" dictates that such change should not be found past the early postnatal period. However, the crucial finding represented by this collection of articles is that synaptic plasticity continues to be a factor that subtly reshapes even primary sensory cortices throughout adulthood. The book is divided into four sections. The first section (seven chapters), "Anatomy and Physiology," deals with changes at the neuronal and synaptic level with emphasis on interneuronal connections. The second section (five chapters), "Low-Level Psychophysics," reviews learning on a systems level mainly investigated by psychophysical techniques. The third section (five chapters), "Higher-Level Psychophysics," covers topics such as cognition and learning of visual objects and tasks. The fourth section (three chapters), "Modeling," presents models that attempt to tie all of this material together. One chapter is particularly interesting because it reviews experimental data regarding the changes found in the receptive fields of cells in the primary visual cortex after retinal lesions, cortical lesions, or artificially induced scotomas. Strengths: The chapters are a balanced mix of relatively broad reviews and are clearly written, detailed presentations of specific experiments and topics. Especially informative are broadly oriented chapters by Manfred Fahle, "Introduction"; Siegrid Löwel and Wolf Singer, "Experience-Dependent Plasticity of Intracortical Connections"; Hubert Dinse and Michael Merzenich, "Adaptation of Inputs in the Somatosensory System"; Annette Sterr, Thomas Elbert, and Brigitte Rockstroh, "Functional Reorganization of Human Cerebral Cortex and Its Perceptual Concomitants"; and Pawan Sinha and Tomaso Poggio, "High-Level Learning of Early Visual Tasks." The chapters are profusely referenced, which allows this to be a good, solitary, up-to-date source for further study. Weaknesses: This is not a textbook and thus is not a start-to-finish development of the topic. It is a specialized collection that assumes a good knowledge of cortical organization and functioning. Some of the more experiment-oriented chapters will be of interest to only a narrow spectrum of readers. Fahle suggests in the Introduction that perceptual learning offers hope for disorders such as amblyopia, prosopagnosia, visual field defects, and Alzheimer disease, but he does not present any supportive evidence for this claim. Throughout the text there are also occasional references to visual training techniques that might reduce visual deficits on the basis of perceptual learning without a critical review of the subject or other plausible explanations for recovery. Recommended audience: Because of the extensive review of experimental data, the text is directed toward scientists in the field of brain physiology and plasticity. However, clinicians in specialties associated with neuroscience may find this book interesting. Critical appraisal: The selection of topics and authors demonstrates that this collection was well thought out as a vehicle to introduce current thinking on the topic. The presentations are readable and attention was clearly paid to reducing jargon. Evidence is given in enough detail to allow the reader to understand the basis of the conclusions and speculations. Mark W. Dubin, PhD Department of Molecular, Cellular, and Developmental Biology; University of Colorado; Boulder, Colorado Victoria S. Pelak, MD Departments of Neurology and Ophthalmology; University of Colorado School of Medicine; Denver, Colorado