Book Review: Blind Vision: The Neuroscience of Visual Impairment

Blind Vision: The Neuroscience of Visual Impairment. Zaira Cattaneo and Tomaso Vecchi. Cambridge, MA: MIT Press, 2011, 269 pp., illustrated, $36. This book's title phrase, Blind Vision, is a concise summary of the book's contents, which comprise arguments and evidence that people who cannot see have the same kinds of perceptions, mental imagery, and knowledge as people who can see. Blindness is a big nuisance, but in most areas of everyday life it doesn't much change what people can notice, what people can remember, or what people can do. Authors Cattaneo and Vecchi take on the enormous task of synthesizing 50 years of cognitive psychology and cognitive neuroscience research conducted with people who are blind. Like the best cognitive psychology, the work examines the cognitive processes and memory representations that underlie the skilled performance of functionally important tasks in everyday life. Like the best neuroscience, the work synthesizes evidence-based findings on the major brain imaging (fMRI and EEG, for example) and brain assessment (TMS, for example) methods that are used to localize brain regions that mediate perception and cognition, and it summarizes what happens to those brain regions when vision is absent or impaired. Cattaneo and Vecchi provide a comprehensive and balanced view of the cognitive neuroscience of blindness, acknowledging its current limitations and highlighting its potential applications. In doing so, they set the stage for others to apply the lessons gained to help learners learn and teachers teach. In terms of topical content, Blind Vision is about how perception, imagery, knowledge, working memory, and spatial cognition are used to accomplish the tasks of daily life that involve locomotion, wayfinding, and object identification and manipulation; as well as academic tasks including those involved in reading, science, and math. Wherever possible, the authors compare total blindness, low vision, and typical vision, and they identify perceptual and cognitive skills (tactile picture identification, for example) that appear to vary based on the age at onset of blindness and those (tactile discrimination, for example) that do not. And although it is not a major part of the book, the authors make an important contribution to the literature by synthesizing what is known about monocular vision-which, in our view, is an important category of low vision that is often overlooked by researchers and teachers alike. ORGANIZED BY THEME Cattaneo and Vecchi organize their topics around four major themes: Amodal information, sensory compensation and substitution, spatial imagery (not visual imagery), and brain plasticity. These themes form the core of the book and are mentioned in most of the chapters. We elaborate on each below. Amodal information Amodal information (meaning "without modality") specifies properties of objects and events that are common in multiple senses. Temporal properties of events like rhythm, tempo, duration, and synchrony can be perceived by listening, looking, and touching. Consider, for example, that the cadence of a person's gait can be heard as well as seen by others; the viscosity of a liquid can be heard when it is poured and felt when it is stirred; and whether a smooth plate is metal or wood can be felt when it is touched and heard when it is struck with a mallet. Different modalities of information specify the same properties, but they are not completely redundant and vary in their precision, breadth of field, and speed. Cattaneo and Vecchi point to the evidence that when amodal information is available, people pragmatically select the mode that is "easy," in the sense that it is best matched to a given task. For example, pedestrians tend to rely on vision for guidance in street crossings, because "with a single gaze we can simultaneously embrace an enormous amount of information, and our foveal acuity allows us to focus on very detailed characteristics of what we are perceiving" (p. …