Search

A new account of how we perceive the 3D shapes of objects and how to design machines that can see shapes the way we do.The uniqueness of shape as a perceptual property lies in the fact that it is both complex and structured. Shapes are perceived veridically—perceived as they really are in the physical world, regardless of the orientation from which they are viewed. The constancy of the shape percept is the sine qua non of shape perception; you are not actually studying shape if constancy cannot be achieved with the stimulus you are using. Shape is the only perceptual attribute of an object that allows unambiguous identification. In this first book devoted exclusively to the perception of shape by humans and machines, Zygmunt Pizlo describes how we perceive shapes and how to design machines that can see shapes as we do. He reviews the long history of the subject, allowing the reader to understand why it has taken so long to understand shape perception, and offers a new theory of shape. Until recently, shape was treated in combination with such other perceptual properties as depth, motion, speed, and color. This resulted in apparently contradictory findings, which made a coherent theoretical treatment of shape impossible. Pizlo argues that once shape is understood to be unique among visual attributes and the perceptual mechanisms underlying shape are seen to be different from other perceptual mechanisms, the research on shape becomes coherent and experimental findings no longer seem to contradict each other. A single theory of shape perception is thus possible, and Pizlo offers a theoretical treatment that explains how a three-dimensional shape percept is produced from a two-dimensional retinal image, assuming only that the image has been organized into two-dimensional shapes. Pizlo focuses on discussion of the main concepts, telling the story of shape without interruption. Appendixes provide the basic mathematical and computational information necessary for a technical understanding of the argument. References point the way to more in-depth reading in geometry and computational vision.

The world is divided into objects: things that are distinct from their backgrounds and that can move or be moved. Objects are food and prey and threats, as well as neutral items, and it is critical to be able to see them. How the form of an object is distinguished is one of the most basic, yet least understood, topics of research in vision perception. The object-defining system needs to operate in the real world, where objects and viewers move, and where the scene is cluttered, rarely offering a clear, unobscured view of any object. How are we able to see and define objects using the complex pattern of light falling on the retina? An object becomes visible if it differs sufficiently from its surroundings in its luminance, color, texture, motion, or depth. Although the processes that use these different cues are quite distinct, research has shown that they share some organizational principles. This book, Seeing Spatial Form, is dedicated to David Martin Regan who has made so many contributions to our understanding of how we see objects. Its chapters bring together ideas from some of the world's leading researchers in form vision to explain what we know about distinguishing form. The book includes a CD-ROM, which contains additional demonstrations and color images that considerably enhance the chapter contents. Seeing Spatial Form will be an invaluable resource for student and professional researchers in vision science, cognitive psychology, and neuroscience.

The best example of filling-in involves the blind spot, a region of the retina devoid of photoreceptors. Remarkably, the region of visual space corresponding to the blind spot is not perceived as a dark region in space, but instead as having the same color and texture as the surrounding background; hence the expression'filling in.'While this type of perceptual completion phenomenon is common in the visual domain, it is argued by the leading scientists who contribute to this book that forms of filling-in also take place in other sensory modalities, including the auditory, somatosensory, and motor systems. In a concluding chapter an integrative approach is taken, which attempts to provide a common framework for completion phenomena occurring on a fast time scale, and cortical reorganization in sensory and motor cortex induced by peripheral damage or skill learning taking place on a slower time scale. It is proposed that systematic changes in the interplay between inhibitory and excitatory inputs permit cortical neurons to become driven by new sources of input, which, in addition to initial perceptual consequences can lead to a long-term structural reorganization of cortex. This book represents a truly interdisciplinary approach to neuroscience, with chapters covering computational modeling, visual psychophysics, functional brain imaging, single-cell physiology, and clinical patient cases. It will be of interest to researchers and graduate students in systems neuroscience, cognitive neuroscience, vision science, neuroimaging, perceptual psychology, computational neuroscience, and philosophy of mind.

The visual system must extract from the light that falls on the retina meaningful information about what is where in our environment. At an early stage it analyzes the incoming sensory data along many dimensions of pattern vision, e.g. spatial frequency, orientation, velocity, eye-of-origin. Visual Pattern Analyzers provides a definitive account of current knowledge about this stage of visual processing. Nowhere else can such a comprehensive summarty of the lower level pattern analyzers be found. The book's emphasis is on psychophysical experiments measuring the detection and identification of near-threshold patterns -- and the mathematical models, such as multidimensional signal-detection theory, used to draw inferences from such experimental results -- but neurophysiological evidence is presented and compared critically to the psychophysical evidence. Introductory material on psychophysical methods, signal detection theory, and the mathematics of Fourier analysis is given in order to make the book more accessible to all who are interested in the lower or higher levels of visual perception. This volume will be of great value to researchers and graduate students in the fields of vision and perception. Within the scientific community there is wide interest in the visual system, and the book will be of use to investigators in many fields, including psychophysics, neuroscience, ophthalmology and optics, computer science, and cognitive and experimental psychology.