Introduction to the Senses

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1 Introduction to the Senses From Biology to Computer Science An understanding of the senses vision, hearing, touch, chemical and other non-human senses is important not only for many fields of biology but also in applied areas such as human computer interaction, robotics and computer games. Using information theory as a unifying framework, this is a wide-ranging survey of sensory systems, covering all known senses. The book draws on three unifying principles to examine senses: the Nyquist sampling theorem; Shannon s information theory; and the creation of different streams of information to subserve different tasks. This framework is used to discuss the fascinating role of sensory adaptation in the context of environment and lifestyle. Providing a fundamental grounding in sensory perception, the book then demonstrates how this knowledge can be applied to the design of human computer interfaces and virtual environments. It is an ideal resource for both graduate and undergraduate students of biology, engineering (robotics) and computer science. is Professor in Computer Systems and Director of the Centre for Research in Complex Systems (CRiCS) at Charles Sturt University, Bathurst, Australia. He is particularly interested in sensory information in the context of vision and hearing, and was involved in the creation of the first degree course in computer games in Australia in 2000.

3 Introduction to the Senses From Biology to Computer Science TERRY R.J. BOSSOMAIER Charles Sturt University, Bathurst, Australia

4 CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Mexico City Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York Information on this title: / C T.R.J. Bossomaier 2012 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2012 Printed in the United Kingdom at the University Press, Cambridge A catalogue record for this publication is available from the British Library Library of Congress Cataloguing in Publication data Bossomaier, Terry R. J. (Terry Richard John) Introduction to the senses : from biology to computer science / Terry Bossomaier. p. cm. ISBN (hardback) 1. Senses and sensation. 2. Human-machine systems. 3. Perception. I. Title. QP431.B dc ISBN Hardback Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

5 Contents Foreword by Professor Allan Snyder Acknowledgements page ix xi 1 Introduction and overview Structure of the book 5 2 Understanding sensory systems Introduction Sensory diversity Sensory information processing Pattern recognition and computation by neurons A tour of the brain Investigative methods of brain science Senses in computer games and virtual worlds 32 3 Introduction to Fourier theory Overview Linear systems and operators Important functions Convolution Fourier Analysis and the Fourier Transform The sampling theorem The discrete Fourier Transform Other frequency related representations Statistical methods for finding representations 61 4 Introduction to information theory Overview Entropy and information Algorithmic information Noise Transmission along channels 85

6 vi Contents 4.6 Neural coding Envoi 91 5 Hearing Physics of sound Anatomy and physiology The range and sensitivity of hearing Specialised hearing adaptations Audio encoding Basic strategies of vision Overview The physical limits Overview of the architecture of the visual systems The optics Transduction: photoreceptors and sampling Transmission to the brain Psychophysical limits Evolution and diversity of eyes Non-visual radiance detection Man-made visual devices Controversies over image recognition The correspondence problem: stereoscopic vision, binaural hearing and movement Introduction and overview Stereopsis Binaural hearing Artificial systems Movement Compression Envoi The properties of surfaces: colour and texture Overview Colour physics Anatomy and physiology Colour pathways Colour psychophysics and behaviour Evolutionary forces in colour Artificial colour Texture 215

7 Contents vii 9 The chemical senses Introduction Physics of olfaction and taste Olfactory anatomy and physiology Psychophysics of olfaction Taste Artificial systems Envoi The somatosensory system Introduction The physical limits to touch Primary somatic detectors Pathways Psychophysics of the somatosensory system Special tactile adaptations Vestibular system Artificial tactile systems Envoi Non-human sensory systems Electrical sense Heat sensors Magnetic sense and navigation Sonar Enhancing the senses with implants Sensing animats Sensory integration Eye movements Cross-calibration Conflict and priority Sensory integration Consciousness 307 References 309 Index 338 Colour plates are to be found between pp. 268 and 269.

9 Foreword What are the commonalities of information gathering and processing in all living creatures? This is the implicit question that underpins Terry Bossomaier s ambitious book The Senses. His is a Herculean task and one to be greatly applauded. Bossomaier addresses the senses using the tools of contemporary information science, in an attempt to provide a unifying perspective, one that allows for quantitative comparison of senses between the species. This fascinates me. It is now nearly 35 years since Simon Laughlin, Doekele Stavenga and I introduced information theory to understand the design of eyes, both compound eyes of insects as well as the simple eyes of humans. We recognised that the fundamental limitations to resolving the power of eyes are the wave (diffraction) and particle (photon noise) nature of light. By appreciating their interrelation we derived insight into the design and limitations of eyes, especially between the optical image quality and the visual photoreceptor mosaic. The capacity of the eye to perceive its spatial environment was quantified by determining the number of different pictures that can be reconstructed by its array of visual cells. We were then able to decide on the best compromise between an animal s capacity for fine detail and contrast sensitivity. In a series of papers, including those with Bossomaier and A. Hughes, we went on to use the tools of information theory to study various aspects of eye design. It was a rewarding and rich endeavour, but one at that time limited to vision. Now, in this book you will read how Bossomaier significantly generalises these early applications of information theory and applies them to all the senses, not just to vision. But, Bossomaier not only stresses the importance of information theory in sensory processing, he also stresses the importance of contextualising it to the animal s lifestyle. Indeed, as I have often emphasised, there is no single optimum design of any particular sense as physicists might like, but rather a variety of different solutions, each dictated by the animal s lifestyle within its environment. Two animals can share the same habitat, yet they can have radically different eyes. This realisation is made all the more transparent by comparative studies of many species besides humans. It is fascinating to learn how diverse animals adapt and make use of the physical properties of the environment, from the earth s magnetic field to the sky s polarisation, from heat, electricity and sound to the odours associated with chemicals and how these continue to inspire the implementation of sensory apparatus in man-made devices such as robots. Interestingly in this regard, it was the birefringent nature of the fly s visual photoreceptors that provided an early

10 x Foreword inspiration for single mode, single polarisation optical fibres for telecommunication and sensor applications. Most importantly Bossomaier stresses that information is not passively collected by the senses, but instead is profoundly influenced by what the animal already knows and anticipates. So, animals perceive not only what they sense. Sensory detail can be modulated and even suppressed by higher level concepts. This remains a crucially important area of research and one which consumes my attention. Indeed, over the last decade or so our thinking about the general strategy of sensory processing and the crucial role of top-down processing has been undergoing a paradigm shift. As Bossomaier says, Across many thousands of studies lies the assumption that information is processed sequentially, from sensors through to high level perception deep within the brain. Yet sensory systems abound in recurrent connections, which strongly suggest that the situation is far more complex. One of the most enjoyable aspects of the book is its comprehensive survey of the senses and the alluring accounts of the way they are adapted to remarkable advantage by animals. This no doubt is contributed to by the fact that Bossomaier approaches the subject from the left field, with both enthusiasm and receptivity to new ideas but admirably armed with the necessary scientific tools and panoramic knowledge of the senses to impart deep insight. Professor Allan Snyder FRS Director of the Centre for the Mind and 150th Anniversary Chair at the University of Sydney

11 Acknowledgements The ideas for this book go back a long way. An interest in photography, images and the sounds of musical instruments goes right back to my father. My friends and colleagues at Ilford Limited put my understanding of image physics and perception on a firm footing, but John Lewis and Alan Kragh were especially motivating and influential. The vision community at the Australian National University was a uniquely stimulating environment, with exciting discussions with many people, too numerous to list, but my grasp of sensory processing would not have been possible without Peter Bishop, Geof Henry, Abbie Hughes, Bill Levick, Ted Maddess, Daniel Osorio, Srini Srinivasan and Allan Snyder. Thanks also to the many computer science games students who read the drafts of this book. Finally, as someone passionate about imagery but with no obvious drawing skills, some help with diagram production proved essential. Rebecca Wotzko fulfilled the role admirably with remarkable patience.

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