Download or read book Models of Horizontal Eye Movements Part II written by John Enderle and published by Springer Nature. This book was released on 2022-06-01 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In this book, a 2009 version of a state-of-the-art model is presented for horizontal saccades that is 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The control of saccades is initiated by the superior colliculus and terminated by the cerebellar fastigial nucleus, and involves a complex neural circuit in the mid brain. This book is the second part of a book series on models of horizontal eye movements. Table of Contents: 2009 Linear Homeomorphic Saccadic Eye Movement Model and Post-Saccade Behavior: Dynamic and Glissadic Overshoot / Neural Network for the Saccade Controller

Download or read book Models of Horizontal Eye Movements Part I written by John Enderle and published by Springer Nature. This book was released on 2022-06-01 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In this book, early models of saccades and smooth pursuit are presented. The smooth pursuit system allows tracking of a slow moving target to maintain its position on the fovea. Models of the smooth pursuit have been developed using systems control theory, all involving a negative feedback control system that includes a time delay, controller and plant in the forward loop, with unity feedback. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The oculomotor plant consists of three muscle pairs and the eyeball. A number of oculomotor plant models are described here beginning with the Westheimer model published in 1954, and up through our 1995 model involving a 4$^{th}$ order oculomotor plant model. The work presented here is not an exhaustive coverage of the field, but focused on the interests of the author. In Part II, a state-of-art model of the saccade system is presented, including a neural network that controls the system. Table of Contents: Introduction / Smooth Pursuit Models / Early Models of the Horizontal Saccadic Eye Movement System / Velocity and Acceleration Estimation / 1995 Linear Homeomorphic Saccadic Eye Movement Model

Download or read book Models of Horizontal Eye Movements Part II written by John Enderle and published by Springer. This book was released on 2010-03-25 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In this book, a 2009 version of a state-of-the-art model is presented for horizontal saccades that is 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The control of saccades is initiated by the superior colliculus and terminated by the cerebellar fastigial nucleus, and involves a complex neural circuit in the mid brain. This book is the second part of a book series on models of horizontal eye movements. Table of Contents: 2009 Linear Homeomorphic Saccadic Eye Movement Model and Post-Saccade Behavior: Dynamic and Glissadic Overshoot / Neural Network for the Saccade Controller

Download or read book Models of Horizontal Eye Movements written by John D. Enderle and published by Morgan & Claypool Publishers. This book was released on 2010 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In this book, early models of saccades and smooth pursuit are presented. The smooth pursuit system allows tracking of a slow moving target to maintain its position on the fovea. Models of the smooth pursuit have been developed using systems control theory, all involving a negative feedback control system that includes a time delay, controller and plant in the forward loop, with unity feedback. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The oculomotor plant consists of three muscle pairs and the eyeball. A number of oculomotor plant models are described here beginning with the Westheimer model published in 1954, and up through our 1995 model involving a 4th order oculomotor plant model. The work presented here is not an exhaustive coverage of the field, but focused on the interests of the author. In Part II, a state-of-art model of the saccade system is presented, including a neural network that controls the system. Table of Contents: Introduction / Smooth Pursuit Models / Early Models of the Horizontal Saccadic Eye Movement System / Velocity and Acceleration Estimation / 1995 Linear Homeomorphic Saccadic Eye Movement Model

Download or read book Models of Horizontal Eye Movements written by Alireza Ghahari and published by Springer Nature. This book was released on 2022-06-01 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book series is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In Part 1, early models of saccades and smooth pursuit are presented. A number of oculomotor plant models are described therein beginning with the Westheimer model published in 1954, and up through our 1995 model involving a 4th-order oculomotor plant model. In Part 2, a 2009 version of a state-of-the-art model is presented for horizontal saccades that is 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. In this book, a multiscale model of the saccade system is presented, focusing on the neural network. Chapter 1 summarizes a whole muscle model of the oculomotor plant based on the 2009 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. Chapter 2 presents a neural network model of biophysical neurons in the midbrain for controlling oculomotor muscles during horizontal human saccades. To investigate horizontal saccade dynamics, a neural circuitry, including omnipause neuron, premotor excitatory and inhibitory burst neurons, long lead burst neuron, tonic neuron, interneuron, abducens nucleus, and oculomotor nucleus, is developed. A generic neuron model serves as the basis to match the characteristics of each type of neuron in the neural network. We wish to express our thanks to William Pruehsner for drawing many of the illustrations in this book. Table of Contents: Acknowledgments / 2009 Linear Homeomorphic Saccadic Eye Movement Model / A Neuron-Based Time-Optimal Controller of Horizontal Saccadic Eye Movements and Glissades / References / Authors' Biographies

Download or read book Eye Movement Disorders written by E.A.C.M. Sanders and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is perhaps no area of neuro-ophthalmology that is advancing more rapidly with respect to an understanding of its anatomy and physiology than the ocular motor system. For this reason, it is difficult not only to keep up with the latest information concerning the basic mechanisms involved in the control of eye movements but also to remain up to date regarding the pathophysiology of specific disorders of eye movement. The material in this book is derived from a two-day course on eye movements held in The Netherlands in 1986. The course was designed as an introduction to the normal ocular motor system and to disorders of eye movements and was aimed toward orthoptists, ophthalmolo gists, optometrists, neurologists, and neurosurgeons. The chapters in this book were compiled by a trio of experts in the field of eye movements and contain discussions of anatomy and physiology of the ocular motor system, techniques of examination of patients with diplopia, and pathophysiology of specific disorders of ocular motility. Many of the authors of these chapters are among the most active investigators of eye movements in the world today, and their comments thus reflect the latest information in the field. This text is both basic and com prehensive and thus has something for everyone, from the student just beginning a study of the ocular motor system to the seasoned 'veteran' who wishes to know the latest information regarding central ocular motor control mechanisms. Neil R.

Download or read book Eye Movements and Vision written by A. L. Yarbus and published by Springer. This book was released on 2013-11-11 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Neurology of Eye Movements Text and CD ROM written by Departments of Neurology R. John Leigh Professor, Neuroscience Otolaryngology and Biomedical Engineering Case Western Reserve University University Hospitals and Veterans Affairs Medical Center Cleveland Ohio and published by Oxford University Press, USA. This book was released on 1999-08-26 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Neurology of Eye Movements provides clinicians with a synthesis of current scientific information that can be applied to the diagnosis and treatment of disorders of ocular motility. Basic scientists will also benefit from descriptions of how data from anatomical, electrophysiological, pharmacological, and imaging studies can be directly applied to the study of disease. By critically reviewing such basic studies, the authors build a conceptual framework that can be applied to the interpretation of abnormal ocular motor behavior at the bedside. These syntheses are summarized in displays, new figures, schematics and tables. Early chapters discuss the visual need and neural basis for each functional class of eye movements. Two large chapters deal with the evaluation of double vision and systematically evaluate how many disorders of the central nervous system affect eye movements. This edition has been extensively rewritten, and contains many new figures and an up-to-date section on the treatment of abnormal eye movements such as nystagmus. A major innovation has been the development of an option to read the book from a compact disc, make use of hypertext links (which bridge basic science to clinical issues), and view the major disorders of eye movements in over 60 video clips. This volume will provide pertinent, up-to-date information to neurologists, neuroscientists, ophthalmologists, visual scientists, otalaryngologists, optometrists, biomedical engineers, and psychologists.

Download or read book Models of Horizontal Eye Movements Part I written by John Enderle and published by Springer. This book was released on 2010-03-25 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In this book, early models of saccades and smooth pursuit are presented. The smooth pursuit system allows tracking of a slow moving target to maintain its position on the fovea. Models of the smooth pursuit have been developed using systems control theory, all involving a negative feedback control system that includes a time delay, controller and plant in the forward loop, with unity feedback. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The oculomotor plant consists of three muscle pairs and the eyeball. A number of oculomotor plant models are described here beginning with the Westheimer model published in 1954, and up through our 1995 model involving a 4$^{th}$ order oculomotor plant model. The work presented here is not an exhaustive coverage of the field, but focused on the interests of the author. In Part II, a state-of-art model of the saccade system is presented, including a neural network that controls the system. Table of Contents: Introduction / Smooth Pursuit Models / Early Models of the Horizontal Saccadic Eye Movement System / Velocity and Acceleration Estimation / 1995 Linear Homeomorphic Saccadic Eye Movement Model

Download or read book Models of Horizontal Eye Movements Part II written by John Enderle and published by Morgan & Claypool Publishers. This book was released on 2010-03-03 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In this book, a 2009 version of a state-of-the-art model is presented for horizontal saccades that is 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. The oculomotor plant and saccade generator are the basic elements of the saccadic system. The control of saccades is initiated by the superior colliculus and terminated by the cerebellar fastigial nucleus, and involves a complex neural circuit in the mid brain. This book is the second part of a book series on models of horizontal eye movements. Table of Contents: 2009 Linear Homeomorphic Saccadic Eye Movement Model and Post-Saccade Behavior: Dynamic and Glissadic Overshoot / Neural Network for the Saccade Controller

Download or read book The Control of Eye Movements written by Paul Bach-y-Rita and published by Elsevier. This book was released on 2012-12-02 with total page 571 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Control of Eye Movements presents the proceedings of the Symposium on the Control of Eye Movements organized by the Smith-Kettlewell Institute of Visual Sciences of the Pacific Medical Center and the Department of Visual Sciences of the University of the Pacific Graduate School of Medical Sciences, San Francisco, California, November 10-11, 1969. The book is organized into two parts. Part I is devoted to presentations of anatomical, physiological, pharmacological, psychological, and clinical aspects of eye movements. The material presented should provide a valuable reference source as well as increase awareness of the need for further investigation of many aspects of the basic physiology of eye movements. Part II presents a series of papers dealing with models of various parts of the oculomotor system. The modeling approach to control of eye movements is still in its infancy and the present work presents the first comprehensive survey of biophysical, mathematical, and engineering aspects of eye movement control.

Download or read book Visual Psychophysics written by Dorothea Jameson and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 822 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume on Visual Psychophysics documents the current status of research aimed toward understanding the intricacies of the visual mechanism and its laws of operation in intact human perceivers. As can be seen from the list of contributors, the problems of vision engage the interest and experimental ingenuity of investi gators from a variety of disciplines. Thus we find authors affiliated with depart ments of biology, medical and physiological physics, ophthalmology, physics, physiology and anatomy, psychology, laboratories of neurophysiology, medical clinics, schools of optometry, visual and othcr types of research institutes. A continuing interplay between psychophysical studies and physiological work is everywhere evident. As more information about the physiological basis of vision accumulates, and new studies and analyses of receptor photochemistry and the neurophysiology of retina and brain appear, psychophysical studies of the intact organism become more sharply focused, sometimes more complex, and often more specialized. Technological advances have increased the variety and precision of the stimulus controls, and advances in measurement techniques have reopened old problems and stimulated the investigation of new ones. In some cases, new concepts are being drawn in to help further our under standing of the laws by which the visual mechanism operates; in other cases, ideas enunciated long ago have been reevaluated, developed more fully, and reified in terms of converging evidence from both psychophysical experiments and unit recordings from visual cells.

Download or read book Eye Tracking written by Kenneth Holmqvist and published by OUP Oxford. This book was released on 2011-09-22 with total page 793 pages. Available in PDF, EPUB and Kindle. Book excerpt: We make 3-5 eye movements per second, and these movements are crucial in helping us deal with the vast amounts of information we encounter in our everyday lives. In recent years, thanks to the development of eye tracking technology, there has been a growing interest in monitoring and measuring these movements, with a view to understanding how we attend to and process the visual information we encounter Eye tracking as a research tool is now more accessible than ever, and is growing in popularity amongst researchers from a whole host of different disciplines. Usability analysts, sports scientists, cognitive psychologists, reading researchers, psycholinguists, neurophysiologists, electrical engineers, and others, all have a vested interest in eye tracking for different reasons. The ability to record eye-movements has helped advance our science and led to technological innovations. However, the growth of eye tracking in recent years has also presented a variety of challenges - in particular the issue of how to design an eye-tracking experiment, and how to analyse the data. This book is a much needed comprehensive handbook of eye tracking methodology. It describes how to evaluate and acquire an eye-tracker, how to plan and design an eye tracking study, and how to record and analyse eye-movement data. Besides technical details and theory, the heart of this book revolves around practicality - how raw data samples are converted into fixations and saccades using event detection algorithms, how the different representations of eye movement data are calculated using AOIs, heat maps and scanpaths, and how all the measures of eye movements relate to these processes. Part I presents the technology and skills needed to perform high-quality research with eye-trackers. Part II covers the predominant methods applied to the data which eye-trackers record. These include the parsing of raw sample data into oculomotor events, and how to calculate other representations of eye movements such as heat maps and transition matrices. Part III gives a comprehensive outline of the measures which can be calculated using the events and representations described in Part II. This is a taxonomy of the measures available to eye-tracking researchers, sorted by type of movement of the eyes and type of analysis. For anyone in the sciences considering conducting research involving eye-tracking, this book will be an essential reference work.

Download or read book Representations of Vision written by Andrei Gorea and published by Cambridge University Press. This book was released on 1991-04-26 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: This stimulating volume on vision extends well beyond the traditional areas of vision research and places the subject in a much broader philosophical context. The emphasis throughout is to integrate and illuminate the visual process. The first three parts of the volume provide authoritative overviews on computational vision and neural networks, on the neurophysiology of visual cortex processing, and on eye-movement research. Each of these parts illustrates how different research perspectives may jointly solve fundamental problems related to the efficiency of visual perception, to the relationship between vision and eye-movements and to the neurophysiological 'codes' underlying our visual perceptions. In the fourth part, leading vision scientists introduce the reader to some major philosophical problems in vision research such as the nature of 'ultimate' codes for perceptual events, the duality of psycho-physics, the bases of visual recognition and the paradigmatic foundations of computer-vision research.

Download or read book Eye Movement Research written by Christoph Klein and published by Springer Nature. This book was released on 2019-10-16 with total page 1017 pages. Available in PDF, EPUB and Kindle. Book excerpt: This edited volume presents fundamentals as well as applications of oculomotor methods in industrial and clinical settings. The topical spectrum covers 1.) basics and background material, 2.) methods such as recording techniques, markov models, Lévy flights, pupillometry and many more, as well as 3.) a broad range of applications in clinical and industrial settings. The target audience primarily comprises research experts and practitioners, but the book may also be beneficial for graduate students.

Download or read book Models of Horizontal Eye Movements written by Alireza Ghahari and published by Springer. This book was released on 2014-10-17 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are five different types of eye movements: saccades, smooth pursuit, vestibular ocular eye movements, optokinetic eye movements, and vergence eye movements. The purpose of this book series is focused primarily on mathematical models of the horizontal saccadic eye movement system and the smooth pursuit system, rather than on how visual information is processed. A saccade is a fast eye movement used to acquire a target by placing the image of the target on the fovea. Smooth pursuit is a slow eye movement used to track a target as it moves by keeping the target on the fovea. The vestibular ocular movement is used to keep the eyes on a target during brief head movements. The optokinetic eye movement is a combination of saccadic and slow eye movements that keeps a full-field image stable on the retina during sustained head rotation. Each of these movements is a conjugate eye movement, that is, movements of both eyes together driven by a common neural source. A vergence movement is a non-conjugate eye movement allowing the eyes to track targets as they come closer or farther away. In Part 1, early models of saccades and smooth pursuit are presented. A number of oculomotor plant models are described therein beginning with the Westheimer model published in 1954, and up through our 1995 model involving a 4th-order oculomotor plant model. In Part 2, a 2009 version of a state-of-the-art model is presented for horizontal saccades that is 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. In this book, a multiscale model of the saccade system is presented, focusing on the neural network. Chapter 1 summarizes a whole muscle model of the oculomotor plant based on the 2009 3rd-order and linear, and controlled by a physiologically based time-optimal neural network. Chapter 2 presents a neural network model of biophysical neurons in the midbrain for controlling oculomotor muscles during horizontal human saccades. To investigate horizontal saccade dynamics, a neural circuitry, including omnipause neuron, premotor excitatory and inhibitory burst neurons, long lead burst neuron, tonic neuron, interneuron, abducens nucleus, and oculomotor nucleus, is developed. A generic neuron model serves as the basis to match the characteristics of each type of neuron in the neural network. We wish to express our thanks to William Pruehsner for drawing many of the illustrations in this book. Table of Contents: Acknowledgments / 2009 Linear Homeomorphic Saccadic Eye Movement Model / A Neuron-Based Time-Optimal Controller of Horizontal Saccadic Eye Movements and Glissades / References / Authors' Biographies

Download or read book Eye Movements and Their Role in Visual and Cognitive Processes written by Eileen Kowler and published by Elsevier Publishing Company. This book was released on 1990 with total page 516 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the first book to deal exclusively with oculomotor performance in a series that, up to this point, has been devoted largely to reviews of research on oculomotor anatomy and physiology. The publication of this volume signifies the recognition of the fact that a genuine understanding of eye movement will not come about through the study of neurons alone. We need to know about the capacity to make different kinds of eye movement, and about how such oculomotor capacity is used to accomplish different sorts of visual and cognitive tasks, i.e. how the eye can move and why it moves in particular ways. Research on respective topics was critically evaluated by the contributing authors, resulting in a controversial and up-to-date appraisal of this subject.