Acoustical Signal Processing in the Central Auditory System

This book gives a superb account of current knowledge of the central auditory system. While many such books run the risk of appealing to arcane interests, this book is different because of its breadth and clarity. Although it is a volume based on the proceedings of a meeting, it has been organized and edited to serve as a basic overview. As such, the book presents an excellent collection of essays from leaders in the field, who have made considerable effort to be up-to-date and speculate on the broader implications of advances in auditory research.While there are diverse topics covered in the book there are two recurrent themes. For example, the plasticity of the auditory system and the consequences of deafness. Auditory function is not as static as was previously thought; for example, learning occurs in the auditory system at the neuronal level. Furthermore, this plasticity or learning is shown to depend on the behavioral state of the organism.Some of the chapters represent an in-depth review of knowledge in a particular field, while other chapters discuss recent hypotheses that are likely to direct auditory research for the next few years. The section on plasticity includes a review of anatomical changes that occur following deafness, which include the shrinkage of neurons, the formation of new connections and an increase in responsiveness of some nuclei. New information about the biochemical changes that also occur following deafness is included, and evidence is presented that suggests the plasticity of the system is greater than previously thought. Thus, while human infants are more sensitive to unilateral deafness than are human adults, in adult ferrets a dramatic reorganization has been shown to occur in response to unilateral deafness. Chronic electrical stimulation of a deafened auditory system can lead to expansion of the central representation of the stimulated structures. The proposal is made, therefore, that unilateral deafening produces a selective disturbance in inhibitory mechanisms rather than generalized degeneration. This suggests that there might be a deafness-induced downregulation of inhibition.The anatomical studies had a recurring theme based on the orthogonal representation of two sources of afferents, which probably indicates a requirement for systematic convergence of input. Periodicity and best-modulation frequencies were both shown to be represented orthogonally to the tonotopic organization in the inferior colliculus. A striking feature of the arrangement of the dorsal cochlear nucleus is that the excitatory and inhibitory inputs are also orthogonally arranged. Auditory space corresponds to maps of visual space and the body surface, which are also orthogonal to the laminae of the superior colliculus.Readers who are not familiar with this field might be most interested in the series of chapters that deal with hearing and deafness in humans. While people with the ability to sense absolute pitch are relatively rare, this ability can be learned during a sensitive period in childhood. Unfortunately, severe deafness in young prelingual children has been shown to affect speech development which, in turn, leads to the question of whether a conductive hearing loss can also affect speech development. It has also been reported that humans with unilateral cortical damage are poorer at localizing sounds. However, other studies show that the auditory cortex is not essential either for accurate localization performance or for frequency discrimination.The book contains many illustrations of excellent quality showing both anatomical detail and graphs or diagrams that simplify the data. A color plate shows the tonotopic organization of auditory cortex and the reference lists provided are reasonably updated, although these vary somewhat from chapter to chapter.Many of the sections will require a neuroscience background for the reader to appreciate fully the information presented. For this reason this would not be a good book for a novice in the area but more useful for scholars wishing to remain abreast of a wide range of current auditory research. While the range of topics is broad, each chapter can be read independently of the others. The chapters vary in quality and readability, which reflects the large number of authors and their various styles of writing. Workers already in the field will find many of the essays interesting and thought provoking, while newcomers, students and others less familiar with auditory research will appreciate the clarity of discussion that runs throughout the text. One obstacle to obtaining this book is the cost involved. However, researchers and students working in the field will find the book worth the price because of the in-depth coverage of such a wide range of topics.In conclusion, this is an excellent book and should be compulsory reading for all students of the central auditory system. It contains history and current research but, additionally, it suggests the direction of future research. It honors the late R. Bruce Masterton and is a fitting tribute to him and his research. It is appropriate that Masterton himself opens the book with a historical overview of the study of auditory cortex. This is probably the best summary of ablation behavior techniques in the last 20 years. Masterton's contributions to the field of auditory neuroscience were the beginnings of the interdisciplinary approach apparent today. His ideas have spawned years of research, the details of which are well-covered in this book.