The function of the vestibular system is not as obvious as those of vision, hearing, touch or smell. Vestibular dysfunction, however, is clearly apparent where lesions are present. It is probably for this reason that the vestibular sense was not discovered until the nineteenth century and that clinicians have continued to playa major role in basic vestibular research right up to the present. The relationship between basic and clinical research is certainly stronger in the vesti bular field than in that of tactile sensation, for instance, as testified by the work of clinicians as MENIERE, BREUER, BARANY, DEKLEIJN and FRENZEL. In this respect the situation is similar in vestibular physiology and in endocrinology, and for the same reason. This second part of the vestibular volume of the Handbook of Sensory Physio logy will be of interest to neurologists, otologists, neurosurgeons, ophthalmologists and physiotherapists on the one hand, and psychologists, physiologists, engineers and aviation specialists on the other. For a full understanding of Part 2, it is necessary to have assimilated the basic anatomy, physiology, and biochemistry of Part 1."

The details of the receptor mechanism are not yet fully understood for any sensory system. However, sufficient data are available (for the vestibular system and for other systems) to permit meaningful tracking of the sensory messages through the nervous system and via conscious experience. The reception, process ing, storage and output of information in man and other animals, as done by means of receptors, neurons, secretory cells and muscle fibers, are collectively referred to as mind. Sensory physiologists tend to disbelieve in extrasensory perception. Sensory physiology in general is an area upon which different sciences and methods converge. Anatomists, physiologists, psychologists, physicists, chemists, and engineers have made important contributions to sensory physiology. What is special about vestibular physiology is the fact that many research workers are clinicians, living under the constant pressure of their patient's demands. This is a disadvantage when it comes to writing handbooks, but an advantage for the pa tient, since research is guided by clinical practice and can be quickly applied. Modern methods, such as recording from single nerve units and the correlation of electrophysiological and psychophysical data, have greatly contributed to our knowledge, yet the study of lesions is still important, especially in the vestibular field."

The issue of the relationship between cognition and motor processes can be - and has been - raised at different levels of analysis. At the neurophysiological level it refers to the interactions between afferent and efferent information. At the neurological and neuropsychological level it relates to the mutual dependencies between the sensory and the motor part of the brain, or, more precisely, between sensory and motor functions of various parts of the brain. In psychology, the issue under debate concerns, at a molecular level, the relationship between percep tion and movement or, at a more molar level, the relations between cognition and action. For the title of this book we deliberately decided to combine two terms that are taken from two of these levels, in order to emphasize both the multilevel structure of the issues involved and the multidis ciplinary nature of the following contributions. Although the term "cognition" has been tremendously misused in recent years (at least in psychology), it is still the only term available to serve as a convenient collective name for all sorts of cognitive processes and functions."