Microelectromechanical systems (MEMS) hold great promise for sensing and actuating on the micron scale. There is a hierarchy of increasing difficulty for placing MEMS devices in the field. Devices that do not allow contact between structural members rely mainly on mechanical properties of freestanding films. High-resolution techniques must be developed within the framework of MEMS to measure properties such as modulus and residual stress. When contact and rubbing contact are allowed, the complexities of adhesion and friction at the microscale must be understood and well controlled. Fluid interactions are similarly important for microfluidic devices. Packaging of MEMS for use in the field also requires special consideration, because it is often application specific. This book investigates various materials, characterization methods and processing techniques. These approaches represent different but useful strategies to solve MEMS challenges, and must be integrated for product realization. Topics include: deposition and characterization of Si; materials and processes for MEMS; tribology; dynamic optical characterization; packaging; LIGA; materials aspects; and characterization of MEMS processing.

This book is the fruit of a study group on perception and action that worked at the Center for Interdisciplinary Research (ZiP) of the University of Bielefeld, FRG in the academic year 1984-1985. We express our gratitude to the ZiF for hosting the group and for providing fmancial and organizational support for its scientific activities, including a meeting of the authors of the present volume that took place at the ZiF in July 1986. This is/ the study group's last common product, and it took considerable time to give the book its fmal shape. Most of the editing was done while one of us (0. N.) was a Fellow at the Netherlands Institute for Advanced Study in the Humanities and Social Sciences (NlAS) during the academic year 1987-1988. Thanks are due to NIAS for its generous support. We also thank all our friends and colleagues who contributed to the book.

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."