To controlforceaccurately under a wide range of behavioral conditions, the central nervous system would either require a detailed, continuously updated representation of the state of each muscle (and the load against which each is acting) or else force feedback with sufficient gain to cope with variations in the properties of the muscles and loads. The evidence for force feedback with adequate gain or for an appropriate central representation is not sufficient to conclude that force is the major controlled variable in (...) normal limb movements.Morton's hypothesis, thatlengthis controlled by a follow-up servo, has a number of difficulties related to the delays, gains, variability, and specificity in feedback pathways comprising potential servo loops. However, experimental evidence is consistent with these pathways providing servo assistance for some movements produced by coactivation of α- and static γ-motoneurons. Dynamic γ-motoneurons may provide an additional input for adaptive control of different types of movements.The idea that feedback is used to compensate for changes in musclestiffnesshas received experimental support under static postural conditions. However, reflexes tend to increase rather than decrease the range of variation in muscle stiffness during some cyclic movements. Theoretical problems associated with the regulation of stiffness are also discussed. The possibilities of separate control systems forvelocityorviscosityare considered, but the evidence is either negative or lacking. I conclude that different physical variables can be controlled depending on the type of limb movement required. The concept of stiffness regulation is also useful under some conditions, but should probably be extended to the regulation of the visco-elastic properties (i.e., the mechanical impedance) of a muscle or joint. (shrink)

I NATURE AND TRADITION Quemcunque aegrum ingenio praestaittem curanJum invisebat , siquidem morbi vehementia pateretur, . . .familiarem cum eo sermonem aliquandiu conferebat, cum pbilosophis Pbilosopkica, cum Mathematicis Mathematica, ..

Physical and chemical processes may act upon the mind; and when we are writing a difficult letter, our mind acts upon our body and, through a chain of physical...

This is a book about how we see: the environment around us (its surfaces, their layout, and their colors and textures); where we are in the environment; whether or not we are moving and, if we are, where we are going; what things are good for; how to do things (to thread a needle or drive an automobile); or why things look as they do.The basic assumption is that vision depends on the eye which is connected to the brain. The (...) author suggests that natural vision depends on the eyes in the head on a body supported by the ground, the brain being only the central organ of a complete visual system. When no constraints are put on the visual system, people look around, walk up to something interesting and move around it so as to see it from all sides, and go from one vista to another. That is natural vision—and what this book is about. (shrink)

The Modularity of Mind proposes an alternative to the or view of cognitive architecture that has dominated several decades of cognitive science. Whereas interactionism stresses the continuity of perceptual and cognitive processes, modularity theory argues for their distinctness. It is argued, in particular, that the apparent plausibility of New Look theorizing derives from the failure to distinguish between the (correct) claim that perceptual processes are inferential and the (dubious) claim that they are unencapsidated, that is, that they are arbitrarily sensitive (...) to the organism's beliefs and desires. In fact, according to modularity theory, perceptual processes are computationally isolated from much of the background knowledge to which cognitive processes have access. The postulation of autonomous, domain-specific psychological mechanisms underlying perceptual integration connects modularity theory with the tradition of faculty psychology, in particular, with the work of Franz Joseph Call. Some of these historical affinities, and some of the relations between faculty psychology and Cartesianism, are discussed in the book. (shrink)

In this book, Granit explains the physiology of vision perception as an input system and motor control as an output system, with the goal-oriented brain mediating between.

First published in 2000. Routledge is an imprint of Taylor & Francis, an informa company.

Describes the various senses as sensory systems that are attuned to the environment. Develops the notion of rich sensory information that specifies the distal environment. Includes a discussion of affordances.

HISTORIANS of psychology are almost unanimously agreed on one point: that psychology is a relatively new science. There may be some disagreement as to when it started--with Weber, or Fechner, or Wundt, or James--but there is almost no dissent from the proposition that psychology as a scientific discipline is less than one and one-half centuries old. Many earlier writers are often discussed in histories of psychology, but invariably they are called speculators, or philosophers, as opposed to scientists. We believe that (...) this is an incorrect appraisal of the career of psychological research. To demonstrate our point, we propose to show how one key psychological idea from Descartes' work has had an extensive and robust scientific history. If it is true that this Cartesian idea has had great influence in science, then many claims concerning the history of psychology will need to be reconsidered. Not everything which happened in psychology prior to the nineteenth century was speculative, nor is everything which happened later scientific. Even more importantly, if Descartes' idea has been of such central concern to several hundred years of research, it must be treated as an important claim about the way the world is, as a law of nature. (shrink)