A perfectly matched layer (PML) absorbing material composed of a uniaxial anisotropic material is presented for the truncation of finite-difference time-domain (FDTD) lattices. It is shown that the uniaxial PML material formulation is mathematically equivalent to the perfectly matched layer method published by Berenger (see J. Computat. Phys., Oct. 1994). However, unlike Berenger's technique, the uniaxial PML absorbing medium presented in this paper is based on a Maxwellian formulation. Numerical examples demonstrate that the FDTD implementation of the uniaxial PML medium (...) is stable, equal in effectiveness as compared to Berenger's PML medium, while being more computationally efficient. (shrink)

Edited by Richard McKeon, with an introduction by C.D.C. Reeve Preserved by Arabic mathematicians and canonized by Christian scholars, Aristotle’s works have shaped Western thought, science, and religion for nearly two thousand years. Richard McKeon’s The Basic Works of Aristotle—constituted out of the definitive Oxford translation and in print as a Random House hardcover for sixty years—has long been considered the best available one-volume Aristotle. Appearing in paperback at long last, this edition includes selections from the Organon, On the Heavens, (...) The Short Physical Treatises, Rhetoric, among others, and On the Soul, On Generation and Corruption, Physics, Metaphysics, Nicomachean Ethics, Politics, and Poetics in their entirety. (shrink)

A model of the neuropsychology of anxiety is proposed. The model is based in the first instance upon an analysis of the behavioural effects of the antianxiety drugs (benzodiazepines, barbiturates, and alcohol) in animals. From such psychopharmacologi-cal experiments the concept of a “behavioural inhibition system” (BIS) has been developed. This system responds to novel stimuli or to those associated with punishment or nonreward by inhibiting ongoing behaviour and increasing arousal and attention to the environment. It is activity in the BIS (...) that constitutes anxiety and that is reduced by antianxiety drugs. The effects of the antianxiety drugs in the brain also suggest hypotheses concerning the neural substrate of anxiety. Although the benzodiazepines and barbiturates facilitate the effects of γ-aminobutyrate, this is insufficient to explain their highly specific behavioural effects. Because of similarities between the behavioural effects of certain lesions and those of the antianxiety drugs, it is proposed that these drugs reduce anxiety by impairing the functioning of a widespread neural system including the septo-hippocampal system (SHS), the Papez circuit, the prefrontal cortex, and ascending monoaminergic and cholinergic pathways which innervate these forebrain structures. Analysis of the functions of this system (based on anatomical, physiological, and behavioural data) suggests that it acts as a comparator: it compares predicted to actual sensory events and activates the outputs of the BIS when there is a mismatch or when the predicted event is aversive. Suggestions are made as to the functions of particular pathways within this overall brain system. The resulting theory is applied to the symptoms and treatment of anxiety in man, its relations to depression, and the personality of individuals who are susceptible to anxiety or depression. (shrink)

In this study William Lyons presents a sustained and coherent theory of the emotions, and one which draws extensively on the work of psychologists and physiologists in the area. Dr Lyons starts by giving a thorough and critical survey of other principal theories, before setting out his own 'causal-evaluative' account. In addition to giving an analysis of the nature of emotion - in which, Dr Lyon argues, evaluative attitudes play a crucial part - his theory throws light on the motivating (...) role of emotions in our lives, our attitudes towards our emotions and our responsibility for them. (shrink)

Donald Olding Hebb, referred to by American Psychologist as one of "the 20th century's most eminent and influential theorists in the realm of brain function and behavior," contributes greatly to the understanding of mind and thought in Essays on Mind. His objective was to learn about thought which he considered "the central problem of psychology -- but also, not less important, to learn how to think clearly about thought, which is philosophy." The volume is written for advanced undergraduates, graduates, professionals, (...) and lay people interested in or studying the mind. Hebb offers an increased understanding of the mind from a biological perspective that affects long-standing philosophical and psychological problems. "Psychology and Philosophy were divorced some time ago but, like other divorced couples, they still have problems in common," writes Hebb. The first three chapters establish the methodological and philosophical basis for his biologically centered theory of behavior, including the evolution of the mind, nature versus nurture, the origination and status of cell-assembly theory, and infant thought and language development. He concludes with a discussion of the workings of scientific thought from a practical rather than theoretical perspective. (shrink)

The philosopher must inform himself of the relevant empirical investigation to arrive at a definition, and the scientist cannot afford to be naive about the..

It is traditionally believed that cerebral activation (the presence of low voltage fast electrical activity in the neocortex and rhythmical slow activity in the hippocampus) is correlated with arousal, while deactivation (the presence of large amplitude irregular slow waves or spindles in both the neocortex and the hippocampus) is correlated with sleep or coma. However, since there are many exceptions, these generalizations have only limited validity. Activated patterns occur in normal sleep (active or paradoxical sleep) and during states of anesthesia (...) and coma. Deactivated patterns occur, at times, during normal waking, or during behavior in awake animals treated with atropinic drugs. Also, the fact that patterns characteristic of sleep, arousal, and waking behavior continue in decorticate animals indicates that reticulo-cortical mechanisms are not essential for these aspects of behavior. (shrink)

Neuroleptic drugs disrupt the learning and performance of operant habits motivated by a variety of positive reinforcers, including food, water, brain stimulation, intravenous opiates, stimulants, and barbiturates. This disruption has been demonstrated in several kinds of experiments with doses that do not significantly limit normal response capacity. With continuous reinforcement neuroleptics gradually cause responding to cease, as in extinction or satiation. This pattern is not due to satiation, however, because it also occurs with nonsatiating reinforcement (such as saccharin or brain (...) stimulation). Repeated tests with neuroleptics result in earlier and earlier response cessation reminiscent of the kind of decreased resistance to extinction caused by repeated tests without the expected reward. Indeed, withholding reward can have the same effect on responding under later neuroleptic treatment as prior experience with neuroleptics themselves; this suggests that there is a transfer of learning (really unlearning) from nonreward to neuroleptic conditions. These tests under continuous reinforcement schedules suggest that neuroleptics blunt the ability of reinforcers to sustain responding at doses which largely spare the ability of the animal to initiate responding. Animals trained under partial reinforcement, however, do not respond as well during neuroleptic testing as animals trained under continuous reinforcement. Thus, neuroleptics can also impair responding (though not responsecapacity) that is normally sustained by environmental stimuli (and associated expectancies) in the absence of the primary reinforcer. Neuroleptics also blunt the euphoric impact of amphetamine in humans. These data suggest that the most subtle and interesting effect of neuroleptics is a selective attenuation of motivational arousal which is (a) critical for goal-directed behavior, (b) normally induced by reinforcers and associated environmental stimuli, and (c) normally accompanied by the subjective experience of pleasure. Because these drugs are used to treat schizophrenia and because they cause parkinsonian-like side effects, this action has implications for a better understanding of human pathology as well as normal motivational processes. (shrink)

The challenge of explaining the emotions has engaged the attention of the best minds in philosophy and science throughout history. Part of the fascination has been that the emotions resist classification. As adequate account therefore requires receptivity to knowledge from a variety of sources. The philosopher must inform himself of the relevant empirical investigation to arrive at a definition, and the scientist cannot afford to be naive about the assumptions built into his conceptual apparatus. The contributors to this volume have (...) approached the problem of characterizing and classifying emotions from the perspectives of neurophysiology, psychology, and social psychology as well as that of philosophical psychology. They discuss the difficulties that arise in classifying the emotions, assessing their appropriateness and rationality, and determining their function in motivating moral action. (shrink)

The concept of dominance is used in the behavioral and biological sciences to describe outcomes in a variety of competitive interactions. In some taxa, a history of agonistic encounters among individuals modifies the course of future agonistic encounters such that the existence of a certain type of relationship can be inferred. If one is to characterize such relationships as dominance, however, then they must be distinguished from other kinds of interaction patterns for which the term tends to be used, as (...) well as from factors such as territoriality and "trained" winners and losers, which may also influence the expression of agonistic behavior. Operational definitions based on causal, functional, evolutionary, and ontogenetic considerations have been proposed. Reliability and validity problems have been discussed, but the dominance concept has proved useful despite methodological difficulties. The confusion of dominance relationships (which involve two or more individuals) with dominance ranks (which are assigned to a single individual) has obscured the possible evolutionary basis of dominance relationships. If benefits accrue to dominant members of pairs, then those attributes which allow an animal to establish dominance can be selected. Dominance per se and dominance ranks, on the other hand, cannot be genetically transmitted since they constitute relationships with other individuals rather than absolute attributes. Dominance rankings in particular may be useful for describing behavioral patterns within a group, but they may reflect our own ability to count rather than any important variable in social organization. (shrink)

The book describes three elementary units of action – the reflex, the oscillator, and the servomechanism – and the principles by which they are combined to make complex units. The combining of elementary units to make complex units gives behavior and the neural circuitry underlying behavior a hierarchical structure. Circuits at higher levels govern the operation of lower circuits by selective potentiation and depotentiation: by regulating the potential for operation in lower circuits – raising the potential for some and lowering (...) it for others – a higher unit establishes the overall pattern to be exhibited in the combined operations of the lower units, while leaving it to the lower units to determine the details of the implementation of this pattern. A theory of motivation of the kind long championed by ethologists and physiological psychologists grows out of the notion of the selective potentiation and depotentiation of hierarchically structured units of behavior. The question then becomes how this conception of motivation may be integrated with a conception of a learned representation of the world to yield a theory of how animals produce novel motivated behavioral sequences based on learned representations. The representation of space, which is central to the behavior of organisms at least as lowly as the digger wasp, is a promising domain for the investigation of this question. Another promising area is the representation of skilled movements, such as handwriting. A number of issues in cognitive and developmental psychology are illumined by this theory about the organization of action. Among these are the degrees-of-freedom problem, the role of practice in development and in the learning of skilled action, and the role of mental rotation of spatial representations. (shrink)