David Lewis (1941-2001) was Class of 1943 University Professor of Philosophy at Princeton University. His contributions spanned philosophical logic, philosophy of language, philosophy of mind, philosophy of science, metaphysics, and epistemology. In On the Plurality of Worlds, he defended his challenging metaphysical position, "modal realism." He was also the author of the books Convention, Counterfactuals, Parts of Classes, and several volumes of collected papers.

This is not your psychoanalyst's unconscious.

In a dynamic world, mechanisms allowing prediction of future situations can provide a selective advantage. We suggest that memory systems differ in the degree of flexibility they offer for anticipatory behavior and put forward a corresponding taxonomy of prospection. The adaptive advantage of any memory system can only lie in what it contributes for future survival. The most flexible is episodic memory, which we suggest is part of a more general faculty of mental time travel that allows us not only (...) to go back in time, but also to foresee, plan, and shape virtually any specific future event. We review comparative studies and find that, in spite of increased research in the area, there is as yet no convincing evidence for mental time travel in nonhuman animals. We submit that mental time travel is not an encapsulated cognitive system, but instead comprises several subsidiary mechanisms. A theater metaphor serves as an analogy for the kind of mechanisms required for effective mental time travel. We propose that future research should consider these mechanisms in addition to direct evidence of future-directed action. We maintain that the emergence of mental time travel in evolution was a crucial step towards our current success. (shrink)

This book presents a comprehensive theory of consciousness. The initial chapter distinguishes six main forms of consciousness and sketches an account of each one. Later chapters focus on phenomenal consciousness, consciousness of, and introspective consciousness. In discussing phenomenal consciousness, Hill develops the representational theory of mind in new directions, arguing that all awareness involves representations, even awareness of qualitative states like pain. He then uses this view to undercut dualistic accounts of qualitative states. Other topics include visual awareness, visual appearances, (...) emotional qualia, and meta-cognitive processing. This important work will interest a wide readership of students and scholars in philosophy of mind and cognitive science. (shrink)

We are prone to gross error, even in favorable circumstances of extended reflection, about our own ongoing conscious experience, our current phenomenology. Even in this apparently privileged domain, our self-knowledge is faulty and untrustworthy. We are not simply fallible at the margins but broadly inept. Examples highlighted in this essay include: emotional experience (for example, is it entirely bodily; does joy have a common, distinctive phenomenological core?), peripheral vision (how broad and stable is the region of visual clarity?), and the (...) phenomenology of thought (does it have a distinctive phenomenology, beyond just imagery and feelings?). Cartesian skeptical scenarios undermine knowledge of ongoing conscious experience as well as knowledge of the outside world. Infallible judgments about ongoing mental states are simply banal cases of self-fulfillment. Philosophical foundationalism supposing that we infer an external world from secure knowledge of our own consciousness is almost exactly backward. (shrink)

If one formulates Helmholtz's ideas about perception in terms of modern-day theories one arrives at a model of perceptual inference and learning that can explain a remarkable range of neurobiological facts. Using constructs from statistical physics it can be shown that the problems of inferring what cause our sensory inputs and learning causal regularities in the sensorium can be resolved using exactly the same principles. Furthermore, inference and learning can proceed in a biologically plausible fashion. The ensuing scheme rests on (...) Empirical Bayes and hierarchical models of how sensory information is generated. The use of hierarchical models enables the brain to construct prior expectations in a dynamic and context-sensitive fashion. This scheme provides a principled way to understand many aspects of the brain's organisation and responses. In this paper, we suggest that these perceptual processes are just one emergent property of systems that conform to a free-energy principle. The free-energy considered here represents a bound on the surprise inherent in any exchange with the environment, under expectations encoded by its state or configuration. A system can minimise free-energy by changing its configuration to change the way it samples the environment, or to change its expectations. These changes correspond to action and perception, respectively, and lead to an adaptive exchange with the environment that is characteristic of biological systems. This treatment implies that the system's state and structure encode an implicit and probabilistic model of the environment. We will look at models entailed by the brain and how minimisation of free-energy can explain its dynamics and structure. (shrink)

If one formulates Helmholtz’s ideas about perception in terms of modern-day theories one arrives at a model of perceptual inference and learning that can explain a remarkable range of neurobiological facts. Using constructs from statistical physics it can be shown that the problems of inferring what cause our sensory inputs and learning causal regularities in the sensorium can be resolved using exactly the same principles. Furthermore, inference and learning can proceed in a biologically plausible fashion. The ensuing scheme rests on (...) Empirical Bayes and hierarchical models of how sensory information is generated. The use of hierarchical models enables the brain to construct prior expectations in a dynamic and context-sensitive fashion. This scheme provides a principled way to understand many aspects of the brain’s organisation and responses. In this paper, we suggest that these perceptual processes are just one emergent property of systems that conform to a free-energy principle. The free-energy considered here represents a bound on the surprise inherent in any exchange with the environment, under expectations encoded by its state or configuration. A system can minimise free-energy by changing its configuration to change the way it samples the environment, or to change its expectations. These changes correspond to action and perception, respectively, and lead to an adaptive exchange with the environment that is characteristic of biological systems. This treatment implies that the system’s state and structure encode an implicit and probabilistic model of the environment. We will look at models entailed by the brain and how minimisation of free-energy can explain its dynamics and structure. (shrink)

Different cognitive functions recruit a number of different, often overlapping, areas of the brain. Theories in cognitive and computational neuroscience are beginning to take this kind of functional integration into account. The contributions to this special issue consider what functional integration tells us about various aspects of the mind such as perception, language, volition, agency, and reward. Here, I consider how and why functional integration may matter for the mind; I discuss a general theoretical framework, based on generative models, that (...) may unify many of the debates surrounding functional integration and the mind; and I briefly introduce each of the contributions. (shrink)

The phenomenology of agency and perception is probably underpinned by a common cognitive system based on generative models and predictive coding. I defend the hypothesis that this cognitive system explains core aspects of the sense of having a self in agency and perception. In particular, this cognitive model explains the phenomenological notion of a minimal self as well as a notion of the narrative self. The proposal is related to some influential studies of overall brain function, and to psychopathology. These (...) elusive notions of the self are shown to be the natural upshots of general cognitive mechanisms whose fundamental purpose is to enable agents to represent the world and act in it. (shrink)

Viewed from a certain perspective, nothing can seem more secure than introspection. Consider an ordinary conscious episode—say, your current visual experience of the colour of this page. You can judge, when reflecting on this experience, that you have a visual experience as of something white with black marks before you. Does it seem reasonable to doubt this introspective judgement? Surely not—such doubt would seem utterly fanciful. The trustworthiness of introspection is not only assumed by commonsense, it is also taken for (...) granted by many of theorists about the mind. Within both philosophy and the science of consciousness it is widely held that introspection is generally reliable, at least with respect to the question of one’s current (or immediately prior) conscious states. Without this assumption, we could not make sense of theorists’ widespread use of introspection, both in support of their own position and to undermine that of their opponents. (shrink)

It has been claimed that the ability to remember the past and the ability to project oneself into the future are intimately related. We sought support for this proposition by examining whether individual differences in dimensions that have been shown to affect memory for past events similarly influence the experience of projecting oneself into the future. We found that individuals with a higher capacity for visual imagery experienced more visual and other sensory details both when remembering past events and when (...) imagining future events. In addition, individuals who habitually use suppression to regulate their emotions experienced fewer sensory, contextual, and emotional details when representing both past and future events, while the use of reappraisal had no effect on either kind of events. These findings are consistent with the view that mental time travel into the past and into the future relies on similar mechanisms. (shrink)

One of the striking, even amusing, spectacles to be enjoyed at the many workshops and conferences on consciousness these days is the breathtaking overconfidence with which laypeople hold forth about the nature of consciousness Btheir own in particular, but everybody =s by extrapolation. Everybody =s an expert on consciousness, it seems, and it doesn =t take any knowledge of experimental findings to secure the home truths these people enunciate with such conviction.

Some monothematic types of delusions may arise because subjects have unusual experiences. The role of this experiential component in the pathogenesis of delusion is still not understood. Focussing on delusions of alien control, we outline a model for reality testing competence on unusual experiences. We propose that nascent delusions arise when there are local failures of reality testing performance, and that monothematic delusions arise as normal responses to these. In the course of this we address questions concerning the tenacity with (...) which delusions are maintained, their often bizarre content, the patients' inability to dismiss them, and their often circumscribed character. (shrink)

It has been claimed that the ability to remember the past and the ability to project oneself into the future are intimately related. We sought support for this proposition by examining whether individual differences in dimensions that have been shown to affect memory for past events similarly influence the experience of projecting oneself into the future. We found that individuals with a higher capacity for visual imagery experienced more visual and other sensory details both when remembering past events and when (...) imagining future events. In addition, individuals who habitually use suppression to regulate their emotions experienced fewer sensory, contextual, and emotional details when representing both past and future events, while the use of reappraisal had no effect on either kind of events. These findings are consistent with the view that mental time travel into the past and into the future relies on similar mechanisms. (shrink)

Researchers from the 1940's through the present have found that normal, sighted people can echolocate - that is, detect properties of silent objects by attending to sound reflected from them. We argue that echolocation is a normal part of our conscious, perceptual experience. Despite this, we argue that people are often grossly mistaken about their experience of echolocation. If so, echolocation provides a counterexample to the view that we cannot be seriously mistaken about our own current conscious experience.

Edward Titchener, one of the great champions of introspectionist psychology, declared that 'the term Introspection, as we find it used today, is highly equivocal, and that the procedure which it connotes may be scientifically illegitimate, or even wholly imaginary' . He made the point because he wanted to insulate his preferred method of doing psychological research from criticisms that were directed against forms of introspection that he conceded to be unreliable. The point, however, is not just that we can introspect (...) more or less carefully. It is that there are 'gross differences in the meaning of the word' . 'Introspection' is Janus-faced. It splinters into several different species, involving different underlying mechanisms. (shrink)

Researchers from the 1940's through the present have found that normal, sighted people can echolocate - that is, detect properties of silent objects by attending to sound reflected from them. We argue that echolocation is a normal part of our perceptual experience and that there is something 'it is like' to echolocate. Furthermore, we argue that people are often grossly mistaken about their experience of echolocation. If so, echolocation provides a counterexample to the view that we cannot be mistaken about (...) our own current phenomenology. (shrink)

Philosophers tend to assume that we have excellent knowledge of our own current conscious experience or 'phenomenology'. I argue that our knowledge of one aspect of our experience, the experience of visual imagery, is actually rather poor. Precedent for this position is found among the introspective psychologists of the late nineteenth and early twentieth centuries. Two main arguments are advanced toward the conclusion that our knowledge of our own imagery is poor. First, the reader is asked to form a visual (...) image, and it is expected that answering questions about certain basic features of that experience will be difficult. If so, it seems reasonable to suppose that people could be mistaken about those basic features of their own imagery. Second, it is observed that although people give widely variable reports about their own experiences of visual imagery, differences in report do not systematically correlate with differences on tests of skills that psychologists have often supposed to require visual imagery, such as mental rotation, visual creativity, and visual memory. (shrink)

This commentary takes a closer look at how “constructive models of subjective perception,” referred to by Collerton et al. (sect. 2), might contribute to the Perception and Attention Deficit (PAD) model. It focuses on the neuronal mechanisms that could mediate hallucinations, or false inference – in particular, the role of cholinergic systems in encoding uncertainty in the context of hierarchical Bayesian models of perceptual inference (Friston 2002b; Yu & Dayan 2002).

Many people argue that privileged self–knowledge is incompatible with semantic externalism. I develop a contextualist approach to self–knowledge, and examine what this approach should lead us to say about the apparent incompatibility. Though such contextualism compels us to re–think the notion of privilege associated with self–knowledge, it can contain the damage wreaked by the externalist doctrine.