Physical symbol systems

On the occasion of a first conference on Cognitive Science, it seems appropriate to review the basis of common understanding between the various disciplines. In my estimate, the most fundamental contribution so far of artificial intelligence and computer science to the joint enterprise of cognitive science has been the notion of a physical symbol system, i.e., the concept of a broad class of systems capable of having and manipulating symbols, yet realizable in the physical universe. The notion of symbol so defined is internal to this concept, so it becomes a hypothesis that this notion of symbols includes the symbols that we humans use every day of our lives. In this paper we attempt systematically, but plainly, to lay out the nature of physical symbol systems. Such a review is in ways familiar, but not thereby useless. Restatement of fundamentals is an important exercise.     

Perceptual systems and realism

Constructivism undermines realism by arguing that experience is mediated by concepts, and that there is no direct way to examine those aspects of objects that belong to them independently of our conceptualizations; perception is theory-laden. To defend realism one has to show first that perception relates us directly with the world without any intermediary conceptual framework. The result of this direct link is the nonconceptual content of experience. Second, one has to show that part of the nonconceptual content extracted from the environment correctly represents features of mind independent objects. With regard to the first condition, I have argued elsewhere that a part of visual processing, which I call “perception,” is theory-neutral and nonconceptual. In this paper, facing the second demand, I argue that a part of the nonconceptual content of perception presents properties that are the properties of mind independent objects. I claim first that nonconceptual content is the appropriate level of analysis of the issue of realism since it avoids the main problems besetting various types of analysis of the issue at the level of beliefs about the world. Then I claim that a subset of the nonconceptual content presents features of objects in the environment as they really are. This paper was mostly written when I was a fellow at the Center of Philosophy of Science in the University of Pittsburgh during the Spring Semester of 2005–2006. A draft of this paper was presented both at the Center’s colloquium and at one of the informal discussion meetings of the fellows. I have very much benefited from the discussion that followed the presentation of the paper and so I would like to thank Gabriele de Anna, Carla Fehr, Malcolm Forster, Lilly Gurova, Nikolay Milkov, and Wang Wei. I am especially indebted to the director of the Center Professor John Norton whose astute comments made me think hard about the issues discussed in the paper. Several of my arguments in Sect. 4 are the result of John’s concerns with the earlier draft of the paper. I would also like to thank the two anonymous reviewers for helping me clarify several points in the paper. Thanks to them (especially the second one) the paper is considerably better than it would have been without them.     

Computational explorations of perceptual symbol systems theory

The aim of this paper is twofold. First, we provide a methodological pathway from theories of situated, embodied cognition to simulations with an eye to empirical evidence, and suggest a possible cross-fertilization between cognitive robotics and psychology. Psychological theories, in particular those formulated at an abstract level, include models which are often severely underspecified at the level of mechanisms. This is true in the synchronic, constructive perspective (how can the effects observed in experiments be concretely generated by the model's mechanisms?) and in the diachronic, developmental perspective (how can such mechanisms be learned and developed?). The synthetic method of artificial cognitive systems research, and in particular of cognitive robotics, can complement research in psychology (and neurosciences) by exploring the constructive and developmental aspects of theories. Our second aim is to provide an example of such a methodology by describing simulations aiming at developing a perceptual symbol system (PSS) (Barsalou, 1999). We then describe the two main theoretical constructs of the PSS, perceptual symbols and simulators, illustrate their development in an artificial system, and test the system in prediction, categorization, and abstraction tasks.     

Bootstrapping the mind: analogical processes and symbol systems

Human cognition is striking in its brilliance and its adaptability. How do we get that way? How do we move from the nearly helpless state of infants to the cognitive proficiency that characterizes adults? In this paper I argue, first, that analogical ability is the key factor in our prodigious capacity, and, second, that possession of a symbol system is crucial to the full expression of analogical ability.     

知觉经验与知觉内容

知觉(perception)是指我们通过视觉、听觉、触觉、嗅觉、味觉等感觉器官而获得的对事物以及外部世界的意识感知.知觉经验(perceptual experience)的一个显著的特点是它具有某种现象特征,即知觉者会体验到一种"那究竟像什么(what it is like)"的感觉.例如,一个人会从红色视觉经验中体验到"红色究竟像什么"的意识感受性(qualia).知觉内容(perceptual content)粗略地讲是指通过知觉经验向知觉者所传递的信息.关于知觉问题在哲学上的重要性,我们可以从以下几点来看:在形而上学方面,知觉是我们了解外部物理世界究竟存在什么的主要手段;在认识论方面,研究知觉是研究我们如何达到关于外部物理世界的知识的主要手段;在语言哲学方面,知觉内容是我们的心灵与外部物理世界的关联及互动在语言实践上的体现;在心灵哲学方面,知觉经验中的现象特征与意识及意向性之间存在着深层的内在联系.     

Perceptual precision

The standard view in philosophy of mind is that the way to understand the difference between perception and misperception is in terms of accuracy. On this view, perception is accurate while misperception is inaccurate. However, there is some evidence (albeit controversial evidence) that perceptual experience actually involves widespread inaccuracy. I add to that evidence in the paper. Then I point toward a way of understanding the difference between perception and misperception, not in terms of accuracy alone, but in terms of precision. That is, I argue that perceptual experience is designed to enable more fine-grained discrimination among the properties that are most useful for action, even if that involves inaccuracy. The view in this paper motivates a new account of illusion, on which illusions are imprecise as well as inaccurate. I call this the Precision Account of Illusion.     

Perceptual Learning

The extent of adult improvement in not only complex but also simple perceptual tasks is remarkable. Although this phenomenon has been noted and studied since the middle of the 19th century, recent advances in the study of brain physiology and anatomy afford new insights. Improvement specificity suggests that changes involve early sensory cortical areas, previously thought to lose their plasticity following the first years. The critical role of selective attention, even in learning the simplest tasks, as well as the precedence of learning easy cases, suggests the involvement of high-level cortical areas. Learning easy cases is more general than learning difficult cases. This pattern suggests the involvement of both high- and low-level areas in an orderly manner, with easy learning beginning at high-level areas and harder cases being resolved by access to low-level areas. The mapping of behavioral findings to underlying brain sites provides a unified framework for this interdisciplinary field.     

Perceptual Particularity

Perception grounds demonstrative reference, yields singular thoughts, and fixes the reference of singular terms. Moreover, perception provides us with knowledge of particulars in our environment and justifies singular thoughts about particulars. How does perception play these cognitive and epistemic roles in our lives? I address this question by exploring the fundamental nature of perceptual experience. I argue that perceptual states are constituted by particulars and discuss epistemic, ontological, psychologistic, and semantic approaches to account for perceptual particularity.     

Perceptual Intuitionism

In the recent metaethical literature there has been significant interest in the prospects for what I am denoting ‘Perceptual Intuitionism’: the view that normal ethical agents can and do have non‐inferential justification for first‐order ethical beliefs by having ethical perceptual experiences, e.g., Cullison 2010, McBrayer 2010, Vayrynen 2008. If true, it promises to constitute an independent a posteriori intuitionist epistemology, providing an alternative to intuitionist accounts which posit a priori intuition and/or emotion as sources of non‐inferentially justified ethical beliefs. As it is formulated, it is plausible that a necessary condition for the view is the truth of Ethical Perception: normal ethical agents can and do have perceptual experiences (at least some of which are veridical) as of the instantiation of ethical properties. In this paper a sophisticated and promising account of Ethical Perception is offered. Extant objections are shown to fail. However, it will be argued that it is far from obvious that the account of Perceptual Intuitionism which emerges constitutes an independent alternative to other intuitionist accounts. This is because we have reason to think that ethical perceptual experience may be epistemically dependent on other epistemic sources, e.g. a priori intuition or emotion.     

Perceptual reasons

The two main theories of perceptual reasons in contemporary epistemology can be called Phenomenalism and Factualism. According to Phenomenalism, perceptual reasons are facts about experiences conceived of as phenomenal states, i.e., states individuated by phenomenal character, by what it’s like to be in them. According to Factualism, perceptual reasons are instead facts about the external objects perceived. The main problem with Factualism is that it struggles with bad cases: cases where perceived objects are not what they appear (illusions, broadly speaking) or where there is no perceived object at all (hallucinations). The main problem with Phenomenalism is that it struggles with good cases: cases where everything is perfectly normal and the external object is correctly perceived, so that one’s perceptual beliefs are knowledge. In this paper we show that there is a theory of perceptual reasons that avoids the problems for Factualism and Phenomenalism. We call this view Propositionalism. We use ‘proposition’ broadly to mean the entities that are contents of beliefs and other doxastic attitudes. The key to finding a middle ground between Phenomenalism and Factualism, we claim, is to allow our reasons to be false in bad cases. Despite being false, they are about the external world, not our phenomenal states.