Locke's theory of classification

In §155 of his New Theory of Vision Berkeley explains that a hypothetical ‘unbodied spirit’ ‘cannot comprehend the manner wherein geometers describe a right line or circle’.1 ¹All references to Berkeley are from, A. A. Luce and T. E. Jessop (eds.), The Works of George Berkeley, Bishop of Cloyne (London: Thomas Nelson and Sons, Ltd., 1948) The following abbreviations are used: An Essay Towards A New Theory of Vision, section x = New Theory x; Philosophical Commentaries, entry x = Commentaries x; Part I of A Treatise concerning the Principles of Knowledge, section x = Principles x. All other references to Berkeley's works are of the form The Works of George Berkeley, Bishop of Cloyne, volume x, page y = Works, x, y. The reason for this, Berkeley continues, is that ‘the rule and compass with their use being things of which it is impossible he should have any notion.’ This reference to geometrical tools has led virtually all commentators to conclude that at least one reason why the unbodied spirit cannot have knowledge of plane geometry is because it cannot manipulate a ruler or a compass. In this article I will show that such an interpretation is flawed. I will instead argue that Berkeley's understanding of Euclidian geometry was based on Isaac Barrow's account of the foundations of geometry. On this view geometrical objects are conceived in terms of the idealized motion that generates the objects of geometry. Consequently, that what the unbodied spirit cannot do in this context is to form an idea of motion rather than being unable to handle geometrical tools.     

Perception of the motion trajectory of objects from moving cast shadows in infant Japanese macaques (Macaca fuscata)

The shadows cast by moving objects enable human adults and infants to infer the motion trajectories of objects. Nonhuman animals must also be able to discriminate between objects and their shadows and infer the spatial layout of objects from cast shadows. However, the evolutionary and comparative developmental origins of sensitivity to cast shadows have not been investigated. In this study, we used a familiarity/novelty preferential looking procedure to assess the ability of infant macaques, aged 7–24 weeks, to discriminate between a ‘depth’ display containing a ball and cast shadow moving diagonally and an ‘up’ display containing a ball with a diagonal trajectory and a shadow with a horizontal trajectory. The infant macaques could discriminate the trajectories of the balls based on the moving shadows. These findings suggest that the ability to perceive the motion trajectory of an object from the moving shadow is common to both humans and macaques.     

The ad hominem argument of Berkeley’s Analyst

This paper responds to two issues in interpreting George Berkeley’s Analyst. First, it explains why the text contains no discussion of religious mysteries or points of faith, despite the claims of the text's subtitle; I argue that the subtitle must be understood, and its success assessed, in conjunction with material external to the text. Second, it’s unclear how naturally the arguments of the Analyst sit with Berkeley’s broader views. He criticizes the methodology of calculus and conceptually problematic entities, and the extent to which they require one to bend the rules of classical mathematics. Yet, elsewhere, Berkeley’s opinion of classical mathematics and its intelligibility is low, and he defends a pragmatic approach to word meaning that should not find fault with so functionally successful a theory. The ad hominem intention of the text makes it difficult to discern to what extent Berkeley is committed to the sincerity of these criticisms. This component of the text is rarely discussed, but I argue that when trying to decide what Berkeley’s true position is in the Analyst, we should treat its ad hominem component as its primary intention.     

Plato’s Cave

Abstract

Current interpretations of Plato’s cave are obviously incorrect because they do not explain how what we hear does not come from what we see. I argue that Plato is saying that the colors we receive from our faculty of vision do not cause the sounds that we receive from our faculty of hearing. I also show how we do not see ourselves or one other, how the shadows on the wall of the cave are images of that which casts them and therefore have less reality than them, and how the cave illustrates the divided line’s concern for the relationship between Forms and visible reality. The paper is structured around the two great riddles of the divided line: how Forms can be more real than everyday objects, and how one can know the unhypothesized beginning with complete certainty. I further argue that the puppets that cast shadows stand for the immanent Forms of the Phaedo and also for the moving Forms of the Timaeus. That of which these puppets are themselves images would thus stand for the Forms as they are in themselves of the Phaedo or the indestructible Forms of the Timaeus.     

The Role of Strategy in Mixed-Gender Group Interactions: A Study of the Television Show “The Weakest Link”

This paper studies mixed-gender group interactions in a strategic game where group members are sequentially eliminated till a single winner takes all. Study 1 tests the hypothesis that female contestants are retained till final rounds where they are eliminated. Using observational data from the US television show The Weakest Link (20 shows), results show that females are finalists but not winners. In a laboratory study (Study 2, 67 Berkeley undergraduates), we show that this effect is attenuated when winnings are shared among finalists (versus one winner takes all) due to the reduction in competitive pressures in the context. This research was supported in part by the Junior Faculty Research Grant awarded by the University of California at Berkeley to the second author.     

The role of effort in perceiving distance

Berkeley proposed that space is perceived in terms of effort. Consistent with his proposal, the present studies show that perceived egocentric distance increases when people are encumbered by wearing a heavy backpack or have completed a visual-motor adaptation that reduces the anticipated optic flow coinciding with walking effort. In accord with Berkeley's proposal and Gibson's theory of affordances, these studies show that the perception of spatial layout is influenced by locomotor effort.     

Use of interreflection and shadow for surface contact

The interaction of light with surfaces results in a number of lighting effects that may serve as valuable visual cues. Previous research on shadows has shown them to be effective in determining the three-dimensional (3-D) layout of a scene, but interreflections have been ignored as cues for spatial layout. Interreflections as well as shadows may help to disambiguate the 3-D layout of objects by providing information about an object's contact with a surface. We generated computer images of a box on an extended textured ground plane that was either in contact with the ground or was slightly above the ground. Images were rendered for four conditions: (1) no shadow + no interreflection, (2) shadow only, (3) interreflection only, and (4) shadow + interreflection. A photometrically incorrect condition was also included. The participants rated the degree of contact for each image on a scale, which was used to generate receiver operating characteristic (ROC) curves and a measure of sensitivity. In the images with no shadows or interreflections, the participants performed at chance levels. Interreflections, shadows, and a combination of interreflections and shadows all resulted in high sensitivity for judging object contact. More important, information from shadows and interreflections can be combined, resulting in near-perfect judgment of surface contact. Interreflections and shadows can be effective cues for object contact.     

Invariant recognition of natural objects in the presence of shadows

Shadows are frequently present when we recognize natural objects, but it is unclear whether they help or hinder recognition. Shadows could improve recognition by providing information about illumination and 3-D surface shape, or impair recognition by introducing spurious contours that are confused with object boundaries. In three experiments, we explored the effect of shadows on recognition of natural objects. The stimuli were digitized photographs of fruits and vegetables displayed with or without shadows. In experiment 1, we evaluated the effects of shadows, color, and image resolution on naming latency and accuracy. Performance was not affected by the presence of shadows, even for gray-scale, blurry images, where shadows are difficult to identify. In experiment 2, we explored recognition of two-tone images of the same objects. In these images, shadow edges are difficult to distinguish from object and surface edges because all edges are defined by a luminance boundary. Shadows impaired performance, but only in the early trials. In experiment 3, we examined whether shadows have a stronger impact when exposure time is limited, allowing little time for processing shadows; no effect of shadows was found. These studies show that recognition of natural objects is highly invariant to the complex luminance patterns caused by shadows.     

Is Shepherd's pen mightier than Berkeley's word?

In 1827, Lady Mary Shepherd published Essays on the Perception of an External Universe, which offers both an argument for the existence of a world of external bodies existing outside our minds and a criticism of Berkeley's argument for idealism in A Treatise Concerning the Principles of Human Knowledge. In this paper, I evaluate Margaret Atherton's criticisms of Shepherd's case against Berkeley, and provide reasons for thinking that, although Shepherd's particular criticisms of Berkeley do not succeed, she correctly identifies an important problem to which Berkeley's reasoning is subject.     

Shadows as sources of cues for distance of shadow-casting objects

Shadows are neglected sources of information about shadow-casting objects' distance (location). In an experiment using real shadows, participants judged the distance of two rods, either with shadows (illumination from the left) or without shadows. Without shadows, a thin rod raised slightly above the surface was incorrectly judged to be more distant than a thick rod, but with shadows the thin rod was accurately judged to be closer. For judgments to be correct, shadows had to overwhelm competing height and stimulus-size cues. Exp. II involved nonoverlapping shadows produced by a light placed in front of the rods. Again, without shadows the thin-elevated rod was incorrectly judged to be more distant, but with shadows it was correctly judged to be closer. Exp. III involved two sets of thick and thin elevated rods and frontal lighting. Judgments were accurate when shadows were present but inaccurate when shadows were absent. Experiments conducted through the American Psychological Society Web-research site replicated results of Exp. I, II, and III. A final Web experiment replicated results of the others, but with shadows produced by illumination from the right. Three properties of shadows--angles, interposition, and positioning--are possible sources of distance information associated with cast shadows.     

The shadow knows: a primer on the informational structure of cast shadows

I list relevant properties of cast shadows that the visual system could exploit (although it may not exploit). The study concerns the various types of information that can be extracted from shadows by systems that are significantly like ours (including embodied artificial systems) in an environment that is significantly like ours.     

Neural Synchrony and the Causal Efficacy of Consciousness

The purpose of this paper is to address a well-known dilemma for physicalism. If mental properties are type identical to physical properties, then their causal efficacy is secure, but at the cost of ruling out mentality in creatures very different to ourselves. On the other hand, if mental properties are multiply realizable, then all kinds of creatures can instantiate them, but then they seem to be causally redundant. The causal exclusion problem depends on the widely held principle that realized properties inherit their causal powers from their realizers. While this principle holds for functional realization, it fails on a broader notion of realization that permits the realization of complex qualitative properties such as spatial and temporal patterns. Such properties are best seen as dependent powerful qualities, which have their causal roles in virtue of being the qualities they are, and do not inherit powers from their realizers. Recent studies have identified one such property—neural synchrony—as a correlate of consciousness. If synchrony is also partially constitutive of consciousness, then phenomenal properties are both multiply realizable and causally novel. I outline a version of representationalism about consciousness on which this constitution claim holds.

     

Sumner On Desires and Well-Being

Berkeley holds that objects in the world are constituted of ideas. Some commentators argue that for Berkeley, ideas are identical to acts of perception; this is taken to proceed from his view that ideas are like pains. In this paper, I evaluate the identity claim. I argue that although it does not follow from the pain analogy, nonetheless the texts suggest that Berkeley does think ideas and acts are identical. I show how Berkeley can account for objects persisting over time and being perceivable by multiple observers, even if the ideas that constitute them are intermittent and dependent on particular actors.     

Cast shadows in wide perspective

We investigated the apparent spatial layout of cast shadows up to very wide fields of view. We presented up to 130 degrees wide images in which two 'flat poles' were standing on a green lawn under a cloudless blue sky on a sunny day. The poles threw sharp cast shadows on the green, of which one was fixed. The observer's task was to adjust the azimuth of the shadow of the other pole such that it fitted the scene. The source elevation was kept constant. The two cast shadows are, of course, parallel in physical space, but generically not in the picture plane because of the wide perspective. We found that observers made huge systematic errors, indicating that, generically, they fail to account for these perspective effects. The systematic deviations could be well described by a weighted linear combination of the directions in the picture plane and in the physical space, with weights that depended on the positions of, and distance between, the poles.     

Something-We-Know-Not-What,Something-We-Know-Not-Why: Berkeley,Meaning and Minds

It is sometimes suggested that Berkeley adheres to an empirical criterion of meaning, on which a term is meaningful just in case it signifies an idea (i.e., an immediate object of perceptual experience). This criterion is thought to underlie his rejection of the term ‘matter’ as meaningless. As is well known, Berkeley thinks that it is impossible to perceive matter. If one cannot perceive matter, then, per Berkeley, one can have no idea of it; if one can have no idea of it, then one cannot speak meaningfully of it. But if this is Berkeley’s position, then there is a puzzle, because Berkeley also explicitly claims that it is impossible to perceive/have ideas of minds. So if he is relying on a criterion on which terms get their meaning by referring to ideas, then, just as Berkeley rejects talk of material substance, so, too, must he reject talk of mental substance. Famously, however, Berkeley insists that there is no parity between the cases of material and mental substance. It is typically suggested that the disparity between matter and minds rests on the fact that although one cannot strictly speaking perceive minds, nonetheless Berkeley thinks that one can have experiential access to minds via reflection, and that this access allows for meaningful talk of minds. Of course, one can only have reflective experience of one’s own mind. But what of other minds, which one cannot reflectively experience? Here the usual tactic is to suppose that, although one cannot have direct reflective experience of other minds, nonetheless one can indirectly experience such minds via analogy to our own minds, and that this indirect experience grounds the meaningfulness of talk of other minds. In this paper, I argue that the reasoning behind Berkeley’s ‘likeness principle,’ that an idea can only be like another idea, can be generalized to argue against this experience-based account of our access to other minds. I claim instead that Berkeley allows for the meaningfulness of talk of other minds by expanding the criterion of meaning in a different way. I argue that Berkeley holds a criterion of meaning on which a term is meaningful just in case it signifies either an object of experience or an object that one has reason to posit on the basis of experience, i.e., an object that is necessary to explain our experiences. When an object is neither experienced nor explains our experiences, then and only then is Berkeley willing to reject it as meaningless. Thus he writes of “the word matter,” that “it is no matter whether there is such a thing or no, since it no way concerns us: and I do not see the advantage there is in disputing about we know not what, and we know not why” (Principles, §77.) The word is not meaningless merely because we do not know what matter might be; it is meaningless because we also do not know why it should be. Correspondingly, I argue that the term ‘mind’ is meaningful because although we have no experience of minds, nonetheless they play an important role in explaining our experiences.     

Rapid processing of cast and attached shadows

We used a visual-search method to investigate the role of shadows in the rapid discrimination of scene properties. Targets and distractors were light or dark 2-D crescents of identical shape and size, on a mid-grey background. From the dark stimuli, illusory 3-D shapes can be created by blurring one arc of the crescent. If the inner arc is blurred, the stimulus is perceived as a curved surface with attached shadow. If the outer arc is blurred, the stimulus is perceived as a flat surface casting a shadow. In a series of five experiments, we used this simple stimulus to map out the shadow properties that the human visual system can rapidly detect and discriminate. To subtract out 2-D image factors, we compared search performance for dark-shadow stimuli with performance for light-shadow stimuli which generally do not elicit strong 3-D percepts. We found that the human visual system is capable of rapid discrimination based upon a number of different shadow properties, including the type of the shadow (cast or attached), the direction of the shadow, and the displacement of the shadow. While it is clear that shadows are not simply discounted in rapid search, it is unclear at this stage whether rapid discrimination is acting upon shadows per se or upon representations of 3-D object shape and position elicited by perceived shadows.     

Action in perception? Empirical and philosophical arguments against the enactive approach to perception

This paper focuses on the epistemic conditions of visual perception, ie it concentrates on the question of what kind of knowledge is required for us in order to be able to see colours and shapes as spatial properties of things. According to contemporary theories of sensory perception that follow the tradition of George Berkeley, like Alva Noe's so-called enactive approach to perception, this type of visual perception requires a certain kind of implicit practical knowledge, namely implicit sensorimotor knowledge of the way sensory stimulation varies as the perceiver moves. Two objections are presented against this central claim of the enactive approach. First, empirical evidence from psychological research on children's cognitive and motor development suggests that visual content is entirely independent of sensorimotor knowledge. Second, the enactive approach gets involved in the characteristic problems of classical sense--datum theories by introducing the extremely problematic claim that the recognition of appearances is the epistemic starting point for the perception of things and their properties.     

Distinguishing the Senses

Seeing, hearing and touching are phenomenally different, even if we are detecting the same spatial properties with each sense. This presents a prima facie problem for intentionalism, the theory that phenomenal character supervenes on representational content. The paper reviews some attempts to resolve this problem, and then looks in detail at Peter Carruthers' recent proposal that the senses can be individuated by the way in which they represent spatial properties and incorporate time. This proposal is shown to be ineffective in distinguishing auditory from either visual or tactual perception, and substantial classes of visual and tactual perceptions are found that the posited spatial and temporal features fail to individuate.