Keith Allen

Hallucination And Imagination

What are hallucinations? A common view in the philosophical literature is that hallucinations are degenerate kinds of perceptual experience. I argue instead that hallucinations are degenerate kinds of sensory imagination. As well as providing a good account of many actual cases of hallucination, the view that hallucination is a kind of imagination represents a promising account of hallucination from the perspective of a disjunctivist theory of perception like naïve realism. This is because it provides a way of giving a positive characterisation of hallucination—rather than characterising hallucinations in negative, relational, terms as mental events that are subjectively indistinguishable from veridical perceptual experiences.

Locke and Sensitive Knowledge

This papers considers the well-known tension between Locke’s definition of knowledge and his claim that we can know by sensation of the existence of things without the mind. I argue (in response to recent suggestions by Rickless and Newman) that sensitive knowledge is knowledge (and Knowledge with a capital ‘K’). I then present an account of sensitive knowledge that is consistent with Locke’s definition of knowledge, which gives a central role to the reflective idea of sensation. I conclude by considering whether Locke’s general epistemological framework leads inevitably to scepticism or idealism, arguing that Locke’s response to the sceptic is more interesting--and more robust--than it might initially appear.

Colour Physicalism, Naïve Realism, and the Argument from Structure

Colours appear to instantiate a number of structural properties: for instance, they stand in distinctive relations of similarity and difference, and admit of a fundamental distinction into unique and binary. Accounting for these structural properties is often taken to present a serious problem for physicalist theories of colour. This paper argues that a prominent attempt by Byrne and Hilbert (Behav Brain Sci 26:3–21, 2003) to account for the structural properties of the colours, consistent with the claim that colours are types of surface spectral reflectance, is unsuccessful. Instead, it is suggested that a better account of the structural properties of the colours is provided by a form of non-reductive physicalism about colour: a naïve realist theory of colour, according to which colours are superficial mind-independent properties.

Mechanism, resemblance and secondary qualities: From Descartes to Locke

the Democritick and Epicurean Atheists . . . acknowledge no other Modes of Matter or Body, but only more or lessMagnitude of Parts, Figure, Site,Motion or Rest. And upon this very account do they explode Qualities, considered as Entities really distinct from these Modes; because in the Generation and Alteration of them, there would be Real Entities made Out of Nothing, or without a Cause; whereupon they Resolve these Qualities into Mechanism and Fancy. Cudworth (1678: 755).

Locke and the Nature of Ideas

Abstract What, according to Locke, are ideas? I argue that Locke does not give an account of the nature of ideas. In the Essay, the question is simply set to one side, as recommended by the “Historical, plain Method” that Locke employs. This is exemplified by his characterization of ‘ideas’ in E I.i.8, and the discussion of the inverted spectrum hypothesis in E II.xxxii. In this respect, Lockes attitude towards the nature of ideas in the Essay is reminiscent of Boyles diffident attitude towards the nature of matter. In posthumously published work, however, Locke suggests that the enquiry into the nature of ideas is one of the things that the enquiry into the extent of human knowledge undertaken in the Essay actually shows to lie beyond the “compass of human understanding”. In this respect, Lockes attitude towards the nature of ideas is reminiscent of Sydenhams attitude towards the nature of diseases.

The nature of shape constancy mechanisms as revealed by shape priming

Five shape priming experiments are reported in which the target was either a five- or six-sided line-drawn figure and participants made a speeded two-alternative forced-choice judgment about the targets number of sides. On priming trials, the target was preceded by a briefly presented smaller line figure (the prime) and performance on these trials was gauged relative to a no-prime condition. In the first two experiments, primes were rendered invisible by the presentation of a backwards visual noise mask, respectively for a short (∼40 ms) or long duration (∼93 ms). No reliable priming effects arose under masked conditions. When these experiments were repeated without the mask, participants were speeded when the prime and target were related by a rigid through-the-plane rotation but not when the prime was a nonrigid, stretched version of the target. The same pattern of priming effects arose when, in a final experiment, novel irregular shapes were used. Collectively, the data reveal the operation of shape constancy mechanisms that are particularly sensitive to shape rigidity. The findings suggest that the visual system attempts to secure a correspondence between the rapid and successive presentations of the prime and the target by matching shapes according to a rigidity constraint.