Online research in philosophy

Marr (1982) may have been one of the first vision researchers to insist that in modeling vision it is important to separate the location of visual features from their type. He argued that in early stages of visual processing there must be “place tokens” that enable subsequent stages of the visual system to treat locations independent of what specific feature type was at that location. Thus, in certain respects a collinear array of diverse features could still be perceived as a line, and under certain conditions could function as such in perceptual phenomena like the Poggendorf illusion.

The specialization of visual function within biological function is reason for introducing “homology thinking” into explanations of the visual system. It is argued that such specialization arises when organisms evolve by differentiation from their predecessors. Thus, it is essentially historical, and visual function should be regarded as a lineage property. The colour vision of birds and mammals do not function the same way as one another, on this account, because each is an adaptation to special needs of the visual functions of predecessors—very different kinds of predecessors in each case. Thus, history underlies function. We also see how homology thinking figures in the hierarchical classification of visual systems, and how it supports the explanation of visual function by functional role analysis.

Sensory classification is a central theme of Mohan Matthen's wonderful book, Seeing, Doing, and Knowing. ( All page references are to Matthen 2005 unless otherwise indicated.) My plan for this commentary is simple: I shall list a series of claims that Matthen makes about the classes involved in sensory classification. Each member of the series is admirable, and seems credible on its own. The question at the end is whether we can hold them all, together.

When I act on something, three kinds of idea (or representation) come into play. First, I have a non-visual representation of my goals. Second, I have a visual description of the kind of thing that I must act upon in order to satisfy my goals. Finally, I have an egocentric position locator that enables my body to interact with the object. It is argued here that these ideas are distinct. It is also argued that the egocentric position locator functions in the same way as a demonstrative, and that the involvement of such demonstratives in visual content negates naive realism. (This is a nearly final draft of a paper that is to be published in Raftopoulos and Machamer (eds), Perception, Realism, and the Problem of Reference (forthcoming from Cambridge UP. It is a shorter revised version of "Visual Reference", posted earlier.).

Ross argues that the location problem for color-the problem of how it is represented as occupying a particular location in space-constitutes an objection to color subjectivism. There are two ways in which the location problem can be interpreted. First, it can be read as a why-question about the relation of visual experience to the environment represented: Why does visual experience represent a patch of color as located in this part of space rather than that? On this interpretation, the subjectivist can answer Ross's objection by appealing to the physical location of reflectance rather than color. Second, it can be read as a how-question about visual representation itself: How does visual experience put together the experience of a color with the experience of its being located in space? This version makes the location problem a problem about visual experience itself and renders the ontology of color irrelevant to its solution. The location problem is thus no more a problem for the color subjectivist than for the color realist.

My aim in this paper is to critically evaluate John Campbell's (2002) characterization of the sense of demonstrative terms and his account of why an object's location matters in our understanding of perceptually-based demonstrative terms. Campbell thinks that the senses of a demonstrative term are the different ways of consciously attending to an object. I will evaluate Campbell's account of sense by exploring and comparing two scenarios in which the actual location of a seen object is different from its perceived location. I do this in order to motivate the following point: Campbell's characterization of the sense of a demonstrative term turns sense into a psychologistic notion. As a consequence of this, it is difficult to see how sense could underwrite reference. In short, I shall be arguing that Campbell's account of the ways of perceiving an object is simply inadequate as an account of the Fregean notion of sense, according to which the senses of a demonstrative term are the different ways of thinking about an object.

I examine John Campbell’s claim that the determination of the reference of a perceptual demonstrative requires conscious visual object-based selective attention. I argue that although Campbell’s claim to the effect that, first, a complex binding parameter is needed to establish the referent of a perceptual demonstrative, and, second, that this referent is determined independently of, and before, the application of sortals is correct, this binding parameter does not require object-based attention for its construction. If object-based attention were indeed required then the determination of the referent would necessarily involve the application of sortal concepts, since object-based attention initiates top-down cognitive effects on visual processing. I also examine Mohan Matthen’s claim that reference to objects is established only through the visual processing in the dorsal visual stream and argue that although it is true that processing in the dorsal stream can determine reference, a thesis that goes against Campbell’s view that the determination of the referent requires conscious attention, processing along the ventral visual stream can also establish the reference of perceptual demonstratives. It also claim that Matthen’s account of dorsal processing underestimates the kind of information processed along the dorsal stream and this has some implications regarding perceptual demonstratives reference fixing.

John Campbell argues that visual attention to objects is the means by which we can refer to objects, and that this is so because conscious visual attention enables us to retrieve information about a location. It is argued here that while Campbell is right to think that we visually attend to objects, he does not give us sufficient ground for thinking that consciousness is involved, and is wrong to assign an intermediary role to location. Campbell’s view on sortals is also queried, as is his espousal of the so-called Referential View of Experience.