Research Projects

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    Spatial Perception

    How do we perceive space and spatial relations?

    Some of our senses provide us with perception that is of the extended space around us. We don't just see redness, but we see a red circle, and we see it as located at a specific place in space. Not all our senses do this. We can hear sounds, for example, that we cannot locate. We hear a pitch at a volume, but we don't hear it as being of any spatial shape, or as being located anywhere in space. Sensory substitution devices, which for example can help blind people to "see" with their ears or tongue, illustrate the issue and point in the direction of the solution.

    In a number of publications I have argued, following Gareth Evans, that the key to spatial perception is the connection between sensation and action. To perceive something as located somewhere in space is to have the relevant sensory episodes dispose certain kinds of action. I should stress that though the bumper-sticker version of the view is not uncommon, my own theory is quite different from other theories that posit a connection between spatial perception and behavioral action.

    The best current expression of my view can be found in Skill Theory v2.0: Dispositions, Emulation and Spatial Perception , where I explain the view, describe how it is implemented neurally, and explain in detail how it differs significantly from the enactive theory of spatial perception.

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    Temporal Perception

    How do we perceive temporally extended events?

    Our perception is not merely of states of the environment (the ball's being red, or whatever), but of processes that unfold in time. I might be able to infer that the hour hand of the clock is moving, but with the second hand I need not engage in any inference. I can simply see that it is moving. My perception makes the motion apparent. But motion can take place only over a temporal interval. So our perception spans temporal intervals.

    But how can it do this? I have argued that our perceptual system presents to us at any time not just a snapshot of the state of the environment, but rather an actively constructed interpretation of about 200 milliseconds' worth of environmental motion and trajectory; about 100 milliseconds worth of representation of the past along with about 100 milliseconds' worth of prediction concerning what will happen in the immediate future.

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    What do the expressions 'this' and 'that' mean?

    All natural languages have demonstratives. In English the demonstrative system includes 'this', 'that', 'these', 'those', and a few others. Most languages have a much richer demonstrative system than English. I believe that analyses of the meaning of demonstratives, in both the philosophical and linguistics literature, is misguided. The philosophical literature has been stymied by a myopic focus on English, which has an unusually thin demonstrative system -- thin enough that it suggests some superficial semantic analyses. The literature in linguistics is better, but has been garden-pathed by a few ideas, namely, the proximal/distal distinction (and related extensions), and a narrow sense of accessibility.

    Contrary to received wisdom, I have argued (along with co-author Amanda Brovold) that the proximal/distal distinction is a symptom of a deeper phenomenon, namely control. In Brovold and Grush (2012) we offer an analysis of the semantics of demonstrative expressions that is adequate cross-linguistically, explains what is correct about previous accounts, and offers a unified account of exophoric and endophoric demonstrative anaphora. Get the paper here: Towards an (improved) interdisciplinary investigation of demonstrative reference. This is an ongoing project, more publications are in the works.

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    Mental representation

    How do our brains represent the world in perception and thought?

    The brain represents the environment, both in perception, and in, so to speak, off-line thought. While this is not entirely uncontroversial -- anti-representationalism is coming back in vogue these days -- it is true nevertheless. But it raises some serious questions. What are representations? How does the brain represent?

    Our understanding of representation generally is informed by two dominant metaphors: representation and linguistic, and representation and pictorial. And the philosophical and scientific literatures have seen both of these metaphors pressed into service in understanding the brain's representational function. But another metaphor is available, even if it is much less common: models.

    In a series of publications, beginning with my PhD dissertation in 1995, I have argued that the most fruitful way to understand how the brain constructs and uses representations is by seeing the brain as in the business of constructing and using internal models of what it is representing: the body, the environment, or whatever. Probably the most definitive expression of this view is in my 2004 BBS article The Emulation Theory of Representation: Motor Control, Imagery, and Perception

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    Group Minds

    When might it be correct to say that a single mind is implemented by a group of people (or other beings)?

    The most common examples we have of minds are human minds, and generally speaking there is one mind per skull. Even extended mind theorists will generally have the same number of minds as skulls, despite the fact that they may argue that the relevant mind is not entirely located inside that skull. But could there be situations in which a single mind is implemented in a group? Science fiction has a few good examples, including the Borg from Star Trek (Next Generation), and the Tines from Vernor Vinge's amazingly excellent A Fire Upon the Deep.

    Science fiction aside, there are suggestive examples from science fact, namely, social insects. While the super-organism hypothesis to the effect that the colony (of bees, ants, termites) is the unit of selection might be controversial, this is distinct from the hypothesis that we can treat the colony as a single cognitive system. The idea would be that perhaps it is most fruitful to see the colony or hive itself as the thing which perceives, moves, decides, attacks, defends.

    Aside from being an interesting theoretical idea, the hypothesis can serve as a test case for various theories of mind -- before you know whether a mind can be implemented in a group, you have to have some idea of what a mind is. It also interacts interestingly with some issues in ethics, namely corporate responsibility. Can it ever be the case that a corporate entity (a corporation, club, government) can be a responsible agent even apart from any responsibility borne by any or all of its members? This question hinges in part on whether the corporate is correctly analyzed as being itself an agent.

    I have taught graduate seminars on group minds, and given a few invited talks on the topic as well. But so far no published work on this topic. Yet.

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    Gareth Evans

    Understanding the work of one of the 20th Century's greatest philosophers.

    Gareth Evans' book The Varieties of Reference is one of the great philosophy books of the 20th Century. It constructs a systematic position that provides novel and powerful theories on a staggering variety of philosophical topics, including demonstratives, proper names, self-reference, objectivity, and spatial representation.

    Evans' work has been a major inspiration for several main lines of my own work, most notably my views on spatial representation, which are essentially a more detailed and version of Evans' account, together with a story about neural implementation. Several of my papers provide analyses of aspects of Evans' work, including Evans on spatial representation in Skill Theory v2.0: Dispositions, Emulation and Spatial Perception , Evans on demonstratives in Brovold and Grush (2012), and Evans on identification-freedom (a version of immunity to error through misidentification) in Evans on Identification Freedom. In addition, I have a Guide to Gareth Evans' _Varieties of Reference_. This is a chapter-by-chapter walk-through and explanation of the book, which hopefully will help make this fantastic but sometimes difficult and misunderstood work more accessible.

    Finally, a number of inaccurate interpretations of Evans' work have been circulating in the philosophical literature, and I am working on an exegetical piece that calls them out and clarifies Evans' actual views.