My research concerns the nature of the mind and its physical implementation
in the brain. These questions are less commonly addressed that you might think.
Psychology, for example, ignores the question. Work in psychology and cognitice
science focuses on the study of things that minds can do, such as language,
color vision, short term memory. But to the question 'what is a mind?' nothing
is said. Note that blind people don't lack a mind, and so color vision, or
even vision tout court, cannot be necessary for being a mind. And if our short
term memory were reduced to 1 item, or increased to 200, we would still have
a mind, though with different abilities. What, if anything, are the essential
components of having a mind, and why? This is one of the main questions driving
my research. The other related area, concerns how a mind, understood via investigations
of the sort I have just described, can be implemented in neural tissue. This
involves me in an embarrassingly large number of areas, including philosophy
of representation, the nature of objective representation, and theoretical
cognitive neuroscience. In addition to these primary interests, I have significant
interests in language, in particular the semantics of demonstratives and indexicals,
and certain 'syntactic' phenomena, such as island constraints. It may come
as some surprise that these are all intimately inter-related in my work. I
discuss each of these and their connections below.
Objectivity. My account of what minds are has centered on
the idea that a mind is something capable of objective thought. This
of course invites the question, what is objective thought? We don't simply,
as the proverbial ostrich does, think that the world stops and ends with our
experience. Rather, we conceive of our experience as objective -- that is,
as experience of a world whose existence is independent of us and our experience.
This feature of our experience was first systematically explored by Kant, and
was developed in detail by P.F. Strawson and his student Gareth Evans. The
common idea (which represents something of a departure from the bulk of the
apparatus Kant brought to bear on the issue) is that it is via our ability
to represent space that we can conceive of objects existing independently of
us: that there are places where those objects are experiencable, but that those
are places where I am not now stationed, to paraphrase Strawson's formulation.
Evans expanded on this, showing how the idea of an objective world depends
on superimposing one's egocentric space on an objective spatial map. I develop
this idea, both via the skill theory of egocentric space (discussed below),
and also via an account of what an 'objective spatial map' amounts to. I argue
that this objective map is best conceived of as an off-line or imaginary view
of some spatial realm from a different vantage point (typically but not always
one within which one is actually located, such as a view from a city from high
above, within which one's own actual location is specified via something like
a 'you are here' arrow). By running an off-line 'emulation' (see below) of
egocentric space, one can generate a conception of space that is independent
of one's actual behavioral exigencies. I argue that mechanisms such as these
can account for the objectivity of our experience, the fact that we conceive
of our experience as experience of things that exist independently of us and
our experience. (For more on my account of objectivity, see Grush (2000). Self,
world and space. Brain and Mind 1(1):59-92. [PDF], though I should point out
that while I still largely agree with everything I said in that paper, I think
there are some mistakes in it.)
Below I discuss various of the components involved in this account of objective
thought.
Emulation theory of representation. Objective thought is a
special sort of representation, and accordingly much of my work has focused
on developing an account of how it is that a physical thing, such as the brain,
can represent other things. My doctoral dissertation (UCSD 1995 [PDF]) developed
and defended the idea that the brain represents 'external' things, such as
the body and the environment, by constructing, maintaining, and using inner
models of these entities. This basic idea has been around a while, but I tried
to make it somewhat precise by exploiting constructs from control theory, specifically
forward models -- which I call emulators. These control theory-inspired ideas
are now commonplace in philosophy, psychology, and cognitive neuroscience,
but in the early 90s it was anything but commonplace, and indeed much of my
work involved trying to get researchers outside of motor control to accept
the ideas. Forward models are devices that mimic the input-output function
of some other entity. For example, I argued, following some researchers in
motor physiology, that certain structures in the cerebellum and brain stem
act as emulators of the musculoskeletal system. This emulator receives efferent
copies of the motor signal sent to the body and produces as output a prediction
of the proprioceptive signal that the body will produce when it executes that
motor command. I showed how such an emulator not only can aid fast goal-directed
movements, but also how, if run off-line, it can produce 'motor imagery', and
might even account for phantom limb phenomena. Similarly, the brain can construct
inner models of the motor-visual loop, in order not only to anticipate, on
the basis of what is currently seen and what motor actions one executes, what
the next visual stimulus will be (for example, if I am looking at a circle
and issue a saccade to the left, what I will see next is a circle slightly
farther to the right on my retina), but in addition I argued that these mechanisms
can account for visual imagery.
More generally, I have
made the claim, and tried to argue, that these mechanisms are responsible
for internal representation generally: not only for inner imagery, but that
such models can be used for planning, and even for perception (via their
employment in a tuned filter). I have argued that this account of representation
is superior to more standard philosophical accounts -- which typically center
on information or causal covariation -- both philosophically and neurobiologically.
For more on the emulation theory of representation, see Grush, Rick (1995).
Emulation and Cognition. PhD. Dissertation, University of California,
San Diego. UMI [PDF], especially
chapters 2 and 3; Grush, Rick (1997a) The architecture of representation. Philosophical
Psychology 10(1):5-25 [PDF];
Grush, Rick (1998), and Grush,
Rick (2004). The emulation theory of representation: motor control, imagery,
and perception. Behavioral and Brain Sciences 27(3):377-396. [PDF].)
Initially much of my work was both a philosophical and scientific presentationa
and defense of these ideas. Fortunately, in the last decade or so, the idea
of forward models has caught on in philosophical and the relevant scientific
circles, and so I have moved on to expanding the basic idea in a variety of
ways.
Spatial and Temporal Representation. Representation is not sufficient
for objective thought. On the Kant-Strawson-Evans line, various kinds of spatial
representation are also needed. One question, mostly philosophical, concerns
what it means to represent space at all. I have done historical work on this
issue (e.g. Grush, Rick (2007). Berkeley and the spatiality of vision. Journal
of the History of Philosophy 45(3):413-442 [PDF])
and also developed the skill theory of spatial perception (e.g. Grush, Rick
(1998) Skill and spatial content. Electronic Journal of Analytic Philosophy
6(6) [HTML], and Grush, Rick
(2007). Skill Theory v2.0: Dispositions, emulation, and the spatiality of perception.
Synthese 159(3):389-416. [PDF])
The theory has since been picked up by many researchers, but I recently realized
that my own earlier formulations, and those of other researchers in the field
(including Alva Noe) were confused and inadequate, and this led me to what
I believe is the correct account of the skill theory of spatial content, which
I published in 'Skill Theory 2.0', cited above.
I also came to see that what is important is not just spatial representation,
but spatiotemporal representation. Accordingly I have explored temporal representation
both in a philosophical context (e.g. Grush, Rick (2005). Brain time and phenomenological
time. In Brook and Akins eds. Cognition and the Brain: The Philosophy and
Neuroscience Movement. Cambridge: Cambridge University Press [PDF],
Grush, Rick (2007). Time and experience. In Thomas Müller (ed.), The
Philosophy of Time, Frankfurt: Klosterman [PDF]),
and also a scientific one. One significant outcome of this was an article,
co-authored with Holly Andersen, sketching the history of the specious present
doctrine and Husserl's phenomenology of time consciousness. (Andersen and Grush,
2009, 'A brief history of time consciousness'. Journal of the History of
Philosophy,
47(2)277-307. [PDF]).
Parallel to this philosophical work on spatial and temporal representation,
I have refined the emulation theory of representation so as to provide, in
quantitative information processing terms, and account of how the brain can
implement the sorts of qualitative schemes I discuss in philosophical contexts.
An article published in the Journal of Neural Engineering (e.g. Grush,
Rick (2005). Internal models and the construction of time: generalizing from
state estimation to trajectory estimation to address temporal features of perception,
including temporal illusions. Journal of Neural Engineering 2(3):S209-S218
[PDF]) explains how to generalize
the notion of emulation to account for aspects of temporal representation.
My paper 'Skill theory 2.0' (cited above) develops information processing tools
for addressing spatial representation in the brain. And in (Grush, Rick (2008).
Space, time and objects. In John Bickel, ed, The
Oxford Handbook of Philosophy and Neuroscience. Oxford University Press.
[PDF]) I expand on, and combine in one synthetic information processing scheme,
a system constructs a spatiotemporal emulator, implemented as a trajectory-estimating
model of spatial relations represented as basis function decompositions of
sensory and postural signals. The resulting account is consistent with what
is known about neurobiology of the posterior parietal cortex, and explains
a great many phenomena in a unified framework.
Semantics.
I have two main interests in semantics. The first is the semantics of singular
reference, especially demonstratives and indexicals. The second more general
interest is in cognitive semantics, especially Ronald Langacker's Cognitive
Grammar.
Singular reference. My interests here are in what might be called grounding
expressions (the term is due to Langacker): expressions whose semantic import
is constitutively tied to the speech event and participants. These include
not only demonstratives (that, this, those, these), and indexicals (I, here,
now), but also verbal elements such as tense and possibly modality. In all
these cases, these expressions or elements have as part of their semantic import
the placing of objects or events in space and/or time relative to spatiotemporally
oriented speech event participants (the thing here, the thing over there, the
person speaking, the current time, the event that occurred before now, the
event that is occurring now). They are the linguistic elements most closely
tied to objective experience, as they are those expressions which key on our
immedaite experience and the objects and events that compose it, including
ourselves. My line on this is that the semantics of these expressions is parasitic
on the semantics of representational mechanisms within the individual language
user: in large part the same mechanisms that provide the language user with
an ability to conceive of an objective spatiotemporal world. I have not published
anything in this area (yet), but my main sources of inspiration are the work
of Gareth Evans (for demonstratives in particular), and, more generally, Ronald
Langacker's Cognitive Grammar framework. I am currently nearing completion
of a significant article on the semantics of demonstratives that I should have
submitted for publication before the end of the year.
Cognitive Grammar. History will record Ronald Langacker (the developer of Cognitive
Grammar) as the person who finally put our understanding of natural language
on the right track, even if a general appreciation of this fact is occurring
more slowly than one would hope. And the 20th century's infatuation with trying
to understand natural language via the tools of formal syntax will eventually
be seen to be the gargantuanly counter-productive historical curiosity it is.
Cognitive Grammar has been the primary topic of three graduate seminars I have
organized (in 1995, 1998, and 1999). My own research interest in the area is,
aside from singular reference (mentioned above), the development of an account
of island constraints within a cognitive grammar framework. This is a long-term
project, and aside from some very schematic ideas in my dissertation (Grush,
1995, chapter 6), I have published nothing on the topic, yet.