Comment on James R. Hurford, The neural basis of predicate-argument structure
By
Peter F. Dominey, Ph.D.
Institut des Sciences Cognitives
CNRS UMR 5015
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dominey@isc.cnrs.fr
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ABSTRACT 53
MAIN TEXT 1031
REFERENCES 88
ENTIRE Document 1224
Commentary Title: Representational Limitations of the One-place Predicate
Abstract:
In the context of Hurford's claim that "some feature of language structure
maps onto a feature of primitive mental representations" I will argue that
Hurford's focus on 1-place predicates as the basis of the "mental representations
of situations in the world" is problematic, particularly with respect to
spatiotemporal events. A solution is proposed.
Text:
Hurford's claim that "some feature of language structure maps onto a feature
of primitive mental representations" is clearly on the right track.
However, I will argue that Hurford's focus on 1-place predicates as the basis
of the "mental representations of situations in the world" is problematic.
Specifically, I will propose that a more appropriate representation is based
on the structure of perceptual events that are functionally and behaviorally
relevant to the non-linguistic individual. Such events would include
physical contact, transfer of possession of objects, etc. that inherently
consist of multiple-argument predicates. In developing this argument
I will exploit Hurford's requirement that the characterization of an appropriate
representation should include: "(i) a plausible bridge between such
representation and the structure of language, (ii) a characterization of
"primitive mental representation" independent of language itself,"
and finally (iii) a plausible story for the neural basis of the representation.
Mapping to Language: With respect to the bridge between the representation
and the structure of language, Hereford argues that "very little of the rich
structure of modern languages directly mirrors any mental structure pre-existing
language." He further states that in contrast to the morphosyntactic complexity
of language, the syntax of logical form is very simple. These
comments reveal the shortcoming of P(x) as the representation - it is too
simple. Indeed it seems that by focusing on a representation that is
appropriate for logic, Hereford steers off the course of a behaviorally useful
representational schema. Non-human primates likely have quite rich representations
of events, their temporal structure, the individuals involved, etc. Constructing
such representations in a neural FOPL would be difficult. Indeed the
difficulty of the mapping is revealed by the quantity of effort expended
in developing a theoretical basis for mapping logic to language and the meanings
that can be expressed in language e.g. Montague (1970; 1973),
Parsons (1990), Kamp and Reyle (1993).
I suggest that while 1-place predicates are certainly useful for representing
object properties, they are inappropriate for (and do not extend in a straightforward
manner to) event representations. Imagine instead that the prelinguistic
representation was based on the perceptual structure of events, with ordered
predicates yielding a structure something like "event(agent, object, recipient)".
In this case the mapping from the mental representation to language becomes
more interesting, and more iconic. The distinct ordered predicates
in the event representation take on specific thematic roles that are iconicly
reflected in regularities in word ordering and/or morphosyntactic and closed
class structure in a cross-linguistic manner. In the example
"A man bites a dog" the representation: bite(e), man(x), dog(y), agent(x),
patient(y) appears arbitrary, unordered, and less informative than bite(man,
dog) in which the relations between the event and the constituent thematic
roles (agent and patient) are encoded in the representation. I would
thus propose that the capability to represent 1 place predicates does not
extend in a useful manner to n>1 place predicates for representing meaning.
Characterization of the primitive mental representation
Having made this claim one is obliged to demonstrate the psychological validity
of n>1 place predicates independent of language. I will approach
this from the perspective of (1) observations from developmental psychology,
and (2) studies of automatic perceptual analysis.
>From the developmental perspective, one of the most salient perceptual primitives
(after motion) is contact or collision between two objects (Kotovsky &
Baillargeon 1998). Prelingual infants appear to represent collisions in terms
of the properties of the "collider" and their influence on the "collidee".
This supports (but does not prove) the hypothesis that contact is represented
by a 2(or greater)-place predicate.
But is the n-place predicate computationally tractable? That is, is
it reasonable to assume that non-linguistic beings can construct such representations?
I have recently explored this question by developing an automated system
that extracts meaning from on-line video sequences of events performed by
a human experimenter in a simple set-up involving manipulation of toy blocks.
The objects are recognized and tracked in the video image, and physical
contact between two objects is easily detected in terms of a minimum distance
threshold. The agent of the contact is then determined as the one of
the two participants that has a greater relative velocity towards the other
in the contact. In this context, the event types of touch, push, give and
take can be defined as variants or types of contact events (Dominey 2002).
This demonstrates that sensitivity to a simple class of perceptual event
(contact) can provide the basis for an multiple ordered predicate representation
of event structure. The objective of developing this perceptual
scene analysis system was to demonstrate the feasibility of generating meaning
in an event(agent, object, recipient) format, based on perceptual scene analysis.
This was motivated by simulation studies of language acquisition based on
the learning of mappings between grammatical structure and predicate-argument
structures (Dominey 2000), that in turn was based on combined modeling and
neurophysiological testing of the underlying functions (Dominey et al. 2003).
These and subsequent studies revealed that the complexity of grammatical
forms (e.g. relative phrases) corresponds to an analoguous complexity in
the predicate-argument representational structure. For example the
mapping of the grammatical construct "The block that pushed the triangle
touched the circle" onto the representation push(block, triangle), touch(block,
circle) we can observe an iconic relation between the relativized structure
of the sentence, and the meaning representation in which the two events share
common
With respect to the neural basis of multiple argument predicates for representing
events, one possibility can be found in the F5 neuron populations described
by Rizzolatti & Arbib (1998) that when observed together allow
distirct representations for grasp(me, raisin) vs. Grasp(someone-else, raisin).
Thus, access to two distinct populations of these neurons allows a event
representation with distinct agent and object coding.
In summary, I want to insist that Hurford's undertaking is quite valid and
interesting with respect to the stated goal of investigating the neural basis
of predicate-argument structure. Where it fails is in the thesis that
"The structures of modern natural languages can be mapped onto these primitive
representations". I hope to have argued that the required representations
for events (and their description) are more complex than those described
by Hereford - and that they cannot be represented by the primitive structure
he describes.
Acknowledgements: This work was supported by the HFSP Organization,
and the French ACI for Computational and Integrative Neuroscience.
References:
Dominey PF (2000) Conceptual Grounding in Simulation Studies of Language
Acquisition, Evolution of Communication, 4:1, 57-85
Dominey PF (2002) Language Learning For Human-Machine Interaction via Mapping
of Grammatical Structure to Visual Scene Structure, Institut des Sciences
Cognitives (ISC) Working Paper 2002-2, http://www.isc.cnrs.fr/wp/DomineyISC.PDF
Dominey PF, Hoen M, Blanc JM, Lelekov-Boissard (2002) Neurological basis
of language and sequential cognition: Evidence from simulation, aphasia
and erp studies, (In press) Brain and Language
Kotovsky A, Baillargeon R (1998) The development of calibration-based reasoning
about collision events in young infants. Cognition 67, 311-351.