Newsgroups: bit.listserv.slart-l
Date:         Wed, 8 Apr 1992 11:39:00 PDT
From:         "Swathi Vanniarajan 213-397-7610" <IHW1020@UCLAMVS.BITNET>
Subject:      PDP and Competition models

PDP and Competition Models:

     In my opinion, there are similarities as well as differences
between MacWhinney's competition model and the PDP models.

     With regard to the major similarities, both claim that they
are interactive models with bidirectional processing; also, both
assume competition and conflict resolution. What follows is my
interpretation of the models in terms of my understanding:

MACWHINNEY'S COMPETITION MODEL:

     MacWhinney's model (parallel interactive activation) is an
interface between linguistics and psychology grounded in the
general learning principles (that language acquisition can be
explained by general learning principles). The model believes that
neither linguistic nor cognitive development can really be
addressed independently of the other.

     According to the model there is both competition and
cooperation among various modes of activation (production); the
model's emphasis, however, is on inhibitory competition. Another
important aspect of the model is its assumption (in my
understanding - if I am wrong, please correct me) of a pattern
matcher - (a kind of goodness of fit decision) (this is somewhat
analogous to the assumption of what is called the central executive
in the memory component in working memory models (Baddeley 1981).


PDP MODELS:

     PDP models are an interface between information processing and
neuropsychology grounded in the structure of brain. PDP models
assume that processing activity results from the processing
interactions among units (in terms of human brain neurons);
language acquisition, in terms of these models, is a weight
adjustment process which itself is a product of processing activity
- in a way, it is learning through connection strengths;
homogeneity of native speakers, can then be explained with an
assumption of homogeneity of connection strengths.

     PDP models are also grounded on inhibitory and excitatory
connections - excitatory connections (bidirectional) between
mutually consistent units and inhibitory connections between
mutually inconsistent units; however, the model differs from
MacWhinney's model in the sense that activations in the PDP models
give rise to further processing activity directly without any need
for a central processor or a production-matching-and application
mechanism; new learning in this paradigm is a kind of settling
down.

     PDP models unlike MacWhinney's model do not explicitly talk
about general learning principles; they do not assume a pattern
matcher; the emphasis is on both excitatory and inhibitory
connections which may lead to further strengthening or further
weakening of connection strengths; also, they assume that there is
a kind of diminishing returns once the maximum strength is
attained; in other words, the incremental effect of an activation
on the strength of a connection is a decreasing function of its
prior strength; that is, a weak connection benefits more from an
activation than a strong one (McClelland & Rumelhart 1981;
Rumelhart & McClelland 1982) (Can we call this PDP insights into
fossilization?). These, I think, are the major differences.

     A word of caution is necessary at this point; researchers in both
camps are well aware of the fact that an interdisciplinary approach
which combines child language research (linguistics) and psychology
(experimental, cognitive, and neuro) is necessary; they furthermore
repeatedly claim that "no one should attempt to view the computer
as brain - the current computational models are (to be) best viewed
as devices for the evaluation of theoretical claims."

FOR SELIGER:

    I don't know whether Barry is on the network; his e-mail
address is: mclaugh@CATS.UCSC

                                     Swathi Vanniarajan (UCLA)
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU