Connectionism & Reasoning: BBS Call for Commentators

[Stevan Harnad]

Below is the abstract of a forthcoming target article on connectionism
and reasoning by Shastri & Ajjanagadde. It has been accepted for
publication in Behavioral and Brain Sciences (BBS), an international,
interdisciplinary journal that provides Open Peer Commentary on
important and controversial current research in the biobehavioral and
cognitive sciences. Commentators must be current BBS Associates or
nominated by a current BBS Associate. To be considered as a commentator
on this article, to suggest other appropriate commentators, or for
information about how to become a BBS Associate, please send email to:

harnad at clarity.princeton.edu  or harnad at pucc.bitnet        or write to:
BBS, 20 Nassau Street, #240, Princeton NJ 08542  [tel: 609-921-7771]

To help us put together a balanced list of commentators, please give some
indication of the aspects of the topic on which you would bring your
areas of expertise to bear if you were selected as a commentator. An
electronic draft of the full text is available for inspection by anonymous
ftp according to the instructions that follow after the abstract.
____________________________________________________________________

        FROM SIMPLE ASSOCIATIONS TO SYSTEMATIC REASONING:
        A Connectionist representation of rules, variables, and dynamic
        bindings using temporal synchrony

                Lokendra Shastri
                Computer and Information Science Department
                University of Pennsylvania
                Philadelphia, PA 19104
                shastri at central.cis.upenn.edu

                Venkat Ajjanagadde
                Wilhelm-Schickard-Institut
                University of Teubingen
                Sand 14 W-7400 Tuebingen, Germany
                nnsaj01 at mailserv.zdv.uni-tuebingen.de

KEYWORDS: knowledge representation; reasoning; connectionism;
dynamic bindings; temporal synchrony, neural oscillations, short-
term memory; long-term memory; working memory; systematicity.

ABSTRACT: Human agents draw a variety of inferences effortlessly,
spontaneously, and with remarkable efficiency --- as though these
inferences were a reflex response of their cognitive apparatus.
Furthermore, these inferences are drawn with reference to a large body
of background knowledge. This remarkable human ability is hard to
explain given findings on the complexity of reasoning reported by
researchers in artificial intelligence. It also poses a challenge for
cognitive science and computational neuroscience: How can a system of
simple and slow neuron-like elements represent a large body of
systematic knowledge and perform a range of inferences with such speed?
We describe a computational model that takes a step toward addressing
the cognitive science challenge and resolving the artificial
intelligence puzzle. We show how a connectionist network can encode
millions of facts and rules involving n-ary predicates and variables
and can perform a class of inferences in a few hundred milliseconds.
Efficient reasoning requires the rapid representation and propagation
of dynamic bindings. Our model achieves this by representing (1)
dynamic bindings as the synchronous firing of appropriate nodes, (2)
rules as interconnection patterns that direct the propagation of
rhythmic activity, and (3) long-term facts as temporal pattern-matching
sub-networks. The model is consistent with recent neurophysiological
findings which suggest that synchronous activity occurs in the brain
and may play a representational role in neural information processing.
The model also makes specific, psychologically significant predictions
about the nature of reflexive reasoning. It identifies constraints on
the form of rules that may participate in such reasoning and relates
the capacity of the working memory underlying reflexive reasoning to
biological parameters such as the frequency at which nodes can sustain
oscillations and the coarseness of synchronization.

--------------------------------------------------------------
To help you decide whether you would be an appropriate commentator for
this article, an electronic draft is retrievable by anonymous ftp from
princeton.edu according to the instructions below (the filename is
bbs.shastri). Please do not prepare a commentary on this draft. Just
let us know, after having inspected it, what relevant expertise you
feel you would bring to bear on what aspect of the article.
-------------------------------------------------------------
   To retrieve a file by ftp from a Unix/Internet site, type either:
ftp princeton.edu
   or
ftp 128.112.128.1
   When you are asked for your login, type:
anonymous
   Enter password as per instructions (make sure to include the specified @),
   and then change directories with:
cd pub/harnad
   To show the available files, type:
ls
   Next, retrieve the file you want with (for example):
get bbs.shastri
   When you have the file(s) you want, type:
quit

   Certain non-Unix/Internet sites have a facility you can use that is
   equivalent to the above. Sometimes the procedure for connecting to
   princeton.edu will be a two step process such as:
ftp
   followed at the prompt by:
open princeton.edu
  or
open 128.112.128.1

   In case of doubt or difficulty, consult your system manager.
----------
   JANET users who do not have the facilty for interactive file
   transfer mentioned above have two options for getting BBS files. The
   first, which is simpler but may be subject to traffic delays, uses
   the file transfer utility at JANET node UK.AC.FT-RELAY. Use standard
   file transfer, setting the site to be UK.AC.FT-RELAY, the userid as
   anonymous at edu.princeton, for the password your-own-userid at your-site
   [the "@" is crucial], and for the remote filename the filename
   according to Unix conventions (i.e. something like
   pub/harnad/bbs.authorname). Lower case should be used where
   indicated, with quotes if necessary to avoid automatic translation
   into upper case. Setting the remote filename to be (D)pub/harnad
   instead of the one indicated above will provide you with a directory
   listing.

   The alternative, faster but more complicated procedure is to log on
   to JANET site UK.AC.NSF.SUN (with userid and password both given as
   guestftp), and then transfer the file interactively to a directory
   on that site (named by you when you log on). The method for transfer
   is as described above under 'Certain non-Unix/Internet sites', or
   you can make use of the on-line help that is available. Transfer of
   the file received to your own site is best done from your own site;
   the remote file (on the UK.AC.NSF.SUN machine) should be named as
   directory-name/filename (the directory name to use being that
   provided by you when you logged on to UK.AC.NSF.SUN). To be sociable
   (since NSF.SUN is short of disc space), once you have received the
   file on your own machine you should go back to UK.AC.NSF.SUN and
   delete it from your directory there.

   [Thanks to Brian Josephson for the above detailed UK/JANET
   instructions; similar special instructions for file retrieval
   from other networks or countries would be appreciated and will
   be included in updates of these instructions.]
---
Where the above procedures are not available (e.g. from Bitnet or other
networks), there are two fileservers --  ftpmail at decwrl.dec.com and
bitftp at pucc.bitnet -- that will do the transfer for you. Send either one the
one line message:

help

for instructions (which will be similar to the above, but will be in
the form of a series of lines in an email message that ftpmail or
bitftp will then execute for you).
-------------------------------------------------------------