The major achievement of this first seniannum was the significant revision and extension of the Recursive Auto-Associative Memory (RAAM) work for publication in the journal Artificial Intelligence. Included as an appendix to this report, the article includes several new elements:%
1) Background z ( , r 51 V erThe work was more clearly set into the area oTiistributed representations, machine learning, and the adequacy of the connectionist approach for high-level cognitive modelingi 2) New Experiment-RAAM was applied to finding compact representations for sequences of letters,
3) AnalysisThe developed representations were analyzed as features which range from categorical to distinctive. Categorical features distinguish between conceptual categories while distinctive features vary within categories and discriminate or label the members. The representations were also analyzed geometrically) A P'>-4) ApplicationsFeasibility studies were performed and described on inference by association, and on using RAAM-generated patterns along with cascaded networks for natural language parsing. Both of these remain long-term goals of the project. \ There are several other areas that are currently being explored, and which should be written up in the second semiannum:
Discrete Analog SystemsOne problem for most recurrent or sequential work i a-connectionism is the default assumption of real arithmetic implemented in floating point. This means that states (or internal representations) are yery imprecise, as there is no equality test. We have been experimenting with a:6 activanon function based upon the inverse of Cantor's function, shown below, which is a sigmoid-shaped step-function, and have be 4XIII .-,.-2-able to use standard neural network learning algorithms with it. One result so far is a RAAM which exactly reconstructs its trees. Inductive Inference J. Feldman set out (on an electronic bulletin board) the problem of inductive inference of finite state automata from language examples as a possible benchmark for connectionist networks. This is now a very active area, with research ongoing at CMU, Toronto, and UMass. Sequential Cascaded Networks had already shown some promise in this area, on the parity and balanced parenthesis languages. With a simple modification, they have worked on more complex test cases (from a 1982 paper by M. Tomita).
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75--Chaotic Behavior One of problems that plague modem connectionist learning algorithms is that gradient descent is susceptible to local minima. This has been discounted by the originators of Back-Propagation, but it is generally known that "sometimes it converges and sometimes it doesn't." It is also known that if all weights start at 0, or any other constant, the networks won't converge. The default initial condition for the technique has thus been to start with small random weights. In the first part of Kolen & Goel's paper, they show that if the weights aren't small, a large percentage of initial conditions lead to non-convergence. We have examined this question in more detail...