p226fig05.35 I had shown in 1976 how a competitive learning or self-organizing map model could undergo catastrophic forgetting if the input environment was sufficiently dense and nonstationary, as illustrated by Figure 5.18.  Later work with Gail Carpenter showed how, if the ART Matching Rule was shut off, repeating just four input patterns in the correct order could also casue catastrophic forgetting by causing superset recoding, as illustrated in Figure 5.36.<BR>||  Code instability input sequences. D  C  A; B  A;  B  C =  ; |D|<|B|<|C|;  where |E| is the number of features in the set E.  Any set of input vectors that satisfy the above conditions will lead to unstable coding if they are periodically presented in the order ABCAD and the top-down ART Matching Rule is shut off.