The influential perturbation model of Estes (1972, 1985, 1997;
Lee, 1992; Lee & Estes, 1977,1981) was one of the first to eschew
item-to-item associations in the representation of short-term memory
for serial order. A central assumption of this model is that
sequences or subsequences of list item representations become
associated to control elements, rather than associations being
formed between the item representations themselves, as in chaining
models. The control nodes can be seen as representing the
context of learning. To the extent that item-context associations
are formed, retrieval of the items will be possible by reactivation
of the relevant control nodes. It is further assumed that a new
group node is set up at each discontinuity in the input and that a
hierarchy of groups is possible. Thus, low-level sequence nodes
might represent phonemes, whereas higher level control nodes
could correspond to higher level units such as syllables, words, or
lists