An alternative to sequential coding is a so-called open bigram encoding (Grainger and Van Heuven, 2004;Schoonbaert and Grainger, 2004;Grainger and Whitney, 2004), which is formed by taking the ordered 2-combination of each letter in a word.
the open bigram encodings of the words 'salt' and 'slat' are {sa, sl, st, al, at, lt} and {sl, sa, st, la, lt, at}, respectively.