“…Symbols are mental encodings of equivalence classes (Abler, 1989;Newell & Simon, 1975;Pylyshyn, 1984Pylyshyn, , 1986Vera & Simon, 1994), which is to say that all members encoded via a particular symbol are treated equally by some higher level operation (Pylyshyn, 1984(Pylyshyn, , 1986. Symbols can encode either individuals (e.g., Donald Duck) or categories (e.g., duck or cartoon character), and can encode either atomic elements (e.g.…”