The fact that the parser learns these labels without explicit annotation of the link between the arguments and the predicate to which they are assigned, but based on the smoothed representation of the derivation of the parse tree and only very limited lexicalisation, appears to confirm linking theory, which assumes a correlation between the syntactic configuration of a sentence and the lexical semantic labels.
belled with a semantic functional label in the original PTB receive the composite semantic role label AM-X, where X stands for labels such as LOC, TMP or ADV, for locative, temporal and adverbial modifiers respectively.