"Comprehension, at levels far above chance, was shown for all of the sentence forms and sentence meanings that could be generated by the lexicon and the set of syntactic rules, and included the understanding of: (a) lexically novel sentences; (b) structurally novel sentences; (c) semantically reversible sentences that expressed relationships between objects; (d) sentences in which changes in modifier position changed sentence meaning; and (e) conjoined sentences (Phoenix). Additional abilities demonstrated included a broad and immediate generalization of the lexical items to different exemplars of objects; an ability to modulate the form of response to given action words, in order to apply the action appropriately to new objects, to different object attributes, or to different object locations; an ability to carry out instructions correctly despite changes in the context or location in which a sentence was given, or in the trainer providing the instructions; an ability to distinguish between different relational concepts; an ability to respond correctly to sentences given with no objects present in the tank until 30 seconds after the instruction was given (displacement tests); and an ability to report correctly that the particular object designated in a sentence was in fact not present in the tank, although all other objects were (Akeakamai).
......
The comprehension approach used was a radical departure from the emphasis on language production in studies of the linguistic abilities of apes; the result obtained offer the first convincing evidence of the ability of animals to process both semantic and syntactic features of sentences. "