Cool finding. I'm more familiar with the primate literature, so I looked over the study and the book summary. The Herman study was published in 1984, which was

Cool finding. I'm more familiar with the primate literature, so I looked over the study and the book summary. The Herman study was published in 1984, which was already a few years after the collapse of most of the primate language efforts. So, the author tries to compensate for many of the flaws that spelled doom in the primate teaching efforts. In particular, they do a decent job of focusing on comprehension rather than language generation, and wisely test primarily novel sentences. On the other hand, they make the same error as the primate researchers in not fully addressing if, and to what extent if so, operant conditioning could also be the method of learning. The response to novel sentences and the 5-word sentences seems suggestive of language, but conditioning can also do a LOT. (E.g., look up rats trained to do Rube Goldberg-style mazes involving dozens of steps to see how complicated behaviors can be achieved by conditioning smaller subpieces and then chaining them.) The novel sentence tests might still be explainable by conditioning as: the dolphins are rewarded for correct answers, and by combining operant conditioning with object identification, are able to infer the correct answer. E.g., they trained a dolphin to answer yes/no on whether a hoop was in the pool, and then asked the same question for items used in earlier studies. This could still be a generalization of a conditioning response from a smart animal receiving rewards for correct answers, and not a demonstration of syntactical understanding.