Is a Phrase Structure Grammar the Important Difference between Humans and Monkeys?
Fitch and Hauser [1] have shown that undergraduate students can learn patterns of syllable sequences of the form AABB, or AAABBB, whereas tamarin monkeys can not. Specifically, the humans could reliably decide whether auditory stimuli fit those patterns or not. The authors and Premack [2] interpret this to mean that humans can learn Phrase Structure Grammars (PSG), whereas the monkeys cannot; such grammars are claimed to be crucial to human language [3]. However, their interpretation suffers from a flaw: although the the patterns used were generated by a PSG, nothing in the experiment constrains how the subjects process the sequences. Specifically, the induction of a PSG is not required to learn them, and the experiment does not establish that the human subjects use any particular grammar when they decide which sequences fit the pattern. Fitch and Hauser have done nothing to investigate whether their human subjects actually used a centre-embedding parse to perform the task, so it would
