Why do non-human primates lack Syntactic (Recursive) Rules?

Finally back to some serious work!! Since last week, was trying my writing skills to build 'tareefon ke pul' for the boss & dignitaries and giving welcome speeches.... being just linguist is not enough in this place, I guess!!! But I was right when I said--- "Dr. D  presents a challenge that calls forth the best in people and brings them together around a shared sense of purpose."

So..... some sounds produced by monkeys are functionally semantic. There is also some evidence of primitive form of syntax in some nonhuman primates. But there appears to be no syntactic structure to the calls or vocalizations of these primates. Instead, sequences of calls tend to consist of either the same call repeated a number of times or of the pairing of two calls typically associated with different emotional states to express an intermediate state. There is also no evidence that an alarm call can be modified to elaborate upon the characteristics of the predator currently in question. Through repetition and changes in amplitude (both of which seem to carry prosodic information), alarm calls can serve to inform others of the immediacy of danger. They cannot, however, specify whether the predator is big or small, sleeping or stalking, in a tree or on the ground. Although the alarm calls can be equated with the first word stage of very young children, by the time the child attains age one, the linguistic capacities of the child surpasses that of the vervets. Children at this stage clearly use grammatical structures to infer the meaning of words (Pinker, 1984), and they will respond differently to a grammatically well-formed command than to an ill-formed one.

Cheney & Seyeafarth (in Why animals don’t have language) has given a possible explanation in the form of non-human primates’ inability to recognize argument structure. They fail to see that an event can be described as a linear sequence in which an agent performs an action. In any case, even if monkeys and apes do mentally tag events with syntactic properties (who does what to whom); they certainly fail to map these tags onto a communicative system in any stable or predictable way. However, some primates such as captive apes, ‘kanzi’ and some dolphins, after much training were able to produce phrases that differ according to agent, action or modifier. Although language-trained animals may be relatively proficient in the comprehension of phrases, it is doubtful whether even language-trained apes can produce phrases with any consistent syntactic structure.


In a recent paper Fitch & Hauser (2004) argued that non human primates can master the finite state grammar (FSG) which is at the lowest level of complexity. However, according to Chomsky, human language use requires the mastery of the next level in the complexity hierarchy, termed the “phrase structure grammar” (PSG). “In addition to concatenating items like a FSG, a PSG can embed strings within other strings, thus creating complex hierarchical structures and long-distance dependencies”. The aim of the F&H paper was to show that although the abilities to master a PSG are available to all normal humans, they are not available to monkeys.

It is a well-established fact human language exhibit hierarchic, generative and recursive nature.

Hierarchy of language:

Sentence   ←        the umpires talked to the players

Phrase      ←        the umpires                    talked to the players

Word       ←        the       umpires              talked         to     the    players

Morpheme ←      the    umpire     -s           talk   -ed    to     the    play-er-s

Phoneme    ←      D@    Vmpayr   z       tOk     t    to   D@    pleI   @r  z

The term recursion needs to be distinguished from iteration. An iterative procedure makes something to repeat over and over again. A recursive procedure, on the other hand, is a procedure, which is defined in terms of itself. Language, in principle can be characterized by a set of recursive rules (embedding sentences within sentences). A rule system which is recursive can not be accounted for by a finite state automation, because the latter can only produce regular grammar. Finite state grammar, although is able to capture left and right embedded recursive structures, can not represent center embedded recursive structures. Examples of center embedded recursion are:

1. The boy the girl saw fell.
2. The boy the girl the cat bit saw fell.
3. The boy the girl the cat the dog chased bit saw fell.

In these sentences one relative is nested within another. In their paper H & F (2004) aimed to show that cotton top tamarin monkeys are unable to process such kind of long distance dependencies.

In their experimental demonstration, F&H used a particular PSG, termed An Bn. This grammar generates center-embedded constructions. The A and B elements were drawn within separate sets of eight CV syllables, and were further distinguished by their acoustic characteristics. The A syllables were spoken by a female and the B syllables by a male, so that the two classes of syllables differed by voice pitch, quality, and other particularities of the voice sources. Participants (undergraduate students on the one hand, and cotton-top tamarins on the other) first heard a set of sentences following the patterns AABB or AAABBB. In the subsequent test phase, they heard novel sentences, half following the same grammar (A_n B_n) and half following a finite-state grammar (AB_n), which generated either ABAB or ABABAB sentences. Students were asked to state whether the pattern of each novel sound was the same as or different from the pattern heard during the familiarization phase. They scored 85% correct on this discrimination task. The performance of the Tamarins was assessed through their visual orientation towards the loudspeaker, an increase in looking rate being taken as indicative that the sounds were perceived as different. Interestingly, Tamarins displayed an equivalent rate of looking to strings that violated the rules of the grammar and to strings that were consistent with those rules. Obviously, their failure to selectively look at the non-consistent strings could be due to multiple causes, such as a perceptual inability to discriminate the acoustic properties of A and B syllables. In order to eliminate alternative interpretations, F&H inverted the two grammars for other groups of subjects. It turned out that Tamarins trained with ABAB or ABABAB sequences showed a significant increase in looking to the AABB or AAABBB strings when they were displayed during the test phase. Because this inverted task involved the same perceptual abilities as the first one, F&H inferred that the failure of tamarins trained with the PSG provided a demonstration of their inability to master this class of grammar.

Perruchet & Rey (Does the Mastery of Center-embedded Structures distinguish humans from nonhuman primates?) however, argues that F & H’s conclusions are not compelling. Their first argument is that since it is not possible to demonstrate that the achievement in a specific task t implies the mastery of a grammar g, then how could it be possible to conclude that the failure in t attests that g cannot be mastered?  The implication is that “the failure of tamarins in the F&H task is relevant with regard to their alleged inability to master a PSG only if it can be asserted with a reasonable confidence that the achievement of humans in the same task attests for their mastery of the PSG” (Learning Hierarchical Structure 1).

Secondly, the center-embedded structures, which F&H designated as their main target throughout their paper, it is doubtful that such structures exist in natural language (even if they exist, they are not manageable whenever the number of embeddings exceeds one), and in fact the instance provided by Chomsky (if…then) is better described as a genuine center-embedded construction (Christiansen & Chater, 1999).