Does the mastery of center-embedded linguistic structures distinguish humans from nonhuman primates?

Abstract

Identifying the specific language abilities that separate humans from nonhuman primates has been the topic of innumerable speculations. In a recent Science article, Fitch and Hauser (2004; hereafter, F&H) argued that the hierarchy of grammars of increasing generative power described by Chomsky (e.g., 1957) provides the key for a response. At the lowest level of complexity are the finite state grammars (FSGs), which generate sequences by concatenating a set of elements (states) while following prespecified transitional probabilities. The extant literature, as F&H pointed out, indicates that nonhuman primates can master such grammars. 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 an FSG, a PSG can embed strings within other strings, thus creating complex hierarchical structures and long-distance dependencies" (F&H, p. 378). An instance of embedding in English is "the rat the cat ate stole the cheese," in which one relative clause ("the cat ate") is nested within the sentence ("the rat stole the cheese"). The aim of F&H's article was to show that although the abilities to master a PSG are available to all normal humans, they are not available to monkeys.In their experimental demonstration, F&H (2004) used a particular PSG, termed A n B n , where n ϭ {2,3}. This grammar generates center-embedded constructions, such as that represented in Figure 1 for n ϭ 3. 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 pattern AABB or AAABBB. In the subsequent test phase, they heard novel sentences, half following the same grammar (A n B n ) and half following an FSG (AB n ), which generated either ABAB or ABABAB sentences. The 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 toward the loudspeaker, an increase in looking rate being taken as indicative that the sounds were perceived as different. Interestingly, the tamarins displayed an equivalent rate of looking to strings that violated the rules of the grammar and looking to strings that were consistent with those rules. Obviously, their failure to selectively look at the nonconsistent 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 (2004)...

Simple rules can explain discrimination of putative recursive syntactic structures by a songbird species

“…The findings in (4) lacked the appropriate controls, but later replications claim that the AABB/ABAB task, which Fitch and Hauser (4) designed to obtain evidence for recursion, can be solved by humans using a simpler strategy instead (5,9) or by a conscious counting strategy that seems unrelated to language (11). At present, there is thus no convincing demonstration of the use of recursive rules in artificial language learning in any species.…”

“…From stimuli constructed of a 1-5 and b [1][2][3][4][5] , each bird was transferred abruptly to stimuli constructed from a 6 -10 and b 6 -10 when it reached criterion performance. See Fig.…”

“…The experiments gave rise to a lively debate, ranging from questions such as whether the stimuli really represented a suitable test of the ability to detect recursive structures, to whether animals as well as humans can ''solve'' the task by using less complex, non-recursive strategies (2,(5)(6)(7)(8)(9)(10)(11)(12).…”

What artificial grammar learning reveals about the neurobiology of syntax

“…Much of the discussion of the recursion-only hypothesis, concerning the narrow faculty of language (FLN, Hauser et al, 2002), has been phrased in terms of concepts derived from the Chomsky hierarchy; for example, non-regular context-free vs. right-linear regular grammars (e.g., de Vries, Monaghan, Knecht, & Zwitserlood, 2008;Fitch & Hauser, 2004;Gentner et al, 2006;Perruchet & Rey, 2005;Uddén et al, 2009). Here, we will show why the Chomsky hierarchy is irrelevant in the context of finite processing systems.…”

Parsing recursive sentences with a connectionist model including a neural stack and synaptic gating

“…Likewise, Gentner, Fenn, Margoliash & Nusbaum (Gentner et al, 2006) claimed that their subjects (starlings) learnt CER using the same kind of structures as Fitch and Hauser (Fitch and Hauser, 2004). This in turn elicited some critique: Corballis (Corballis, 2007a;Corballis, 2007b) called attention to the fact that the sentences used could be parsed by simple counting, while others (De Vries et al, 2008;Perruchet and Rey, 2005) showed that in experimental situation similar to that of Fitch & Hauser (Fitch and Hauser, 2004) even human subjects used alternative strategies to solve the tasks.…”