Evaluating the “Narrow Language Faculty” Hypothesis

Jessica Lammert *

The differences between animal communication systems and human language have been an area of considerable research. The aim of the present review was to evaluate Fitch, Hauser, and Chomsky’s Narrow Language Faculty hypothesis. This theory claims the sole property that distinguishes human language from animal communication is recursion, defined as the ability to embed one linguistic representation within another in a hierarchy. The current review examined evidence of animal grammar learning and assessed the claim that recursion is a universal property of human language. Other abilities that may be unique to human language are discussed. Conclusions on the current state of empirical evidence and the existence of continuity between animal communication and human language are made.

Animal communication refers to the embedding of one linguistic representation transfer of information by an animal that within another in a hierarchical structure, elicits a change in the behaviour of the allowing for natural language strings such as animal receiving this information (Gillam, “The milk that I bought the other day was 2011). Examiners of human and animal spoiled.” The Narrow Language Faculty communication systems seek to understand hypothesis predicts that animals are unable the cognitive mechanisms and processes that to learn recursive grammars and recursive underlie their respective abilities. The goal grammar is the sole cognitive mechanism of this research is to understand how and that is unique and universal to human why human language differs from the language. The goal of this essay is to refute communicative abilities of other species and this hypothesis by reviewing several is often framed as a contrast between empirical studies of recursive abilities in continuous and discontinuous theories of humans and animals. The current paper will evolution. Continuity theorists propose begin with a description of the Narrow human language is a refinement of abilities Language Faculty hypothesis and supporting that are present in other species while evidence to be reconsidered. This will be discontinuity theorists propose human followed by a detailed review of empirical language abilities are qualitatively different studies on recursive abilities in various and emerged suddenly in the course of animal species and evidence of a human human evolution. language that does not utilize recursion. The review will close with a discussion of other One prominent argument against properties that may be unique to human continuity is the Narrow Language Faculty language. hypothesis (Fitch, Hauser, & Chomsky, 2005; Hauser, Chomsky, & Fitch, 2002). The Narrow Language Faculty According to the Narrow Language Faculty Hypothesis hypothesis, the sole property that How is human language different distinguishes human language from animal from the communicative abilities of other communication systems is recursion. animals? One suggestion in line with the Recursion refers to the potentially infinite discontinuity approach is that animals are *Initially submitted for 4420 at the University of Western Ontario. For inquiries regarding the article, please email the author at [email protected]. NARROW LANGUAGE HYPOTHESIS 2 unable to represent and process a particular Fitch and colleagues (2005) find syntactic operation: recursion. Fitch, Hauser, support for the FLN hypothesis and the and Chomsky (2002) divide human language central role of recursion in their review of abilities into narrow and broad language the animal communication literature. They faculties (Fitch et al., 2005; Hauser et al., note that no known animal communication 2002). The broad language faculty (FLB) system demonstrates recursion nor do includes abilities required for language that studies of trained apes, dolphins, and parrots are shared with other cognitive processes (for a review, see Pepperberg, 2017; ten (such as problem-solving and decision- Cate & Okanoya, 2012). However, this making) and with other species. In contrast, conclusion is erroneous because it is the narrow language faculty (FLN) consists assumed that the absence of recursion in of abilities required for language that are not animal communication is evidence that it used for any other cognitive tasks and are does not exist. It is unknown whether not shared with other species. Specifically, researchers have found null results either recursion is described as the vital component because recursion does not exist in animal of the FLN that differentiates human communication or because they lack the language from other forms of cognition and proper means of detection. Fitch and animal communication systems. colleagues’ justification of placing recursion in the FLN would be falsified by empirical These theorists also claim that evidence of recursive abilities in other recursion is the syntactic operation that species. delineates finite-state grammars from phrase-structure grammars. Both finite-state The primary purpose of the current grammars and phrase-structure grammars review is to evaluate the claims of Fitch, are representational processing systems that Hauser, and Chomsky (Fitch et al., 2005; allow linguistic symbols (words, phrases) to Hauser et al., 2002). The first of these is that be combined into extended strings. Some animals lack the ability to acquire phrase- linguists contend that embedded structures structure grammars and process recursion. and long-distance dependencies are only The second is that recursion is unique to permissible in grammars that feature human language and universally represented recursion (Chomsky, 2010; Corballis, 2013; in all languages. The third claim, implicit Hauser et al., 2002). While a finite-state with the second, is that no other language grammar can produce patterns of alternating ability is unique to humans aside from symbols such as ABAB, a phrase-structure recursion. Sufficient evidence against these grammar is required to generate patterns claims would challenge Fitch and such as AAABBB where each A-element is colleagues’ explanation of human language paired with a corresponding B-element and as consisting of a FLN with recursion as its may be separated by intervening elements sole occupant. (Chomsky, 1957). Thus, only phrase Grammar Learning in Animals structure grammars are recursive because relations among constituents allow To determine whether recursion representational units to be embedded within constitutes the FLN, an investigation into larger structures. whether non-human species can represent

NARROW LANGUAGE HYPOTHESIS 3 hierarchical relations among discrete units is (two transitions in finite-state sequences, warranted. Other primates, who have already one transition in phrase-structure sequences; demonstrated a rich set of cognitive Hochmann et al., 2008; Perruchet & Rey, capacities, are perhaps the most likely to 2005). possess recursive abilities (Shettleworth, In the test phase, novel sequences of 2001). Researchers have investigated syllables that were either consistent or whether inconsistent with the trained grammar were non-human primates can acquire phrase- played over speakers. Researchers measured structure grammar using exposure-test if and for how long the tamarins oriented research methods where participants are toward the speaker. If the tamarins presented with stimuli and later must recognized the sequence as being familiar, discriminate between trained and novel test they should orient to the speaker for a items. Evidence that other primates can shorter period of time compared to those acquire phrase-structure grammar would who recognized the sequence as being novel. invalidate the first claim of the FLN The experimenters found the hypothesis, that only humans can process tamarins acquired the finite-state grammar recursive representations. but were incapable of acquiring the phrase- Fitch and Hauser (2004) employed structure grammar. Animals trained on the an experimental paradigm where finite-state sequences spent more time meaningless syllables are combined in oriented toward the speaker when the different sequences to explore whether non- sequences violated the grammar than the human primates can learn a phrase-structure animals trained on the phrase-structure grammar. While some sequences could be grammar. The preferential looking generated using a finite-sate grammar, paradigm, used extensively in infant others could only be generated using a cognition research, has been subject to phrase-structure grammar. This paradigm interpretative issues (Aslin, 2007). While in has been used to test the ability of cotton-top some studies, longer looking times are tamarins, birds, and humans to learn a interpreted as an individual recognizing phrase-structure grammar. novel stimuli, in others, longer looking times are interpreted as recognizing familiar To determine whether cotton-top stimuli (Hauser & Carey, 2003; Jordan, tamarins can learn complex syllable Brannon, Logothetis, & Ghazanfar, 2005). sequences, researchers exposed them to a As well, questions remain on the extent to 20-minute recording of sequences generated which looking can be interpreted as by either a finite-state grammar (ABAB) or knowledge (Shinskey & Munakata, 2005). phrase-structure grammar (AAABBB). As These findings support Fitch and colleagues critics have pointed out, “A” and “B” (2005) but should be interpreted with syllables were further differentiated by the caution. gender of the speaker, which made it possible for tamarins to distinguish between The results of the cotton-top tamarin the two types of grammars based on the investigation contrast with the results of number of male-female voice transitions similar studies conducted on birds. Gentner,

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Fenn, Margoliash, and Nusbaum (2006) it begins with two A’s; withhold pecking if examined whether European starlings could it does not begin with two A’s”, would discriminate between sequences generated allow a bird to successfully discriminate by finite-state and phrase-structure phrase-structure generated strings grammars. Starlings were taught to peck for (AAABBB) from finite-state strings a food reward if they were presented with a (ABAB) while erroneously accepting sound sequence matching the grammar on ungrammatical test strings (AABBB). which they had been trained. A subset of the Furthermore, the finches who were able to starlings required 9400 exposure trials to successfully discriminate finite-state and reach maximum accuracy; others required phrase-structure strings were not able to up to 56,000 trials and some were never able generalize this ability to new strings that to discriminate between the different types used different sounds. The findings of strings. The researchers concluded that presented by the zebra finch study supports starlings have some ability to learn a phrase- Fitch and colleagues (2002) by criticizing structure grammar. These findings challenge whether the European starlings could Fitch and colleagues’ claim that the FLN recognize recursive strings as their consists of recursion because the ability to performance may have been the result of recognize recursive sequences is heuristic use rather than grammar learning demonstrated in a non-human species. as well. Critics have noted that the starlings These studies identify a larger could discriminate sequences without problem for the comparative approach to actually processing embedding or long- grammar learning. Humans sometimes fail distance relationships (Corballis, 2007; van the “AAABBB” paradigm despite being Heijningen, de Visser, Zuidema, & ten Cate, capable of acquiring phrase-structure 2009). Zebra finches exposed to similar grammars, indicating this test may not be a AAABBB (phrase-structure) and ABAB valid assessment of grammar learning (finite-state) sequences were tested with abilities. In a study by Perruchet and Rey other sequences consistent with part of the (2005), the ability of human participants to training strings but considered acquire phrase-structure sequences was ungrammatical overall (van Heijningen et tested under two conditions. In one al., 2009). Additional testing strings might condition, meaningless syllables were all have looked like AABBB, inconsistent with spoken by the same voice (male or female). the phrase-structure grammar because a B Like the tamarin study above, half of the syllable lacked a corresponding A syllable. syllables (“A”) were recorded in a male The zebra finches incorrectly recognized voice while the other half (“B”) were these ungrammatical test sequences as recorded in a female voice in the second grammatical. condition. Participants successfully discriminated between grammatical and Each finch appeared to adopt a ungrammatical phrase-structure sequences strategy which it used to respond when the syllables were differentiated by appropriately to the strings without actually gender but were unable to learn the grammar internalizing a phrase-structure grammar. when all of the syllables were spoken by the For example, a heuristic specifying “peck if same voice. These findings suggest that, like

NARROW LANGUAGE HYPOTHESIS 5 the zebra finches, humans most likely pass (2002), suggesting the human ability for the “AAABBB” test by using a heuristic recursion may not be species-specific but method rather than acquiring the abstract results from cognitive processes shared with grammar. non-human primates. More accurate tests are necessary to Does Language Require Syntactic provide strong empirical evidence of Universals? whether animals are able to acquire phrase- Fitch and colleagues’ (2002) second structure grammars. In an appropriate test, claim is that recursion, as the sole correct responses would be exclusively component of the FLN, is a universal attributed to a participant’s ability to learn characteristic of all human languages. This the grammar. Successful performance would formulation may be unsupported if there is rely on learning dependent relationships evidence of a human language that does not between A and B elements rather than use recursion. learning to predict sequences based on the number of A elements or transitions between Pirahã, spoken by approximately 300 male and female voices. A more reliable test hunter-gatherers in the Brazilian Amazon of recursive abilities would also be one that River basin, may provide evidence against humans consistently pass, reflecting their recursion as a universal language property. ability to learn recursive grammars. This According to linguist Everett (2009), who new test would be administered to both has spent nearly three decades living among humans and animals, especially those that the Pirahã, the language lacks any form of are more likely to demonstrate recursive recursive grammar. While an English abilities due to genetic similarity with sentence such as “Give me the bread Sarah humans, such as chimpanzees and bonobos. bought” contains a recursive element as in “Give me (the bread) that Sarah bought (the Though not without their limitations, bread)”, a Pirahã speaker would express this Fitch, Hauser, and Chomsky (2002) claim thought as “Give me the bread. Sarah bought the above studies support their theory by that very bread. They are the same.” Pirahã demonstrating that animals are unable to speakers do not embed related units in a learn a recursive grammar for syllable hierarchical structure like the majority of sequences. However, recursion has also been languages in the world. Instead, demonstrated in a visual cognition paradigm corresponding units are represented in administered to baboons. Rey, Perruchet, separate structures and their relationship is and Fagot (2012) trained baboons to referenced explicitly by the speaker. associate pairs of visual shapes, reflecting their associative and working memory Assuming Everett’s account of capabilities. It was found that when baboons Pirahã is correct, the existence of a language were required to pair the associated visual without recursion would contest the FLN shapes in the testing session, they claim that recursion is the sole ability that spontaneously ordered their responses makes human language unique and is keeping to a recursive structure (i.e. pairing universal to all languages. If recursion is the A1 with B1 when A2 intervenes). These sole occupant of the FLN and it is assumed results challenge Fitch and colleagues that the cognitive processes of the FLN

NARROW LANGUAGE HYPOTHESIS 6 influence overt language behaviour, the “one assertion per utterance” rule following absence of recursion in the overt form of any the Pirahã cultural value of only expressing human language would provide evidence ideas for which there is direct evidence. In a that recursion is not present in the processes recursive sentences such as “Give me the generating that language. Fitch and bread Sarah bought,” the idea that “Sarah colleagues (2005) claim a distinction bought the bread” is implied but not directly between overt language and underlying expressed. In line with this rule, the Pirahã cognitive abilities. Recursion is present in have eliminated pre-supposition by the FLN in Pirahã speakers even if it is not disallowing recursive structures. Overall, expressed in the overt form of the language. evidence from Pirahã suggests a human They propose a Pirahã child raised in language can exist without recursion, another language environment will master nullifying the claim of Fitch, Hauser, and that language and could learn any recursive Chomsky (2002) that recursion is the sole embedding principle such as those found in occupant of the FLN. mathematics and computer programming as This discussion of universal they are still capable of recursive thinking. recursion and its role in the FLN versus the There are many theories as to why FLB relates to a larger debate on the nature there is no overt recursion to be found in of grammatical representation in human Pirahã. In contrast to Fitch and colleagues language acquisition. In the nativist (2005), Coolidge, Overman, and Wynn approach to language development, syntactic (2010) claim that the absence of recursion in representations are considered innate to all the overt form of the Pirahã language humans, as transmitted through the human reflects the absence of recursive genome (Chomsky, 1965). However, representations in Pirahã speakers. Instead advanced mathematical models have of attributing the absence of recursion to demonstrated it is possible to acquire aspects of the FLN, Coolidge and colleagues grammar without pre-existing grammatical (2010) attribute this to abilities in the FLB. categories resulting from an innate linguistic Specifically, they claim Pirahã speakers are disposition (e.g. Abbot-Smitt & Tomasello, unable to process recursion because they 2010; Banard, Lieven, & Tomasello, 2009; lack the required working memory capacity. Waterfall, Sandbank, Onnis, & Edelman, This explanation is consistent with Rey and 2010). Autonomous and self-organizing colleagues (2012), who claimed working computational systems have yielded similar memory, a domain-general cognitive ability, results (Steels, 2003). These alternative allowed baboons to process recursion. approaches to language acquisition do not depend on recursion to bring about language Another explanation for the lack of development. Thus, a human language like recursion in Pirahã comes from Everett Pirahã, that lacks recursion, does not (2009), who claims its absence reflects challenge these theories. The models Pirahã cultural values. He describes the provide further support against the FLN Pirahã as committed to literal hypothesis and nativist approach to language interpretations, suggesting their culture only acquisition, challenging the assumption that permits direct statements of fact and does recursive processing is necessary for not allow inferences. One example is the language and found in all human languages.

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Instead, language may result from domain- order intentionality because there is a general cognitive mechanisms in the FLB, relationship between a mental representation such as working memory and attention, that and an external entity. Animals’ humans share with other species. communication does not exhibit second- order intentionality because animals are Other Unique Abilities unable to represent others’ internal states or Fitch and colleagues’ (2002) third share their knowledge with others when argument is that the sole occupant of the communicating. Vygotsky’s (1934,1986) FLN is recursion. If other language abilities hypothesis provides a possible explanation are found to be unique to humans, this for this phenomenon. According to theory would be unsupported. Evidence Vygotsky, only humans can talk about their from animal communication systems internal knowledge due to a connection suggests two possibilities: intentionality and between thought and language that emerges abstract thinking. around two years old. Under this hypothesis, animals possess basic thoughts but are Animal vocalizations are often unable to functionally link these concepts viewed as lacking intentionality. Primate with processes that support communication. calls are direct reactions to events or physical states and are produced without the Likewise, although there is evidence intention to inform others of an absent that animals are able to associate symbols referent (Ouattara, Lemasson, & (sounds, lexigrams, signs) with concrete Zuberbühler, 2009). However, there is meanings, they appear to be unable to evidence that chimpanzees possess some associate symbols with abstract meanings ability to recognize the intentional states of (Petitto, 2005). For example, researchers others (Tomasello, Call, & Hare, 2003). comparing naturally observed birdsong and Chimpanzees are able to gather some human speech have determined a few key information on the knowledge and goals of differences. Chiefly, birdsong cannot others when planning their own behaviour. communicate abstract meanings while human language allows abstractions and In response to this evidence, Fitch (2010) flexible associations (Doupe & Kuhl, 1999). suggests a distinction between first- and One explanation is that animal second-order intentionality. First-order communication cannot transmit information intentionality implies a bond between a regarding non-existent or abstract entities mental representation and physical referent because it is limited to representing concepts formed without the specific intent to modify that can be perceived through the senses another individual’s behaviour. Second- (Bickerton, 1990; Ghazanfar & Hauser, order intentionality additionally requires the 1999; Liszkowski, Schäfer, Carpenter, & communicator to have a goal of changing Tomasello, 2009). Considering the dances of another individual’s knowledge during honeybees about distant resource patches interactions. and vervet monkey calls referencing If Fitch’s (2010) theory is correct, displaced predators, animals are able to animal communication is intentional. represent non-present concrete entities and However, animals may exhibit only first- form representations of things they have experienced in the world (Dornhaus &

NARROW LANGUAGE HYPOTHESIS 8

Chittka, 2004; Seyfarth, Cheney, & Marler, between the cognitive abilities of humans 1980). and animals because the test is susceptible to heuristic use and humans do not always pass Like intentionality, the main factor it. A more stringent test and converging that may impede the existence of abstract evidence presented by other paradigms associations in animal communication could should be considered before it is concluded be an incomplete connection between that recursion does not exist among animals. communication and conceptual representations (Vygotsky, 1934/1986). This Furthermore, the discussion of explains the division between possessed human language abilities should extend knowledge and overt behaviour and the lack beyond recursion. This broader discussion of communication about abstract entities in may include recursion is not necessary for non-human species through a disconnection all human languages and language between thought and language. The development. There is more evidence of possibility that intentionality or abstract recursive abilities in animals than second- thinking may also be unique to human order intentionality and abstract thinking. language challenges Fitch, Hauser, and Both abstract thinking and intentionality Chomsky’s (2002) claim that recursion is may be exclusively human skills related to the sole ability in the FLN that distinguishes the ability to connect language with human language from animal questions of whether recursion is innate and communication system. universal and whether other abilities are unique to humans. As evidenced by Pirahã Conclusions and computational models of language In this review, the FLN hypothesis acquisition recursion is not necessary for was re-evaluated (Fitch et al., 2002; Hauser all human languages and language et al., 2005). This hypothesis predicts that 1) development. There is more evidence of animals are not able to learn recursive recursive abilities in animals than second- grammar, and 2) recursive grammar is the order intentionality and abstract thinking. sole cognitive mechanism that makes human Both abstract thinking and intentionality language distinct from animal may be exclusively human skills related to communication systems. Empirical evidence the ability to connect language with thought against these claims has been presented in while recursion may be supported by general the current paper. This evidence challenges cognitive skills. the depiction of human language as consisting of a FLN with recursion as its In summary, it is likely that there is a sole component and a separate FLB certain degree of continuity between containing cognitive abilities shared with different aspects of human language and other processes and species. animal communication systems, including recursion. Human linguistic ability is In studies of recursive grammar comprised of multiple factors which may learning, birds pass the “AAABBB” test for find precursors in animal communication. phrase-structure grammar acquisition while The nature of the commonalities and primates do not. These findings may reflect differences between humans and animals is test limitations rather than a divergence yet to be decided due to the limitations of

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