© 2018 WUPJ, April 2018, Volume 6 Is Language Unique to Humans? 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