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Do Animal Communication Systems Have Phonemes?
TICS 1486 No. of Pages 2
Spotlight
Do Animal Communication Systems Have Phonemes? Daniel L. Bowling,1 and W. Tecumseh Fitch1,* Biologists often ask whether animal communication systems make use of conceptual entities from linguistics, such as semantics or syntax. A new study of an Australian bird species argues that their communication system has phonemes, but we argue that imposing linguistic concepts obscures, rather than clarifyies, communicative function. Human spoken language is fundamentally combinatorial. Speech sounds combine to form words, and words combine to form phrases and sentences. The flexibility of these combinations, transforms our limited-precision motor and perceptual systems into an unbounded system of thought and communication. Wilhelm von Humboldt characterized this as ‘making infinite use of finite means’ [1]. Linguists tradtionally separate the combinatorial nature of language, into two levels, each operating on a different time-scale [2]. At the shorter phonological level, meaningless sounds are combined to form meaningful words (e.g., /c/+/æ/+/t/ = ‘cat’). At the longer syntactic level, words are combined to form sentences (‘cats purr’). Research on animal communication often makes use of such linguistic terminology, characterizing systems as primarily phonological or primarily syntactic, sometimes drawing parallels between specific elements of animal vocalization and particular linguistic concepts.
A new paper by Engesser and colleagues [3] provides an interesting example: they propose that certain elements of chestnut-crowned babbler (Pomatostomus ruficeps) vocalizations behave like human phonemes (Box 1). They focus on two tonal call elements, ‘A’ and ‘B’, differentiated by pitch contour. These elements occur naturally as part of behavior associated with flight (in the sequence ‘AB’) and prompting begging during nestling provisioning (in the sequence ‘BAB’). Using playback experiments with captured wild birds, the authors demonstrate that the prompt call sequence BAB stimulates changes in listener behavior that are not observed in response to the B element alone or in response to the flight call sequence AB. Accordingly, they argue that the addition of the B element to the sequence AB changes the meaning of the call, just as an additional phoneme changes the meaning of a word (e.g., /b/+ ‘it’ = ‘bit’). This is an intriguing demonstration of a novel form of combinatoriality in animal communication. However, several key differences between the elements of babbler vocalization and human phonemes suggest that a parallel is incomplete. First, the babbler system is not very generative. Neither A nor B occurs in the babbler repertoire outside of flight and prompt calls, whereas human phonemes are widely distributed throughout a language. Second, A and B are acoustically isolated (separated by silences), whereas most human phonemes are fused together into unbroken syllables. Third, the difference between AB and BAB is a case of presence or absence (like ‘cat’ versus ‘at’), whereas human phonemic contrasts are typically discriminative (like ‘cat’ vs ‘bat’). While these superficial issues might be argued to represent matters of degree rather than kind, a deeper issue arises when the term ‘phoneme’ is applied outside human language. In linguistics, a phoneme is defined as the smallest unit in the sound system of a language that serves to
distinguish meaning [4]. Because this definition relies on ‘meaning’ – a subjectively informed concept that currently defies neurobiological analysis – it cannot be transparently applied to other species. Attempts to shoehorn elements of animal communication into the phoneme concept quickly lead to questions that do not allow empirical analysis, such as what do babbler vocalizations mean. In human language, the same phoneme string can be uttered with myriad different intonations and flourishes, conveying subtly different emotional and pragmatic intentions (e.g., saying ‘no’ can convey displeasure, sarcasm, sincerity, uncertainty, etc.). The lack of an objective definition for meaning renders parallels between animals and humans problematic, if not theoretically misleading. Similar issues arise when other linguistic concepts are applied to animal communication. For example, the distinction between phonology and syntax is also dependent on meaning. Given that our access to meaning in animal communication is fundamentally limited to what we can infer from behavioral observation’ – we have no introspective access as for human language – characterizing certain levels of organization as phonological and others as syntactic risks anthropomorphically obscuring rather than clarifying how animal communication systems work. These issues aside, Engesser et al.’s [3] experimental results provide new evidence that nonhuman animals, can combine acoustically differentiable elements productively, and that different sequences can affect listener behavior in different ways. Similar abilities have been reported in mammals and other birds. For example, field studies with Campbell's monkeys (Cercopithecus campbelli) have shown that boom calls are associated with group cohesion and movement, and krak-oo calls with nonspecific predator activity, but sequences of booms followed by sequences of krak-oos occur almost exclusively with falling trees or branches [5,6]. Among birds, black-capped chickadees (Poecile atricapillus) have been
Trends in Cognitive Sciences, September 2015, Vol xx. No. x
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TICS 1486 No. of Pages 2
Box 1. Definition of Terms Phones and Phonemes: Linguists define a phone as the smallest perceptually distinguishable segment of sound in a stream of speech (e.g., the /c/ in ‘the cat meowed’). The concept of a phoneme was initially motivated by a desire to understand patterns of organization among the tremendous diversity of phones heard in languages. The traditional method of demonstrating phonemes is to find word pairs (e.g., ‘pat/bat’), where a minimal change in the phone results in a different meaning. If it does, the sounds (/p/ versus /b/) are considered to be phonemes. If it doesn’t, the new sound is considered an allophonic variant or allophone [4,9]. Combinatoriality and Compositionality: Combinatoriality is a property by which new compounds are built out of smaller parts. This definition is independent of meaning. Many animal communication systems are clearly combinatorial. Compositionality is a property of human language whereby semantic units (like words) are combined into larger compounds (phrases and sentences) whose composite meanings are functions of, but not wholly determined by, the independent units. By present knowledge, no animal communication system has this property. The eminent birdsong biologist Peter Marler addressed this issue with his distinction between phonological syntax, which is combinatorial, and lexical syntax, which is combinatorial and compositional [10].
shown to alter the number of trailing dee elements in their eponymous chick-a-dee alarm calls as a function of predator size, responding with more dees to more dangerous predators [7]. Thus, call sequences appear to be a level of organization worthy of further attention in animal communication and playback studies, which have typically focused mostly on single calls: This is true regardless of whether we label elements as phonemes, or categorize systems as phonology or syntax. Finally, this new work on babblers marks what we hope will be a promising resurgence of interest in ‘phonological’ aspects of animal communication which, after a
2
flurry of interest in the 1970s, has largely languished (cf. [8]). Research in animal communication focusing on issues of syntax or meaning often neglects equally fascinating questions about combinatoric power at the level of acoustically differentiable units. Some of the most complex and generative animal communication systems known to science are traditionally termed ‘song’ (e.g., birdsong or humpback whale song), suggesting that parallels with music (which lacks propositional meaning) may be more profitable than parallels with language. Accordingly, these systems may provide a richer source of insight for understanding how combinatoric communication systems
Trends in Cognitive Sciences, September 2015, Vol xx. No. x
can evolve than do such ‘meaningful’ calls as alarm or food calls. Thus, parallels between animal communication and music or phonology may ultimately prove more useful for understanding the evolution of communication than parallels with syntax or semantics. 1
Department of Cognitive Biology, University of Vienna, Vienna, Austria *Correspondence: tecumseh.fi[email protected] (W.T. Fitch).
http://dx.doi.org/10.1016/j.tics.2015.08.011 References 1. von Humboldt, W. (1836) Über die Verschiedenheit des menschlichen Sprachbaues und ihren Einfluss auf die geistige Entwickelung des Menschengeschlechts, F. Dümmler 2. Hockett, C.F. (1960) Logical considerations in the study of animal communication. In Animal Sounds and Communication (Lanyon, W.E. and Tavolga, W.N., eds), pp. 392–430, American Institute of Biological Sciences 3. Engesser, S. et al. (2015) Experimental Evidence for Phonemic Contrasts in a Nonhuman Vocal System. PLOS Biol. 13, e1002171 4. Crystal, D. (1997) The Cambridge Encyclopedia of Language. (2nd edn), Cambridge University Press 5. Ouattara, K. et al. (2009) Campbell's monkeys use affixation to alter call meaning. PLoS ONE 4, e7808 6. Ouattara, K. et al. (2009) Campbell's monkeys concatenate vocalizations into context-specific call sequences. Proc. Natl. Acad. Sci. U.S.A. 106, 22026–22031 7. Templeton, C.N. et al. (2005) Allometry of alarm calls: blackcapped chickadees encode information about predator size. Science 308, 1934–1937 8. Yip, M.J. (2006) The search for phonology in other species. Trends Cogn. Sci. 10, 442–446 9. Crystal, D. (1985) A Dictionary of Linguistics and Phonetics. (2nd edn), Basil Blackwell Ltd 10. Marler, P. (2000) Origins of music and speech: insights from animals. In The Origins of Music (Wallin, N.L. et al., eds), pp. 31–48, The MIT Press
Spotlight
Do Animal Communication Systems Have Phonemes? Daniel L. Bowling,1 and W. Tecumseh Fitch1,* Biologists often ask whether animal communication systems make use of conceptual entities from linguistics, such as semantics or syntax. A new study of an Australian bird species argues that their communication system has phonemes, but we argue that imposing linguistic concepts obscures, rather than clarifyies, communicative function. Human spoken language is fundamentally combinatorial. Speech sounds combine to form words, and words combine to form phrases and sentences. The flexibility of these combinations, transforms our limited-precision motor and perceptual systems into an unbounded system of thought and communication. Wilhelm von Humboldt characterized this as ‘making infinite use of finite means’ [1]. Linguists tradtionally separate the combinatorial nature of language, into two levels, each operating on a different time-scale [2]. At the shorter phonological level, meaningless sounds are combined to form meaningful words (e.g., /c/+/æ/+/t/ = ‘cat’). At the longer syntactic level, words are combined to form sentences (‘cats purr’). Research on animal communication often makes use of such linguistic terminology, characterizing systems as primarily phonological or primarily syntactic, sometimes drawing parallels between specific elements of animal vocalization and particular linguistic concepts.
A new paper by Engesser and colleagues [3] provides an interesting example: they propose that certain elements of chestnut-crowned babbler (Pomatostomus ruficeps) vocalizations behave like human phonemes (Box 1). They focus on two tonal call elements, ‘A’ and ‘B’, differentiated by pitch contour. These elements occur naturally as part of behavior associated with flight (in the sequence ‘AB’) and prompting begging during nestling provisioning (in the sequence ‘BAB’). Using playback experiments with captured wild birds, the authors demonstrate that the prompt call sequence BAB stimulates changes in listener behavior that are not observed in response to the B element alone or in response to the flight call sequence AB. Accordingly, they argue that the addition of the B element to the sequence AB changes the meaning of the call, just as an additional phoneme changes the meaning of a word (e.g., /b/+ ‘it’ = ‘bit’). This is an intriguing demonstration of a novel form of combinatoriality in animal communication. However, several key differences between the elements of babbler vocalization and human phonemes suggest that a parallel is incomplete. First, the babbler system is not very generative. Neither A nor B occurs in the babbler repertoire outside of flight and prompt calls, whereas human phonemes are widely distributed throughout a language. Second, A and B are acoustically isolated (separated by silences), whereas most human phonemes are fused together into unbroken syllables. Third, the difference between AB and BAB is a case of presence or absence (like ‘cat’ versus ‘at’), whereas human phonemic contrasts are typically discriminative (like ‘cat’ vs ‘bat’). While these superficial issues might be argued to represent matters of degree rather than kind, a deeper issue arises when the term ‘phoneme’ is applied outside human language. In linguistics, a phoneme is defined as the smallest unit in the sound system of a language that serves to
distinguish meaning [4]. Because this definition relies on ‘meaning’ – a subjectively informed concept that currently defies neurobiological analysis – it cannot be transparently applied to other species. Attempts to shoehorn elements of animal communication into the phoneme concept quickly lead to questions that do not allow empirical analysis, such as what do babbler vocalizations mean. In human language, the same phoneme string can be uttered with myriad different intonations and flourishes, conveying subtly different emotional and pragmatic intentions (e.g., saying ‘no’ can convey displeasure, sarcasm, sincerity, uncertainty, etc.). The lack of an objective definition for meaning renders parallels between animals and humans problematic, if not theoretically misleading. Similar issues arise when other linguistic concepts are applied to animal communication. For example, the distinction between phonology and syntax is also dependent on meaning. Given that our access to meaning in animal communication is fundamentally limited to what we can infer from behavioral observation’ – we have no introspective access as for human language – characterizing certain levels of organization as phonological and others as syntactic risks anthropomorphically obscuring rather than clarifying how animal communication systems work. These issues aside, Engesser et al.’s [3] experimental results provide new evidence that nonhuman animals, can combine acoustically differentiable elements productively, and that different sequences can affect listener behavior in different ways. Similar abilities have been reported in mammals and other birds. For example, field studies with Campbell's monkeys (Cercopithecus campbelli) have shown that boom calls are associated with group cohesion and movement, and krak-oo calls with nonspecific predator activity, but sequences of booms followed by sequences of krak-oos occur almost exclusively with falling trees or branches [5,6]. Among birds, black-capped chickadees (Poecile atricapillus) have been
Trends in Cognitive Sciences, September 2015, Vol xx. No. x
1
TICS 1486 No. of Pages 2
Box 1. Definition of Terms Phones and Phonemes: Linguists define a phone as the smallest perceptually distinguishable segment of sound in a stream of speech (e.g., the /c/ in ‘the cat meowed’). The concept of a phoneme was initially motivated by a desire to understand patterns of organization among the tremendous diversity of phones heard in languages. The traditional method of demonstrating phonemes is to find word pairs (e.g., ‘pat/bat’), where a minimal change in the phone results in a different meaning. If it does, the sounds (/p/ versus /b/) are considered to be phonemes. If it doesn’t, the new sound is considered an allophonic variant or allophone [4,9]. Combinatoriality and Compositionality: Combinatoriality is a property by which new compounds are built out of smaller parts. This definition is independent of meaning. Many animal communication systems are clearly combinatorial. Compositionality is a property of human language whereby semantic units (like words) are combined into larger compounds (phrases and sentences) whose composite meanings are functions of, but not wholly determined by, the independent units. By present knowledge, no animal communication system has this property. The eminent birdsong biologist Peter Marler addressed this issue with his distinction between phonological syntax, which is combinatorial, and lexical syntax, which is combinatorial and compositional [10].
shown to alter the number of trailing dee elements in their eponymous chick-a-dee alarm calls as a function of predator size, responding with more dees to more dangerous predators [7]. Thus, call sequences appear to be a level of organization worthy of further attention in animal communication and playback studies, which have typically focused mostly on single calls: This is true regardless of whether we label elements as phonemes, or categorize systems as phonology or syntax. Finally, this new work on babblers marks what we hope will be a promising resurgence of interest in ‘phonological’ aspects of animal communication which, after a
2
flurry of interest in the 1970s, has largely languished (cf. [8]). Research in animal communication focusing on issues of syntax or meaning often neglects equally fascinating questions about combinatoric power at the level of acoustically differentiable units. Some of the most complex and generative animal communication systems known to science are traditionally termed ‘song’ (e.g., birdsong or humpback whale song), suggesting that parallels with music (which lacks propositional meaning) may be more profitable than parallels with language. Accordingly, these systems may provide a richer source of insight for understanding how combinatoric communication systems
Trends in Cognitive Sciences, September 2015, Vol xx. No. x
can evolve than do such ‘meaningful’ calls as alarm or food calls. Thus, parallels between animal communication and music or phonology may ultimately prove more useful for understanding the evolution of communication than parallels with syntax or semantics. 1
Department of Cognitive Biology, University of Vienna, Vienna, Austria *Correspondence: tecumseh.fi[email protected] (W.T. Fitch).
http://dx.doi.org/10.1016/j.tics.2015.08.011 References 1. von Humboldt, W. (1836) Über die Verschiedenheit des menschlichen Sprachbaues und ihren Einfluss auf die geistige Entwickelung des Menschengeschlechts, F. Dümmler 2. Hockett, C.F. (1960) Logical considerations in the study of animal communication. In Animal Sounds and Communication (Lanyon, W.E. and Tavolga, W.N., eds), pp. 392–430, American Institute of Biological Sciences 3. Engesser, S. et al. (2015) Experimental Evidence for Phonemic Contrasts in a Nonhuman Vocal System. PLOS Biol. 13, e1002171 4. Crystal, D. (1997) The Cambridge Encyclopedia of Language. (2nd edn), Cambridge University Press 5. Ouattara, K. et al. (2009) Campbell's monkeys use affixation to alter call meaning. PLoS ONE 4, e7808 6. Ouattara, K. et al. (2009) Campbell's monkeys concatenate vocalizations into context-specific call sequences. Proc. Natl. Acad. Sci. U.S.A. 106, 22026–22031 7. Templeton, C.N. et al. (2005) Allometry of alarm calls: blackcapped chickadees encode information about predator size. Science 308, 1934–1937 8. Yip, M.J. (2006) The search for phonology in other species. Trends Cogn. Sci. 10, 442–446 9. Crystal, D. (1985) A Dictionary of Linguistics and Phonetics. (2nd edn), Basil Blackwell Ltd 10. Marler, P. (2000) Origins of music and speech: insights from animals. In The Origins of Music (Wallin, N.L. et al., eds), pp. 31–48, The MIT Press