Influence of mirror neurons on the evolutionary path of gestures into spoken language and sign language.

This section is devoted to neurological research on the origins of language (specifically, the role of neurons in the construction of language) and on the relationship between sign language and spoken language. The first few paragraphs discuss the discovery of canonical and mirror neurons, which is followed by a description of several experiments, demonstrations and hypotheses. We learn that, on a neurological level, spoken language and sign language may share the same grammar and there may also be a definite continuity between human and animal language, and pre-language and language. The title of the text is “Influence of mirror neurons on the evolutionary path of gestures into spoken language and sign language.”

GIACOMO RIZZOLATTI ET AL. (1988), discovered canonical neurons in the upper ventral pre-motor area (F4 area) that are activated when the macques monkey completes an action.1

Unlike the pure motor neurons, canonical neurons are activated also when those objects enter the visual field of the animal. It seems to enable the brain to anticipate future possible interactions and prepare the body accordingly. Later again, Giacomo Rizzolatti et al. (1996)2 and Gallese et al. (1996)3, discovered mirror neurons in macaques in their ventral pre-motor area (F5 area) – these neurons are active when their owners perform a certain task.

But, interestingly, these neurons fire, whenever their owner watches someone else perform that same task. It suggests a possible neural circuit for transforming visual pattern into motor commands.

Rizzolatti also noticed that the ventral pre-motor area may be a homologue of Broca’s area (BA 44 and 22), which is associated with the expressive and syntactic aspects of language in humans. He found activation in Broca's area when people observed manual actions, similar to the activation seen in macques’ F5 area.

By the late 1990s, as their findings gained prominence throughout the scientific community, anthropologists, linguists, psychologists and cognitive scientists applied these findings by Rizzolatti et al into their own theories. A general consensus developed that the mirror neurons aided in imitation learning and mind-reading empathy as well as provide a link between gesture and language. Gallese et al. (1998)4 hypothesized that mirror neurons could be a more general matching system that represents “goals, emotions, body states and the like to map the same states in other individuals”. This ability to share and infer goals would confer evolutionary advantages in primate society.

Some neuroscientists (Ramachandran, 2000) 5 even went so far as to predict that mirror neurons would do for psychology what DNA did for biology. However, Rizzolatti cautions that they could equally be involved in simply understanding. Just as in language, where we know that there is a big difference between being able to understand a sentence and being able to construct and pronounce it, so mirror neurons may just assist with being able to understand gestures rather than being able to construct and generate gestures6.

Researchers in other related fields found similar evidence, such as Perani et al. (2003)7, who found that Broca's area is active during lip-reading implying that Broca's area in humans, related through evolution to macques’ F5 area, is linked not only with language processing, but also with hand and mouth actions. In fact, the more deaf participants recognized syllables and attributed the correct word to a pattern of lip movements, the more active Broca's area was during lip reading.

Researchers also attempted to utilize mirror neurons to explain the evolution of language. Rizzolatti et al. (1998) invoked mirror neurons to hypothesize that human language evolved from a basic mechanism that was not originally related to communication, and the capacity to recognize actions.

From a gestural origins viewpoint, mirror neurons can explain how signs could be made that were readily understood and provide a logical means by which hand movements could take on the new role of gestures; they could process not only their production but also their perception, and hence be responsible for Broca's area turning into a specialized language area. It can also explain how spoken language arose from these abilities after early gestural language became extinct, as they can provide a means by which gesture-signs can be made and identified.

Rizzolatti also proposed that evolution led to a set of generic structures for matching action, observation, and execution. These structures coupled with appropriate learning mechanisms proved great enough to support cultural evolution of human languages in all their richness. If imitation and language require the development of a common neural system, it is not surprising that both skills are observed to develop within the same stage of development.

Anthropologists and linguists have observed that “home signs”, pidgins and creoles have more gesture and less grammar than fully evolved natural languages, which reflects the degree of morphological and syntactical structuring. A more direct example is the observation that even congenitally blind gesture as they talk; they could not possibly have acquired the habit by observing others (Goldin-Meadow et al, 1996).8

Goldin-Meadow observed that 12 blind speakers gestured as they spoke at the same rate as a group of sighted people, conveying the same information and using the same range of gesture forms! For example, a tilted C-shaped hand in the air was used to indicate that a liquid had been poured from a container.

Remarkably, the blind people would gesture while they spoke regardless of whether the listener was sighted or not, suggesting that gestures are tightly coupled to the act of speaking. Yet another example occurs when you stick your tongue out at a new born baby, and it reciprocates.

The picture Petitto and others see is one of a brain that evolved to process certain signals, be they acoustic, as with speech, or visual, as with signed languages--in terms of a grammatical structure.9 The precursor to this ability, the theory states, lies in our ancestors' abilities to process general hand movements, such as grasping or picking, that themselves have a simple, grammatical structure. That is, they contain an agent, an action and an object as when a monkey (self as agent) grabs (action) a piece of food (object).

Such a theory suggests that the ability to process language grew in our distant evolutionary ancestors out of less complex abilities still seen in modern-day nonhuman primates. "This kind of theory is much more satisfying" than the more traditional idea that language developed specially in humans, says Michael Arbib, PhD, director of the University of Southern California Brain Project. "You don't have the grammar built in. Rather you have a normal set of abilities, evolved from more basic abilities in our prelinguistic ancestors, that allow us to learn grammar."

Key to the connection between hand movements and language is the argument that our ancestors developed a mechanism for observing another's actions and comprehending at an abstract level the meaning of those actions. McGill's Petitto says, is finding evidence that the human brain processes hand signals as efficiently as it does acoustic signals. Petitto has uncovered such evidence. In a series of now classic studies, she found that deaf children learn sign language on the exact same developmental trajectory as hearing children learn spoken language. In fact, children raised in households in which one parent speaks and the other signs, show no preference for learning spoken language over signed language.

“Whatever controls the timing of spoken language also controls the timing of sign language, and it certainly isn't based exclusively on sound,” says Petitto. “The brain is working over some other computation, not raw sound.” She hypothesizes that the human brain has evolved a sensitivity to certain patterns that natural language has exploited. And these patterns can appear on the hand or on the tongue.

To test this theory, Petitto teamed up with Robert Zatorre, at the Montreal Neurological Institute's McDonald-Pew Centre for Cognitive Neuroscience, where she is also a research scientist, to examine where in the brain adults process the building blocks of signed or spoken language.

They used positron emission tomography (PET) to look at the superior temporal gyrus within the secondary auditory cortex--a brain area that the scientific community largely agrees processes the phonetic and syllabic units of spoken language. In the study, Petitto, Zatorre and their colleagues imaged the brains of hearing and deaf people as they viewed various stimuli. Among the many test conditions, the researchers included meaningless hand movements that happen to form phonetic and syllabic units in sign language.

When hearing participants saw these hand movements, as expected, their brains showed massive activation in the visual cortex, but, as expected, no activation in the left hemisphere areas associated with language. However, when deaf participants viewed the movements, they not only showed activity in the visual cortex but also in the exact tissue that's active in hearing people when they listen to phonetic and syllabic units of spoken language.

This finding is particularly interesting because this tissue receives input from the primary auditory cortex via the ears and has been thought to only process auditory information. "It's a remarkable finding," says Petitto. "The pathways into that tissue are from the ear, but in deaf people this is tissue that never heard sounds. And yet we saw robust activation in that tissue when they were looking at moving hands that represented phonetic and syllabic information. What it suggests is that the brain evolved sensitivity to very specific patterns that are critical to natural language; in this case, patterns of the phonetic and syllabic levels of language organization."

Rizzolatti and Arbib argue that there is an inherent, though basic, grammar to nonhuman primate manual actions: When a monkey grasps a raisin, for example, "grasp" is the verb, "raisin" is the object and "self" is the subject.10 And when they watch others perform actions--a researcher grasping a raisin, for example--"grasp" is the verb, "raisin" is the object and the person is the subject.

The ancestral brain, they posit, developed a general mechanism for understanding these basic grammatical patterns. In humans, this mechanism evolved to handle even more complex types of grammar that could be linked to pantomimed gestures, then abstract gestures and finally signed and spoken languages, they argue.

Many parts of this theory are still speculative, admits Arbib. But some psychologists and linguists have for years linked action and spoken language, calling speech "articulatory gestures." Instead of motions with the hands, speaking uses motions of the mouth and vocal chords, explains Arbib. Studies of Deaf apraxic patients (Corina et al, 1xxx) have shown that sign language expression can be impaired independently of gestures.11

McNeill (1992) performed a study whose findings strongly supported the view that there is a remarkable continuity between prelinguistic and linguistic development, and that symbolic skills that are most evident in vocal linguistic productions are inextricably linked to, and co-evolve with more general cognitive and representational abilities, as is most apparent in the tight relationship between gestures and words, which continues through adulthood.12

He also notes that gestures are intricately interwoven into our present- day speech patterns, although speech carries the burden of grammar and most of the load of symbolic representation so that we can listen to taped lectures or listen to the radio with little loss of information.

Nevertheless, gesture supplies a visual, iconic component that can provide extra information or circumvent prolonged explanation. Ask someone to tell you what a spiral is or to tell you the size of the fish they claim to have caught. Moreover, people naturally resort to manual gestures when trying to communicate with people who speak a different language.

Gesture quickly takes on a grammatical role if people are prevented from speaking (Goldin-Meadow, xxxx).13] In these instances, gesture takes over the full burden of communication usually shared by the two modalities.

She shows how one can communicate via proto-language without outside help, or indeed even invent basic language for communication needs. She proposes resilience of language both in the face of external and organic variation. Indeed, deaf and hearing children exposed from an early age only to sign language go through the same basic stages of acquisition as children learning to speak, including a stage when they babble using signs.

She notes that the forms and functions of gestures complement grammar in early language development among hearing children, and investigates gesture when it takes over communicative tasks in deaf children.

In hearing children, gestures are found to combine with speech but not with other gestures. However, in deaf children without exposure to natural sign language, in the absence of the auditory channel, gestures combine together, and develop into “home signs” which resemble sign languages, and includes deictic and iconic gestures based on pantomime.14

It becomes more segmented and discrete, and its structure becomes more language-like, with ordering rules at the sentence level, paradigms at the word level, and grammatical categories. Emmorey (1xxx) argues that native signers tend to produce gestures alternately with signs, thus indicating that gestures, which are more mimetic than idiosyncratic, and signs are not co-expressive. Signers also perform prosodic body, facial or vocal gestures, which differ from mimetic gestures by lending themselves to simultaneous occurrence with signs. Finally, signers can also produce discourse gestures that monitor discourse co-ordination, e.g. turn-taking.

Olga, et al. (1xxx) performed a longitudinal study on 3 children from 10 to 23 months of age, and found that there is continuity between the production of the first action schemes, the first gestures and the first words produced by children.

In addition, some important parallelism between the symbolic level of actions, gestures and words produced were observed.

Moreover the relationship between gestures and words changed over time: at the beginning, children demonstrate a clear preference for gestural communication; in a second period children make extensive use of both the gestural and the vocal modalities in their efforts to communicate; prior to the onset of two-words utterances, a clear shift toward the vocal modality was observed.

Finally, the onset of two-word speech was preceded by the emergence of gesture-word combinations and changes in the informational relationship between gesture and speech.

Gestures and postures almost certainly preceded natural language. This idea was suggested by the 17th-century French philosopher Étienne Condillac and revived in the 1970s by the American anthropologist Gordon W. Hewes. Although unpopular at first, it has gained acceptance, especially after the discovery of mirror neurons.

Most animals utilize body postures to communicate mood and intention (such as a rattlesnake warning). Primates carry this further to utilize arm or face posture sequences for even more bandwidth for broadcasting their feelings and intentions.

However, human speech is unbounded in its capacity to express thought and in its freedom from stimulus control, whereas primate vocalizations are “holistic,” containing a message in themselves, whereas human vocalizations can be combined in novel ways to create a message. These primate emotional vocalizations persist today in the emotional cries of modern human beings—such as crying, laughing and screaming.

However, primates are capable of deception even with emotional vocalizations. A young baboon (Byrne, xxxx) who learned to scream in order to steal food from an adult baboon. He figured out that if he was near an adult baboon with food and his mother was out of sight, then he could scream and his mother would rush in and chase away the baboon—who would often drop the prized food. Importantly, the young baboon only did this with baboons that were of lower rank than his mother.

If the earliest language were indeed gestural, this would help to explain why words represent objects and events in arbitrary fashion. Words are abstract rather than iconic (onomatopoeic).

There is nothing in the actual sound of a word that gives a clue as to its meaning, which developed by necessity, as spoken language is one-dimensional, structured in time and not space, whereas critical events in our world are four- dimensional, structured in time and space. This restriction does not apply to manual gestures, which might well have emerged from early attempts to physically mimic the physical world. But what may have begun as an iconic system could plausibly have evolved more abstract properties over time, and at some point arbitrary patterns of sound may have been linked to gestures that may themselves have become abstract symbols rather than icons.

Of course, there are other interpretations of the anatomical relation between hand gestures and the language areas in the brain. Elizabeth Bates of the University of California at San Diego suggests that language is a parasitic system that is overlaid on areas of the brain that originally evolved to do more basic kinds of sensorimotor work.

Elsewhere I have argued at length that icons and indexes very likely played a greater role in the earliest stages of language than they do in spoken language today (Burling, in press). All the early writing systems that we know about used pictographs, which are obvious icons (Boltz 1976, Kramer 1963), but with time the iconicity has been almost or completely lost. Present day sign languages of the deaf still use both indexical pointing gestures and hand shapes which iconically resemble the objects for which they stand, but the long term drift, even in sign language, has been away from iconicity and indexicality and toward increasing conventionality and arbitrariness (Klima and Bellugi 1979, Frishberg 1975). It seems likely that the earliest human language would also have made extensive use of both icons and indices. When first creating signs to be used in any conventional form of communication, iconicity and indexicality are the most obvious principles to exploit, and they were very likely more important when words were first used than they are in modern spoken language (See also, Armstrong, Stokoe, and Wilcox 1995).15

If language originated in manual gestures, why do modern-day human beings speak? Although the early hominids would have been much better preadapted to manual communication, and silent signs may have been preferred on the savanna, there were surely eventual advantages to switching to vocalization. For one thing, speech can be carried on in the dark, or when obstacles prevent communicating parties from viewing one another, or over relatively long distances.

Goldin-Meadow and her colleagues have made the further point that if hands and voice are to share the burden of communication, it is more efficient for syntax to carry the grammatical component, leaving the iconic component to the hands, than to have the hands carry syntax as well as meaning. More importantly, perhaps, speech would have freed the hands yet again, allowing our ancestors to verbally instruct others in manual arts, such as the use and manufacture of tools, while at the same time demonstrating them.

More references :
—Armstrong, D. (1999), Original Signs: Gesture, Sign, and the Sources of Language, Washington, D.C.: Gallaudet University Press.
—Gibson, K. and Ingold, T., Eds. (1993), Tools, Language and Cognition in Human Evolution, Cambridge/New York: Cambridge University Press.
—Bickerton, D. (1995), Language and Human Behavior, Seattle, Wash.: Univ. of Washington Press.
—Corballis, M. C. (1991), The Lopsided Ape, New York: Oxford University Press.
—Corballis, M. C. (1998), Cerebral asymmetry: Motoring on. Trends in Cognitive Science, 2:152–157.
—Erhard, P., T. Kato, P. L. Strick and K. Ugurbil. (1996). Functional MRI activation pattern of motor and language tasks in Broca's area. Society for Neuroscience (Abstract) 22:260.2.
—Savage-Rumbaugh, S., and R. Lewin. (1994), Kanzi: An ape at the brink of the human mind, New York: Wiley.


  • Raja S. Kushalnagar, proposed by Bassem Abdel Ghaffar
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5. V. Ramachandran:
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15. Armstrong, D., Stokoe, W., and Wilcox, S. (1995). "Gesture and the Nature of Language." Cambridge/New York: Cambridge University Press.
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