Communicative capability is an obviously essential innate property of all social species. Humans and other social mammals typically use two communication systems:
The first is an intimate system that two individuals use to establish and maintain their relationship. Touch dominates, but it uses all sensory modalities. It’s called grooming in primates, but no equivalent single word exists for humans that covers everything from social dancing to a handshake to a military salute to a caress to a pat on the back to a swat on the rear.
The second is a signal system that uses a set of sounds to alert others to specific group dangers and opportunities. Primate signal systems are holistic in that a single cry communicates the nature and location of the challenge. It’s innate in that an infant monkey who hadn’t previously heard a specific signal (such as for danger above) will still respond appropriately (by looking up).
Human language, which functions at both an intimate and corporate level, removes the meaning from individual sounds and inserts it into sound sequences. For example, the phonemes D and O are meaningless, but the verb DO is meaningful. Adding a G creates an entirely different word – DOG (which also differs in meaning from its reverse, GOD).
Combinations of selected groups from the 44 phonemes (or 26 letters) that English uses can thus form hundreds of thousands of words, and sequences of words can combine into an infinite number of narratives. Similarly, the 12 tones on the musical scale can combine into an infinite number of melodies, and the ten digits into an infinite representation of quantity.
More amazing, genetics uses a similar sequential coding system. Specific combinations of the 20 different amino acids arrayed in a DNA genetic sequence can create an infinite number of proteins. Genetic sequences of amino acids thus build and maintain our biological body, and linguistic sequences of phonemes help to build and maintain our social species.
Parents and scientists have long been curious about how children learn to talk, and how they then know what to say. This column will explain a recent discovery that helps to explain the onset of speech, and next month’s column will explore how humans transfer thought into speech.
Learning How To Talk
Our brain’s recently discovered mirror neuron system resolves much of the mystery of how we learn to talk. Some brain memory networks store and recall facts and experiences, such as the sequence of letters that spell shoelaces, or the memory of a broken shoelace at an inopportune time. Mirror neuron and related networks store and recall specific movement sequences (or skills), such as the sequence of hand movements that tie shoelaces.
Mirror neurons activate the motor neurons that carry out a mastered specific action, but they also activate when we observe someone else carry out that action. They create a mental template of the observed action, and so allow us to feel what the other person is experiencing as if it were happening to us.
Since mirror neurons allow us to imitate (or mirror) an action the first time that we observe it, they are central to the development and maintenance of memories of basic actions. Smile at a newborn infant and she’ll smile. Yawn and observers will either yawn or stifle a yawn. Children have so many basic actions to learn that they tend to automatically imitate whatever actions they observe, and thus begin their mastery of basic movements.
When we have learned a fact or skill, we can comprehend it in its entirety. For example, when we hear someone spell the first three letters of Xerox or observe someone picking up a pencil we can infer what will probably follow. Think of how your computer will complete the address of a frequently used website after you’ve typed in the first few letters. A previous column explained how this capability allows us to easily and correctly read misspelled words.
We use language to teach a child how to spell shoelaces, but not how to tie them. Children learn how to tie shoelaces by observing us do it. One problem with learning how to speak is that speaking involves complex internal mouth and vocal system movements that children can’t see. What’s wonderful about our brain is that information that enters one sensory modality easily transfers to others. So if we hear the word shoelace, we can visualize it in our mind, even though no shoelace is visible. Learning to speak makes use of this cognitive transfer property.
Hearing articulate speech activates the same mirror neurons in the child’s brain that the speaker used to sequence the uttered sounds and words. Speech (like learning to tie shoelaces) is a complex motor activity, so the infant initially babbles in awkward incoherent imitation, but over time in a verbal environment, the child begins to correctly utter simple phonemic combinations, and finally smooth articulate speech emerges.
We enhance this learning process with motherese, a universal behavior in which an adult holds an infant in a close face-to-face position, and then speaks in a slowed-down, high-pitched, exaggerated, repetitive, melodic format that engages the infant’s attention and so easily activates her mirror neuron system.
Children who have specific auditory deficiencies will be delayed in the development of their ability to understand speech, and so to develop speaking competence. Computerized interventions such as Fast ForWord products can slow down incoming speech to match the child’s auditory rate, and then gradually increase it as the child’s brain adapts to the faster rates.
It now appears that at least some children who suffer from the autism spectrum have a deficient mirror neuron system, and this would explain their inability to infer the behaviors and thoughts of others and to easily master articulate speech (Ramachandran, 2006)
Most complex behaviors are combined sequences of shorter actions, just as short words combine into longer words, and words combine sequentially into sentences. A relatively small number of memorized units can thus process a very complex language. Because of this, young children master spoken language with less explicit instruction than might otherwise be expected.
Knowing What To Say
Knowing how to speak is different than knowing what to say. Do we think in words, or is speech simply the verbal representation of non-verbal thought? Next month’s column will explore this fascinating question.