Nature, Nurture and Language in the Brain

1The patient called “Tan”

In April 1861 the French surgeon Paul Broca examined a 51-year-old patient, Louis Victor Leborgne, at the Bicêtre hospital near Paris. For more than twenty years Leborgne had been able to say almost nothing except one syllable, “tan”, which became his nickname, yet he understood what was said to him and answered with gestures. He died a few days later. When Broca examined his brain, he found damage in the left frontal lobe. Over the next few years Broca collected similar cases and in 1865 concluded: “we speak with the left hemisphere.”

Leborgne’s brain was preserved in a Paris museum. In 2007 Nina Dronkers and colleagues scanned it with modern MRI and found that the damage went much deeper than the surface area Broca had described. Broca’s basic insight survived, but the brain’s language system turned out to be larger and more connected than one spot.

21. Language areas and aphasias

Figure 1. The classic language areas of the left hemisphere (simplified; not to scale).

How lateralised is language? Stefan Knecht and colleagues (2000) used a brain-imaging method with 326 healthy people and found that language depended mainly on the left hemisphere in about 96% of strongly right-handed people and about 73% of strongly left-handed people. The right hemisphere still contributes, especially to the melody of speech, emotion in the voice and understanding jokes and metaphors. Modern imaging shows language is handled by networks spread across both hemispheres, with the classic areas as important hubs.

32. Nature or nurture?

Chomsky’s poverty of the stimulus argument holds that the speech children hear is too limited and messy to explain the rich grammar they end up with, so much must be inborn. Most researchers today take an interactionist position, in which inborn learning abilities and rich social input work together (Unit 6).

43. Is there a critical period?

• Genie. In 1970 a 13-year-old girl was found in Los Angeles after years of extreme isolation and neglect, during which she was hardly spoken to. With care and teaching she learned many words but never mastered grammar. Her case is often cited for a critical period, but it is weak evidence: she suffered severe trauma, may have had a disability from birth, and is a single case. The research also raised serious ethical concerns about her treatment.
• Immigrants’ grammar. Jacqueline Johnson and Elissa Newport (1989) tested 46 Chinese and Korean speakers who had moved to the United States between the ages of 3 and 39. Those who arrived before about age 7 judged English grammar like native speakers; performance declined the later people had arrived, up to puberty.
• A very large online test. Joshua Hartshorne, Joshua Tenenbaum and Steven Pinker (2018) analysed nearly 670,000 people who took an online English grammar quiz. The ability to learn grammar stayed high until about 17 to 18 years and then declined; to reach native-like grammar, learners needed to start by about age 10.
• A language born in a school. In the late 1970s and 1980s, deaf children brought together in new schools in Nicaragua created a new sign language among themselves. Each new group of young children made it more systematic than the older users had, which suggests that children do not just copy language but actively build its grammar (Senghas and Coppola, 2001).