A visitor to my blog, Janet Kwasniak, tipped me to an article reporting a possible neurological basis for humanity’s unique powers of joint attention. Regulars on this blog will know that it leans toward an attention-based view of language. My working assumptions are that words are tools for piloting attention and that speech requires a speaker and a listener paying joint attention to a topic. Thus, the evolution of speech required the evolution of joint attention, so I was delighted when Janet told me about an article in last October’s Current Directions in Psychological Science, “Attention, Joint Attention, and Social Cognition,” by Peter Mundy and Lisa Newell (abstract here).
The article holds that human brains have two distinct attention systems which, when working together, produce joint attention. The older system, located in the rearward (posterior) part of the brain is reflexive and tracks external stimuli. When something moves, this system responds. A separate, voluntary system is located in the brain's frontal (anterior) region and pays attention to one’s own purposeful behavior.
These systems exist in humans and chimpanzees, but in humans the two can be integrated into one unified system that permits joint attention. For example, two people are seated in a restaurant booth facing one another. Suddenly the posterior attentional system of one customer directs his eyes toward the sight of a waiter pouring soup on a diner’s head. Meanwhile the customer uses his anterior system to say to the companion, “Will you look at that,” and point to the unexpected scene. Joint attention comes from the capacity to integrate these two, separately-developed brain systems.
Mundy and Newell break joint attention into two parts:
responsive joint attention (RJA): the reflexive portion of joint attention under the control of the posterior attentional system. In speech, it handles the listening side. In speech, it handles the listening side. Chimpanzees can engage in this kind of joint attention. That is to say, they can look where another looks. Infants too will look where adults look. Responsive joint attention can be measured in children as young as six months and is a good predictor of language ability at 24 months.
initiating join attention (IJA): the portion of joint attention under the control of the anterior attentional system. In speech, it handles the speaking side. Chimpanzees do not initiate joint attention. The “lack of spontaneous sharing experiences” “such as showing” [p. 270] has often been noted in autistic children.
These two halves of joint attention develop before speech appears in infants, although the two are not well coordinated in infant development. That is to say that RJA and IJA seem to develop separately, suggesting the different functions had separate evolutionary histories.
The exciting part of this analysis is the way it enables us to think concretely about things that have been tangled, abstract categories. For example, in Herbert Terrace’s famous effort to teach sign language to an ape given the satirical name of Nim Chimpsky the ultimate problem seemed to be Nim’s lack of interest in vocal communication. He could join in when asked, but never initiated anything or kept the ball bouncing once a human started a verbal interaction. There has always been some controversy over how seriously to take this limitation since Nim’s responsive joint attention was so strong. Mundy and Newell’s paper shows a way to understand the difference.
Mundy Nim had a normal “RJA” system in the back of his brain, but a weak or non-existent IJA system in the front of his brain.
This work also clarifies the biological differences between a human saying, “Oh, oh! Leopard!” and a vervet monkey making its leopard call. The vervet’s call is part of some automatic system while the human’s under this control of the IJA. Thus, despite the functional similarities between the two events, their biological basis is very different.
The evolution of speech marked the introduction of something new under the sun. It was not an extension of a long-evolving primate system of communications, but the introduction of a new kind of social attention. Long ago apes, if not earlier, developed the ability to take into account another’s attention, but by itself RJA is parasitic, taking advantage of another’s discovery without contributing anything to the pot.
Mundy and Newell’s report gives a biological explanation for the peculiar fact that there are no species with partial languages. Chimpanzees and gorillas are smart enough to use symbols, but they don’t do so. This blog regularly argues that the reason for that silence is that something other than intelligence is at issue. Now we’ve got a biological fact to point to. Apes lack initiating joint attention.
An evolutionary path becomes imaginable:
- Long ago, reflexive attention to stimuli appeared and began evolving.
- Later, attention to one’s own planning appeared, enabling animals to adjust their behavior according to how they were doing.
- By the time of the great apes, reflexive attention included the ability to track where others were looking.
- The ability to deliberately use of that reflexive attention appeared somewhere along the human lineage. Individuals could use their planning attention to direct another’s attention. (Note “misdirection” of attention is the magician’s and con-man’s tool, so this development was not unambiguously pro-group.)
- If directing another’s attention was parasitic, we would expect to see the evolution of ignoring mechanisms. Instead the capacity to integrate RJA and IJA evolved, suggesting IJA was (or had become) a group adaptation.
- At this point protolanguage probably evolved.
However, if protolanguage depends on joint attention, what happened to get us to true language? Last week’s post talked about a third attentional capacity, attention to oneself, not just to one’s plans but one’s knowledge and nature. That knowledge comes from speech itself, but is also likely to be supported by something in the brain. So is there a third area of the brain that eventually connects to the earlier joint attention hookup and allows the use of full language?
Whatever answers those questions finally get, it seems to me that the idea that words are pilots of attention and not symbols carrying meaning is becoming well established. But I wonder how it seems to other readers on this blog. What do you think?