Peter Carruthers began his career studying philosophy as an undergraduate at the University of Leeds, an outpost for Wittgenstein scholarship. Carruthers waded through the Austrian-British philosopher's thinking for the early part of his career, getting a doctorate from Oxford and publishing books on Wittgenstein along the way.

He decided at one point to join a reading group discussing the ideas of Daniel Dennett, Jerry Fodor and Thomas Nagel, whose work deals with philosophy of mind. "It was just so much more fun," he says. "I just started to move sideways. Having done my Wittgenstein books, I never picked up Wittgenstein again."

Carruthers is now in the philosophy department at the University of Maryland and his interests, like those of his adoptive mentors, focus on philosophy of mind and cognitive science. His recent work involves an exploration of the nature of working memory. Last year, he delivered a lecture on working memory and how it evolved for the Arthur M. Sackler Colloquium at the National Academy of Sciences and then wrote a paper (PDF) on the topic for the Proceedings of the National Academy of Sciences. I asked Carruthers to explain what we know about this temporary mental storage area and whether the human version is special in any way.

What is working memory?

Working memory is the capacity to sustain in an active and conscious state a representation which can be then used in further processing or further reasoning. One example that’s often used is when someone tells you their phone number and you have to keep that number in mind while you go into another room and get a paper and a pencil.

In studying the nature of human cognition, why is working memory so important?

Differences in working memory capacity turn out to correlate with other cognitive capacities that matter. Differences in working memory correlate very strongly with fluid g or general intelligence. They correlate with reasoning ability. Many have come to think that working memory is what we are considering when we think of fluid g, though perhaps not the whole of it.

Why is this mental scratch pad so important to general intelligence?

Many sorts of routine intelligent activities we have to do, such as performing a little bit mental arithmetic, take place in working memory. Trying to focus on the road while carrying on a conversation with someone in a car also takes place in working memory because you have to hold in your mind what’s going on in the conversation while concentrating on something else. At the same time, you have to suppress or ignore certain distractor items. Being able to maintain focused attention is at the heart of fluid general intelligence

How, if at all, does working memory in humans differ from that of other primates and other animals

In its basic structure it might not differ at all. I don’t think we have enough studies to show this, but there is evidence that indicates that other animals can sustain representations. After the stimuli have gone away, they can also call up representations using visual imagery. They can manipulate those representations for long-term or medium-term planning. All the stuff we do with working memory, it looks like other animals can do that too.

So is anything special about human working memory?

There’s no good evidence about exactly what’s going on. But it may be that what’s distinctive is that we’re chronic users of working memory. We fantasize all the time. We’re using working memory at every moment of the day. When we’re not on task, we’re off task imagining something. That means you’re always playing around with alternative plans and alternative ways of doing things and so forth.

Is there any evidence that certain brain circuits unique to humans allow us to use these mental faculties that involve imagination?

I think it’s much more likely to be motivational. There might be a subtle difference in the wiring of circuits but it won’t be a major one. It’s more about motivation. One is motivated to call up and generate working memory as a kind of intrinsic reward to be able to use the imagination.

I’ve speculated along with a grad student in a paper I wrote recently that maybe this is the function of distinctively human pretend play. There are a lot of animals that engage in rough and tumble play. But imaginative play seems to be uniquely human. All humans do it. It comes online at about the same age in every culture. Maybe what that’s for is to get the brain in the mode of generating representations that are suggested by the environment.

There’s the famous example of pretending that a banana is a telephone. It’s roughly the same sort of shape. What you do is imagine it’s a telephone and impose a representation on it and use it accordingly. That self-generated activity can be internalized and eventually, as you get older, you don’t have to externalize your play at all. You just use your imagination.

Image Source: Cindy Phillips