World authority on human memory function
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Cognitive psychologists study the human mind. “Cognitive” comes from the Latin verb cognoscere, to know, so cognitive psychologists study how people know things — how we see, hear, acquire information, remember, believe, understand, speak, think, solve problems, make decisions and much more. As a memory researcher, Tulving explores how people learn and know facts, and how they remember their experiences. Knowing and remembering are very important facets of mind, and for Tulving the human mind is by far the biggest and most complex unsolved mystery in the universe.
Sometimes people wonder what a “mind” is. Tulving believes only a life can have a mind. To him a rock cannot have a mind. But does a virus or a blade of grass have a mind? He defines the occurrence of mind in living organisms as a point in evolution when a living thing does something without expressing any overt behaviour. For instance, when you are remembering something, you are doing something, but your body is not outwardly doing anything. Tulving points out that different species have different minds. A bee can remember the location of a flower by using its bee mind. A human remembers a flower’s location in a different way, with a different type of mind.
In the early 1960s, guided by others who had gone before him, Tulving devised experiments to study the way people learn words and organize them in their own minds — so-called subjective organization.
Tulving wondered why subjective organization helps people learn and retain verbal information. He assumed that organized information in memory is more readily accessible than unorganized information; that better “access routes” to it must exist. He made a distinction between two kinds of learned information in memory, one that is “available” and another, more organized form, that is “accessible,” if not immediately available. In 1966 Tulving and his research assistant, Zena Pearlstone, published the results of a large experiment involving more than 900 high school students. It was based on the 1963 classroom demonstration described above. The experiment showed how storage of information could be distinguished from retrieval of information and how studies could isolate and capture the two components. This paved the way for further work that culminated in one of Tulving’s best-known discoveries: the “encoding specificity principle,” the relation between storage and retrieval necessary for the remembering of an event.
Tulving is best known for his concept of episodic memory. Again guided by earlier work of others, in 1972 he proposed a basic distinction between two kinds of memory. He called one episodic and the other semantic memory. At the time, psychologists believed there was only one kind of long-term memory, so Tulving’s idea of two separate memory systems was not accepted at first. According to Tulving, episodic memory is used to recall events we have personally experienced or witnessed, while semantic memory taps into mental stores of general facts and knowledge. Thus, episodic memory is more about remembering, and semantic memory is more about knowing.
According to Tulving’s theory, we use semantic memory to know that the Eiffel Tower is a famous landmark in Paris, and that Paris is the capital of France, but we use episodic memory to remember a trip we took to Paris to visit the Eiffel Tower and any events that occurred there. Other psychologists do not agree. They maintain that knowing about the Eiffel Tower being in Paris and remembering one’s trip to Paris rely on one and the same kind of memory. The only difference, they say, is the information the memory contains.
Tulving also believes that animals do not have episodic memory, not even higher primates such as chimpanzees and gorillas. To him, they have only semantic memory. They always live for the moment, lacking the human ability to travel back and forth in time in their mind. That is, they cannot remember what they did yesterday or imagine what they will do tomorrow. This capacity for mental time travel seems to be unique to humans. Animals do not have this capacity, nor do some people who have suffered a certain type of brain damage.
Psychologists have done experiments on brain-damaged people with no episodic memory and have found that some can learn new facts, if rather slowly. However, such people cannot recall how, when or where they learned these facts. They have no memory of taking the lessons. One fellow for many weeks went to Tulving’s clinic, where he was taught certain facts and phrases such as, “Sun’s rays soften asphalt.” At the end of the course he was given a test and he did quite well. When asked what the rays softened, he would say “asphalt.” But when he was asked to describe how he learned these things he had no recollection of the lessons and had no idea how he knew all the material.
Tulving extends his theory to children less than four years old. They learn quickly using their semantic memory abilities, but they cannot imagine the past or think of a future time in their own minds. According to Tulving, so far there is no objective evidence that animals or young children have episodic memory.
Tulving goes even farther. He believes that some perfectly intelligent and healthy people also lack the ability to remember personal experiences. These people have no episodic memory; they know but do not remember. Such people have not yet been identified, but Tulving predicts they soon will be.
Tulving believes one could use a PET scanner to tell whether a person is using episodic memory, remembering an event such as a wedding, or semantic memory, recalling what a wedding ceremony means. In other words, it is now possible to “read people’s minds,” though in a very limited way. Reading minds is one of the dreams of cognitive science and now, thanks to functional neuroimaging, it seems much more possible than only a short time ago. In this respect, cognitive psychology and other branches of brain science have made great progress. As Tulving says, “Progress: knowing more about nature now than we did before is what the game called science is all about.”
One method Tulving has used to understand human memory is called functional neuroimaging, a way of seeing inside a living, functioning brain without hurting it. A positron emission tomograph (PET) is a brain-scanning instrument that shows which parts of a brain are functioning during the scan. pet shows where sugar, the body’s energy source, is being used up fastest in the brain. Neurologists believe that increased brain activity requires increased sugar consumption at the site of the activity. A person having a pet scan is injected with a special kind of radioactive sugar tracer during the procedure. By looking at pet scan maps of the brain, scientists can tell which parts of the brain were functioning during the scan. The procedure can be done while a person is learning something, or while the same person recalls what they have learned. Glowing sections of the brains below show active, functioning regions.
A pet scan subject is fitted with a plastic face mask to minimize head movement. For a typical session, usually six to 10 single scans are done, spaced about 10 minutes apart. Each scan lasts about two minutes, during which the subject is engaged in a particular mental activity. The cognitive activity begins at the beginning of the two-minute period, shortly after the subject receives the injection. The tracer reaches the brain in about eight seconds and then the actual scanning begins, lasting 40 to 60 seconds.
Encoding Brain: Tulving’s experiments show that when people are trying to “encode” words in memory (learning), the frontal and temporal cortex in the left hemisphere “lights up” with activity, but the right hemisphere encoding left does not.
Retrieving Brain: When people “recall” previously learned material, the right frontal cortex comes very much alive retrieval right. The left hemisphere is active in retrieval, too, but to a smaller extent than the right.
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Human memory is still a big mystery to Tulving. For instance, how do we travel back into our own personal past using only our minds?
Endel Tulving, “Episodic Memory: From Mind to Brain,” Annual Review of Psychology, 2002.
Endel Tulving and Fergus I. M. Craik, The Oxford Handbook Of Memory, Oxford University Press, 2000.
McGill University website on how memory works.