I’m trying to find some solid ground. Here are the questions I’m trying to get straight on:
- Suppose someone didn’t believe in the existence of a separate short-term memory system, just as (apparently) people in the ’50s and ’60s were skeptical. How would you convince a skeptic?
- What is the working memory system, anyway?
- Say that you were a behaviorist, someone uncomfortable with talk of the cognitive. How would you make sense of the observational findings?
- More concretely, what were the problems that Baddeley and Hitch were trying to solve when they introduced their working memory model?
The case is fascinating:
“K. F., a man aged 28, had a left parieto-occpital (“head” – MP) fracture in a motor-bicycle accident eleven years before, when a left parietal subdural (“brain” – MP) haematoma was evacuated. He was unconscious for ten weeks.”
He had lasting brain damage, especially when it came to language:
“His relatively poor language functions were reflected in his verbal I.Q. His ability to express himself was halting, and some word-finding difficulty and circumlocutions were noted.”
His short-term verbal memory in particular was damaged:
“The most striking feature of his performance was his almost total inability to repeat verbal stimuli. His digit span was two, and on repeated attempts at repeating two digits his performance would deteriorate, so that on some trials his digit span was one, or even none. His repetition difficulty was not restricted to digits; he had a similar difficulty in repeating letters, disconnected words and sentences. Single verbal items would be repeated correctly with the exception of polysyllabic words which were on occasion mispronounced.”
The thing that made him especially interesting was that, for a guy with significant short-term memory damage, there were a lot of things that he could do:
“Memory for day-to-day happenings was good and he had an adequate knowledge of recent and past events. Immediate memory for the Binet figures was accurate.”
Here is the real surprise, for people in the 1960s: his long-term learning was, actually, not bad. Consider the ten-word learning task, at which he performed admirably:
“A list of 10 high-frequency words was presented auditorily at the standard rate. Subjects were required to recall as many words as possible from the list immediately after presentation. This procedure was repeated until all the 10 words were recalled (not necessarily in the correct order). K. F. needed 7 trials. Twenty normal (“didn’t fall off a motorcycle” – MP) controls too an average of 9 trials, 4 of the subjects failing on the task after 20 trials. After an interval of two months he was able to recall 7 of these 10 words without relearning.”
On two other long-term memory tests, K. F. seemed to be performing normally as well.
And, what’s the significance of all this?
This was written when the existence of a short-term memory system was not universally accepted. (Is it universally accepted now? It feels like it but I don’t actually know.) And it’s useful to me for identifying what the core, foundational findings are that we have to grapple with in memory. There really aren’t very many, it seems.
At the core of things is the “digit span” task. This is the finding that there is some sort of limit on how many random things we can remember. This itself was the core finding that was supposed to support short-term memory. (“All subjects have a limited capacity to recall a series of digits or letters, and this limitation is regarded as a characteristic of the ‘short-term’ memory store.”)
The strongest evidence that this digit-span task was measuring a totally different system of memory was the evidence of amnesiacs, whose long-term memory is severely impaired:
“The question as to whether the organization of memory is a unitary process or a two-stage process has received much attention in recent years. The strongest evidence that there are separate short- and long-term memory systems is provided by the specific and isolated impairment of long-term memory in amnesic subjects.”
If you can have short-term memory but no long-term memories, and you can measure this with all sorts of repetition and digit span tasks, then there needs to be some distinction between two memory systems. Right?
Here, though, they found the opposite. A patient could have pretty normal long-term memory performance even though their short-term memory system was severely impaired.
In a different paper (1970) they lay out the implications of this for then-current controversies about short- and long-term memory:
“Most important, the results present difficulties for those theories in which STM and LTM are thought to use the same physical structures in different ways. (Because, I suppose, they’ve shown STM and LTM to be doubly independent of each other.-MP) They also indicate that the frequently used flow-diagrams in which information must enter STM before reaching LTM may be inappropriate. On this model, if the STM system were greatly impaired, one would expect impairment on LTM tasks, since the input to the LTM store would be reduced.”
What do they suggest?
“In light of these findings, it is suggested that a model in which the inputs to STM and LTM are in parallel rather than in series should be considered.”
One way of thinking of this could be that their patient, K. F., had damaged his ability to encode information about verbal sounds, but not his ability to encode the meanings behind those words, and that long-term memory is a system for storing meanings while short-term memory is just a system for storing sounds.
This is all fifty years ago, of course. But I think it’s helpful for me to understand what it took to get from a world where this seemed as plausible as the alternatives, to a world where scientific communities seem to universally accept that alternative.
That there’s a distinction between STM and LTM is beyond question. This is something that is confirmed a million-times over. Amnesiacs and people like K. F. speak to the distinctness of short- and long-term memory systems. We also experience this a million-times daily.
What is up for debate in the early 1970s is the relationship between these two systems. Is it one big system (“unitary”), with STM feeding directly into LTM? This study challenged that, suggesting that they were two fully independent memory systems.
Current models of memory suggest that they are connected, though in a more complex way than was understood before Baddeley and Hitch came along. (At least, I think that’s what’s going on…)