I agree with @what. I was going to edit his answer, but thought it would be better to post this as an adjunct to his answer.
The conclusions I have drawn here are my own ideas.
For individuals who are in the full-time occupation of deep concentration, through work, study, interests, their working memory is getting very little downtime.
Working memory is your brain's Post-it note, says Tracy Packiam
Alloway, PhD, assistant professor of psychology at the University of
North Florida in Jacksonville, Florida. “It makes all the difference
to successful learning,” she says.
You can think of working memory as the active part of your memory
system. It's like mental juggling, says H. Lee Swanson, PhD,
distinguished professor of education with the Graduate School of
Education at the University of California, Riverside. “As information
comes in, you're processing it at the same time as you store it,” he
says. A child uses this skill when doing math calculations or
listening to a story, for example. She has to hold onto the numbers
while working with them. Or, she needs to remember the sequence of
events and also think of what the story is about, says Swanson.
Brief by design, working memory involves a short-term use of memory
and attention, adds Matthew Cruger, PhD, neuropsychologist with the
Learning and Diagnostics Center at the Child Mind Institute in New
York City. “It is a set of skills that helps us keep information in
mind while using that information to complete a task or execute a
challenge,” he says. Working memory is like a foundation of the
brain's executive function. This is a broad and deep group of mental
processes. They allow you to do things like plan ahead, problem solve,
organize and pay attention.1
“Working memory helps us stay involved in something longer and keep
more things in mind while approaching a task,” says Cruger. “And, how
can you plan ahead if you don't use working memory to keep your goal
in mind, resist distractions and inhibit impulsive choices?”
(What Is Working Memory and Why Does It Matter? By Annie Stuart)
An individual engrossed in mental tasks is going to be coming in and out of states where the working memory is, potentially, overloaded. So, for instance, coming to a site like this, may serve as a distraction from learning or working (This answer discusses the value of distraction as beneficial to work productivity); however a great deal of attention is required to focus effectively on the site.
So if an individual chooses a mentally demanding "distraction" (as in this example posting on a Cognitive Sciences site; for others it may be another form of intellectual hobby), they are flitting from one state of deep concentration, with an occupied working memory, to another. I would suggest that the focus upon one mentally demanding task and an alternate, less mentally consuming, distraction task would alleviate this overload.
The term working memory refers to a brain system that provides
temporary storage and manipulation of the information necessary for
such complex cognitive tasks as language comprehension, learning, and
reasoning. This definition has evolved from the concept of a unitary
short-term memory system. Working memory has been found to require the
simultaneous storage and processing of information. It can be divided
into the following three subcomponents: (i) the central executive,
which is assumed to be an attentional-controlling system, is important
in skills such as chess playing and is particularly susceptible to the
effects of Alzheimer's disease; ....
(Working memory. Baddeley A.)
Although working memory itself, is not the same as long term memory, I am suggesting that an overloaded working memory, would interfere with the ability to multi task from one mentally demanding task to another completely different mentally demanding task.
This does not touch upon the effects of stress on memory, nor does it discuss the effects of attention on memory, as I think the notion of working memory being in a constant overloaded state would explain this phenomena.
After feedback, I would like to make my point clearer.
- I am proposing that a working memory, that is being fully utilised, is not so easy to "clear" to create a concentrated focus on another mentally consuming task.
- I have stated clearly that WM is different to long term memory (which stores the memory)
- I am suggesting (if the problem isn't the actual storage of the memory, ie within long term memory) and given the description of the problem, that it could be the limitations of working memory.