No subject

Did you consider the possibility that the training on the
second task could have affected the same synapses used for
the first task ? If this should have happened, it could be
another explanation of what has been observed. To check
which hypothesis is the right one, I would suggest to 
repeat the experiment in a slightly different way:

The second group should be trained on the second task not
immediately after the first task, but, for example, ten
hours later.Now the following two things can happen:
1) People from this group still have reduced levels of 
skill on the first task.
2) They perform well on both tasks.

In the first case maybe the same synapses have been used to
learn both tasks, with or without the temporary and
permanent kinds of memory you described. So the new
information could have been (partially) rewritten over the
previous one.

In the second case I can see two choices: yours is the first one.
Here is the second one:  the brain seems to have a modular
and hierarchical structure. Let's assume that different
experiences are stored in different modules; so, when there
is something new to remember, the "brain's operative 
system" has to find an "empty" module to store the
information. This fact, if it should be real, could explain
why the younger a person is, the less time he takes to 
learn new things: in his brain the number of "empty" 
modules would be much greater than the number of "full"
modules, so it should be quite fast to find the right 
place. A way to check this hipothesys would be to make the
test you wrote about, and to consider the age of the people
involved. If the time the information takes to move from
temporary storage to permanent storage is roughly
indipendent on age, what I wrote can be thrown
away.

P.S.:
Considering I am still a student, please do not take what I
wrote too seriously !

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APPENDIX

COULD THERE BE REAL-TIME, INSTANTANEOUS LEARNING IN THE BRAIN?


One of the fundamental beliefs in neuroscience, cognitive science
and artificial neural networks is that the brain "learns" in
real-time. That is, it learns "instantaneously" from each
and every learning example provided to it by adjusting the
synaptic strengths or connection weights in a network of
neurons.  The learning is generally thought to be
accomplished using a Hebbian-style mechanism or some other
variation of the idea (a local learning law). In these
scientific fields, real-time learning also implies
memoryless learning. In memoryless learning, no training
examples are stored explicitly in the memory of the
learning system, such as the brain. It can use any
particular training example presented to it to adjust
whatever network it is learning in, but must forget
that example before examining others. The idea is to obviate the
need for large amounts of memory to store a large number of
training examples. This section looks at the possibility of
real-time learning in the brain from two different perspectives.
First, some factual behavioral evidence from a recent neuroscience
study on learning of motor skills is examined. Second, the idea of
real-time learning is examined from a broader behavioral
perspective.

A recent study by Shadmehr and Holcomb [1997] may lend some
interesting insight on how the brain learns. In this study, a
positron emission tomography (PET) device was used to monitor
neural activity in the brain as subjects were taught and then
retested on a motor skill. The task required them to manipulate an
object on a computer screen by using a motorized robot arm. It
required making precise and rapid reaching movements to a series of
targets while holding the handle of the robot. And these movements
could be learned only through practice. During practice, the blood
flow was most active in the prefrontal cerebral cortex of the
brain. After the practice session, some of the subjects were
allowed to do unrelated routine things for five to six hours and
then retested on their recently acquired motor skill. During
retesting of this group, it was found that they had learned the
motor skill quite well. But it was also found that the blood flow
now was most active in a different part of the brain, in the
posterior parietal and cerebella areas.

The remaining test subjects were trained on a new motor task
immediately after practicing the first one. Later, those subjects
were retested on the first motor task to find out how much of it
they had learnt. It was found that they had reduced levels of skill
(learning) on the first task compared to the other group.

So Shadmehr and Holcomb [1997] conclude that after practicing a new
motor skill, it takes five to six hours for the memory of the new
skill to move from a temporary storage site in the front of the
brain to a permanent storage site at the back. But if that storage
process is interrupted by practicing another new skill, the
learning of the first skill is hindered. They also conclude that
the shift of location of the memory in the brain is necessary to
render it invulnerable and permanent. That is, it is necessary to
consolidate the motor skill.

What are the real implications of this study? One of the most
important facts is that although both groups had identical training
sessions, they had different levels of learning of the motor task
because of what they did subsequent to practice. From this fact
alone one can conclude with some degree of certainty that
real-time, instantaneous learning is not used for learning motor
skills. How can one say that? One can make that conclusion because
if real-time learning was used, there would have been continuous
and instantaneous adjustment of the synaptic strengths or
connection weights during practice in whatever net the brain was
using to learn the motor task. This means that all persons trained
in that particular motor task should have had more or less the same
"trained net," performance-wise, at the end of that training
session, regardless of what they did subsequently. (It is assumed
here that the task was learnable, given enough practice, and that
both groups had enough practice.) With complete, permanent learning
(weight-adjustments) from "real-time learning," there should have
been no substantial differences in the learnt skill between the two
groups resulting from any activity subsequent to practice. But this
study demonstrates the opposite, that there were differences in the
learnt skill simply because of the nature of subsequent activity.
So real-time, instantaneous and permanent weight-adjustment
(real-time learning) is contradictory to the results here.

Second, from a broader behavioral perspective, all types of
"learning" by the brain involves collection and storage of
information prior to actual learning. As is well known, the
fundamental process of learning involves: (1) collection and
storage of information about a problem, (2) examination of the
information at hand to determine the complexity of the problem, (3)
development of trial solutions (nets) for the problem, (4) testing
of trial solutions (nets), (5) discarding such trial solutions
(nets) if they are not good enough, and (6) repetition of these
processes until an acceptable solution is found.  Real-time
learning is not compatible with these learning processes.

One has to remember that the essence of learning is generalization.
In order to generalize well, one has to look at the whole body of
information relevant to a problem, not just bits and pieces of the
information at a time as in real-time learning. So the argument
against real-time learning is simple: one cannot learn (generalize)
unless one knows what is there to learn (generalize). One finds out
what is there to learn  (generalize) by collecting and storing
information about the problem. In other words, no system,
biological or otherwise, can prepare itself to learn (generalize)
without having any information about what is to be learnt
(generalized).

Learning of motor skills is no exception to this process. The
process of training is simply to collect and store information on
the skill to be learnt. For example, in learning any sport, one not
only remembers the various live demonstrations given by an
instructor (pictures are worth a thousand words), but one also
remembers the associated verbal explanations and other great words
of advise. Instructions, demonstrations and practice of any motor
skill are simply meant to provide the rules, exemplars and examples
to be used for learning (e.g. a certain type of body, arm or leg
movement in order to execute a certain task). During actual
practice of a motor skill, humans not only try to follow the rules
and exemplars to perform the actual task, but they also observe and
store new information about which trial worked (example trial
execution of a certain task) and which didn't. One only ought to
think back to the days of learning tennis, swimming or some such
sport in order to verify information collection and storage by
humans to learn motor skills.

It shouldn't be too hard too explain the "loss of skill"
phenomenon, from back-to-back instructions on new motor skills,
that was observed in the study. The explanation shouldn't be
different from the one for the "forgetting of instructions"
phenomenon that occurs with back-to-back instructions in any
learning situation. A logical explanation perhaps for the "loss of
motor skill" phenomenon, as for any other similar phenomenon, is
that the brain has a limited amount of working or short term
memory. And when encountering important new information, the brain
stores it simply by erasing some old information from the working
memory. And the prior information gets erased from the working
memory before the brain has the time to transfer it to a more
permanent or semi-permanent location for actual learning. So "loss
of information" in working memory leads to a "loss of skill."

Another fact from the study that is highly significant is that the
brain takes time to learn. Learning is not quick and instantaneous.


Reference:

Shadmehr, R. and Holcomb, H. (August 1997). "Neural Correlates of
Motor Memory Consolidation." Science, Vol. 277, pp. 821-825.