>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.
>
>
>
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Ruediger Oehlmann e-mail: oehlmann@essex.ac.uk
University of Essex oehlmann@psych.stanford.edu
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