|
|
|||||||
Features |
School of Life Sciences, Faculty of Organismal, Integrative and Systems Biology, Arizona State University, Tempe, AZ 85287-4501
Submitted March 21, 2006; Accepted March 21, 2006
| NOTE FROM THE EDITOR |
|---|
|
|
|---|
The focus of all contributed features and research articles in Issues in Neuroscience Education is the teaching and learning of neuroscience, from elementary school to graduate school audiences. However, neuroscience is unique as a branch of biology in that it includes the study of neuronal and brain mechanisms that may underlie learning. To highlight this unique position of neuroscience, we have chosen to focus this issue's Points of View on how research findings in the field of neuroscience may or may not have implications for the teaching and learning of science in general. We invited authors to address the following questions:
| INTRODUCTION |
|---|
|
|
|---|
| SOME BASICS OF BRAIN DEVELOPMENT |
|---|
|
|
|---|
How does environmental interaction lead to an increase in the number of functional dendrites? According to neural network theory (Grossberg, 1982, 2005; Jani and Levine, 2000), dendrites become functional when neurotransmitter release rate increases at synaptic knobs. The increase in release rate makes signal transmission from one neuron to the next easier. Hence, learning is understood as an increase in the number of "operative" synaptic connections among neurons. That is, learning occurs when transmitter release rate at synaptic knobs increases so that the signals can be easily transmitted across synapses that were previously there, but inoperative. How, then, does experience strengthen connections?
| HOW DOES EXPERIENCE STRENGTHEN CONNECTIONS? |
|---|
|
|
|---|
|
|
For example, consider Pavlov's classical conditioning experiment in which a dog is stimulated to salivate by the sound of a bell. When Pavlov first rang the bell, the dog, as expected, did not salivate. However, upon repeated simultaneous presentation of food, which did initially cause salivation, and bell ringing, the ringing alone eventually caused salivation. Thus, the food is the unconditioned stimulus (US). Salivation upon presentation of the food is the unconditioned response (UCR). And the bell is the conditioned stimulus (CS). Pavlov's experiment showed that when a CS (e.g., a bell) is repeatedly paired with a US (e.g., food), the CS alone will eventually evoke the UCR (e.g., salivation). How can the US do this?
Figure 1 shows a simple neural network capable of explaining classical conditioning. Although the network is depicted as just three cells (A, B, and C), each cell represents many neurons of the type A, B, and C. Initial food presentation causes cell C to fire. This creates a signal down its axon that, because of prior learning (i.e., a relatively large Zcb), causes the signal to be transmitted to cell B. Thus, cell B fires, and the dog salivates. At the outset, bell-ringing causes cell A to fire and send signals toward cell B. However, when the signal reaches knob NAB, its synaptic strength ZAB is not large enough to cause B to fire. So the dog does not salivate. However, when the bell and the food are paired, cell A learns to fire cell B according to Grossberg's learning equation. Cell A firing results in a large S'AB and the appearance of food results in a large E[XB]+. Thus, the product S'AB[XB]+ is sufficiently large to drive an increase in ZAB to the point at which it alone causes node VB to fire and evoke salivation. Food is no longer needed. The dog has learned to salivate at the ringing of a bell. The key theoretical point is that learning is driven by simultaneous activity of pre- and postsynaptic neurons, in this case activity of cells A and B.
|
| ADAPTIVE RESONANCE: MATCHING INPUT WITH EXPECTATIONS |
|---|
|
|
|---|
|
Now suppose the new input to F(1) does not match the expected pattern X from F(2). Mismatch occurs and this causes activity at F(1) to be turned off by lateral inhibition, which in turn shuts off the inhibitory output to the nonspecific arousal source. This turns on nonspecific arousal and initiates an internal search for a new pattern at F(2) that will match X1.
Such a series of events explains how information is processed across time. The important point is that stimuli are considered familiar if a memory record of them exists at F(2) such that the pattern of excitation sent back to F(1) matches the incoming pattern. If they do not match, the incoming stimuli are unfamiliar and orienting arousal (OA) is turned on to allow an unconscious search for another pattern. If no such match is obtained, then no coding in LTM will take place unless attention is directed more closely at the object in question. Directing careful attention at the unfamiliar object may boost presynaptic activity to a high enough level to compensate for the relatively low postsynaptic activity and eventually allow a recording of the sensory input into a set of previously uncommitted cells.
| HOW IS VISUAL INPUT PROCESSED IN DIFFERENT PARTS OF THE BRAIN? |
|---|
|
|
|---|
|
For example, suppose while driving your car you observe what seems to be a puddle of water in the road ahead. Thanks to connections in associative memory, you know that water is wet. So when you continue driving, you expect that your tires will splash through the puddle and get wet. But upon reaching the puddle, it disappears and your tires stay dry. Therefore, your brain rejects the puddle hypothesis and generates another hypothesis, perhaps a mirage hypothesis. The pattern of information processing involved in this example can be summarized as follows:
If ... the object is a puddle of water,
and ... you continue driving toward it,
then ... your tires should splash through the puddle and they should get wet.
But ... upon reaching the puddle, it disappears and your tires do not get wet.
Therefore ... the hypothesis is not supported; the object was probably not a puddle of water.
In other words, as one seeks to identify objects, the brain generates and tests stored patterns selected from memory. Kosslyn and Koenig even speak of these stored patterns as hypotheses, where the term hypothesis is used in its broadest sense. Thus, brain activity during visual processing uses an If/then/Therefore hypothetico-deductive pattern. One looks at part of an unknown object and the brain spontaneously and immediately generates an idea of what it isa hypothesis. Thanks to links in associative memory, the hypothesis carries implied consequences (i.e., expectations/predictions). Consequently, to test the hypothesis one can carry out a simple behavior to see whether the prediction does in fact follow. If it does, one has support for the hypothesis. If it does not, then the hypothesis is not supported and the cycle repeats.
| IS AUDITORY INPUT PROCESSED IN THE SAME HYPOTHETICO-DEDUCTIVE WAY? |
|---|
|
|
|---|
Details of this hypothesized word recognition subsystem are not important. Rather, what is important is that word recognition, like visual recognition, involves brain activity in which hypotheses arise immediately, unconsciously, and before any other activity. In other words, the brain does not make several observations before it generates a hypothesis of what it thinks is out there. Instead, from the slimmest piece of input, the brain immediately generates an idea of what it "thinks" is out there. The brain then acts on that initial idea until subsequent behavior is contradicted. In other words, the brain is not an inductivist organ. Rather, it is an idea-generating and -testing organ that works in a hypothetico-deductive way. There is good reason in terms of human evolution why this would be so. If you were a primitive person and you look into the brush and see stripes, it would certainly be advantageous to get out of there quickly as the consequences of being attacked by a tiger are dire. And anyone programmed to look, look again, and look still again in an "inductivist" way before generating the tiger hypothesis would most likely not survive long enough to pass on his plodding inductivist genes to the next generation.
The important point is that learning does not happen the way you might think. Your brain does not prompt you to look, look again, and look still again until you somehow internalize a successful behavior from the environment. Rather, your brain directs you to look and, as a consequence of that initial look, the brain generates an initial hypothesis that then drives behavior, behavior that carries with it a specific expectation. Hopefully, the behavior is successful in the sense that the prediction is matched by the outcome of the behavior. But sometimes it is not. So the contradicted behavior then prompts the brain to generate another hypothesis and so on until eventually the resulting behavior is not contradicted. In short, we learn from our mistakesfrom what some would call trial and error.
| CAN NEURAL NETWORKS EXPLAIN HIGHER LEVELS OF REASONING AND LEARNING? |
|---|
|
|
|---|
In 1610 in his Sidereal Messenger, Galileo reported observations made by a new telescope of his invention. In the report Galileo claims to have discovered four "planets" circling Jupiter. As he put it: "I should disclose and publish to the world the occasion of discovering and observing four planets, never seen from the beginning of the world up to our times" (Galilei, 1610, as translated and reprinted in Shapley et al., 1954, p. 59).
Unlike most modern scientific papers, Galileo's report is striking in the way in which it chronologically reveals the steps in his thinking. Thus, it provides an extraordinary opportunity to gain insight into the thinking involved in an important scientific discovery. What follows is a brief recapitulation of part of that report followed by an attempt to fill in gaps in Galileo's reasoning as he interpreted his observations. Galileo's reasoning will then be modeled in terms of Kosslyn and Koenig's neural network principles. Let's start with Galileo's initial observations on January 7.
January 7
Galileo made a new observation on January 7 that he deemed worthy of mention. In his words, "I noticed a circumstance which I had never been able to notice before, owing to want of power in my other telescope, namely that three little stars, small but very bright, were near the planet (i.e., Jupiter)."
This statement suggests that Galileo's observation was immediately assimilated by a fixed star category. In other words, he knew from past experiences that some of the objects in the night sky were fixed stars (i.e., stars that were part of the unchanging celestial sphere). But Galileo's continued thinking led to some initial doubt as this following remark reveals: "... and although I believed them to belong to the number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude."
Why would this observation lead Galileo to somewhat wonder? Perhaps he was reasoning along these lines:
If ... the three objects are fixed stars,
and ... their sizes, brightness, and positions are compared with each other and to other nearby stars,
then ... variations in size, brightness, and position should be random, as is the case for other fixed stars.
But ... "they seem to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars."
Therefore ... the fixed-star hypothesis is not supported. Or as Galileo put it, "yet they made me wonder somewhat."
January 8
The next night Galileo made another observation. Again, in his words: "... when on January 8, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night, and they were separated from one another by equal intervals, as the accompanying figure shows."
The new observation puzzled Galileo and raised another question. Again, in Galileo's words: "At this point, although I had not turned my thoughts at all upon the approximation of the stars to one another, yet my surprise began to be excited, how Jupiter could one day be found to the east of all the aforementioned stars when the day before it had been west of two of them." Presumably this observation was puzzling because it was not the expected one based on his fixed-star hypothesis.
Galileo continues, "... forthwith I became afraid lest the planet might have moved differently from the calculation of astronomers, and so had passed those stars by its own proper motion." This statement suggests that Galileo has not yet rejected the fixed-star hypothesis. Instead, he has generated an ad hoc hypothesis that the astronomers made a mistake, i.e., perhaps their records were wrong about how Jupiter moves relative to the fixed stars in the area. This hypothesis could subsequently be tested as follows:
If ... the astronomers made a mistake,
and ... I observe the next night,
then ... Jupiter should continue to move east relative to the stars, and the objects should look like this:
Of course, we cannot know whether this is what Galileo was thinking, but if he were thinking along these lines, he would have had a very clear prediction to compare with the observations he hoped to make the next night.
January 9 and 10
Galileo continues: "I therefore waited for the next night with the most intense longing, but I was disappointed of my hope, for the sky was covered with clouds in every direction. But on January 10th the stars appeared in the following position with regard to Jupiter, the third, as I thought, being hidden by the planet."
What conclusion can be drawn from this observation in terms of the astronomers-made-a-mistake hypothesis? Consider the following reasoning:
If ... the astronomers made a mistake,
and ... I observe the next night,
then ... Jupiter should continue to move east relative to the "stars," and the objects should look like this:
But ... the objects did not look like this, instead they looked like this:
Therefore ... the astronomers-made-a-mistake hypothesis is not supported.
Interestingly, Galileo states:
When I had seen these phenomena, as I knew that corresponding changes of position could not by any means belong to Jupiter, and as, moreover, I perceived that the stars which I saw had always been the same, for there were no others either in front or behind, within the great distance, along the Zodiacat length, changing from doubt into surprise, I discovered that the interchange of position which I saw belonged not to Jupiter, but to the stars to which my attention had been drawn.(p. 60)
So, Galileo concluded that the astronomers had not made a mistake, i.e., the changes of position were not the result of Jupiter's motion. Instead, they were due to motions of the "stars."
January 11 and Later
Galileo is now left with the task of formulating and testing another hypothesis. The following observation and remarks make it clear that he did not take long to do so:
Accordingly, on January 11 I saw an arrangement of the following kind:
namely, only two stars to the east of Jupiter, the nearer of which was distant from Jupiter three times as far as from the star to the east; and the star furthest to the east was nearly twice as large as the other one; whereas on the previous night they had appeared nearly of equal magnitude. I, therefore, concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury round the sun.
(p. 60)
Galileo's remarks make it is clear that he has "conceptualized" a situation in which these objects are traveling around Jupiter in a way analogous to the way our moon travels around the Earth. Thus, he has rejected the fixed star hypothesis and accepted an alternative hypothesis in which the objects are traveling around Jupiterthey are moons of Jupiter. How could Galileo have arrived at such a conclusion? Consider the following reasoning:
If ... the objects are orbiting Jupiter,
and ... I observe the objects over several nights,
then ... some nights they should appear to the east of Jupiter and some nights they should appear to the west. Further, they should always appear along a straight line on either side of Jupiter.
And ... this is precisely how they appeared.
Therefore ... the moons-of-Jupiter hypothesis is supported.
Galileo's previous statement continues as follows:
... which at length was established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions round Jupiter ... These are my observations upon the four Medicean planets, recently discovered for the first time by me.(pp. 6061)
| MODELING GALILEOS REASONING |
|---|
|
|
|---|
|
| INSTRUCTIONAL IMPLICATIONS |
|---|
|
|
|---|
| ACKNOWLEDGMENTS |
|---|
| FOOTNOTES |
|---|
Address correspondence to: Anton E. Lawson (anton.lawson{at}asu.edu)
| REFERENCES |
|---|
|
|
|---|
American Association for the Advancement of Science. (1989). Science for All Americans , Washington, DC: American Association for the Advancement of Science.
Carpenter G. A. and Grossberg S. (2003). Adaptive resonance theory. In: The Handbook of Brain Theory and Neural Networks, 2nd ed., ed. M. A. Arib , Cambridge, MA: MIT Press.
Diamond M. C. (1996). The Brain. Use It or Lose It. Mind Shift Connection 1(1). http://www.newhorizons.org/neuro/diamond_brain_response.htm (accessed 18 April 2006).
Galilei G. (1610). The Sidereal Messenger. A Treasury of Science (1954) eds. Shapley H., Rapport S., Wright H., New York: Harper & Brothers.
Grossberg S. (1982). Studies of Mind and Brain , Dordrecht, Holland: D. Reidel.
Grossberg S. (2005). Linking attention to learning, expectation, competition, and consciousness. Neurobiology of Attention eds. Itti L., Rees G., Tsolsos J., Elsevier: San Diego.
Jani N. G. and Levine D. S. (2000). A neural network theory of proportional analogy making. Neural Netw 13, 149183.[CrossRef][Medline]
Kosslyn S. M. and Koenig O. (1995). Wet Mind: The New Cognitive Neuroscience , New York: The Free Press.
Lawson A. E. (2002). What does Galileo's discovery of Jupiter's moons tell us about the process of scientific discovery? Sci & Educ 11, 124.[CrossRef]
Lawson A. E., Alkhoury S., Benford R., Clark B., Falconer K. A. (2000). What kinds of scientific concepts exist? Concept construction and intellectual development in college biology. J. Res. Sci. Teach 37, 9961018.[CrossRef]
Levine D. S. and Prueitt P. S. (1989). Modeling some effects of frontal lobe damage: novelty and perseveration. Neural Netw 2, 103116.
National Research Council. (1996). National Science Education Standards , Washington, DC: The National Academies Press.
National Research Council. (2001). Educating Teachers of Science, Mathematics, and Technology , Washington, DC: The National Academies Press.
National Science Foundation. (1996). Shaping the Future: New Expectations for Undergraduate Education in Science, Mathematics, Engineering, and Technology , Arlington, VA: National Science Foundation.
This article has been cited by other articles:
![]() |
S. Ramos Goyette and J. DeLuca A Semester-long Student-directed Research Project Involving Enzyme Immunoassay: Appropriate for Immunology, Endocrinology, or Neuroscience Courses CBE Life Sci Educ, December 1, 2007; 6(4): 332 - 342. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | ARCHIVE | SEARCH | TABLE OF CONTENTS |