Conservation of liquid volume in young children
- From: tchow@xxxxxxxxxxxxx
- Date: 03 Sep 2007 20:51:31 GMT
According to conventional wisdom, children below a certain age lack the
concept of the conservation of liquid volume.
It has long bothered me that the results of the standard experiments
that supposedly demonstrate the aforementioned lack seem to admit many
alternative explanations. For example, here is a description that I
just pulled off the web more-or-less randomly.
Thirty children participated in this project: ten 3 year olds, ten
4 year olds and ten 5 year olds. Each child was presented with two
identical, clear glass containers. An equal volume of blue water
was poured into each. The child was asked to determine whether each
glass has the same volume, or whether one has more. Then the child
watched as one of these containers of blue water was poured into
a third container which was also clear glass, but was much taller
and thinner than the original pair. The tall, thin container of blue
water was compared to the original container of blue water, which was
shorter and wider. The child was asked to determine whether this new
pair has the same volume, or whether one has more.
In the absence of a video recording, or at least a verbatim transcript,
it is difficult to be certain about exactly how the experiment was carried
out. In particular, it's not completely clear whether the words "same
volume" and "more" were used to pose the questions, or whether other
wordings that the experimenter regarded as equivalent were used instead
(or in addition). But let us suppose that "same volume" and "more" were
used. It is entirely plausible to me that what the experiment demonstrates
is that the children's understanding of the *meaning* of the words "volume"
and "more" differs from that of most adults. In other words, it may be
that the children have the concept of conservation of volume, but that
this concept is not (yet) linked firmly to the *words* "volume" and "more"
the way they are linked in the adult mind. Suppose, for example, that
the children use "more" to refer to the concept that an adult would describe
as "taller." Then indicating that the tall thin container has "more" is
a completely correct answer from a scientific standpoint, and the test
merely demonstrates a *linguistic* difference between adults and children.
This objection suggests alternative ways of performing the experiment.
For example, suppose one designs an experiment centered on the word
"overflow." One begins by asking the child if he or she knows what
the word "overflow" means. The meaning of the word is taught (or
reinforced) by a series of demonstrations using various containers of
water. The initial demos should not involve any "tricky" cases such
as a tall thin container versus a short fat container, but should
involve simple examples such as filling a very large container with
water and pouring its contents into a container whose dimensions are
smaller in every way, and watching the water overflow the smaller
container. There should also be examples of *not* overflowing.
Now comes the "testing" phase.
1. Take two identical containers A and B, fill A with water, and pour
the contents into B. Now ask, "If I pour all the water back, will it
overflow?" Note the answer, pour the water back, and remark that it
did not overflow.
2. Repeat, but now use two containers A and B with the same volume but
different shapes, with A short and fat but B tall and thin.
Now, I came up with the above protocol off the top of my head, and
perhaps it can be criticized/improved. But even in its current rough
form, the new protocol has, I would argue, significant advantages over
the protocols that I have seen before. In particular, if the child
answers "incorrectly," it is harder to argue that the "error" is based
on a linguistic ambiguity.
Another objection to the standard experiment that a friend of mine has
raised is that there is a confounding issue lurking in the background,
namely the difficulty that most people, including adults, have in judging
whether two containers have the same volume. To clarify, suppose that
one were to design an experiment in which two empty containers of different
shapes but similar capacity are presented to a subject, and the subject is
asked to say which container has the greater capacity. I am sure that
many adults would not judge correctly. Clearly, this experiment does
*not* test whether the subject possesses the *concept* of "conservation
of volume."
What, then, makes us regard the original experiment as a test of whether
the subject possesses the concept of volume conservation, and not a test
of whether the subject possesses the ability to judge whether two objects
of dissimilar shape have the same volume? The reason is that the original
experiment involves a liquid-pouring protocol that we, as adults, recognize
as a reliable method of determining the answer to the volume-comparison
question. Shown the results of the protocol, an adult will not attempt to
answer the volume-comparison question by "judging by eye," but will simply
accept the protocol results.
Therefore another alternative explanation of a young child's reaction to
the standard experiment is that the child is simply trying to answer the
volume-comparison question by eye, and what he or she lacks is not the
*concept of volume comparison*, but the ability to appreciate the
*relevance* of the liquid-pouring protocol to the problem at hand. As
adults we are so used to the concept of physical measurements and the
superiority of measuring tools over our own intuition, that when we observe
a measurement being performed then we immediately grasp its significance
and abandon our own instincts in favor of the objective measurement. A
child, however, may not have a mature concept of "measurement" or may not
recognize measurement protocols as such.
My "overflow" protocol does not fully address this latter objection. The
child may not recognize the significance of pouring the liquid from A to B
and may simply ignore this preliminary step, judging whether the overflow
will occur on the basis of direct visual comparison of the containers. It
seems to me that my protocol does a slightly better job of drawing the
subject's attention to the relevance of the pouring, but this is partly
a matter of opinion. Perhaps an even better protocol can be designed.
Anyway, one reason that I'm posting these ideas here is to determine
1. whether these issues have already been addressed by other researchers;
2. if not, whether there is someone who might be seriously interested in
pursuing these ideas and performing carefully controlled experiments
along the above lines, with a view to publishing the findings.
Any names of experts in this field would be much appreciated.
--
Tim Chow tchow-at-alum-dot-mit-dot-edu
The range of our projectiles---even ... the artillery---however great, will
never exceed four of those miles of which as many thousand separate us from
the center of the earth. ---Galileo, Dialogues Concerning Two New Sciences
.
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