Developmental psychology.pdf

296 Motivation and Emotion
Method of intake
Oral
Intragastric
Intravenous
Intracranial
For study of
Mouth and throat
Stomach
Blood
Central nervous system
Figure 11.9
Study of Hunger. Several
approaches are necessary to
Investigate the various factors. In the
oral method of food intake, the
subject sucks on a steel straw,
sometimes while immersed in a tank
of water in which the temperature
can be regulated. In the intragastric
method, he swallows a flexible tube
and pumps the liquid directly into his
stomach, thus eliminating the
influence of the mouth and throat
factors. In the intravenous mode,
solutions are delivered directly into
the veins. In the intracranial mode,
used only with animals, chemicals are
introduced directly into the brain cells
thought to be responsible for hunger
(Stellar & Jordan, 1970).
absent in experimental animals, they may become three times their normal size. Consequently,
these brain regions have been called the satiety cells, meaning that without
them the organism simply does not know when to stop eating.
These studies add further evidence that eating is complexly determined. The
stomach is involved, as are the blood and the brain as well. Within the brain, the different
regions of the hypothalamus serve different functions, and both areas contribute
to eating in other ways, one of which is through the control of secretions of adrenalin
in the ventromedial nucleus. Altogether, these brain areas serve as regions of interconnections
for many neural tracts involved in eating (Thompson, 1975; Dalton, Carpenter,
& Grossman, 1981; Figure 11.9).
Specific Hungers Often we want to eat not just food but instead crave a particular
kind of food, which is called a specific hunger. At the end of a big meal you may be
too full to eat anything except a sweet dessert. During his voyage, Robin Graham
reported a strong desire for fresh fish on several occasions.
Specific hungers have been investigated in cafeteria-feeding experiments, in
which many different foods are available. Human infants allowed to choose their own
foods on this basis for a period of one year selected a balanced diet. One of the subjects,
suffering from rickets, ate large amounts of cod-liver oil, a substance that tends to
counteract the vitamin deficiency causing this disease (Davis, 1928). But this research
suffers from one significant defect. Nonnutritious foods were not offered to the infants,
and of course harmful products also were avoided. The results simply show that with
nutritious foods available, human infants will choose a balanced diet.
Cafeteria-feeding experiments with rats are less restricted, and it has been
found that these animals will avoid certain poisonous foods. Even the pups avoid the
food, apparently on the basis of ingredients in the mother's milk. Furthermore, when
rats are fed a sugar-free or fat-free diet, they demonstrate a marked preference for
sugar or fat, respectively, compensating for the deficiency (Young, 1936, 1938). And