CONTACT: MARY GERAGHTY
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Iowa City IA 52242
(319) 384-0011; fax (319) 384-0024
Release: Dec. 15, 1999
UI psychologists show flaws in imposing human qualities on animals
IOWA CITY, Iowa Do infant rats cry? Scientists discovered 45 years
ago that when separated from the nest rats emit an ultrasonic "distress call."
But is this the same as a human infant crying for its mother? In a paper to
be published in January in Psychological Science, a group of University
of Iowa psychologists says the answer is No.
Human infants cry because they are hungry, wet, cold, or otherwise in
need of attention from a parent. But rat pups cry involuntarily as a result
of a physiological process, the UI team says. Mark Blumberg, a UI associate
professor of psychology and primary investigator for this project, says the
rat cries are a by-product of a maneuver that increases blood flow to the
infants heart when that flow is reduced. Although the cries often also
result in the rat mother retrieving the pup to the nest, Blumberg says it
is important not to assume that the two are directly related.
"We can't infer the intent to communicate based on the response of the
receiver," Blumberg says. "For example, although a sneezing child may prompt
a parent to hand over a tissue, we dont infer from this that the child
sneezed in order to communicate to the parent that a tissue was needed."
Infant rats emit cries when they are exposed to extreme cold, which causes
a significant decrease in cardiac rate. The cries are also heard after rats
have been injected with clonidine, a drug that causes withdrawal of central
nervous system stimulation to a number of organs, including the heart, resulting
ultimately in decreased blood flow back to the heart. Based on these and other
factors, Blumberg and his team hypothesized that the cry, produced by strong
compressions of the abdominal muscles, might be an acoustic by-product of
a physiological process that propels venous blood back to the heart.
In support of their hypothesis, Blumberg and his team were able to measure
venous blood pressure after pups were treated with clonidine and show that
the vocalizations were indeed associated with large increases in venous return.
Based on this evidence, the cries can be understood as involuntary vocalizations
that result from a physiological process. Thus, while a rat pup's cry may
prompt the mother to retrieve the pup to the nest, the pup has not cried in
order to seek maternal care.
"It is natural for people to attribute human thoughts and feelings to
animals," Blumberg says. "It is important, however, not to allow these anthropomorphic
tendencies to interfere with our actually figuring out why animals do what