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Dennis H. Karpowitz

LEAD POISONING

Lead is an environmental toxin that can cause mental
retardation, brain damage, or death in children.
Young children are particularly at risk because they
can accidentally eat leaded paint chips or breathe
lead-contaminated dust. Although lead-based paint
for household use has been banned in the United
States since 1977, deteriorated older houses remain
important sources. Once inside the body, lead affects
the brain, heart, liver, kidney, and blood. Initially

only high measurable blood lead levels (<60 micro-

grams/deciliter or μg/dL) associated with seizures,

coma, or death were recognized as lead poisoning;

learning and behavior problems have been shown at

lower levels (10–20 μg/dL). Although national surveys

have shown decreases in blood lead levels in children

one to five years of age from 88 percent during 1976–

1980 to 4 percent during 1991–1994, poor young mi-

nority children in inner cities remain at risk for signif-

icant exposure. Treatment consists of eliminating

lead from the home environment, adding iron to the

diet, and, if necessary, providing medications to re-

move lead from the body.

See also: DEVELOPMENTAL DISABILITIES

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Hwang, Mi Young, Richard Glass, and Jeff Molter. ‘‘JAMA Patient

Page: Protect Your Child Against Lead Poisoning.’’ Journal of

the American Medical Association 281 (1999):2406.

Markowitz, Morri. ‘‘Lead Poisoning.’’ Pediatrics in Review 21

(2000):327–335.

John I. Takayama

LEARNING

Learning can occur in a variety of manners. An organ-

ism can learn associations between events in their en-

vironment (classical or respondent conditioning),

learn based upon the reinforcements or punishments

that follow their behaviors (operant or instrumental

conditioning), and can also learn through observa-

tion of those around them (observational learning).

Learning principles are of particular importance for

school performance.

Classical or Respondent Conditioning

In the early twentieth century, Ivan Pavlov, a Rus-

sian scientist, unwittingly stumbled upon an impor-

tant discovery for the field of behavioral psychology.

While studying digestion in dogs, he discovered that

after being fed a few times, the animals would salivate

before actually receiving food. The dogs were associ-

ating external cues such as the sound of the food cabi-

net being opened with being fed, so they would

salivate upon hearing these sounds before they saw

the food.

This phenomenon is called classical conditioning

or respondent conditioning. Pavlov found that by

LEARNING 235