T

TABULA RASA

English philosopher John Locke (1632–1704) pro-
posed that the mind of the newborn infant is a tabula
rasa, or blank slate, on which experience writes. Al-
though research on infant cognition has shown that
this view is too extreme, some psychologists (known
as empiricists) continue to believe that development
is primarily a process of learning from the environ-
ment. Other psychologists (known as nativists) believe
that knowledge emerges through a developmental
process directed primarily by the genes.

Most contemporary psychologists, however, are
interactionists. Rejecting the nativist/empiricist (or
nature-nurture) dichotomy, interactionists argue that
development is an ongoing interaction of genetic and
environmental forces. Psychologists known as con-
structivists, moreover, acknowledging the interactive
roles of genes and environment, add that the mind it-
self is an active agent in the construction of knowl-
edge. Thus psychologists continue to debate how
much knowledge we should attribute to the infant at
birth and how development proceeds from there.

See also: INFANCY

Bibliography
Moshman, David. Adolescent Psychological Development: Rationality,
Morality, and Identity. Mahwah, NJ: Lawrence Erlbaum, 1999.
Spelke, Elizabeth, and Elissa Newport. ‘‘Nativism, Empiricism, and
the Development of Knowledge.’’ In William Damon ed.,
Handbook of Child Psychology, 5th edition, Vol. 1: Theoretical

Models of Human Development, edited by Richard Lerner. New

York: Wiley, 1998.

David Moshman

TAY-SACHS DISEASE

Tay-Sachs disease is a rare, inherited degenerative

disorder of the nervous system associated with defi-

ciency of the enzyme β-hexosaminidase A (HEXA).

When the condition is present, a particular lipid,

called a ganglioside, accumulates in the cells of the

central nervous system. Functional and anatomical

abnormalities result, and are clinically manifested by

motor disturbances, seizures, speech problems, psy-

chiatric illness, and dementia. Age of onset and clini-

cal severity depend upon the magnitude of the

enzyme deficiency. The classic or infantile form is

rapidly progressive, leading to death within the first

few years of life. Adult onset cases are milder and the

disease may not be life threatening. Certain ethnic

groups, such as those of Ashkenazi Jewish, French Ca-

nadian, or Turkish origin, are more commonly affect-

ed. Research is directed toward understanding the

biological activity of gangliosides and the effects of

their excessive accumulation. As there is no cure, in-

tervention involves identifying those who carry the

genetic defect in order to provide reproductive coun-

seling to them.

See also: GENOTYPE

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