community volunteers to speak in court for the best
interests of abused and neglected children. This first
program was very successful and soon judges across
the country began using citizen advocates. In 1990
U.S. Congress encouraged the expansion of CASA
with passage of the Victims of Child Abuse Act. By the
beginning of the twenty-first century, more than 900
CASA programs were in operation, with more than 42
million women and men serving as CASA volunteers.
See also: DELINQUENCY
Bibliography
Child Welfare League of America [web site]. 2001. Available from
http://www.cwla.org; INTERNET.
Children’s Defense Fund [web site]. 2001. Available from http://
http://www.childrensdefense.org; INTERNET.
National CASA Association. Available from http://www.casanet.org;
INTERNET.
National Office of Juvenile Justice and Delinquency Prevention
[web site]. 2001. Available from http://www.ncjrs.org/jjhome.
htm; INTERNET.
Neil J. Salkind
CRITICAL/SENSITIVE PERIODS
The concept of critical/sensitive periods is of interest
in discussions of the influence of biological and expe-
riential factors during periods of developmental
change. A critical or sensitive period is defined as a
period when certain experiences are particularly im-
portant because they have a significant influence on
later development. Let us begin our consideration of
this concept with a case example that illustrates some
of the significant developmental changes that occur
during the period of infancy and early childhood.
Eve is a typical, healthy newborn human infant.
She is raised by parents who are sensitive to her
unique needs and characteristics, and who regularly
provide her with appropriate stimulation and parent-
ing. The first five years of Eve’s life will be witness to
rapid, significant changes in her behavior and abili-
ties.
Language development provides one example of
these changes. As a newborn, Eve prefers the sound
of human voices to other sounds and can discriminate
between the language of her culture and other lan-
guages. She cries, usually when she has some physical
needs, such as hunger. By five to six months of age,
she will coo when contented and may be babbling or
producing simple combinations of consonants and
vowels. By twelve to eighteen months of age, she will
be speaking in single word sentences and will under-
stand more than fifty words. By twenty-four months
of age her vocabulary will have expanded to approxi-
mately 200 words and she will be producing hundreds
of different two- and three-word sentences. By the age
of five, Eve will have a vocabulary of about 2,000
words and will use many of the grammatical struc-
tures of her native language, without ever taking part
in a formal language lesson.
The period from birth to five years of age will also
include significant changes in Eve’s social relation-
ships. As a newborn, she can discriminate her moth-
er’s face, voice, and smell from all others. By three
months of age, she will smile at her parents and will
react positively to most strangers. Between seven and
twelve months of age she will begin to demonstrate
specific attachments to her parents, will display anxi-
ety when strangers approach, and will be distressed
by separation from her parents. By three to four years
of age, Eve will continue to be securely attached to her
parents, but her distress at separation from them will
diminish, and she will be able to confidently partici-
pate in a nursery school program.
The study of human development is the study of
change. As the case of Eve illustrates, the changes that
occur during infancy and childhood are happening at
a pace that is more rapid and impressive than at any
other period in the lifespan. Although psychologists
agree that these developmental changes during in-
fancy and childhood are impressive and extraor-
dinary, they often disagree on the best way to under-
stand and explain these changes.
One area of disagreement is the discussion of
whether developmental changes are the result of bio-
logical, genetic factors or of the kinds of experiences
that the child has had. Another area of disagreement
is the discussion of whether developmental changes
occur in a series of unique stages or periods.
The concept of a critical/sensitive period is relat-
ed to both of these areas of discussion. The critical/
sensitive period is determined by biological matura-
tion and characterized by increased vulnerability or
responsivity to specific experiences. If these specific
experiences occur during this period, then develop-
ment will continue on its typical course. If these spe-
cific experiences do not occur, there may be a
significant disruption or difficulty in subsequent de-
velopment.
What evidence is there supporting this notion of
a critical period in development? Is there a difference
between a critical period and a sensitive period?Language Development: Critical or
Sensitive Period?
Language development provides one example
that can illustrate the concept of a critical/sensitiveCRITICAL/SENSITIVE PERIODS 101