Critical period
Encyclopedia
This article is about a critical period in an organism's or person's development. See also America's Critical Period
.
In general, a critical period is a limited time in which an event can occur, usually to result in some kind of transformation. A "critical period" in developmental psychology
and developmental biology
is a time in the early stages of an organism's life during which it displays a heightened sensitivity to certain environmental stimuli, and develops in particular ways due to experiences at this time. If the organism does not receive the appropriate stimulus during this "critical period", it may be difficult, ultimately less successful, or even impossible, to develop some functions later in life.
For example, the critical period for the development of a human child's binocular vision
is thought to be between three and eight months, with sensitivity to damage extending up to at least three years of age. Further critical periods have been identified for the development of hearing
and the vestibular system
. There are critical periods during early postnatal development in which imprinting
can occur, such as when a greylag goose
becomes attached to a parent figure within the first 36 hours after hatching. A young chaffinch
must hear an adult singing before it sexually matures, or it will never properly learn the highly intricate song. These observations have led some to hypothesise a critical period for certain areas of human learning, particularly language acquisition
.
Experimental research into critical periods has involved depriving animals of stimuli at different stages of development. Other studies have looked at children deprived of certain experiences due to illness (such as temporary blindness), or social isolation (such as feral child
ren). Many of the studies investigating a critical period for language acquisition have focused on deaf children of hearing
parents.
) language acquisition is much more difficult and ultimately less successful. The critical period hypothesis was proposed by linguist Eric Lenneberg
in 1967.
Evidence supporting this hypothesis comes from feral
children who failed to develop language after being deprived of early linguistic input. The most famous cases are Genie
and Victor of Aveyron
. However, it is also possible that these children were retarded from infancy and abandoned because of this, or that inability to develop language came from the bizarre and inhuman treatment they suffered. Other evidence comes from neuropsychology
where it is known that adults, well beyond the critical period, are more likely to suffer permanent language impairment from brain damage than are children, believed to be due to youthful capabilities of neural reorganization. The nature of this phenomenon, however, has been one of the most fiercely debated issues in psycholinguistics
and cognitive science
in general for decades.
, although this is much less widely accepted. Certainly, older learners of a second language
rarely achieve the native-like fluency that younger learners display, despite often progressing faster than children in the initial stages. David Singleton (1995) states that in learning a second language, "younger = better in the long run," but points out that there are many exceptions, noting that five percent of adult bilinguals master a second language even though they begin learning it when they are well into adulthood — long after any critical period has presumably come to a close. Evidence is controversial the Second Language Acquisition involves a critical period, nevertheless, it is generally agreed that younger people learning a second language typically achieve fluency more often than older learners. Older learners may be able to speak the language but will lack the native fluidity of younger learners. The Second Language Acquisition Critical Period coincides approximately with the Formal Operational Stage
of Jean Piaget
's theory of cognitive Development (Age 11+).
and Torsten Wiesel
showed that cats which had one eye sewn shut at birth (monocular deprivation
) could not see properly, even though the eyes were anatomically normal. The kittens had abnormally small ocular dominance
columns (part of the brain that processes sight) connected to the closed eye, and abnormally large columns connected to the open eye. This did not happen to adult cats even when one eye was sewn shut for a year. Later experiments in monkeys found similar results. The critical period for cats is about three months and for monkeys, about six months.
In humans, some babies are born blind in one or both eyes, for example, due to cataracts. Even when their vision is restored later by treatment, their sight would not function in the normal way as for someone who had binocular vision
from birth or had surgery to restore vision shortly after birth. Therefore, it is important to treat babies born blind soon if their condition is treatable.
America's Critical Period
The term, Critical Period, coined by John Quincy Adams, refers to the 1780s, a time right after the American Revolution where the future of the newly formed nation was in the balance. More specifically, the "Critical Period" refers to the period of time following the end of the American...
.
In general, a critical period is a limited time in which an event can occur, usually to result in some kind of transformation. A "critical period" in developmental psychology
Developmental psychology
Developmental psychology, also known as human development, is the scientific study of systematic psychological changes, emotional changes, and perception changes that occur in human beings over the course of their life span. Originally concerned with infants and children, the field has expanded to...
and developmental biology
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
is a time in the early stages of an organism's life during which it displays a heightened sensitivity to certain environmental stimuli, and develops in particular ways due to experiences at this time. If the organism does not receive the appropriate stimulus during this "critical period", it may be difficult, ultimately less successful, or even impossible, to develop some functions later in life.
For example, the critical period for the development of a human child's binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
is thought to be between three and eight months, with sensitivity to damage extending up to at least three years of age. Further critical periods have been identified for the development of hearing
Hearing (sense)
Hearing is the ability to perceive sound by detecting vibrations through an organ such as the ear. It is one of the traditional five senses...
and the vestibular system
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...
. There are critical periods during early postnatal development in which imprinting
Imprinting (psychology)
Imprinting is the term used in psychology and ethology to describe any kind of phase-sensitive learning that is rapid and apparently independent of the consequences of behavior...
can occur, such as when a greylag goose
Greylag Goose
The Greylag Goose , Anser anser, is a bird with a wide range in the Old World. It is the type species of the genus Anser....
becomes attached to a parent figure within the first 36 hours after hatching. A young chaffinch
Chaffinch
The Chaffinch , also called by a wide variety of other names, is a small passerine bird in the finch family Fringillidae.- Description :...
must hear an adult singing before it sexually matures, or it will never properly learn the highly intricate song. These observations have led some to hypothesise a critical period for certain areas of human learning, particularly language acquisition
Language acquisition
Language acquisition is the process by which humans acquire the capacity to perceive, produce and use words to understand and communicate. This capacity involves the picking up of diverse capacities including syntax, phonetics, and an extensive vocabulary. This language might be vocal as with...
.
Experimental research into critical periods has involved depriving animals of stimuli at different stages of development. Other studies have looked at children deprived of certain experiences due to illness (such as temporary blindness), or social isolation (such as feral child
Feral child
A feral child is a human child who has lived isolated from human contact from a very young age, and has no experience of human care, loving or social behavior, and, crucially, of human language...
ren). Many of the studies investigating a critical period for language acquisition have focused on deaf children of hearing
Hearing (person)
The term hearing or hearing person, from the perspective of mainstream English-language culture, refers to someone whose sense of hearing is at the medical norm. From this point of view, someone who is not fully hearing has a hearing impairment or is said to be hard of hearing or deaf. The...
parents.
First language acquisition
The Critical Period Hypothesis states that the first few years of life constitute the time during which language develops readily and after which (sometime between age 5 and pubertyPuberty
Puberty is the process of physical changes by which a child's body matures into an adult body capable of reproduction, as initiated by hormonal signals from the brain to the gonads; the ovaries in a girl, the testes in a boy...
) language acquisition is much more difficult and ultimately less successful. The critical period hypothesis was proposed by linguist Eric Lenneberg
Eric Lenneberg
Eric Heinz Lenneberg was a linguist and neurologist who pioneered ideas on language acquisition and cognitive psychology, particularly in terms of the concept of innateness....
in 1967.
Evidence supporting this hypothesis comes from feral
Feral
A feral organism is one that has changed from being domesticated to being wild or untamed. In the case of plants it is a movement from cultivated to uncultivated or controlled to volunteer. The introduction of feral animals or plants to their non-native regions, like any introduced species, may...
children who failed to develop language after being deprived of early linguistic input. The most famous cases are Genie
Genie (feral child)
Genie is the pseudonym for a feral child who spent nearly all of the first thirteen years of her life locked inside a bedroom strapped to a potty chair. She was a victim of one of the most severe cases of social isolation ever documented...
and Victor of Aveyron
Victor of Aveyron
Victor of Aveyron was a feral child who apparently lived his entire childhood naked and alone in the woods before being found wandering the woods near Saint-Sernin-sur-Rance, France, in 1797. He was captured, but soon escaped after being displayed in the town...
. However, it is also possible that these children were retarded from infancy and abandoned because of this, or that inability to develop language came from the bizarre and inhuman treatment they suffered. Other evidence comes from neuropsychology
Neuropsychology
Neuropsychology studies the structure and function of the brain related to specific psychological processes and behaviors. The term neuropsychology has been applied to lesion studies in humans and animals. It has also been applied to efforts to record electrical activity from individual cells in...
where it is known that adults, well beyond the critical period, are more likely to suffer permanent language impairment from brain damage than are children, believed to be due to youthful capabilities of neural reorganization. The nature of this phenomenon, however, has been one of the most fiercely debated issues in psycholinguistics
Psycholinguistics
Psycholinguistics or psychology of language is the study of the psychological and neurobiological factors that enable humans to acquire, use, comprehend and produce language. Initial forays into psycholinguistics were largely philosophical ventures, due mainly to a lack of cohesive data on how the...
and cognitive science
Cognitive science
Cognitive science is the interdisciplinary scientific study of mind and its processes. It examines what cognition is, what it does and how it works. It includes research on how information is processed , represented, and transformed in behaviour, nervous system or machine...
in general for decades.
Second language acquisition
The theory has often been extended to a critical period for second language acquisitionSecond language acquisition
Second-language acquisition or second-language learning is the process by which people learn a second language. Second-language acquisition is also the name of the scientific discipline devoted to studying that process...
, although this is much less widely accepted. Certainly, older learners of a second language
Second language
A second language or L2 is any language learned after the first language or mother tongue. Some languages, often called auxiliary languages, are used primarily as second languages or lingua francas ....
rarely achieve the native-like fluency that younger learners display, despite often progressing faster than children in the initial stages. David Singleton (1995) states that in learning a second language, "younger = better in the long run," but points out that there are many exceptions, noting that five percent of adult bilinguals master a second language even though they begin learning it when they are well into adulthood — long after any critical period has presumably come to a close. Evidence is controversial the Second Language Acquisition involves a critical period, nevertheless, it is generally agreed that younger people learning a second language typically achieve fluency more often than older learners. Older learners may be able to speak the language but will lack the native fluidity of younger learners. The Second Language Acquisition Critical Period coincides approximately with the Formal Operational Stage
Theory of cognitive development
Piaget's theory of cognitive development is a comprehensive theory about the nature and development of human intelligence first developed by Jean Piaget. It is primarily known as a developmental stage theory, but in fact, it deals with the nature of knowledge itself and how humans come gradually to...
of Jean Piaget
Jean Piaget
Jean Piaget was a French-speaking Swiss developmental psychologist and philosopher known for his epistemological studies with children. His theory of cognitive development and epistemological view are together called "genetic epistemology"....
's theory of cognitive Development (Age 11+).
Vision
In mammals, neurons in the brain which process vision actually develop after birth based on signals from the eyes. A landmark experiment by David H. HubelDavid H. Hubel
David Hunter Hubel is the John Franklin Enders Professor of Neurobiology, Emeritus, at Harvard Medical School. He was co-recipient with Torsten Wiesel of the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was...
and Torsten Wiesel
Torsten Wiesel
Torsten Nils Wiesel was a Swedish co-recipient with David H. Hubel of the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was shared with Roger W...
showed that cats which had one eye sewn shut at birth (monocular deprivation
Monocular deprivation
Monocular deprivation is an experimental technique used by neuroscientists to study central nervous system plasticity. Generally, one of an animal's eyes is sutured shut during a period of high cortical plasticity...
) could not see properly, even though the eyes were anatomically normal. The kittens had abnormally small ocular dominance
Ocular dominance
Ocular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one eye to the other. It is somewhat analogous to the laterality of right or left handedness; however, the side of the dominant eye and the dominant hand do not always match...
columns (part of the brain that processes sight) connected to the closed eye, and abnormally large columns connected to the open eye. This did not happen to adult cats even when one eye was sewn shut for a year. Later experiments in monkeys found similar results. The critical period for cats is about three months and for monkeys, about six months.
In humans, some babies are born blind in one or both eyes, for example, due to cataracts. Even when their vision is restored later by treatment, their sight would not function in the normal way as for someone who had binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
from birth or had surgery to restore vision shortly after birth. Therefore, it is important to treat babies born blind soon if their condition is treatable.
See also
- Behavioral CuspBehavioral cuspA behavioral cusp is any behavior change that brings an organism's behavior into contact with new contingencies that have far-reaching consequences...
- Child developmentChild developmentChild development stages describe theoretical milestones of child development. Many stage models of development have been proposed, used as working concepts and in some cases asserted as nativist theories....
- Critical Period HypothesisCritical Period HypothesisThe critical period hypothesis is the subject of a long-standing debate in linguistics and language acquisition over the extent to which the ability to acquire language is biologically linked to age...
- Developmental PsychologyDevelopmental psychologyDevelopmental psychology, also known as human development, is the scientific study of systematic psychological changes, emotional changes, and perception changes that occur in human beings over the course of their life span. Originally concerned with infants and children, the field has expanded to...
- Malleable intelligenceMalleable intelligenceMalleability of intelligence describes the processes by which human intelligence may be augmented through changes in neuroplasticity. These changes may come as a result of genetics, pharmacological factors, psychological factors, behavior, or environmental conditions...
- Universal grammarUniversal grammarUniversal grammar is a theory in linguistics that suggests that there are properties that all possible natural human languages have.Usually credited to Noam Chomsky, the theory suggests that some rules of grammar are hard-wired into the brain, and manifest themselves without being taught...
- Sensitive periodsSensitive periodsSensitive periods is a term coined by the Dutch geneticist Hugo de Vries and adopted by the Italian educator Maria Montessori to refer to important periods of childhood development....