Are there things you can only learn as a baby? Was your adolescent self a faster learner than you are now? This article will give examples of critical and sensitive periods, moments in development when something can be learned very quickly given the right conditions. These are the times when the environment has a big say in development.
Are there things you can only learn as a baby? Was your adolescent self a faster learner than you are now? This article will give examples of critical and sensitive periods, moments in development when something can be learned very quickly given the right conditions. These are the times when the environment has a big say in development.
Photo by Sarah Laszlo
Sensitive and critical periods delineate special developmental moments when the learning of a certain behavior or skill is very intense. Sensitive periods are windows of time in your life when learning certain skills is much faster and less effortful than at some other times. You can generally learn these skills and become better at them at any point in your life, but learning is optimal during these sensitive periods. Critical periods, on the other hand, are windows of time where humans are particularly receptive to input from the environment and it is only in that period that they can develop a skill. No matter how hard they try afterward, the skills cannot be acquired at a later time, even with the best instruction and stimulation. Below you can find some of the areas where researchers have hypothesized the existence of a critical or sensitive period.
Language
Perhaps the most studied area for critical and sensitive periods is language. It is a known fact that infants who have been deprived of language input (through isolation, brain disease or auditory impairment) in their first year of life will not develop correct syntax. They will not be able to correctly place words in sentences, although they might be able to understand vocabulary to some extent (Friedman & Rusou, 2015). This means that the first year of life is a critical year for language acquisition.
It was hypothesized that there is also a critical period from birth until puberty for learning a second language at a native level, but studies failed to find such a clear threshold. Instead, the ability to learn a second language for children who are not born into bilingual families steadily decreases with age (Hakuta et al, 2003). Still, studies show that children learn a second language the fastest when they are exposed to it before age 10 (Ghasemi & Hashemi, 2011), and the earlier the better. Children who learn two languages from birth (have bilingual caretakers) learn both languages just as fast as children who only learn one language (Callan, 2008).
Acculturation
There seems to be a sensitive period for acculturation. People who move to a foreign country are able to adapt faster and they identify more with the host culture if they arrive in the new country while they are young. Cheung et al. (2011) argue the cut-off age is around 15 years old. People who immigrate before this age acculturate more as a function of the time they spend inside the culture. As time passes, they identify more and more with the host culture. On the other hand, people moving between 16 and 30 years old seem to have a steady level of identification with the culture the more they interact with it (it remains the same), while people who move when they are older than 30 years old seem to identify less with the culture the more they live in a foreign country.
Food preference
Food preference has both sensitive and critical periods. Only two preferences are hardwired and babies show them at birth: sweet and bitter (Crook, 1978, cited in Harris & Mason, 2017). Harris and Mason’s (2017) review of food acceptance literature found a sensitive period for taste acceptance and a possible critical period for texture acceptance. Children start eating complementary food (liquid and solid foods given besides milk) between 4 and 6 months so in this period they are exposed to new tastes. If they are introduced to a variety of foods and vegetables at the very beginning of this period, they are more likely to eat a diverse range of food and vegetables and accept strange tastes more easily when they are 7 years old, compared to children introduced to new tastes later. The same is observed for preterm babies compared to full-term babies of the same age. They express happier faces when they are fed new foods, presumably because they were technically first introduced to new tastes earlier in development, which again indicates that early exposure to new tastes leads to a greater taste receptivity later (Longfier et al., 2016, cited in Harris & Mason, 2017).
Between 6 and 12 months of age, infants should be given solids to chew on. If infants have not experienced textured food in their first year of life they will show low levels of acceptance towards various solid foods as children. Apart from a decreased preference for such foods, children will not develop certain chewing movements needed for particular foods. Therefore, they will be unable to eat them properly – a sign of a critical period for accepting food texture (Mason et al., 2005, cited in Harris & Mason, 2017).
Socio-emotional development
Woodard and Pollack (2020) suggest that socio-emotional development involves overlapping sensitive periods that correspond to separate aspects such as processing faces, processing rewards, and fear conditioning. For instance, learning when a situation is safe or not during infancy determines how fast children learn to fear certain stimuli during childhood (Porges, 2015, cited in Woodard & Pollack, 2020). A lasting impact of caregiver deprivation in infancy is thought to exist in the domain of attachment as well because of a sensitive period of corticolimbic development in the first year of life (Gee, 2020). Therefore, the role of parents in making the child feel safe and protected is crucial in this period.
Sensitive periods in adolescence
Adolescence is a period where several sensitive periods are thought to exist. There is indirect evidence for sensitive periods during adolescence regarding memory, the impact of social stress, and drug use. People remember personal events from their adolescence and beginning adulthood the best compared to any other times in their life (Rubin & Schulkind, 1997, cited in Fuhrmann et al., 2015) and the peak of verbal and spatial memory seems to be between 14 and 26 years old (Murre et al., 2013, cited in Fuhrmann et al., 2015). Not only that, but people best remember historical events that happened during their adolescence, or information from books they read and the songs listened to back then, compared to any other time in their life (Janssen et al., 2007, cited in Fuhrmann et al., 2015).
Adolescence is also the onset of many psychological disorders which makes researchers suspect that the impact of social stress is particularly harmful in this time frame (Fuhrmann et al., 2015). Studies on rodents show that social stress in the form of threat or isolation is particularly damaging during adolescence and less so during adulthood.
Moreover, adolescence seems to be a period of increased vulnerability to drugs. Consumption of cannabis has been linked to brain atrophy in adolescents but not adults, and persistent cannabis use between 13 and 15 has been associated with declines in IQ, something not observed in adults (Battistella et al., 2014; Meier et al., 2012, cited in Fuhrmann et al., 2015). Lastly, several cognitive skills are also thought to show sensitive periods during adolescence. Knoll et al. (2021) showed that cognitive skills training yields the greatest gain for people between 16 to 33 years old in the case of numerosity discrimination and for people between 16 to 18 in terms of relational reasoning.
The best time to learn is the environment’s best time to teach
What happens during critical and sensitive periods has a big impact on human development. So far, all these periods have been shown to take place early in the lifetime of individuals. This stands to reason evolutionarily. All organisms are born with specific tendencies that were accumulated through evolutionary time, but having a sensitive or critical period could work as a check to see if they are still useful for the current environment. In other words, these periods of heightened sensitivity to the environment are nature’s Bayesian updating (Frankenhuis et. al, 2019). They happen early to give the best fit of the individual to the environment, just in case the environment is different from what he or she was prepared for. For us humans, who can deliberately change the physical environment and the experiences of our children, this is a great opportunity and responsibility.
References
-Callan, E. (2008). Critical Review: Does bilingualism slow language development in children?. Retrieved November, 20(2012), 2007-08.
-Cheung, B. Y., Chudek, M., & Heine, S. J. (2011). Evidence for a sensitive period for acculturation: Younger immigrants report acculturating at a faster rate. Psychological Science, 22(2), 147-152.
-Friedmann, N., & Rusou, D. (2015). Critical period for first language: the crucial role of language input during the first year of life. Current opinion in neurobiology, 35, 27-34.
-Frankenhuis, Willem E., and Nicole Walasek. “Modeling the evolution of sensitive periods.” Developmental cognitive neuroscience 41 (2020): 100715.
-Fuhrmann, D., Knoll, L. J., & Blakemore, S. J. (2015). Adolescence as a sensitive period of brain development. Trends in cognitive sciences, 19(10), 558-566.
-Gee, D. G. (2020). Caregiving influences on emotional learning and regulation: applying a sensitive period model. Current opinion in behavioral sciences, 36, 177-184.
-Ghasemi, B., & Hashemi, M. (2011). Foreign language learning during childhood. Procedia-Social and Behavioral Sciences, 28, 872-876.
-Hakuta, K., Bialystok, E., & Wiley, E. (2003). Critical evidence: A test of the critical-period hypothesis for second-language acquisition. Psychological science, 14(1), 31-38.
-Harris, G., & Mason, S. (2017). Are there sensitive periods for food acceptance in infancy?. Current nutrition reports, 6(2), 190-196.
-Knoll, L. J., Fuhrmann, D., Sakhardande, A., Speekenbrink, M., & Blakemore, S. J. (2021). Is adolescence a sensitive period for relational reasoning?. Training, 1(T2), T3.
-Woodard, K., & Pollak, S. D. (2020). Is there evidence for sensitive periods in emotional development?. Current opinion in behavioral sciences, 36, 1-6.
Sensitive and critical periods delineate special developmental moments when the learning of a certain behavior or skill is very intense. Sensitive periods are windows of time in your life when learning certain skills is much faster and less effortful than at some other times. You can generally learn these skills and become better at them at any point in your life, but learning is optimal during these sensitive periods. Critical periods, on the other hand, are windows of time where humans are particularly receptive to input from the environment and it is only in that period that they can develop a skill. No matter how hard they try afterward, the skills cannot be acquired at a later time, even with the best instruction and stimulation. Below you can find some of the areas where researchers have hypothesized the existence of a critical or sensitive period.
Language
Perhaps the most studied area for critical and sensitive periods is language. It is a known fact that infants who have been deprived of language input (through isolation, brain disease or auditory impairment) in their first year of life will not develop correct syntax. They will not be able to correctly place words in sentences, although they might be able to understand vocabulary to some extent (Friedman & Rusou, 2015). This means that the first year of life is a critical year for language acquisition.
It was hypothesized that there is also a critical period from birth until puberty for learning a second language at a native level, but studies failed to find such a clear threshold. Instead, the ability to learn a second language for children who are not born into bilingual families steadily decreases with age (Hakuta et al, 2003). Still, studies show that children learn a second language the fastest when they are exposed to it before age 10 (Ghasemi & Hashemi, 2011), and the earlier the better. Children who learn two languages from birth (have bilingual caretakers) learn both languages just as fast as children who only learn one language (Callan, 2008).
Acculturation
There seems to be a sensitive period for acculturation. People who move to a foreign country are able to adapt faster and they identify more with the host culture if they arrive in the new country while they are young. Cheung et al. (2011) argue the cut-off age is around 15 years old. People who immigrate before this age acculturate more as a function of the time they spend inside the culture. As time passes, they identify more and more with the host culture. On the other hand, people moving between 16 and 30 years old seem to have a steady level of identification with the culture the more they interact with it (it remains the same), while people who move when they are older than 30 years old seem to identify less with the culture the more they live in a foreign country.
Food preference
Food preference has both sensitive and critical periods. Only two preferences are hardwired and babies show them at birth: sweet and bitter (Crook, 1978, cited in Harris & Mason, 2017). Harris and Mason’s (2017) review of food acceptance literature found a sensitive period for taste acceptance and a possible critical period for texture acceptance. Children start eating complementary food (liquid and solid foods given besides milk) between 4 and 6 months so in this period they are exposed to new tastes. If they are introduced to a variety of foods and vegetables at the very beginning of this period, they are more likely to eat a diverse range of food and vegetables and accept strange tastes more easily when they are 7 years old, compared to children introduced to new tastes later. The same is observed for preterm babies compared to full-term babies of the same age. They express happier faces when they are fed new foods, presumably because they were technically first introduced to new tastes earlier in development, which again indicates that early exposure to new tastes leads to a greater taste receptivity later (Longfier et al., 2016, cited in Harris & Mason, 2017).
Between 6 and 12 months of age, infants should be given solids to chew on. If infants have not experienced textured food in their first year of life they will show low levels of acceptance towards various solid foods as children. Apart from a decreased preference for such foods, children will not develop certain chewing movements needed for particular foods. Therefore, they will be unable to eat them properly – a sign of a critical period for accepting food texture (Mason et al., 2005, cited in Harris & Mason, 2017).
Socio-emotional development
Woodard and Pollack (2020) suggest that socio-emotional development involves overlapping sensitive periods that correspond to separate aspects such as processing faces, processing rewards, and fear conditioning. For instance, learning when a situation is safe or not during infancy determines how fast children learn to fear certain stimuli during childhood (Porges, 2015, cited in Woodard & Pollack, 2020). A lasting impact of caregiver deprivation in infancy is thought to exist in the domain of attachment as well because of a sensitive period of corticolimbic development in the first year of life (Gee, 2020). Therefore, the role of parents in making the child feel safe and protected is crucial in this period.
Sensitive periods in adolescence
Adolescence is a period where several sensitive periods are thought to exist. There is indirect evidence for sensitive periods during adolescence regarding memory, the impact of social stress, and drug use. People remember personal events from their adolescence and beginning adulthood the best compared to any other times in their life (Rubin & Schulkind, 1997, cited in Fuhrmann et al., 2015) and the peak of verbal and spatial memory seems to be between 14 and 26 years old (Murre et al., 2013, cited in Fuhrmann et al., 2015). Not only that, but people best remember historical events that happened during their adolescence, or information from books they read and the songs listened to back then, compared to any other time in their life (Janssen et al., 2007, cited in Fuhrmann et al., 2015).
Adolescence is also the onset of many psychological disorders which makes researchers suspect that the impact of social stress is particularly harmful in this time frame (Fuhrmann et al., 2015). Studies on rodents show that social stress in the form of threat or isolation is particularly damaging during adolescence and less so during adulthood.
Moreover, adolescence seems to be a period of increased vulnerability to drugs. Consumption of cannabis has been linked to brain atrophy in adolescents but not adults, and persistent cannabis use between 13 and 15 has been associated with declines in IQ, something not observed in adults (Battistella et al., 2014; Meier et al., 2012, cited in Fuhrmann et al., 2015). Lastly, several cognitive skills are also thought to show sensitive periods during adolescence. Knoll et al. (2021) showed that cognitive skills training yields the greatest gain for people between 16 to 33 years old in the case of numerosity discrimination and for people between 16 to 18 in terms of relational reasoning.
The best time to learn is the environment’s best time to teach
What happens during critical and sensitive periods has a big impact on human development. So far, all these periods have been shown to take place early in the lifetime of individuals. This stands to reason evolutionarily. All organisms are born with specific tendencies that were accumulated through evolutionary time, but having a sensitive or critical period could work as a check to see if they are still useful for the current environment. In other words, these periods of heightened sensitivity to the environment are nature’s Bayesian updating (Frankenhuis et. al, 2019). They happen early to give the best fit of the individual to the environment, just in case the environment is different from what he or she was prepared for. For us humans, who can deliberately change the physical environment and the experiences of our children, this is a great opportunity and responsibility.
