A CRITICAL PERIOD: Does it Exist in Language Acquisition?

I Made Sujana

PBS FKIP Universitas Mataram

Abstract. The launching of a critical period hypothesis (CPH) by Lenneberg in 1967 has been so provocative that various experiments for proving or refuting the existence of the age factor in language acquisition have been conducted. Most of the experiments are in support Lenneberg’s CPH; however, the notion of the critical period has changed from “a sudden drop-off” at puberty (i.e. the capacity of learning language will be lost if it is not activated during the critical period, before puberty) to “a continuous linear decline” (i.e. the language acquisition is still possible after puberty but it will be more difficult and incomplete). The later notion leads to the use of “sensitive period” term instead of “critical period”. With this notion, in long term the younger they start to learn a language, the more proficient they will be in all aspects the language.


Abstrak. Bahwa ada masa kritis dalam belajar bahasa yang dimunculkan oleh Lenneberg tahun 1967 yang lebih dikenal dengan Lenneberg’s Critical Period Hypothesis (CPH)  telah memprovokasi para ahli dalam bidang ilmu terkait untuk mengadakan eksperimen untuk membuktikan keberadaan faktor usia dalam belajar bahasa. Kebanyakan eksperimen tersebut mendukung CPH; akan tetapi, terjadi perubahan ide dari hilangnya kapasitas belajar bahasa kalau tidak diaktifkan pada masa pubertas ke penurunan secara linear kemampuan menguasai bahasa sejalan dengan penambahan usia. Sebagai pengganti istilah ‘critical period’, para ahli lebih cendrung memakai ‘sensitive period’. Dengan ide ini, dalam jangka waktu panjang, pembelajar yang mulai pada usia dini akan mampu menguasai bahasa secara sempurna untuk semua aspek berbahasa.


Key words: first and second language acquisition, Lenneberg’s critical period hypothesis (CPH), age factor, age of onset (AO)




That there is a specific and limited time period for language acquisition poses lively debate in language acquisition area since the launching of Critical Period Hypothesis (henceforth CPH) by Lenneberg in 1967 (Wode, 1994; Long, 1990). According to Lenneberg (cited in Long, 1990), the capacity for the first language learning will be lost if it is not activated or exercised during the critical period which runs from 2 to 13 years of age. This hypothesis has led to two important predictions or versions, namely the strong version and the weak version. The followers of the strong version believe that the first language must be acquired by puberty or it will never be learnt from subsequent exposure (e.g. Lenneberg cited in Long, 1990); on the other hand, the followers of the weak version argues that the language acquisition is still possible after puberty but it will be more difficult and incomplete (e.g. Curtiss, 1977 cited in Long, 1990).

            Such a controversial notion has attracted many researchers’ attention to conduct  research from various point of view in both first and second language acquisition in order to support or refute the existence of  the age factor and the critical period in language acquisition. This paper aims at reviewing and synthesizing the results of some experiments and of the experimenters’ interpretation of those results so that a conclusion as to a position or status of Lennerberg’s CPH to date can be made.


Lenneberg’s CPH was initially based firstly on the idea that lateralization for language has taken place by puberty and left hemisphere of brain is no longer able to acquire language; and secondly on the fact that children whose brain-damaged and who became aphasic before puberty recovered language virtually intact, whereas people whose brain-damaged after puberty never sounded like native speakers of the language (Hurford, 1991; Johnson & Newport, 1989). However, the Lenneberg’s thesis of lateralization by puberty has been challenged by a number of findings. Krashen (1973 cited in Singleton, 1989), for example, by reanalyzing of Basser’s data on unilateral brain damage and on hemispherectomy, which was previously reanalyzed by Lenneberg, found that in all cases of injury to the right hemisphere resulting in speech disturbance, the lesion was incurred before five. Studies that include a description of children injured after five indicated that the effect of right lesions in older children is the same as in adults (p.162). Based on this finding, he came to a conclusion that the lateralization for language is complete by the age of five years, not by puberty.

            Furthermore, Marcotte & LaBarba (1987 cited in Marcotte & Morere, 1990), examining lateralization patterns in deaf children acquiring a severe to profound bilateral hearing loss between the age of 2 and 36 months, suggested that hearing loss which is caused by lack of contact with environment at any point in the first three years of life can result in reorganization of speech function. However,  this study did not cover the isolation of endpoint of such a critical period after which interruption of environmental stimulation does not alter left cerebral specialization of speech.

            Replicating Marcotte & LaBarba’s study, Marcotte & Morere (1990) designed study for isolating a critical development period, that is, a period which profound loss of hearing in the first five years of life due to environmental deprivation leads to cortical reorganization and alteration of a typical pattern of left hemispheric specialization for speech production. The results of this study support that of Marcotte and LaBarba, that is, there is a critical development period during which environmental deprivation plays an important role in the ultimate brain organization for speech control and regulation. More specifically, the critical development period spans approximately the first three years of life. This span is in accordance with Milner’s finding of myelinization of Broca’s area, which takes place in the first three years of life.

            Palij (1990:60), in his research based on a question whether a person’s current English processing is affected more by its position in a sequence of acquisition of languages or the age of the English acquisition, provides evidence of the existence of a critical period in language acquisition. He found that the subjects’ English processing systematically relates to the ages of onset (AO) of the language acquisition, not to the position in a sequence of acquisition of languages. He comes to this conclusion after an analysis of the language background of 273 people he researched in New York University psychology department subject pools. His finding, among other, is that there is no difference in English language acquisition between native speakers of English and non-native speakers who acquired English before the age of 6, but there are consistent differences with those who acquired English after the ages of 6 and 12.

            History has also documented ‘natural experiments’ on first language acquisition which involved children being deprived  contact with a language. A case of ‘Victor’ is one of the most famous natural experiments. When he was found at the age of 12 years old, he apparently had no contact with humankind. After five years of rehabilitation, Jane Marc-Gaspard Itard, a doctor who is responsible for his civilization, succeeded in developing his sociability, memory, judgment, and all functions of his senses, but Itard failed to teach him a language. Victor managed to speak only words ‘lait’ (milk) as an excited exclamation, not as communication of his need and ‘O Dieu’ (Oh, God) as his governess frequent exclamation (Shattuck, 1980 cited in Singleton, 1989).

            ‘Genie’ was another child who was deprived contact of a language in her early years. She had been almost completely isolated since the age of 20 months and discovered at the age of 13:7 with no language. After five years of exposure, she managed in accelerated, somewhat irregular passage progress through normal language learning sequences but stopped well short of native-like attainment especially in morphology and syntax. She was better at vocabulary and semantic than at syntax and comprehension than production (Curtiss, 1977 cited in Long 1990). Genie’s case is in accordance with the idea that a critical period for language acquisition is not an “all or none” phenomenon but some ability to acquire language still remains when first language acquisition begins after puberty (Fromkin, Krashen, Curtiss, & Rigler cited in Mayberry & Eichen, 1991). To the second language acquisition, Genie’s case suggests that SLA is still possible after puberty but the learning will be irregular and incomplete (Curtiss, cited in Long, 1990).

            Both Victor’s and Genie’s cases support both strong and weak versions of the Lenneberg’s CPH, that is Victor’s case is in accordance with the strong version — no language will be acquired after puberty (as cited from Itard by Lane, 1976 in Singleton, 1989); while Genie’s case supports the weak version of the CPH, that is, the language acquisition is still possible but native-like speakers will not be attained (Curtiss, cited in Long, 1990). However, in terms of Genie’s case, there are some arguments not in support of the CPH. Mayberry & Eichen (1991), for example, argued that Genie’s linguistic difficulties may have been compounded by the cognitive and emotional deprivation she additionally suffered. Similar arguments were also given by Singleton (1989).

            A number of observations to prove the existence of age factor in language acquisition involving deaf people (children and adults) have also been reported in language acquisition literature. Newport (1994) and Newport & Supalla (1987,1990), Johnson & Newport (1989) and Hurford (1991), for examples, found clear evidence of sensitive periods of first language development. By studying congenitally deaf subjects exposed to American Sign Language (ASL)  for equivalent period of time (10 years) with age of onset (AO) at different ages, they found that (1) subjects exposed to ASL between birth and six were capable of reaching native standard and shown uniform error types along the ways; (2) subjects exposed after seven made some errors in closed item (grammatical morphology) after ten years of uses and shown more evidence on holistic (unanalysed) learning the later they started; (3) subjects exposed to ASL after 12 reached far short of native standard and shown much greater variations in error types. These findings not only provide evidence that the age of exposure to language plays an important role in language acquisition but also tell us that Lenneberg’s CPH is partially incorrect in two regards: firstly, language acquisition is not a sudden-drop-off at puberty but a continuous linear decline; and secondly, language acquisition is not totally blocked (unlearnable) — it is still possible but it is hard for the to reach high level of proficiency.

            Evidence for language acquisition from sign language was also offered by Maberry & Eichen (1991). By involving 49 deaf signers having used sign language for an average of 42 years with initial exposure of ages ranging from birth to 13 years and testing them on sentence recall, lexical preservation and change, semantic lexical changes, bound morpheme preservation, constituent ordering, response grammaticality and paraphrase, and digit span, they found that the age factor for language acquisition exerts long-lasting effect on sign language processing at all levels of linguistic structure. This is shown by the difference between the early and late learners’ performance in the processing of lexical, morphological, and grammatical levels in which early learners outperformed linearly the late learners, that is to say,  the increases of age of acquisition is gradually followed by the declines of understanding of proportion of stimulus. This finding, therefore, provides evidence of Lenneberg’s CPH and supports the results of previous findings showing that the critical period of language acquisition is not “all or none” phenomenon, but some ability to acquire language still remains when the language acquisition begins after puberty (e.g. Fromkin, et al., 1974 cited in Mayberry & Eichen, 1991).

            Criticism of Lenneberg’s CPH to the existence of the age factor in language acquisition comes from Johnson & Newport (1989) who pointed out that the CPH was somewhat ambiguous. According to them, the CPH can be interpreted as containing two distinct notions, namely, “the exercise hypothesis” (i.e. the capacity of acquiring languages will depend on whether or not the capacity is activated or exercised in early life) and “the maturational state hypothesis” (i.e. the capacity disappears along with maturation). Based on the former hypothesis, there should be no differences between children and adults in second language acquisition, or even adult starters will be better due to their greater skills in their first language and in other related domains. The latter hypothesis, on the other hand, clearly makes a distinction between first and second language acquisition by child and adult starters, that is, the child starter will be better in both first and second language acquisition.

            In their research on age-related effect on learning grammar of a second language, Johnson & Newport (1989) intended to prove the truth of these notions by assuming that if there are critical periods in SLA, then learners beginning their exposure to the language in early childhood should reach high level of proficiency in that language than those beginning at later ages, particularly  at adulthood. By comparing the grammatical proficiency on 12 basic structures of English grammar by Korean and Chinese speakers arriving at USA between the ages of 3 and 39, and living in the USA for the average of 10 years by the time of testing, they found a systematic relationship between the performance on the basic properties of English grammar and the age of arrival (AO), with those who arrived at between the age of 3 and 7 performed at the native level while the remaining groups performed significantly poorer as the age of arrival (AO) increased. These results suggest that the age factor has an impact on the acquisition of basic properties of English grammar and at the same time support the maturational state hypothesis, not exercise hypothesis.

            Furthermore, Johnson & Newport (1991) extended their previous study (Johnson & Newport (1989) to test whether or not the age of acquisition  also influenced second language learners’ use of principles of English syntax.  Chinese native speakers who arrived in the USA between the ages of 4 and 38 years old and learned English as a second language were tested on universal principle subjacency (universal syntactic principle). The subjects were immersed in English for a minimum of 5 years and were adults when tested. Their performance was then compared to that of native speakers of English. The results of the study are (1)  subjects’ performance on subjacency regardless the ages of arrival is significantly below that of native speakers. In other words, non-native performance on subjacency  was found for subjects of all ages of arrival; (2) a gradual decline in the accessibility of subjacency with the increasing age of arrival. These findings provide stronger support to the claim of prior studies, showing that there is a critical or sensitive period for either first language acquisition (e.g. Curtiss, 1977; 1988; Newport & Supalla, 1990 both cited in Johnson & Newport, 1991) or second language acquisition (e.g. Oyama, 1978  and Patkowski, 1980 cited in Long, 1990; Johnson & Newport, 1991; Johnson and Newport, 1989).

            Lenneberg’s CPH, however, has been challenged in recent years from different points of view and by involving older and younger learners in first and second language acquisition. These counters come, among others, from Ellis (1985), Flege (1987), Genesee (1988), Neufeld (1979) cited in Long 1990 and Snow & Hoefnagel-Hohle (1978). Their findings suggested that the older learners surpassed the younger learners and rejected the notion of “the younger = the better” in language acquisition (Long, 1990), even for second language pronunciation ability (Genesee in Long, 1990). Genesee’s idea about second language acquisition of phonology  was supported by Neufeld’s (1977, 1978, 1979 cited in Long, 1990) series findings. Twenty native speakers of English were involved to received eighteen-hour instructions in Japanese and Chinese phonology with the results that three of them attained a native speaker rating in one language, one of whom did so in both languages. In another study, adult starters with long exposure in Canadian French were classified as native speakers on “read aloud” samples. From these findings, Neufeld claimed that “accent-free” performance is possible by adults who learn the language after the sensitive period. However, Long (1990) criticized these findings as suffering from methodology flaws used in those studies such as representativeness of Canadian bilingual environment in French studies (although not Japanese/Chinese studies), the heterogeneous English-French speech communities lead to a question of who native speakers are, the limitation on the speech samples and materials, and the ambiguity of instructions to raters (see Long, 1990 for details).

            Different findings on second language phonological attainment from those of Genesee and Neufeld were offered by Oyama (1976) and Patkowski (1980), both cited in Long (1990; see also Flege, 1987). Oyama, in looking at the effect of ages in pronunciation ability, studied 60 Italian immigrants with different AO in the USA ranging from 6 to 20 and who have lived in the USA for different periods (8 to 18 years. She obtained that the age of arrival (AO), not the length of residence (LOR)  or motivation, does exert main effect in second language acquisition. Those arriving before puberty (before 12 years old) performed in the range of native speaker controls, and those who were older than 12 on arrival did not. Patkowski (1980 cited in Long), after replicating Oyama’s study, came to similar conclusion.

            A counterevidence to the existence of the age factor in language acquisition was also presented by Snow and Hoefnagel-Hohle (1978) who studied longitudinally the progress of groups of English speakers at different ages who were learning Dutch. After testing them three times at 4 – 5 month intervals on pronunciation, auditory discrimination, morphology, sentence repetition, sentence translation, comprehension, storytelling, etc., they found that adults and 12-15 year old subjects outperformed the 3-5 and 8-10 year old group in the first few months and that the adolescent (8-10 and 12-15 years old) groups were the most successful learners while the 3-5 year old group scored the lowest on all the test employed. From these findings, they concluded that there is no critical period in language acquisition. However, these results are questionable in terms of the tasks used in the experiment. Such tasks as translation, storytelling, or sentence judgment might be difficult for children.

            Similar result to those of Snow & Hoefnagel-Hohle were also obtained by Winitz (1981 cited in Flege, 1987) who found that the native English adults were better in discriminating Chinese tones and obstruent consonants than the eight-year-old children.

            In relation to debates on the notion of “the younger = the better versus “the older = the better”in second language acquisition, Krashen, Long, & Scarcella (cited in Long, 1990: 260), reviewing the available literature on age differences in second language acquisition, come to conclusion that three generalizations could be drawn if short-term (rate) and long-terms (ultimate attainment) differences are made. Those are (1) adults proceed through early stages of morphological and syntactic development faster than children (where time and exposure are held constant); (2) older children acquire faster than younger children (again in early stages of morphology and syntax, where time and exposure are held constant); and (3) child starters outperform adult starters in the long run. Putting together, adults and adolescents learn at a faster rate (short-term), whereas children surpass adults and adolescent in eventual/ultimate attainment (long-term).


  • The existence critical period in language acquisition seems still controversial, in the sense that some experiments are capable of supporting that notion, while some others manage to prove that the critical period does not exist in language acquisition. Therefore, more experiments need to be conducted in order to prove the ‘status’ of the critical period or age factor in language acquisition. The experiments must involve experts from related disciplines.
  • Most of recent literature are in support Lenneberg’s CPH; however, the notion of the critical period has changed from “a sudden drop-off” at puberty (i.e. the capacity of learning language will be lost if it is not activated during the critical period, before puberty) to “a continuous linear decline” (i.e. the language acquisition is still possible after puberty but it will be more difficult and incomplete). The later notion leads to the use of “sensitive period” instead of “critical period”. With this notion, in long term the younger they start to learn a language, the more proficient they will be in all aspects of the language.


Flege, J.E., 1987. “A critical period for learning to pronounce foreign language?” Applied Linguistics, 8, 2, pp. 162-178.

Hurford, J.R., 1991. “The evolution of the critical period for language acquisition”. Cognition, 40, pp. 159-201.

Johnson, J.S. & Newport, E.L., 1989. “Critical period effects in second language learning: The influence of maturation state on the acquisition of a second language”, Cognitive Psychology, 21, pp. 60-99.

Johnson, J.S. & Newport, E.L., 1991. “Critical period effects on universal properties of language: The status of subjacency in the acquisition of a second language”, Cognitive, 39, pp. 215-258.

Long M., 1990. “Maturation constraints on language development”, Studies in Second Language Acquisition, 12, pp. 251-285.

Marcotte, A.C. & Morere, D.A., 1990. “Speech lateralization in deaf populations: Evidence for a developmental critical period”. Brain and Language, 39, pp. 134-152.

Mayberry, R.I & Eichen, E.B., 1991. “The long-lasting advantage of learning sign language in childhood: Another look at the critical period  for language acquisition”. Journal of Memory and Language, 30, pp. 486-512.

Palij, M., 1990. “Acquiring English at different ages: The English displacement effect and other findings”. Journal of Psycholinguistic Research, 19, pp. 57-70.

Singleton, D., 1989. Language Acquisition: The Age Factor.  Philadelphia: Multilingual Matters Ltd.

Snow, C.E. & Hoefnagel-Hohle, M., 1978. “The critical period for language acquisition: Evidence for second language learning”. Child Development, 49, pp. 1114-1128.

Wode, H., 1994. “Nature, nurture, and age in language acquisition: The study of speech perception. Studies in Second Language Acquisition, 16, pp. 325-345.


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