critical periodn.
/ˌkrɪtᵻkl ˈpɪərɪəd/, U.S. /ˌkrɪdək(ə)l ˈpɪriəd/ 1.
a. Biology. A period of life, esp. embryonic or fetal life, during which development may be altered irrevocably, typically by the presence or absence of some external or internal factor. Cf. sensitive period n. (a) at sensitive adj. and n. Compounds 1.
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1864 H. Lawson tr. A. de Quatrefages Metamorph. Man & Lower Animals xii. 112 It is indeed a critical period, not only for insects in general, but for butterflies in particular, in which the animal is, so to speak, re-cast and constructed upon a very different plan from that which was adopted before.
1915 Amer. Jrnl. Physiol. 37 2 The point of junction of these cycles is a critical period in the growth of guinea-pigs... Premature delivery of young, which are usually dead, occurs at this period much more frequently than at any other.
1967 Brit. Jrnl. Psychiatry 113 923/1 I should like to offer a testable theory on how the male child might have incorrect hormone levels at the ‘critical period’ when his sex-controlling centre is maturing.
1999 Nature 29 July 419/3 The critical period for thalidomide-induced typical limb malformations (amelia and phocomelia) is very early.
2007 New Yorker 19 Nov. 56/3 The idea was that the fetus set its metabolic thermostat during critical periods of gestation.
b. Biology and Psychology. A period of (usually early) life during which certain types of learning, esp. imprinting and socialization, must occur or occur most easily. Cf. sensitive period n. (b) at sensitive adj. and n. Compounds 1.
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1952 Systematic Zool. 1 164/1 The initial reproductive isolating mechanism is much more likely to be some such phenomenon as imprinting, in which certain adult behavior patterns are determined by stimuli received in a critical period early in the lives of the birds.
1992 Appl. Linguistics 13 290 Second language researchers have long speculated on critical periods and fossilization (i.e. when individuals cease to improve their second language proficiency beyond a certain point).
2015 D. E. Papalia & G. Martorall Experience Human Devel. (ed. 13) i.15 If ducklings' rearing conditions are varied to slow their growth, the usual critical period for imprinting can be extended.
2. Botany. A length of daylight or of darkness during the daily cycle which must be reached or exceeded in order for a particular type of plant to be stimulated to produce flowers. Cf. photoperiod n.
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1933 Plant Physiol. 33 353 A day length between the two critical periods would produce a flowering stem; while day lengths in excess of the upper critical period would lead to extensive elongation of the axis without flowering.
1959 F. W. Went in W. B. Turrill Vistas in Bot. 526 Spring and summer flowering plants..will produce flowers only when they are exposed to a day length longer than the critical period.
2017 D. B. Egli Seed Biol. & Yield Grain Crops (ed. 2) v. 125 The duration of the critical period has also been related to seed number in wheat.
This entry has been updated (OED Third Edition, March 2022).
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