Employed to illustrate the earl of Derby’s private menagerie in the 1830s, he later produced Book of Nonsense (1846) for the earl’s grandchildren. His other works include Nonsense Songs, Stories,
Botany and Alphabets (1871), con¬ taining “The Owl and the Pussy- Cat,” and Laughable Lyrics (1877).
He is best known for popularizing the limerick. He also published vol¬ umes of bird and animal drawings and seven illustrated travel books.
Epileptic and depressive, he lived mainly abroad after 1837.
Lear, Norman (Milton) (b. July 27, 1922, New Haven, Conn., U.S.)
U.S. producer, writer, and director.
He first worked in public relations and later in television as a comedy writer and director (1950-59). He wrote and produced movies such as Come Blow Your Horn (1963), Divorce American Style (1967), and Cold Turkey (1971) before returning to television to create and produce hit series such as All in the Family (1971-83), for which he received four Emmy Awards; Maude (1972-78); Sanford and Son (1972-77); and The Jejfersons (1975-85). He founded the progressive activist group People for the American Way.
Lear, William Powell (b. June 26, 1902, Hannibal, Mo., U.S.—d. May 14, 1978, Reno, Nev.) U.S. electrical engineer and industrialist. Fol¬ lowing military service during World War I, he designed a practicable car radio and sold it to the future Motorola, Inc. During and after World War II, his companies Lear Avia and Lear, Inc., built radio navigators, auto¬ pilots, and other precision devices for Allied aircraft. In 1963 Lear formed Lear Jet, Inc., which produced small private and corporate jet aircraft. In 1964 he developed the stereo eight-track player for automobiles.
learned helplessness In psychology, a mental state in which a labo¬ ratory subject forced to bear aversive stimuli becomes unable or unwill¬ ing to avoid subsequent applications, even if they are “escapable,” presumably through having learned that situational control is generally out of one’s hands. Experiments, first on dogs and later on humans, led some researchers, including Martin E.P. Seligman (b. 1942) in Helpless¬ ness (1975), to believe that chronic failure, depression, and similar con¬ ditions are forms of learned helplessness. Critics have argued that different conclusions can be drawn from such tests and that broad generalizations are unwarranted.
learning Process of acquiring modifications in existing knowledge, skills, habits, or tendencies through experience, practice, or exercise. Learning includes associative processes (see association; conditioning), discrimination of sense-data, psychomotor and perceptual learning (see per¬ ception), imitation, concept formation, problem solving, and insight learning. Animal learning has been studied by ethologists and comparative psy¬ chologists, the latter often drawing explicit parallels to human learning (see comparative psychology; ethology). The first experiments concerning asso¬ ciative learning were conducted by Ivan Pavlov in Russia and Edward L. Thorndike in the U.S. Critics of the early stimulus-response (S-R) theories.
Red-banded leafhopper (Graphoceph- ala)
STEPHEN COLLINS/PHOTO RESEARCHERS
Edward Lear, drawing by William Hol¬ man Hunt, 1857; in the Walker Art Gallery, Liverpool
COURTESY OF THE WALKER ART GALLERY, LIVERPOOL
© 2006 Encyclopaedia Britannica, Inc.
learning disabilities ► Lebanon I 1089
such as Edward C. Tolman, claimed they were overly reductive and ignored a subject’s inner activities. Gestalt-psychology researchers drew attention to the importance of pattern and form in perception and learning, while structural linguists argued that language learning was grounded in a geneti¬ cally inherited “grammar.” Developmental psychologists such as Jean Piaget highlighted stages of growth in learning. More recently, cognitive scientists have explored learning as a form of information processing, while some brain researchers, such as Gerald Maurice Edelman, have proposed that thinking and learning involve an ongoing process of cerebral pathway building. Related topics of research include attention, comprehension, moti¬ vation, and transfer of training. See also behaviour genetics; behaviourism;
EDUCATIONAL PSYCHOLOGY; IMPRINTING; INSTINCT; INTELLIGENCE.
learning disabilities Chronic difficulties in learning to read, write, spell, or calculate, which are believed to have a neurological origin. Though their causes and nature are still not fully understood, it is widely agreed that the presence of a learning disability does not indicate subnor¬ mal intelligence. Rather it is thought that the learning-disabled have a neurologically based difficulty in processing language or figures, which must be compensated for with special learning strategies or with extra effort and tutoring. Examples of learning disabilities include difficulty in reading (dyslexia), writing (dysgraphia), and mathematics (dyscalcula). Learning disabilities may be diagnosed through testing, and children may be enrolled in programs offering special help; left unrecognized, learning disabilities may result not only in poor classroom performance but also in low self-esteem and disruptive behaviour.
least squares method Statistical method for finding a line or curve—the line of best fit—that best represents a correspondence between two measured quantities (e.g., height and weight of a group of college students). When the measurements are plotted as points on a graph and seem to fall near the same line, the least squares method may be used to determine the best-fitting line. The method uses calculus techniques to find the minimum of the sum of the squares of the vertical distances of each data point from the proposed line. More generally, the process is called regression or, when the fitted curve is a line, linear regression.
leather Animal skins and hides treated to preserve them and make them suitable for use. Tanning converts the otherwise perishable skin to a stable and nondecaying material. Though the skins of such diverse animals as ostrich, lizard, eel, and kangaroo have been used, the more common leath¬ ers come from cattle, including calf and ox; sheep and lamb; goat and kid; horse, mule, and zebra; buffalo; pig and hog; and seal, walrus, whale, and alligator. Leather making is an ancient art that has been practiced for more than 7,000 years. See also parchment.
Leavis Vle-vasN, F(rank) R(aymond) (b. July 14, 1895, Cambridge, Cambridgeshire, Eng.—d. April 14, 1978, Cambridge) British literary critic. He attended and later taught at Cambridge University. He brought a new seriousness to criticism, believing that the critic’s duty is to assess works according to the author’s moral position. He cofounded Scrutiny, a journal (published 1932-53) often regarded as his greatest contribution to English letters. His books include New Bearings in English Poetry (1932) and The Great Tradition (1948), in which he reassessed the English novel.
Lebanese Civil War (1975-91) Civil conflict resulting from tensions among Lebanon’s Christian and Muslim populations and exacerbated by the presence in Lebanon in the 1970s of fighters from the Palestine Libera¬ tion Organization (PLO). In 1975 Lebanon’s Muslims and leftists sup¬ ported the PLO and sought more political power; its Christians, seeking to maintain their political dominance, opposed the PLO. The factions fought fiercely through early 1976, and Lebanon became effectively par¬ titioned, with the Christians in power in the north and the Muslims in the south. Fearing an expanded war, both Israel and Syria intervened on the side of the Christians, who had begun to lose ground. Fighting continued at a lower level of intensity until 1982, when Israel invaded southern Lebanon to destroy Palestinian guerrilla bases; PLO forces were driven out of Beirut, and by 1985 Israel had withdrawn from most of Lebanon, which by then was split internally over whether to accept Syria’s lead¬ ership. In 1989 the Christian leader General Michel Aoun attempted to drive Syria from Lebanon but was defeated, and the Arab League medi¬ ated a peace deal; his removal from power in 1990 eliminated the largest obstacle to implementing a 1989 peace accord. In southern Lebanon, fighting between Israeli and Hezbollah forces continued even after Israel’s final withdrawal from Lebanese territory in 2000.