physiological psychology Study of the physiological basis of behaviour. Traditional specializations in the field cover perception, moti¬ vation, emotion, learning, memory, cognition, or mental disorders. Also con¬ sidered are other physical factors that affect the nervous system, including heredity, metabolism, hormones, disease, drug ingestion, and diet. An experimental science, physiological psychology relies heavily on labora¬ tory research and quantitative data.
physiology \,fi-ze-'a-l9-je\ Study of the functioning of living organ¬ isms or their constituent tissues or cells. Physiology was usually consid¬ ered separately from anatomy until the development of high-powered microscopes made it clear that structure and function were inseparable at the cellular and molecular level. An understanding of biochemistry is fun¬ damental to physiology. Physiological processes are dynamic; cells change their function in response to changes in the composition of their local environment, and the organism responds to alterations in both its internal and external environment. Many physiological reactions are aimed at preserving a constant physical and chemical internal environ¬ ment (homeostasis). See also cytology.
phytoflagellate \ .fi-to-'fla-j s-lst\ Any of several protozoans that have flagella in addition to sharing many characteristics with typical algae, especially the pigment chlorophyll and various other pigments. Some spe¬ cies, though similar in form, lack chlorophyll. Phytoflagellates may obtain nutrients by photosynthesis, by absorption through the body surface, or by ingestion of food particles. Cryptomonads are among the more impor¬ tant phytoflagellates.
phytoplankton V.fi-to-'plaqk-tsnV Flora of freely floating, often minute organisms that drift with water currents. Like land vegetation, phytoplankton uses carbon dioxide, releases oxygen, and converts min¬ erals to a form animals can use. In fresh water, large numbers of green algae often colour lakes and ponds, and cyanobacteria may affect the taste of drinking water. Oceanic phytoplankton is the primary food source, directly or indirectly, of all sea organisms. Composed of groups with silica-containing skeletons, such as diatoms and dinoflagellates, phy¬ toplankton varies seasonally in amount, increasing in spring and fall with favourable light, temperature, and minerals.
pi In mathematics, the ratio of the circumference of a circle to its diameter. An irrational number (see also transcendental number), it has an approximate value of 3.14, but its exact value must be represented by a symbol, the Greek letter 7t. Pi is used in calculations involving lengths, areas, and vol¬
umes of circles, spheres, cylinders, and cones. It also arises frequently in problems dealing with certain periodic phenomena (e.g., motion of pen¬ dulums, alternating electric currents). By the end of the 20th century, com¬ puters had calculated pi to more than 200 billion decimal places.
Piaf, Edith \'pyaf\ English \'pe-,af\ orig. Edith Giovanna Gassion
(b. Dec. 19, 1915, Paris, France—-d. Oct. 11, 1963, Paris) French popular singer and actress. Her mother, a cafe singer, abandoned her at birth; Piaf became blind at age three as a result of meningitis but recovered her sight four years later. Her father, a circus acrobat, took her along on tours and encouraged her to sing. She sang for years in the streets of Paris until discovered by a cabaret owner who gave her her first nightclub job and suggested she change her name to Piaf, Parisian slang for “sparrow.” She was soon singing her chansons (ballads) in the large music halls of Paris. During World War II she entertained French prisoners of war and aided several in their escapes. She spent the postwar years touring, gaining worldwide fame with her intense performances of songs such as “Non, je ne regrette rien” (“No, I regret nothing”). Her throaty, expressive voice, combined with her fragile appearance and a dramatic tight spotlight on her face and hands, made her concerts memorable.
Piaget \pya-'zha\, Jean (b. Aug. 9, 1896, Neuchatel, Switz.—d. Sept. 17, 1980, Geneva) Swiss psychologist. Trained in zoology and philoso¬ phy, Piaget later studied psychology in Zurich (from 1918) with Carl Gustav Jung and Eugen Bleuler, and he was subsequently affiliated with the University of Geneva from 1929 until his death. He developed a theory of “genetic epistemology,” a natural timetable for the development of the child’s ability to think in which he traced four stages—the sensorimotor (ages 0-2), preoperational or symbolic (2-7), concrete operational (7-12), and formal operational (through adulthood)—each marked by increased cognitive sophistication and ability to use symbols. In 1955 Piaget founded and became director (to 1980) of an international centre for genetic epistemology in Geneva. His numerous books include The Lan¬ guage and Thought of the Child (1923), Judgment and Reasoning in the Child (1924), The Origin of Intelligence in Children (1948), and The Early Growth of Logic in the Child (1964). He is regarded as the foremost developmental psychologist of the 20th century.
piano or pianoforte Keyboard instrument with wire strings that sound when struck by hammers operated by a keyboard. It was invented in Florence by Bartolomeo Cristofori before 1720, with the particular aim of permitting note-to-note dynamic variation (lacking in the harpsichord). It differs from the older clavichord in that its hammers (rather than tan¬ gents) are thrown at the strings and bounce back, permitting the struck string to vibrate loudly. A cast-iron frame is needed to withstand the strings’ tremendous tension. Pianos have taken various shapes. The origi¬ nal harpsichord (or wing) shape has survived in the modern grand piano; the less-expensive square (actually rectangular) piano, standard in the early 19th century, was replaced by the upright piano, in which the strings are vertical. For at least 150 years the piano was the most important instrument in Western music. See illustration on following page.
piano nobile \,pya-n6-'n6-bi-la\ (Italian: “noble floor”) In a Renais¬ sance building, the first floor above ground level. In the typical palace erected by an Italian prince, the large, high-ceilinged reception rooms were in this upper, main story. Often a grand exterior staircase or pair of staircases led from ground level up to the piano nobile.
Piave River \'pya-va\ River, northeastern Italy. Rising in the Carnic Alps south of Lienz near the Austrian frontier, it flows south and south¬ east into the Adriatic Sea, east of Venice. It is 137 mi (220 km) long. Dur¬ ing World War I, its valley was the scene of several battles against the Austrians (see Battle of Caporetto). In 1966 the river burst its dikes in a major flood.
piazza \pe-'at-s9, pe-'a-z9\ Open square or marketplace, surrounded by buildings, in an Italian town or city. It was equivalent to the plaza of Spanish-speaking countries. The term became more widely used in the 16th-18th century, denoting any large open space with buildings around it. In 17th-18th-century Britain, long covered walks or galleries with roofs supported by columns were called piazzas; in the U.S. in the 19th cen¬ tury, piazza was another name for a veranda formed by projecting eaves.
Piazzetta \pyat-'tsat-ta\, Giovanni Battista or Giambattista Piazzetta (b. Feb. 13, 1682, Venice—d. April 28, 1754, Venice) Italian painter, illustrator, and designer. Trained as a wood carver by his father, he turned to painting and became one of the outstanding Venetian artists