ment are simply the effects of a normal environment; the abnormal condition is isolation, resulting in impaired development, as is seen with children raised in extreme isolation.

Indeed, wild rats and laboratory rats raised in semiwild environments (which may be rich in stress) have the same cortical development as rich rats. Thus, the available evidence suggests that the normal environment provided by caring parents or other caregivers is sufficient for normal brain development.

A common misconception is that the brain grows in spurts and is particularly sensitive to specific educational procedures at these critical growth times. This is not the case. Critical periods—periods in development during which brain systems are especially vulnerable—are indeed real, as demonstrated by the literature on visual deprivation. These periods are important, however, only in abnormal or extreme circumstances. Nor is it true that no new nerve cells form after birth. Studies in rats indicate that particular learn-

ANNEX BOX 3–1The Mozart Effect

Several years ago, great excitement arose over a report published in Nature that claimed listening to the music of Mozart enhanced intellectual performance, increasing IQ by the equivalent of 8 to 9 points as measured by portions of the Stanford-Binet Intelligence Scale (Rauscher, Shaw, and Ky, 1993). Dubbed “the Mozart effect,” this claim was widely disseminated by the popular media. Articles encouraged parents to play classical music to infants and children and even to listen to such music during pregnancy. Companies responded by selling Mozart effect kits including tapes and players. (An aspect of the Nature account overlooked by the media is that the Mozart effect is reported to last about 10 to 15 minutes.) The authors of the Nature report subsequently offered a neurophysiological rationale for their claim (Rauscher, Shaw, and Ky, 1995). This rationale essentially held that exposure to complex musical compositions excites cortical firing patterns similar to those used in spatial-temporal reasoning, so that performance on spatial-temporal tasks is positively affected.

Several groups attempted to replicate the Mozart effect, with consistently negative results (Carstens, Huskins, and Hounshell, 1995; Kenealy and Monsef, 1994; Newman et al., 1995; Steele, Ball, and Runk, 1997;. In a careful study, Steele, Bass and Crook (1999) precisely replicated the conditions described by Rauscher and Shaw as critical. Yet the results were entirely negative, even though subjects were



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