such experiments. In order to respond to the stimulus change required in classical conditioning treatments, the infant must develop the ability to perceive differences in stimuli. The newer studies we cited previously, however, suggest that even neonates are able to make some rudimentary discriminations of stimuli; hence the next few years may see some experimentation with the classical conditioning of infants.
Conception occurs when a sperm cell from male seminal fluid unites with an ovum that has been proceeding down one of the Fallopian tubes leading from an ovary. The fertilized ovum, or zygote, immediately begins to divide and subdivide, becoming a blastocyst that proceeds further into the uterus. Embedded in the uterine wall, the zygote within a few days becomes an embryo and develops a placenta, the indirect connection between the mother and the growing organism, through which nutrients are exchanged for waste products.
By the end of the first month, the embyro is about ¼ inch long, is curled in the form of a crescent, and possesses buds that will become limbs. Development proceeds extremely rapidly during the early weeks and months. By the end of the second month it is about 1½ inches long and has assumed some human features; it is now termed a fetus. By the time the fetus is seven months old, it is about 16 inches long, weighs about three pounds, and can survive in a specially sheltered environment if prematurely born. The fact that fetuses move about, apparently spontaneously, has made it possible to conduct conditioning experiments. Although such experiments yield positive results, they are rather difficult to interpret because of the possibility that it is the mother rather than the fetus who has been conditioned.
Children born to economically deprived mothers tend to be smaller, probably because of substandard maternal nutrition. Low-birth-weight, or premature, infants have a higher mortality rate than normal-sized infants. Mothers who live in poor environments are also more prone to infections, like cytomegalovirus (CTV), which produce birth defects and may cause mental retardation, blindness, and deafness in their infants. The habitual use of narcotics and other psychoactive drugs by pregnant women has an adverse effect on fetuses. Expectant mothers who are confirmed smokers tend to produce a higher than average percentage of low-birth-weight infants. Other medical problems that produce abnormalities in fetuses include the use of thalidomide, excessive X-ray exposure, and incompatibility of Rh blood factors.
Pregnancy is a developmental crisis in a woman's life. Attitudes formed during pregnancy will carry over into the mother's relationship with the child later on. Mothers with attitudes which are generally