The data from these wild children are difficult to interpret, in part because we do not know why or how the children were abandoned. Clearer data come from the (unfortu-nately many) cases of children raised by humans but under conditions that were hideously inhumane, for their parents were either vicious or deranged. Sometimes such parents will deprive a baby of all human contact. For example, “Isabelle” (a code name used to protect the child’s privacy) was hidden away, apparently from early infancy, and given only the minimal attention necessary to sustain her life. No one spoke to her (the mother was deaf and also emotionally indifferent).
At the age of 6, Isabelle was discovered by other adults and brought into a normal environment. Of course, she had no language, and her cognitive development was below that of a normal 2-year-old. But within a year she learned to speak, her tested intelligence was normal, and she took her place in an ordinary school (R. Brown, 1958; K. Davis, 1947). Thus, Isabelle at 7 years, with 1 year of language practice, spoke about as well as her peers in the second grade, all of whom had had 7 years of practice.
But rehabilitation from isolation is not always so successful. “Genie,” discovered in California about 40 years ago, was 14 years old when she was found. Since about the age of 20 months she had lived tied to a chair; she was frequently beaten and never spo-ken to but sometimes was barked at, because her father said she was no more than a dog. Once discovered, Genie was brought into foster care and taught by psychologists and linguists (Fromkin, Krashen, Curtiss, Rigler, & Rigler, 1974). But Genie did not become a normal language user. She says many words and puts them together into meaningful propositions as young children do, such as “No more take wax” and “Another house have dog.” Thus, she has learned certain basics of language. Indeed, her semantic sophistication—what she means by what she says—is far beyond that of young children. Yet even after years of instruction, Genie has not learned the function words that appear in mature English sentences, nor does she combine propositions together in elaborate sentences (Curtiss, 1977).
Why did Genie not progress to full language learning? The best guess is that the cru-cial factor is the age at which language learning began. Genie was discovered after she had reached puberty, while Isabelle was only six years old when her rehabilitation began. As we shall see later, there is some reason to believe that there is a sensitive developmental period for language learning during which it is most easily acquired.