Final answer:
Danielle's and Genie's cases demonstrate the negative impacts of isolation on language development. Lack of socialization hindered Danielle's verbal abilities, while Genie acquired substantial vocabulary but struggled with syntax due to late exposure to language.
Step-by-step explanation:
The case of children like Genie and Danielle highlights the critical nature of the critical period hypothesis in language development. Nearly complete isolation during childhood, as in the case of Danielle, severely impacted verbal abilities. This lack of social interaction meant that Danielle had not been properly socialized, leading to her inability to speak, understand, or use gestures effectively. Genie, on the other hand, began learning language after being rescued from an abusive environment, which made it evident that although she developed a substantial vocabulary, she struggled with syntax ; hence, she showed significant developmental delays and never quite mastered the grammatical aspects of language.
These cases underline the importance of timely and rich linguistic and social interaction for the normal development of language and cognitive abilities in children. The premise is supported by various theories, including Noam Chomsky's claim of a biological predisposition to language acquisition and the observed difficulties faced by individuals like those with dyslexia when learning to read due to disordered brain processing. All these conditions, to some degree, emphasize the importance of language acquisition during the so-called critical period.