First Language Acquisition
Language acquisition is the process whereby children acquire their first languages. All humans (without exceptional physical or mental disabilities) have an innate capability to acquire language. Children may acquire one or more first languages. For example, children who grow up in an environment in which only English is spoken and heard will acquire only English as their first language. However, children who grow up in an environment in which both German and English are spoken and heard equally will acquire both German and English as their first languages. Acquisition occurs passively and unconsciously through implicit learning. In other words, children do not need explicit instruction to learn their first languages but rather seem to just "pick up" language in the same way they learn to roll over, crawl, and walk. Language acquisition in children just seems to happen.
Acquisition (as opposed to learning) depends on children receiving linguistic input during the critical period. The critical period is defined as the window of time, up to about the age of twelve or puberty, in which humans can acquire first languages. Children must receive adequate linguistic input including phonology (speech sounds), semantics (vocabulary and meaning), grammar (syntax or word order and morphology or grammatical markers), and pragmatics (use and context) and prosody (intonation, rhythm, stress) before the end of the critical period in order to acquire their first languages. If linguistic input is not adequate, children will never fully acquire language (as is the case of Genie, an abused and neglected girl who was discovered by authorities in 1970). Language acquisition cannot normally occur after the critical period because the brain becomes "hardwired" to the first language.
Second Language Learning
Language learning, in contrast to language acquisition, is the process whereby humans past the critical period learn second languages. All humans have the ability to learn additional languages although, just as with other areas of study like math or science, some people are better at learning second languages than others. Older children and adults may learn one or more second languages. For example, a woman who acquired French as a child and learned English as an adult would have one first language (French) and one second language (English). Similarly, a man who acquired Japanese as a child and learned English and Spanish as an adult would also have one first language (Japanese) but two second languages (English and Spanish).
As opposed to acquisition, learning occurs actively and consciously through explicit instruction and education. In other words, older children and adults past the critical period need explicit teaching to learn their second languages. Language learning requires explicit instruction in speaking and hearing additional languages. For example, while children who acquire English as their first language just seem unconsciously and without instruction to "know" that most adjectives precede nouns in English, those same children as adults must be taught that most adjectives follow nouns in Spanish. The brains of first language English speakers have become "hardwired" to innately accept only an adjective-noun pattern; in order to successfully learn Spanish as a second language, those English speakers must consciously learn the different pattern of noun-adjective. Or rather, second language learners must "retrain" the brain to accept language systems outside the confines of the first language.
Language immersion is a second language learning method in which language learners immerse themselves in the target (second) language. For example, Spanish language learners might plan a Spanish immersion experience through an extended vacation to a Spanish-speaking country and communicate only with the Spanish language. Parents who want their children to learn French as a second language might enroll their children into a school with a language immersion program that teaches all subjects (math, science, social studies) in the French language. The goal of language immersion is to create a linguistic environment that mimics the environment of first language acquisition. The idea behind language immersion is that, if all incoming (auditory) communication is in the target language, then students will eventually be compelled to use the target language for all outgoing (spoken) communication. The outcome of language immersion is language learning, not language acquisition.
Second Language Acquisition
The theory behind language learning programs (with Rosetta Stone as the most well-known) is that adults past the critical period can acquire language. Although some older children and adults can seemingly acquire languages in addition to their first, most people must learn second languages. Such language learning programs fail to take into account that people learn second languages differently from the acquisition of first languages, by ignoring the differences between language acquisition and language learning. While all children before the critical period can innately acquire their first languages, most adults past the critical period must learn second languages through explicit education and instruction.
In addition to the problems with the claim of second language acquisition, many language learning programs also mistakenly claim to teach second languages through language immersion. For example, Rosetta Stone proclaims that its language learning programs help people learn second languages naturally by providing a "completely immersive environment" that recreates on the computer the childhood experience of "speaking instinctively by experiencing the world." Instant Immersion similarly claims to "immerse learners in authentic dialogue and traditions" through its language learning programs. However, authentic language immersion cannot happen through a computer program. Instead, real language learning through language immersion can only occur when language learners physically and mentally immerse themselves in a linguistic environment with adequate linguistic input from the target language. Computer software cannot replicate actual linguistic interactions.
The Roles of Language Learning Programs
Although second language learners cannot acquire languages through language learning programs, such learners can learn second languages through such programs. For example, the Learn English Now! program available through Transparent Language promises not only to teach vocabulary and pronunciation through simulated English language conversations but also to reference English grammar. The Everywhere German Audio Course similarly provides explicit German language instruction including grammar and vocabulary lessons. Language learning programs are legitimate means for learning second languages so long as the language instruction is explicit especially in the area of grammar education. However, once language learners learn second languages, language immersion programs like Rosetta Stone can help to review and reinforce language learning. For example, first-year Spanish students might use the Rosetta Stone Latin American Spanish Online Language Learning program over the summer to practice the Spanish language before second-year classes begin in the fall.
First language acquisition differs from second language learning in that children acquire first languages innately and passively while adults learn second languages actively through explicit education and instruction. Older children and adults past the critical period can successfully learn second languages through language immersion. However, many language learning programs that promise language acquisition through immersion fail to take into account the differences between first language acquisition and second language learning as well as the necessary linguistic environment for authentic language immersion. Nonetheless, language immersion programs can reinforce the learning that language learners gained through explicit second language education and instruction.