Wednesday, December 12, 2007

Final Paper: The Long-term Effects of Early Language Exposure After Language Attrition Has Occurred

The long-term effects of early language exposure after language attrition has occurred

Zenas Lee
Psych 17N Final Paper
Stanford University

1. Introduction
Babies have the seemingly magical ability to acquire language without effort. The widely accepted critical period hypothesis claims that after a certain age, people lose this ability. This theory has been extended to second-language acquisition. Supporters of this extended theory point to evidence of age as a factor affecting achievement of native-like fluency. Children are able to learn a second language “quickly, automatically, effortlessly, and to a level indistinguishable from that of native speakers,” while for adults, second-language learning is perceived to be “slow, effortful, and often less than perfectly successful” (Snow, 1987). Language acquired at a young age can also be forgotten. There are many people who claim to have been fluent in a certain language when they were young but cannot remember a word now. Such language loss or attrition occurs when exposure to that language is cut off or outweighed by another language, such as in the case of international adoption or immigration to a foreign country. Given these two characteristics of language (the critical period and language attrition), this paper aims to explore the long-term benefits of being exposed to a language in the developmental ages. First, a brief overview of language attrition will be followed by research on the effects of early language exposure. Then, the results of the various studies will be discussed. Finally, a conclusion will be drawn from the discussion and the author’s personal insights.

2. Brief Overview of Language Attrition
“Language attrition” refers to loss or attrition of skill in one’s native language (L1) or a second or foreign language (L2). The phenomenon can be observed in both large groups and individuals, but this paper refers to the latter form of language attrition. Individual language attrition can be subdivided into four categories: L1 loss in an L1 environment (e.g. aphasia), L1 loss in an L2 environment (e.g. immigrants), L2 loss in an L1 environment (e.g. L2 learners), and L2 loss in an L2 environment (e.g. older immigrants who revert to L1). This paper does not consider L1-in-L1 loss, as it has more to do with physical reasons than influence of another language. The degree of attrition in the other three categories depends on various factors, such as age, skill level, amount of other language exposure and use, etc. Although a highly interesting topic in itself, this will be the extent of the introduction to language attrition, as it is sufficient to understand how one could “lose” language, thereby allowing us to consider the effects of early language exposure after attrition has occurred.

3. Research on the Effects of Early Language Exposure
To properly discuss the effects of early language exposure, it is necessary to first compare language acquisition between adults and children. One prediction of the critical period hypothesis is that second language acquisition will be relatively fast, successful, and qualitatively similar to first language only if it occurs before the age of puberty, when cerebral lateralization is about complete. Thus, to test the hypothesis, many studies have focused on the age factor.
Studies examining the correlation between age of exposure and language ability have looked at immigrants and their language skills. One particular study compared the perceived foreign accent and grammaticality scores of 240 native Korean speakers who acquired English as a L2 at different ages (Flege et al., 1999). The participants’ age of arrival (AOA) in the United States ranged from 1 to 23 years, and their mean length of residence was 15 years. They were first required to complete a language background questionnaire so that the study could be analyzed using different variables as controls. Subsequently, they took two tests: 1) a test asking them to repeat English sentences that contained a wide variety of English vowels and consonants, and 2) a grammaticality judgment test. Results showed that as the AOA increased, the strength of perceived foreign accent increased and the grammaticality scores decreased, but when variables confounded with AOA were controlled, grammaticality scores turned out to be less relevant to AOA and more dependent on education and use of English/Korean. The findings from this study actually did not support the critical hypothesis theory because if the hypothesis were correct, there should have been a correlation between AOA and L2 performance for individuals who began learning their L2 before the age of puberty (12 years), but not for those who began learning their L2 later in life. However, the AOA–foreign accent correlations and the AOA–morphosyntax correlations were significant for both Koreans with AOAs of 2–12 years and those with AOAs of 13–23 years. These findings did, however, lend credibility to the theory that with increasing age, the ability to acquire or perceive phonemes that are not in our L1 decreases.
Now that we’ve examined the age factor, we can turn to research on the effects of early language exposure. Research on the beneficial and lasting effects, if any, of exposure to language during childhood is too limited to provide any conclusive evidence. However, recent studies have ventured into this area, and one study interestingly examined the effects of overhearing a language during childhood (Au et al., 2002). They tested the idea that having auditory exposure to a language during childhood may help people learn to speak that language with a more native-like accent later on as adults when they start studying it. The study compared adult learners of Spanish who had overheard Spanish regularly during childhood with those who had no regular exposure until around age 14. Both groups were students enrolled in a 2nd-year Spanish class at the University of California, Los Angeles. The overhearers had heard native spoken Spanish for at least several hours each week for at least 3 years between birth and age 6. The exposure decreased significantly after this period, and they had spoken and been spoken to in Spanish minimally (occasional Spanish words or short phrases embedded in English sentences) until they started taking Spanish classes around age 14. The L2 learners had minimal (the occasional word or short phrase in Spanish) or no regular exposure to Spanish until they started taking classes around age 14. Similar to the Flege et al. experiment, participants were asked to read Spanish sentences aloud. These were recorded and later phonetically (voice onset time) and phonologically (phonemic patterns and phonological rule) analyzed to rate the accents of the participants. Additionally, a second test was run with the same group of participants, examining whether morphosyntax could be more readily acquired by overhearers. The participants were asked to verbally complete five simple jigsaw puzzles, which were designed to test number and gender agreement among determiners, adjectives, and nouns in Spanish. Parallel to the Flege et al. study, the results of this study showed that overhearers were able to produce more native-like accents than L2 learners but did not have any measurable advantage in morphosyntax.
The third study that this paper will examine is similar to the previous experiment but differs in that it looks at childhood speakers of languages (Oh et al., 2003). The participants in this study were enrolled in 1st-year college Korean language classes and divided into three groups: 1) childhood speakers who had spoken Korean regularly for a few years during childhood; 2) childhood hearers who had heard Korean regularly during childhood but had spoken Korean minimally, if at all; and 3) novice learners who had no prior Korean experience. The first two groups both had experienced a sharp drop in hearing and speaking Korean around age 5 to 7. A fourth group of native Korean speakers were also tested for comparison. The participants’ first task was to listen to a Korean word and identify the word from several similar sounding choices. The second task was to read a Korean sentence aloud. The first task tested phoneme perception, and the second task tested phoneme production. The results of the study showed that childhood speakers were as good as native speakers at hearing the phonemic contrasts of Korean, outperforming the novice learners. They were also able to produce native-like accents, outperforming both novice learners and childhood hearers. These findings bring to light the benefits of childhood speaking experience and suggest that the benefits of early language experience are long-lasting even with little or no subsequent experience with the language. The nature of early language experience also seemed to be important: childhood hearers outperformed novice learners in the perception but not production of Korean phonemes. This evidence seems to point to early hearing experience helping later perception, and early speaking experience helping later production. However, the study recognizes that this cannot be the simple, general conclusion because the previous study showed that early hearers had a benefit in phonology production in Spanish.
There has also been research presenting evidence contrary to those of the studies above. A study examined the language abilities of monolingual adult speakers of French who had been adopted as monolingual Korean speakers by French families from Korea to France between 3 to 8 years of age and never again exposed to Korean (Pallier et al., 2003). The adoptees took two behavioral tests: 1) listening to Korean, Japanese, Polish, Swedish, and Wolof sentences and assessing whether they were Korean or not; 2) choosing the translational equivalent of a French word after auditory presentation of two Korean words. Also, while they listened to Korean, Japanese, French, and Polish, their brain activities were also analyzed using fMRI. Results of the behavioral tests showed that the adoptees were not able to better distinguish Korean from other languages or identify Korean words in a forced-choice task than native French speakers who had no prior exposure to Korean. Moreover, event-related fMRI activation patterns did not differ while listening to Polish (an unfamiliar language) and Korean, and adoptees' activation patterns for French and Korean did not differ from those of the native French speakers.

4. Discussion of the Research
The findings of the research explored above seem to generally show that at least the phonological aspect of language is retained after exposure to the language in the developmental ages. This seems like a plausible result when we consider the fact that babies are born with the ability to differentiate all phonemes but only acquire the ones of his/her native language and lose the rest. The studies suggest that if a person is sufficiently exposed to a language as a young child, the phonemes of that language are kept even after he/she has experienced language attrition. However, early exposure seems to offer no advantage for the morphosyntactic aspect of language. This suggests that morphosyntax is something you can acquire with effort when studying a language. While this seems logical, real-life experience and personal observation of Koreans studying English lead the author to believe that more effort is required of people without early exposure. One explanation for this is the difference between certain languages. While it is easier for Spanish speakers to learn French because of the similar characteristics in the two languages, it is more difficult for Korean speakers to learn French or Spanish because Korean does not assign gender to its vocabulary other than when identifying a man or woman and has different sentence structure.
The suggestion by the Oh et al. study of a difference in benefits arising from the nature of language experience in childhood seems logical, but as they pointed out themselves, doesn’t exactly agree with the Au et al. study. However, this disparity can be explained by several possible factors affecting the study. First, the Spanish overhearers had had limited but some experience speaking Spanish words, which means they were able to produce the phonemes they had acquired through auditory means. Second, the length of language education was longer for the Spanish overhearers than for the Korean hearers. The Spanish overhearers had studied Spanish since the age of 14, while the Koreans were taking first-year classes in college. If the Korean hearers had studied Korean for a longer time, they might exhibit better phoneme production.
The last study also contradicts the suggestion of an existence of beneficial effects from early language exposure. This can be plausibly explained. The study assumed that because they had known Korean as children, the adoptees would be able to recognize Korean. However, after experiencing language attrition (L1-in-L2), the adoptees could not be reasonably expected to identify what Korean sounded like without knowing what it was. They also would not know Korean words they had not used in over 20 years or ever (they may have never learned the word as a child). The adoptees could still potentially be better at acquiring Korean than native French speakers with no Korean exposure. A one-time experiment may not be sufficient enough to test these potential abilities. In the other studies, the participants were students who were taking Spanish or Korean classes, which could have triggered their abilities and lead to better performance on the tests. Therefore, a new study comparing the perception and production abilities of the adoptees and native French speakers after they have both taken Korean classes should be run.

5. Conclusion
The questions initially posed by this paper were: Does language exposure in the developmental ages help in acquiring that language later on in life? If so, which aspects of the language are retained? After exploration of related research, the author is convinced that early exposure to language leaves an imprint of phonemes that one can retain later on in life even after language attrition has occurred. This seems to correspond with the author’s personal experience of speaking both English and Korean more predominantly at different times in life as well as the author’s observation of friends who had varying degrees of early exposure to English. The author had exposure to both Korean and English at a young age. However, because of the occurrence of language attrition, the author had transition periods when she had to take ESL classes in kindergarten in America after living in Korea from age 3 to 5 and the ESL-counterpart of Korean in sixth grade when she moved back to Korea. She is now perceived by both native English speakers and native Korean speakers as a native of both languages. However, the author recognizes that her case is specific to her and cannot be generalized without further studies. The author would like to see future studies better examining the effects of early language exposure, so that this paper’s questions can be answered more conclusively and also further questions, such as how many different languages can an infant be exposed to and reap the benefits of such exposure from without it negatively affecting his/her linguistic abilities.

Au, T. K., Knightly, L. M., Jun, S. & Oh, J. S. Overhearing a Language During Childhood. Psychological Science, Vol. 13, No.3. pp. 238-243. (May 2002)
Flege, J. E., Yeni-Komshian, G. H. & Liu, S. Age constraints on second-language acquisition. Journal of Memory and Language, 41, pp. 78–104 (1999).
Oh, J. S., Jun, S., Knightly, L. M., & Au, T. K. Holding on to Childhood Language Memory. Cognition, Vol. 86, No. 3, pp B53-B64. (Jan. 2003)
Pallier, C., Dehaene, S., Poline, J.-B., LeBihan, D., Argenti, A.-M., Dupoux, E. & Mehler, J. Brain Imaging of Language Plasticity in Adopted Adults: Can a Second Language Replace the First? Cerebral Cortex. pp. 155–161, 1047–3211 (Feb. 2003)
Snow, C. E. & Hoefnagel-Höhle, M. The Critical Period for Language Acquisition: Evidence from Second Language Learning. Child Development, Vol. 49, No. 4. pp. 1114-1128 (Dec. 1978)

Tuesday, December 4, 2007

#17. Dreaming in Another Language

A 67-year-old man talks in Spanish in his sleep. This doesn't seem weird at all. But take into account that he has forgotten almost all his Spanish, which he learned as a child until the age of 10, when he moved to the Netherlands and started learning Dutch and other languages. He says that Spanish is the only language he was ever fluent in but now all that is left of it is only in his dreams. (link to article below)
In Korea, dreaming in English is people's "dream." They think that if they dream in English, it means that they have achieved a significant level in English. This doesn't seem totally nonsensical, so I wanted to find out how much correlation, if any, there is between dreams and language ability.
Steve Kaufmann, author of The Linguist, founder of, and speaker of nine languages, offers his opinion on the topic: "In my experience it does not mean much. It sometimes happens to me, I think it reflects the fact that we are really committed to the language, listening to it, and wanting to speak it. In our dreams we are not inhibited so we do well." In an online forum (, people seem to share the opinion that dreaming in a foreign language doesn't mean you have the language down solid. Citing their experiences, they seem to agree with Kaufmann that people dream in the foreign language when they're studying it intensely.
Other than other personal accounts, I couldn't find any research that pointed to a correlation between dreaming in a foreign language and ability in that language. Apparently, we're "smarter" when we're asleep, so we can speak the foreign language better in our dreams. However, some people have experiences of dreaming in a language they never learned, which they perfectly understand while they're asleep. A lot of sites that I came across as I researched this topic were about interpreting dreams, premonitions (dreams predicting the future), and sleep disorders like somniloquy (sleep talking). So it seems that a lot of the dream world is unknown, because we do things in our sleep that seem unexplainable like carrying out a conversation with someone.
As for me, I don't think I'm very conscious about which language I dream in, but I do find it odd when my English-speaking friends and my Korean-speaking friends come out together in my dreams and seem to communicate perfectly with each other. I think I've had dreams where I understood French perfectly, but the memory is vague, so I'm not really sure. My roommate tells me I sometimes say random words in Korean while I sleep, but as she doesn't know Korean, I'm not sure if it's just gibberish or actual Korean. Although I didn't find any substantial evidence, the majority opinion seems to be that one's actual ability in a foreign language and dreaming in that language have little correlation. Just because you dreamt in German, that doesn't mean you've achieved fluency or even proficiency in it.


Thursday, November 29, 2007

#16. Faking Body Language

Body language is probably an interesting topic for most people. We all "apeak" it--usually subconsciously. According to an article title "The Body Language of Love," 55% of what we say is understood through visual components (gestures, postures, facial expressions, etc.). The words we say apparently only account for 7%. Many have probably read something similar elsewhere that body language reveals a lot about what we actually think and feel. For example, when we mimic what someone else's body language, it's an indication that we like that person.
Body language is obviously telling, but is there any way we can manipulate people by faking body language? There is a lot of literature on using and interpreting body language, especially for dating or job interviews. Politicians have to look and act charismatic and confident.
So if you know what your body is saying, then isn't it possible to fake it? I think it is possible to consciously send messages with your body, such as making eye contact and leaning forward when you're interested in someone and you want to indicate that what they're saying is interesting to you. However, if you don't feel a certain way but have to act contrary to your feelings, such as when you're hosting relatives whom you don't particularly like, a lot of people fake smile and fake laugh. But when people fake such body language, is it really undetectable or are their true feelings revealed in their other subconscious body language? A few weeks back, I saw a clip of Fox News's "Body Language" segment on The O'Reilly Factor, where a body language analyst analyzing an interview with Hilary Clinton. The analyst said that her laughter was "evil." She could tell that Clinton wasn't genuinely laughing because she was laughing for too long and only her mouth was laughing and not her face (as far as I recall).
These two factors are actually on a site I found that tells you how to detect lies:
Most of the listed indications of lies are things we normally know but do not pay a lot of attention to. So if we pay attention, can we know when someone is being deceitful? If we are analyzed by a professional body language analyst, can we get away with our fake gestures?
I couldn't find a good answer to this question (most search results turned up how to interpret body language or "improve" body language), but I assume that as with all lies and liars, there are good ones and bad ones. Good liars will be able to deceive other people by faking their body language and bad liars won't. However, because a lot of body language is subconscious, it seems to be much harder to disguise your true feelings.


Tuesday, November 27, 2007

#15. Esperanto

Is there a universal language?
Nowadays, knowing English helps a lot in communicating with people from different countries. Even if two people's native languages aren't English, it's likely that they can only communicate in English. I think I feel this especially more at Stanford. There are many kids who speak another language fluently. A lot of the time, this is due to their ethnic background and the language their family uses at home. When I talk with my Thai or Chinese friends, I can only communicate with them in English. We can't use Thai, Chinese, or Korean. So English seems to be taking the place of the universal language, but it's still very far off from actually becoming such a language. I don't know if we can ever reach that goal. However, many years ago, there was an attempt to make such an international language: Esperanto.
When I first heard about Esperanto, I was intrigued. I'd never heard of it or heard anybody speak it, but supposedly, it was the international language. Obviously, it failed, but I thought it was topic worth researching a little bit more into, so it's the topic of my blog entry for today. :)

Esperanto was invented in 1887 by Dr. Ludovic Lazarus Zamenhof, a Polish eye doctor. He published the first book in Esperanto, Unua Libro, under the pseudonym "Doktoro Esperanto," which is where the name of the language comes from. Contrary to my initial conception of it as a language made to unite the world under one universal language, Esperanto is an international second language that helps promote peaceful communication between people of different countries. Nobody has an advantage to Esperanto because it’s not a national language, so everybody is “equal” when they speak Esperanto. It’s a neutral language which theoretically protects minority languages because they have a better chance of surviving in a world that has a universal second language rather than in one dominated by a few “strong” languages. According to most of the sites I found on Esperanto, there are approximately 1,000 native speakers of Esperanto, 10,000 fluent speakers, 100,000 active speakers, 1 million who understand a lot of Esperanto, and about 10 million who have studied it to some extent. These numbers are much higher than I’ve expected because I’ve never met anyone who had even attempted to learn Esperanto. But apparently, Esperanto is “the most widely used international auxiliary language” today and particularly popular in Eastern Europe and China. There is a whole world of literature and music in Esperanto; there are more than 25,000 books in circulation written originally in Esperanto, many others translated from other languages into Esperanto, Esperanto songs, and radio stations that broadcast news bulletins in Esperanto.
The roots used in Esperanto are mostly derived from Latin and some of its vocabulary comes from modern Romance languages, English, German, Polish, and Russian. The alphabet is basically the same with some new additions (Ĉĉ, Ĝĝ, Ĥĥ, Ĵĵ, Ŝŝ, Ŭŭ), and the pronunciation is phonetic. It has few grammatical rules. Words are made by combining prefixes, roots, and suffixes. The word order in a sentence is pretty much free, so for example, Japanese speakers and French speakers can just say the words in the order that their languages use respectively. There aren’t irregular forms when forming plurals, different tenses of verbs, etc. Therefore, Esperanto is supposed to be pretty easy to learn. I don’t know what the standards are for this measurement, but according to my research, for a native English speaker, Esperanto is about 5 times as easy to learn as Spanish or French, 10 times as easy to learn as Russian, 20 times as easy to learn as Arabic or spoken Chinese, and infinitely easier to learn than Japanese. People generally seem to find they learn Esperanto much more quickly than other languages. In fact, some studies say that learning Esperanto before learning a foreign language helps you learn that language faster because it gives you a good base.
There are many places and sources you can use to learn Esperanto, including this site: I don’t know how practical it is to learn Esperanto, but the goal of Esperanto is to facilitate communication between speakers of different languages, so if you learn it, you can find other people who speak it to help you when you visit other countries.

For me, I think Esperanto would be interesting to learn, but I would choose to learn French or Spanish instead because I can easily find a lot more people who speak French and Spanish than Esperanto. However, if anybody wants to, there seem to be a wealth of resources out there, and I encourage you to make use of them and wish you luck!

If you want to hear Esperanto being spoken, here is a link that has a sample sentence:


Tuesday, November 13, 2007

#14. What is Language?

What exactly is language? Which sounds, motions, or symbols qualify as language, and which don't? We've talked about the definition of language in the past few classes, and it made me think more deeply about what language really is.
Originally, I thought language was any means of communication. So I would have said that the high-pitched sounds dolphins make and the meowing noises that my cat makes when she's hungry are all language. But apparently, language is a faculty unique to humans and it has to have certain levels of sophistication to be recognized as "real" language.

So I looked up the definition of language on the online Merriam-Webster Dictionary:

1 a: the words, their pronunciation, and the methods of combining them used and understood by a community b (1): audible, articulate, meaningful sound as produced by the action of the vocal organs (2): a systematic means of communicating ideas or feelings by the use of conventionalized signs, sounds, gestures, or marks having understood meanings (3): the suggestion by objects, actions, or conditions of associated ideas or feelings (4): the means by which animals communicate (5): a formal system of signs and symbols (as FORTRAN or a calculus in logic) including rules for the formation and transformation of admissible expressions

And I wanted to discuss each of the definitions a little.

1a: This definition implies that language has to be verbal and widespread, or at least used in common by a significant number of people. According to this definition, sign language is not a language, and languages that are almost dying out (like those with just one or two speakers left) no longer qualify as language. This doesn't seems right. Vocalization of language is an important part of language. It's the most convenient way to communicate, in my opinion, because the response is immediate. However, deaf people who cannot speak have made up a beautiful, complex language that doesn't require sounds. So this definition doesn't seem to encompass the true meaning of language.

1b(1): Again, this definition also implies that language is verbal. The intent of this definition, I think, was to rule out animal sounds as language. Most people probably would agree that mooing, chirping, barking, etc. aren't "audible, articulate, meaningful" sounds.

1b(2): I like this definition the best so far because it doesn't require a verbal quality for language. If limiting language to human communication, I think it has the right amount of restrictions. Language has to be "systematic," "conventionalized," and "understood." It excludes animal sounds but includes all forms of language--written, verbal, and gestures.

1b(3): This definition refers to a different kind of language, I think. It's still a form of communication but more symbolic. A gift of roses would be a "suggestion" of attraction and language according to this definition.

1b(4): This one is close to my original definition of language. "Communication" and "animals" are the only two requirements.

1b(5): The important word in this definition is "rules." This definition would also exclude animal sounds, but it would include "scientific languages" like the symbols and equations used in chemistry and math. I think these should also qualify as languages. They are actually rather important languages because they are international. Most of the symbols are used uniformly throughout the world, which is amazing, if you think about it.

After my short analysis of the definition of language, I still think that language should mean any sounds, motions, or symbols that communicate meaning--even the simplest feelings like hunger. When my cat meows at us, we know that she wants food. When she purrs, we know that she's content. She expresses something, and we understand it. I think those two things (expression of emotions/thoughts & understanding of the expression) are the only two qualifications language has. Of course there are varying degrees of complexity in language, but as long as something is communicated between two or more living creatures, I'll call it "language."

Thursday, November 8, 2007

extra article for #11

I found a new article on the dominance of English that was interesting and pretty comprehensive:
Whose Language?
It talks about why English is becoming a world language, whether it will stay the dominant language, how many non-native speakers there are, what variations of English there are and how they're being reconciled, etc.

#13. Losing Language

Many people say that they've forgotten a language they knew sometime earlier in their lives. One of my friends who lived for three years in Japan when she was young (preschool & kindergarten age) says she doesn't understand a word of Japanese now. We often forget second languages if we don't constantly practice them (like my French). However, having learned a language at an early age seems to work to one's advantage when learning that language again. It's easier to pick up the language, and one is likely to have a more accurate pronunciation.
Thankfully, I didn't really lose English when I moved to Korea, but my English did get rusty. I still have trouble conjuring up words sometimes because I think of them in Korean. I get nervous about making a mistake, which makes it more difficult to say what I want to say. However, it's the same the other way around. The other day, I was talking to my Korean friend on the phone and I couldn't remember the Korean word for raccoon for some reason. That's why I prefer Konglish, as I've said before. Anyway, getting back on track of the topic, so I was curious... Can we really "lose" a language?
I don't know how reliable this source is, but apparently, there was recently a French study that looked at Korean-born children who were adopted by French parents and thus, were no longer exposed to Korean. The key finding was that these individuals, when tested in their 20s and 30s, could not distinguish between Korean and Japanese. The conclusion was that learning a second language in childhood is in vain if exposure to that language isn't sustained, which seems correct based on our experiences.
There was also a study conducted by psychologist Benjamin Levy and his colleague Dr. Michael Anderson at the University of Oregon that found something called "first language attrition." The subjects of the study were native English speakers who had learned about a year of Spanish. They were told to repeat a word for a certain object in Spanish numerous times. After that, they were told to recall the word for the object in English. The researchers found that people had a more difficult time retrieving the English word after such Spanish exercises. The conclusion is that learning a second language can negatively affect your first language ability. You don't actually forget the word, but it is hard to roll it out on your tongue. So, vice versa, it's usually hard to learn a new language because our first language inhibits us from thinking in the other language. We have to temporarily "forget" our first language in order to learn the second language more quickly.
However, this research didn't really answer my question because it talked about short-term loss of language. I couldn't really find substantial research that would prove that we really can lose our languages, but it seems safe to conclude so.
I don't know if I just couldn't find the right study on the internet, but I feel this is an interesting topic worth researching. Some things I would want to know more about are: how much being exposed to a language at the developmental ages helps in acquiring that language later on in life, which aspect of language benefits most (because on personal intuition, I feel that having once spoken a language at least leaves the memory of the pronunciation, so when you learn it later on, you still have the capacity to produce the distinctive sounds in that language), how many languages a normal child can acquire and keep, etc.