This post was written by Kyle Swanson, a Ph.D. candidate in the Department of Second Language Studies at Indiana University.
We humans have a unique capacity to acquire language, even as adults. However, if you have ever used Duolingo, you might have realized that children are more successful at acquiring languages than adults. This observation is puzzling; since adults are smarter than children, shouldn’t it be the other way around?
One set of explanations for this paradox focuses on parsing — that is, applying our knowledge of grammar as sentences unfold incrementally. On the one hand, the Shallow Structure Hypothesis claims that adults who acquire a new language simply cannot apply their new grammatical knowledge to sentences as they reveal themselves word-by-word. On the other hand, the Full Parse Hypothesis claims that these adults automatically apply their grammatical knowledge about their new language as sentences play out one word at a time. The Full Parse Hypothesis further recognizes that adults who acquire new languages face challenges that native speakers do not. For example, these adults need to keep their grammatical knowledge about their native language from interfering as they parse sentences in their new language. Importantly, this task might drain mental energy that native speakers are otherwise free to use in order to apply their grammatical knowledge robustly.
Here at IU, the Department of Second Language Studies and its L2 Brain Lab have played an important role in exploring these ideas. The faculty in this department include Laurent Dekydtspotter and Rex Sprouse, who co-formulated the Full Parse Hypothesis, and Professor Dekydtspotter also heads the L2 Brain Lab.
The L2 Brain Lab conducts two types of studies to put the competing hypotheses above to the test. First, it conducts behavioral studies — for instance, the lab has measured how long participants take to read each word in a sentence. The lab also conducts neurocognitive studies, which use electroencephalography (EEG) to examine “brain waves” as participants read each word in a sentence.
In addition, the L2 Brain Lab conducts studies on different language pairings, which help us understand how the degree of difference between native and non-native languages might affect acquisition. For example, the lab has conducted behavioral and neurocognitive studies about native speakers of English who learned French as a second language, and it has also conducted behavioral studies on native speakers of Mandarin who learned English as a second language. Clearly, English and French are more similar than English and Mandarin. Because we had not yet done a neurocognitive study about native Mandarin speakers who learned English as a second language, I took up the task for my dissertation.
My study included 24 native English speakers and 17 native Mandarin speakers who acquired English as a second language after age 10. Participants came to the Imaging Research Facility in the Department of Psychological and Brain Sciences, and they wore a net of electrodes on their head so that I could record EEG “brain waves” as they read sentences that showed up one word at a time on a computer screen.
Example sentences included: Which picture of himself did William say that Amy posted on the website? and Which video of him did Mike say that Rebecca played for the guests? Sentences like this require participants to figure out who reflexives like himself or pronouns like him identify. Crucially, reflexives and pronouns are subject to different grammatical restrictions. Given these facts, if the Full Parse Hypothesis is correct that non-native speakers do parse, then event-related potentials (ERPs) — that is, differences in “brain waves” — should appear when the distinct grammatical restrictions on reflexives and pronouns come into play. Instead, if the Shallow Structure Hypothesis is correct that non-native speakers cannot parse, then no ERPs should appear.
My findings support the Full Parse Hypothesis and contradict the Shallow Structure Hypothesis; native speakers and non-native speakers read sentences differently depending on the type of grammatical restriction at play. For example, native speakers and non-native speakers both exhibited an ERP for the sentences in the paragraph above at the verb say, where syntactic theory expects the difference between reflexives and pronouns to be important.
Intriguingly, my findings also suggest that the brain’s activity may differ in parsing a native and non-native language. In particular, the ERPs arose at electrodes on different parts of the head and at different times in native speakers and in non-native speakers. While this result may seem to suggest that native and non-native speakers use different regions of their brain for parsing, this is not necessarily the case; a more likely explanation is that native and non-native speakers use the same brain regions, but in different ways.
In broad strokes, my findings echo those from previous behavioral studies from the L2 Brain Lab on non-native speakers of French and non-native speakers of English, as well as previous neurocognitive studies from the Lab on non-native speakers of French. Native speakers and non-native speakers all parse, but their brains may not approach the task identically.
Now, think about enrolling in a course to learn one of the other 80+ languages that the College of Arts and Science teaches. Let’s see what your brain can do! You can also learn more about second language acquisition and get involved in expanding our knowledge of it by taking a course in the Department of Second Language Studies. For undergraduates, the Department offers a minor in Second Language Studies as well as a certificate in Second Language Acquisition/Teaching English to Speakers of Other Languages. For graduate students, the Department offers a M.A., Ph.D. major, and Ph.D. minor in Second Language Studies, as well as a M.A. and a certificate in Teaching English to Speakers of Other Languages/Applied Linguistics.