Humans Mentally Edit Language
April 30, 2013

Your Brain Mentally Edits Language To Make Sense Of The World

redOrbit Staff & Wire Reports - Your Universe Online

A new MIT study says people make “mental edits” when interpreting speech and other forms of linguistic input, and seem to use specific strategies for making sense of confusing information. The scientists say these edits are the brain´s way of reducing the “noise” that sometimes interferes with the signals conveyed in language.

“Even at the sentence level of language, there is a potential loss of information over a noisy channel,” said the study´s lead author, Edward Gibson, a professor at MIT´s Department of Brain and Cognitive Sciences (BCS) and Department of Linguistics and Philosophy, during an interview with MIT News.

“As people are perceiving language in everyday life, they´re proofreading, or proof-hearing, what they´re getting,” explained study co-author Leon Bergen. “What we´re getting is quantitative evidence about how exactly people are doing this proofreading. It´s a well-calibrated process.”

The researchers conducted a series of experiments using the Amazon Mechanical Turk survey system, in which subjects were presented with a series of sentences, some sensible and others less so, and then asked to judge what those sentences meant.

One of the more unexpected and significant findings of the study was that given a sentence with only one apparent problem, people were more likely to believe something was incorrect than when presented with a sentence where two edits may be needed. In the latter case, people seem to assume the sentence has an entirely different meaning and is not merely flawed.

“The more deletions and the more insertions you make, the less likely it will be you infer that they meant something else,” Gibson said.

When readers have to make only one ℠editorial´ modification to a sentence, they think the original version was correct about half of the time. However, when they have to make two changes, they tend to think the sentence is correct about 97 percent of the time, the researchers said.

For example, the sentence, “Onto the cat jumped a table,” which might seem to make no sense, can be made plausible with two changes — one deletion and one insertion — so that it reads, “The cat jumped onto a table.” However, in almost every case the subjects did not infer that those changes were needed and assumed that the literal, surreal meaning was the one intended.

This particular finding correlates with another part of the study which found a systematic asymmetry between insertions and deletions on the part of listeners.

“People are much more likely to infer an alternative meaning based on a possible deletion than on a possible insertion,” Gibson said.

Suppose you hear or read a sentence that says, “The businessman benefitted the tax law.” Most people will assume the sentence has a word missing from it — “from” in this case — and fix the sentence so that it now reads, “The businessman benefitted from the tax law.”

But people will less often think sentences containing an extra word, such as “The tax law benefitted from the businessman,” are incorrect, as improbable as that may sound.

Another strategy we appear to use relates to inferring lower levels of ℠noise´ when presented with an increasing proportion of seemingly nonsensical sentences, meaning people adapt when processing language.

For instance, if every sentence in a longer sequence seems silly, people are reluctant to think all the statements must be wrong, and instead search for a meaning in those sentences. By contrast, they perceive greater amounts of noise when only the occasional sentence appears to be wrong because the mistakes are so obvious.

“People seem to be taking into account statistical information about the input that they´re receiving to figure out what kinds of mistakes are most likely in different environments,” Bergen said.

Gibson and colleagues describe the strategies in a paper, entitled “Rational integration of noisy evidence and prior semantic expectations in sentence interpretation,” published in the Proceedings of the National Academy of Sciences.