Thursday, March 14, 2013

Sereno, O'Donnell, and Rayner: "Eye Movements and Lexical Ambiguity Resolution" (2006)

In the literature on word comprehension, some studies have found that people usually take quite a long time looking at an ambiguous word if it occurs in a context that strongly favors one of its less frequent meanings.

This paper raises the issue of whether this is mainly because of clash between the high contextual fit and the low frequency, or mainly because of the frequency.

The Needle-in-a-Haystack Effect

A context preceding a word can either be neutral or biased, and a meaning of an ambiguous word can either be dominant (more frequent) or subordinate (less frequent). When a biased context favors the subordinate meaning, it is called a subordinate-biasing context.

The subordinate-bias effect is the phenomenon that people spend more time looking at an ambiguous word in a subordinate-biasing context than they take looking at an unambiguous word in the same context — given that the two words have the same frequency.

For instance, the word port can mean either "harbor" or "sweet wine," but the former is much more frequent than the latter. In this case, the subordinate-biasing effect is that people take longer to read the sentence
  • I decided to drink a glass of port
than the sentence
  • I decided to drink a glass of beer
This is true even though the words port and beer have almost equal frequencies (in the BNC, there are 3691 vs. 3179 occurrences of port vs. beer, respectively).

Balanced Meaning Frequencies = Balanced Reading Time

The question is whether these absolute word frequencies are the right thing to count, and Sereno, O'Donnell, and Rayner argue that they aren't. Instead, they suggest that it would be more fair to compare the sentence
  • I decided to drink a glass of port
to the sentence
  • I decided to drink a glass of rum
This is because port occurs in the meaning "sweet wine" approximately as often as the word rum occurs in absolute terms — i.e., much more rarely than beer. (A casual inspection of the frequencies of the phrases drink port/rum and a glass of port/rum seem to confirm the close match.)

What the Measurements Say

This means that you get three relevant conditions:
  1. one in which the target word is ambiguous, and in which its intended meaning is not the most frequent one;
  2. one in which the target word has the same absolute frequency as the ambiguous word;
  3. and one in which the target word has the same absolute frequency as the intended meaning of the ambiguous word.
Each of these are then associated with an average reading time:

It's not like the effect is overwhelming, but here's what you see: The easiest thing to read is a high-frequent word with only a single meaning (middle row); the most difficult thing to read is a low-frequent word with only a single meaning (top row).

Between these two things in terms of reading time, you find the ambiguous word whose meaning was consistent with the context, but whose absolute frequency was higher.

Why are Ambiguous Words Easier?

In the conclusion of the paper, Sereno, O'Donnell, and Rayner speculate a bit about the possible causes of this "reverse subordinate-biasing effect," but they don't seem to find an explanation they are happy about (p. 345).

It seems to me that one would have to look closer at the sentences to find the correct answer. For instance, consider the following incomplete sentence:
  • She spent hours organizing the information on the computer into a _________
If you had to bet, how much money would you put on table, paper, and graph, respectively? If you would put more money on table than on graph, that probably also means that you were already anticipating seeing the word table in its "figure" meaning when your eyes reached the blank in the end of the sentence.

If people in general have such informed expectations, then that would explain why they are faster at retrieving the correct meaning of the anticipated word than they are at comprehending an unexpected word. But checking whether this is in fact the case would require a more careful information-theoretic study of the materials used in the experiment.

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