Eye movement registration
The self-paced reading paradigm is a good technique for establishing that one kind of sentence requires more processing time than another (presumably very comparable) type of sentence. However, one drawback to this technique is its lack of ecological validity. In contrast to normal reading, participants in a self- paced reading task are permitted to see only one word at a time, and moreover, are not permitted to look back at earlier regions of the sentence. In contrast, in free reading, people frequently move their eyes leftward (or regress) to reexamine earlier parts of the text. Another deficit of the self-paced reading paradigm is that it provides little information about the nature of the processing difficulty that readers encounter. For example, longer reading times for sentences that ended as jokes than straight controls in Coulson and Kutas (1998) suggests the jokes engendered more processing difficulty. However, reading time data do not indicate whether this difficulty occurs in the initial stages of word processing, or later as the reader moves on to inferential aspects of processing.
To address these questions, Coulson, Urbach and Kutas (2006) conducted an eye movement study comparing reading times for sentences that ended as jokes to reading times for the same sentences with the unexpected straight endings (Coulson and Kutas 1998). They found that just as in the reading time study, readers spent reliably longer on the joke endings, and that this difference was far more pronounced for the high constraint sentences. Moreover, this effect arose in the later stages of processing associated with subsequent fixations of the sentence final word (rather than in the initial phase of processing). Further, in both high and low constraint sentences, participants were more likely to regress when they encountered joke endings than straight ones. This finding is consistent with the psychological reality of frame-shifting, suggesting readers literally revisit aspects of the preceding context in order to get the jokes.