The use of pupillometry in the study of on-line verbal processing: evidence for depths of processing.

The effect of context and task demand upon the perception and resolution of lexical ambiguities was investigated in three experiments using pupillary measurements. Sentence type (ambiguous, disambiguous, and control) was tested under three conditions ("recall," "define word," and "choose best meaning"). All types of ambiguous sentences had higher pupillary curves than unambiguous sentences, with a particularly sharp rise in pupil size following the homophone. In addition, differences were observed in total sentence rise among the three task demands, such that the definition task was higher than recall, while the "choice" task exhibited a continuing rise after the sentence, which both other tasks did not have. Results are discussed in relation to putative processing stages of sentences, such as lexical search and sentence integration, and the more general issue of depths of processing.