Word identification: Imageability, semantics, and the content-functor distinction

It has often been suggested that different special-purpose mechanisms underlie the processing of content words and function words. The received view is that processing differences in various tasks arise because of differences between these word classes in terms of their semantic/syntactic function, despite the fact that these tasks often involve word processing in the absence of any sentence context. It is also well known that the ease with which a word arouses a sensory impression is often a good predictor of word-processing performance, yet the literature largely ignores the fact that, typically, imageability and word class are confounded factors. A series of three experiments shows that in the context of a Stroop task, the typical content-function word difference can be obtained, but that this word class difference disappears completely when the items are matched on the dimension of imageability. It is suggested that the processing of decontextualized content and function words does not necessarily engage distinct special purpose processing mechanisms. Implications for understanding previously published work on word class effects in other paradigms are briefly noted.