No prediction error cost in reading: Evidence from eye movements

- Two eye-tracking experiments examined predictability effects in sentence reading.
- The availability of a highly predictable word did not inhibit processing of an unpredictable word.
- Processing of unpredictable but semantically related words was facilitated.
- The results support a model of broad pre-activation of potential continuations.

Two eye movement while reading experiments address the issue of how reading of an unpredictable word is influenced by the presence of a more predictable alternative. The experiments replicate the robust effects of predictability on the probability of skipping and on early and late reading time measures. However, in both experiments, an unpredictable but plausible word was read no more slowly when another word was highly predictable (i.e., in a constraining context) than when no word was highly predictable (i.e., in a neutral context). In fact, an unpredictable word that was semantically related to the predictable alternative demonstrated facilitation in the constraining context, in relatively late eye movement measures. These results, which are consistent with Luke and Christianson's (2016) corpus study, provide the first evidence from a controlled experimental design for the absence of a prediction error cost, and for facilitation of an unpredictable but semantically related word, during normal reading. The findings support a model of lexical predictability effects in which there is broad pre-activation of potential continuations, rather than discrete predictions of specific lexical items. Importantly, pre-activation of likely continuations does not result in processing difficulty when some other word is actually encountered.