Taylor [TAY 53] was the first to instruct participants to fill a cloze with an appropriate word. The percentage of participants who fill in the respective word serves as cloze completion probability. For instance, when exposed to
the sentence fragment “He mailed the letter without a_”, 99% of the
participants complete the cloze by “stamp”, thus CCP equals 0.99 [BLO 80]. Kliegl et al. [KLI 04] logit-transformed CCPs to obtain pred = ln(CCP/(1-CCP)).
Event-related potentials are computed from human EEG data. For the case of the N400, words are often presented word-by-word, and the EEG waves are averaged across a number of participants relative to the event of word presentation. As brain-electric potentials are labeled by their polarity and latency, the term N400 refers to a negative deflection around 400 ms after the presentation of a target word.
After Kutas and Hillyard [KUT 84] discovered the sensitivity of the N400 to cloze completion probabilities, they suggested that it reflects the semantic relationship between a word and the context in which it occurs. However, there are several other factors that determine the amplitude of the N400 [KUT 11]. For instance, Dambacher et al. [DAM 06] found that word frequency freq), the position of a word in a sentence (pos), as well as predictability (pred) affect the N400.
While the eyes remain relatively still during fixations, readers make fitful eye movements called saccades [RAD 12]. When successfully recognizing a word in a stream of forward eye movements, no second saccade to or within the word is required. The time the eyes remain on that word is called singlefixation duration (SFD), which shows a strong correlation with word predictability from sentence context (e.g. [ENG 05]).