Predictability effects in natural reading are logarithmic: Evidence from an eye-movement replication of Brothers and...

The question of whether the relationship between a word's predictability and its processing time is linear or logarithmic is of substantial theoretical importance, as it arbitrates between theories of the predictability effect (preactivation vs. surprisal) and has implications for sentence processing generally. While several previous corpus studies have obtained evidence for a logarithmic relationship, Brothers and Kuperberg (2021b) obtained evidence for a linear relationship in a large self-paced reading study with well-controlled experimental materials. Here, the authors use Brothers and Kuperberg's materials in an eye tracking during reading experiment. The authors find clear evidence for a logarithmic relationship between predictability and the eye-movement measures of first fixation duration and gaze duration; this relationship is clearest when using predictability estimates from the large language model Generative Pre-Trained Transformer-2, which can distinguish small differences in predictability at the low end of the scale. The authors find that this conclusion is robust to log transformation of the reading time measures, and the authors find that the relationship between predictability and the log odds of word skipping may also be logarithmic. These results support surprisal as an account of predictability effects in natural reading. (PsycInfo Database Record (c) 2026 APA, all rights reserved).