Spatial extension of parafoveal processing predicts reading speed gain during reading acceleration.

Fast and efficient reading involves not only processing the currently fixated word but also simultaneous processing of the upcoming text. Although the role of extrafoveal processing in natural reading has been extensively documented, its contribution to reading acceleration benefits has remained unexplored. In the present study, we sought to investigate whether reading acceleration might act by influencing the efficiency and spatial extent of parafoveal processing. Participants read at either a natural or an accelerated pace while the availability of parafoveal information was independently manipulated for the first (N+1) and second (N+2) words beyond fixation. Results showed a significant increase in reading speed during accelerated reading, accompanied by more strategic oculomotor behaviors. Importantly, fixation durations analyzed across valid and invalid (random-letters masking) preview conditions revealed an increased sensitivity to orthographic irregularities in parafoveal vision at greater eccentricities from fixation during accelerated reading. Moreover, participants who exhibited greater parafoveal preview effects demonstrated a more pronounced increase in reading speed. These results demonstrate that, during accelerated reading, readers flexibly adjust the spatial allocation of their limited processing resources, strategically widening the window from which extrafoveal information is extracted. Furthermore, they offer new insights into reading efficiency and promising avenues for targeted interventions in poor or impaired readers.