The latent mechanism behind binocular advantage in reading

Most individuals read binocularly, and previous studies have found a binocular advantage in reading speed. However, the underlying mechanism of the binocular advantage in reading remains unclear. In our study, we quantified contributions from basic visual functions, basic oculomotor functions, and reading-specific eye movements to the binocular advantage in Chinese reading speed, using six tasks and 32 metrics. Consistent with prior research, we confirmed a binocular advantage in Chinese text reading, with binocular reading being approximately 4% faster than monocular reading. Interestingly, although basic visual and oculomotor functions themselves exhibited binocular advantages, they did not account for the observed binocular advantage in reading among individuals with normal vision. This finding is particularly noteworthy because it provides an important normative reference for individuals with impaired vision, in whom basic visual and oculomotor functions may serve as critical explanatory factors for reading performance. In contrast, the concurrent reduction of three reading-specific eye movement metrics-fixation count, average fixation duration, and progressive saccade count-under binocular conditions well explained the binocular advantage in reading, despite these metrics not demonstrating a binocular advantage in isolation. Our results suggest that efficient parafoveal preprocessing and faster neural processing in binocular vision might play critical roles in binocular advantage in reading for individuals with normal vision.