Reading at the speed of speech: the rate of eye movements aligns with auditory language processing

Abstract

Across languages, the speech signal is characterized by a ~4-5 Hz rhythm of the amplitude modulation spectrum, reflecting the processing of linguistic information chunks approximately every 200 ms. Interestingly, ~200 ms is also the typical eye-fixation duration during reading. Prompted by this observation, we estimated the frequency at which readers sample text, and demonstrate that they read sentences at a rate of ~5 Hz. We then examined the generality of this finding in a meta analysis. While replicating the experimentally measured 5 Hz sampling rate in the language in which it was obtained, i.e., German, we observe that fixation-based sampling frequencies vary across languages between 3.1 and 5.2 Hz, with the majority of languages lying between 4 and 5 Hz. Remarkably, we identify a systematic rate reduction from easy to difficult writing systems. Reading in easy-to-process writing systems thus is aligned with the rhythm of speech, which may constitute an upper boundary for reading. We argue that reading is likely tuned to supply information to linguistic processes at an optimal rate, coincident with the typical rate of speech. Across languages, speech is produced and perceived at a rate of 4-5Hz. When listening to speech, our brain ‘picks up’ this temporal structure. Here we report that during reading, our eyes sample text at the same rate. We demonstrate this empirically in one language, and generalize this finding in a meta analysis of 124 empirical studies, covering 14 different languages. Reading rates vary between 3.1 and 5.2 Hz - i.e., broadly in the range of the speech signal. We demonstrate that this variance is determined by the orthographical difficulty of different writing systems, and propose that the rate at which our brain processes spoken language acts as a driving force and upper limit for the voluntary control of eye movements during reading.