Lexical Word Processing is Unaffected by Rapid Invisible Frequency Tagging in Reading: Evidence from Eye Movements

Attention plays a critical role in reading and lies at the core of the theoretical debate between parallel and serial processing. However, direct measurements of attention have long remained elusive. Recently, Rapid Invisible Frequency Tagging (RIFT) has shown promise in directly measuring covert attention allocated to parafoveal words. RIFT involves flickering the background of the target word(s) at an imperceptible frequency (≥60Hz), but imperceptibility does not necessarily equate to the absence of a cognitive effect. The current study examined the potential impact of the RIFT paradigm on eye movements. High- and low-frequency target words were embedded in one-line sentences and displayed randomly in three condition blocks: no tagging, invisible tagging at 60Hz (i.e., RIFT) and visible tagging at 30Hz. Linear Mixed-Effect modelling and Divergence Point Analysis revealed a robust frequency effect, with high-frequency words processed faster than low-frequency words, but no significant differences across the three conditions in terms of its magnitude or onset latency. Overall fixation durations (irrespective of lexical frequency) did not differ between the no tagging and RIFT conditions, but were significantly longer in the visible tagging condition, suggesting that deliberately drawing attention to the tagging area actually slowed down reading. Furthermore, a post-experiment questionnaire indicated relatively low RIFT awareness. These findings suggest that RIFT is a valid tool for measuring attention during that does not interfere with word processing and highlight its potential for application in ecologically valid settings involving eye movements.