Occipital Alpha-TMS causally modulates Temporal Order Judgements: Evidence for discrete temporal windows in vision

Abstract

Recent advances in neuroscience have challenged the view of conscious visual perception as a continuous process. Behavioral performance, reaction times and some visual illusions all undergo periodic fluctuations that can be traced back to oscillatory activity in the brain. These findings have given rise to the idea of a discrete sampling mechanism in the visual system. In this study we seek to investigate the causal relationship between occipital alpha oscillations and Temporal Order Judgements using neural entrainment via rhythmic TMS. We find that certain phases of the entrained oscillation facilitate temporal order perception of two visual stimuli, whereas others hinder it. Our findings support the idea that the visual system periodically compresses information into discrete packages within which temporal order information is lost. Significance StatementCorrelational evidence for a relationship between brain states and perception is abundant. However, in order to truly understand the causal relationship between the two, we need to be able to manipulate one and observe changes in the other. Neural entrainment via TMS serves as a valuable tool to interfere with cortical rhythms and observe changes in perception. Here, using rhythmic TMS-pulses at 10 Hz, we investigate the effect of the phase of entrained oscillations on performance in a temporal order judgement (TOJ) task. We observe that the causally entrained oscillation indeed modulates time perception rhythmically. On top of previous work on discrete perception we were able to 1. causally influence brain rhythms in a far more direct fashion using TMS, and 2. show that previous work on discrete perception cannot simply be explained by rhythmic fluctuations in visibility. In conclusion our findings support the long discussed idea that the temporal organization of visual processing is discrete rather than continuous, and is causally modulated by cortical rhythms. To our knowledge, this is the first study providing causal evidence via TMS for an endogenous periodic modulation of time perception.