Toward understanding the role of visual hierarchy in flicker-induced time dilation: A preregistered study

When a temporal interval is marked by flickering stimuli, its subjective duration is overestimated. The cortical origin of this temporal illusion, termed flicker-induced time dilation (FITD), is not yet well understood. In this pre-registered study, we aimed to explore whether the higher-level regions of ventral visual stream contribute to FITD. By using the semantic wavelet-induced frequency tagging (SWIFT) technique, four experimental conditions were created. Luminance and semantic flickers were created to selectively target the lower- and higher-level regions of the visual hierarchy, respectively. A combined luminance and semantic flicker condition was additionally created to probe the effect of simultaneous entrainment of lower- and higher-level visual regions on FITD. Lastly, to account for the single-pixel modulations and ripple-like motions induced by SWIFT, a control scramble condition was included. The phase-clustering analysis (N = 20) confirmed that the control scramble condition did not result in neural entrainment, whereas the flicker conditions showed entrainment whose magnitude and topography were consistent with their respective experimental manipulations. Nonetheless, the behavioral results indicated that the time dilation effect was not modulated by the flickering conditions neither was its magnitude correlated with the size of entrained oscillations. Moreover, the SWIFT scrambles led to a time dilation effect which was comparable to the flickering conditions. We discussed that while our results are not in agreement with neural entrainment account of FITD, they are not in agreement with the processing principles definition of salience either. Based on the putative shared cortical sources of SWIFT scrambles and luminance-modulated flickers, we conjectured that FITD, and motion-induced time dilation may rely on the same mechanism based on activation of motion sensitive regions. Finally, our results indicated that, at least at the presence of steadily activated lower-level visual and/or motion sensitive areas, periodic activation of ventral stream does not contribute to FITD.