Cortical Origins of the Flash-Lag Effect distortions: The Influence of Retinotopic Map Architecture

The flash-lag effect (FLE) is an illusion whereby the position of a moving object is perceived as being offset in the direction of movement relative to a flashed object. This perceptual misalignment has been posited as a key phenomenon in explaining our ability to accurately predict the future position of moving objects, despite the delays in neuronal processing. Our working hypothesis is that the FLE is resulting from the anticipation generated by propagation of neural activity within visual cortical retinotopical maps. According to this hypothesis, the FLE should be affected by discontinuities and anisotropies of the retinotopic map architecture. Using psychophysics in humans (female ratio of 15/24) we show that the FLE is strongly affected by crossing and the direction of motion in respect to retinotopic features, such as vertical and horizontal meridians and the fovea. The specificity of how early visual cortical retinotopic maps are splitted and magnified around these features led us to suggest that the FLE distortions emerge from propagation in retinotopically organized networks, particularly V1. This work bridges the gap between human psychophysics and the known constraints of retinotopic maps layout, offering a testable framework for future studies of motion position encoding in the visual hierarchy.Significance Statement The flash-lag effect (FLE) has long served as a compelling phenomenon in visual neuroscience, offering a window into how the brain enables us to interact accurately in time and space with moving objects, despite inherent processing delays. However, after decades of research, the mechanisms underlying the FLE remain largely debated, with explanations often divided among predictive coding, differential latencies, and postdiction. In our study, we proposed a new hypothesis that attributes a specific role to intracortical travelling waves and tested its behavioral consequences exploiting the known retinotopic architecture of the visual cortex.