Podcast with Lars Muckli on predictive processing and visual cortex

Does the brain see the world or predict it? Visual neuroscientist Lars Muckli presents evidence that early visual cortex receives top-down predictive signals from higher areas, challenging the textbook view of vision as a purely bottom-up feature extraction process and raising hard questions about where prediction ends and perception begins. Subscribe for more from the Convergent Science Network podcast series. Lars Muckli joins Paul Verschure and Tony Prescott to explain how apparent motion, one of the simplest visual illusions, became a window into the predictive architecture of the visual brain. Using fMRI with retinotopic mapping, Muckli's lab discovered that the space between two alternating dots is filled with neural activity that cannot be explained by local V1 processing alone. EEG experiments revealed that motion-sensitive area V5 responds approximately 40 milliseconds before retinotopic V1 regions, and TMS applied to V5 before stimulus onset eliminates the predictability effect on the apparent motion trace , both pointing to a feedback signal carrying predictive information. The conversation becomes a rigorous methodological interrogation. Verschure challenges whether the data truly require a hierarchical predictive model or could be explained by lateral interactions within V1, where 97 percent of synapses originate locally. Muckli acknowledges that lateral and top-down contributions likely combine, proposing a model where higher areas provide a coarse motion envelope while local V1 circuitry adds spatial precision. Layer-specific fMRI analysis of occluded scene regions shows predictive content distributed across cortical layers rather than confined to specific laminae, suggesting the implementation of prediction in cortical circuits may be more distributed than canonical models assume. Key topics include why the predictive processing framework offers a more parsimonious account of visual processing than feedforward hierarchies, the methodological challenges of distinguishing prediction from postdiction, what layer-specific fMRI reveals about cortical feedback, and whether the predictive coding framework survives contact with detailed neurophysiological data. Part of the Convergent Science Network podcast series from the BCBT Summer School.