Speaker
Description
Top-down signalling across the visual hierarchy is thought to support invariant perception, enabling object recognition despite changes in viewpoint, noise, and ambiguity. A central unresolved question is whether high-level prior knowledge shapes neural representations throughout the visual hierarchy, including early visual cortex, or whether its influence is largely confined to higher-order visual regions. While feedback-related modulation has been demonstrated in primary visual cortex (V1) for simple stimuli, evidence that early representations of complex scenes are reorganised towards high-level priors remains mixed. To address this, we presented ambiguous naturalistic images during functional magnetic resonance imaging (fMRI) and tested how prior-knowledge-driven perceptual reorganisation altered neural representations across the visual hierarchy. We found that perceptual reorganisation was accompanied by representational changes in higher-order visual regions, including posterior fusiform (pFs) and lateral occipital cortex (LOC), such that activity patterns became more similar to those associated with the cued percept. By contrast, early visual areas V1 and V2 remained dominated by the sensory input and did not show significant shifts towards the prior-driven percept. These findings challenge accounts of widespread top-down reorganisation across visual cortex with transformative effects for early visual representations. Crucially, our design controlled for temporal-order confounds that commonly affect perceptual reorganisation paradigms, allowing a stronger attribution of representational change to prior-knowledge-dependent mechanisms. Together, the results reveal a steep hierarchical gradient, from input-dominated encoding in early visual cortex to prior-driven representations in higher-order visual areas.
Lay Abstract
The brain combines incoming sensory inputs with prior knowledge to help recognise objects, especially in unclear or noisy images. However, the extent to which this 'prior knowledge' reshapes neural activity patterns across the visual system, including in the earliest cortical areas that process visual input, is unclear. To test this, we used fMRI with ambiguous two-tone images that are automatically recognised after seeing a clear photo cue. We found that, after cueing, higher-level visual brain regions produced activity patterns more closely aligned to the clear photo version. However, early visual areas (V1 and V2) remained dominated by visual input, and showed no meaningful shift toward the perceived outcome. Importantly, our study design ruled out timing-related confounds that are prevalent in cueing experiments. The results reveal a clear hierarchy: early visual brain areas remain faithful to sensory input, while higher brain areas actively use prior knowledge to 'reconstruct' what we perceive. This challenges previous findings of strong top-down effects reaching the earliest stages of vision, and supports distinct hierarchical functions of the visual system.
| Lay Title | Early visual cortex predominantly represents visual inputs, not percepts |
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| Role | PhD Student |