Learning by doing: Effects of visually-guided action learning on highly degraded visual stimuli

The visual ventral and visual dorsal pathways mediate visual perception and visually guided action, respectively. While perceptual learning is well established, it is still debated whether action learning-training motor responses to visual features-can operate under degraded vision when conscious visual perceptual learning is minimized, and it remains unclear what factors govern its success. These questions strongly limited the application of action learning. Here, we trained 24 adults to grasp low-contrast vertical or horizontal bars rendered highly degraded using continuous flash suppression, testing their contrast thresholds and grasping performance before and after training. We found that at the group level, action learning not only enhanced visual sensitivity but also improved grasping performance despite no improvement in the perceptual visibility of the stimuli. Critically, learning success correlated with gains in contrast sensitivity rather than initial stimulus visibility, suggesting that action learning depends on enhanced sensory encoding rather than conscious perception. Additionally, participants who had no initial learning with low contrast stimuli started to show improvements when stimulus contrast was increased, indicating that action learning requires sufficient (but not necessarily visible) sensory input. These findings demonstrate the dorsal stream's capacity for implicit, action-driven plasticity, even with degraded stimuli, and clarify that successful action learning is governed by improvements in sensory encoding rather than perceptual awareness. Overall, our findings suggest that action-based training could serve as a promising rehabilitative approach for degraded vision, provided stimulus strength is carefully optimized, opening new avenues for rehabilitation in vision deficits (e.g., amblyopia, cortical blindness).