Repetition Hampers Flexible Object Manipulation Under Visual Uncertainty.

Seemingly simple actions, like reaching for and lifting an object, involve the coordination of distinct neural pathways within the dorsal and ventral streams. These components can be differentially affected by repetition-induced anterograde interference, where extensive practice on one task impairs performance on subsequent tasks. Repetition leads to rigid movement patterns, making it harder to adapt flexibly to new situations, especially in tasks with sensory uncertainty that require the brain to rely more on past experiences (i.e., sensorimotor memories). To explore this, we tested whether object-use tasks, which depend on the ventral stream, are more affected by this interference than a simpler reach-to-button task with helpful visual cues. Participants completed two tasks: a reach-to-button task involving pressing buttons on either side of a symmetrical object and an object-use task where the same object had a hidden, asymmetric center of mass (CoM). To measure interference, we manipulated how many times participants lifted the object with the weight on one side before switching it to the other side. Our results showed that interference was strongest in the object-use task, where uncertain visual information forced participants to rely on sensorimotor memories. In contrast, the reach-to-button task, supported by helpful visual cues, showed no significant interference. This suggests that tasks relying on the ventral stream are more vulnerable to interference, particularly when sensory feedback is unclear. Our findings highlight how repetition affects different movement types and emphasize the need for a balance between repetition and flexibility in motor learning.