Task complexity and onset of visual information influence action planning in a natural foraging task

Picking fruits or playing with LEGO® bricks are everyday examples for tasks that not only involve visual search for multiple objects, but also action planning to grasp the visually selected objects and place them somewhere. How a selection movement is planned should also depend on the complexity of a task. We first asked if differences in task complexity would elicit differences in movement onset, and second, if the availability of visual information during task instructions influences action planning. Participants engaged in a non-exhaustive natural foraging task, where they had to pick and place LEGO® bricks of a particular color in predefined areas. Placing instructions (collect, sort, pile) differed between trials to implement different precision requirements. More complex tasks should require more time for planning the grasping movement and accurate placing, which should be reflected in differences in movement onset. Further, participants wore shutter glasses to manipulate when visual information became available. On one day, participants listened to the task instructions while the shutter glasses were open. On the other day, the shutter glasses were closed while participants listened to the task instructions. Results revealed a later movement onset in the piling condition, irrespective of vision availability during instructions. Moreover, the trajectory of the first reach in the late vision condition showed a larger curvature, indicating that vision during task instructions aids action preparation for target selection. Our findings show that more complex tasks can delay action initiation even if vision is available during instruction in a natural foraging task. However, the availability of vision still influences the curvature of the planned movement, potentially reflecting uncertainty in target choice when vision was not available during task instruction.