Time course analysis of closed- and open-loop grasping of the Muller-Lyer illusion

The authors investigated whether the early or later stages of closed-loop (CL) and open-loop (OL) grasping rnovernents were differentially influenced by the Muller-Lyer (ML) illusion. Participants (N = 21) reached out and grasped small (5 cm) and large (7 cm) objects embedded within fin -in and fins-out ML configurations. Grasping time (GT) was normalized, and absolute grip aperture (GA) as well as scaled illusion effects were computed at 20%, 40%. 60%. and 80% of GT. The results indicated that CL trials were refractory to the illusory array (i.e., from 20% to 80% of GT), whereas OL trials were influenced by the ML figure during that same time. Those findings suggest that CL trials were supported by unitary and metrical visual information. whereas OL trials were entirely supported by perception -based visual information.