Perception of object motion in three-dimensional space induced by cast shadows

Area of Science:

• Neuroscience
• Computational Vision
• Perception Psychology

Background:

• Cast shadows serve as significant depth cues in three-dimensional (3D) vision.
• The influence of cast shadow motion on perceived object trajectory remains an area of active investigation.

Purpose of the Study:

• To investigate the cortical mechanisms underlying 3D vision using cast shadows as depth cues.
• To explore how variations in cast shadow trajectory affect the perception of a moving object's 3D path.

Main Methods:

• Utilized a motion illusion involving a ball and its cast shadow with varying shadow trajectory slopes.
• Employed functional magnetic resonance imaging (fMRI) to measure brain activity during the illusion.
• Analyzed cortical activation in response to perceived changes in the ball's 3D trajectory.

Main Results:

• Perceived ball trajectory shifted from rolling on the bottom to floating in the front plane as the shadow slope changed.
• Bilateral posterior-occipital sulcus (POS) and right ventral precuneus showed significant activation.
• Right POS activation correlated with inferring the ball's trajectory based on ball-shadow spatial relationships.

Conclusions:

• The perception of a ball's 3D trajectory in this illusion is strongly modulated by cast shadow motion.
• The posterior medial parietal cortex, particularly the right posterior-occipital sulcus, plays a role in 3D vision mediated by cast shadows.