The perception of three-dimensional cast-shadow structure is dependent on visual awareness

Area of Science:

• Visual perception
• Computational neuroscience
• Psychophysics

Background:

• Cast shadows provide crucial cues for inferring 3D scene structure.
• The cast-shadow motion illusion demonstrates depth perception from moving shadows.
• The role of visual awareness in processing shadow-derived depth remains unclear.

Purpose of the Study:

• To investigate if depth perception from cast shadows depends on visual awareness.
• To quantify the relationship between cast shadow motion and perceived depth.
• To determine if suppressed cast shadows still influence visual processing.

Main Methods:

• Utilized the cast-shadow motion illusion as a measure of depth perception.
• Employed continuous flash suppression (CFS) to control visual awareness of cast shadows.
• Measured stereo motion perception to match illusory motion under varying shadow speeds and lighting.

Main Results:

• Shadows with light from above yielded stronger illusory effects.
• Increasing shadow speed increased the perceived depth, indicating quantitative depth extraction.
• Visual suppression of cast shadows via CFS significantly diminished illusory motion perception.

Conclusions:

• Conscious awareness of cast shadows is critical for deriving depth information.
• While awareness is necessary for illusory motion, suppressed shadows still elicit aftereffects, suggesting continued processing.
• Cast shadows are significant contributors to 3D scene perception, mediated by conscious visual processing.