The open-object illusion: size perception is greatly influenced by object boundaries.

Area of Science:

• Visual Perception
• Cognitive Psychology
• Experimental Psychology

Background:

• The perception of object size is fundamental to visual processing.
• Understanding how contour closure influences perceived size is crucial for visual science.

Purpose of the Study:

• To introduce and investigate a novel visual illusion where open objects are perceived as larger than identical closed objects.
• To determine the impact of missing boundaries on perceived object dimensions.

Main Methods:

• A continuous-response adjustment procedure was used to quantify perceived size.
• Experiments involved varying stimulus types and parameters to test the robustness of the illusion.
• Observers consistently judged open objects as larger than closed objects.

Main Results:

• Lack of vertical boundaries inflated perceived width; lack of horizontal boundaries inflated perceived length.
• Inclusion of inner boundaries led to underestimation of object size.
• The open-object illusion was robust across various stimuli and parameters, affecting nearly all observers.

Conclusions:

• Perceived object area is not veridical and critically depends on contour closure.
• The visual system appears to extend missing boundaries of open contours, leading to size overestimation.
• This illusion has implications for graphics, design, and understanding visual perception mechanisms.