Ponzo’s Illusion in 3D: Perspective Gradients Dominate Differences in Retinal Size

Area of Science:

• Visual perception
• Psychophysics
• 3D scene perception

Background:

• The Ponzo illusion commonly uses linear perspective cues on a 2D surface to create a false sense of depth.
• Perceived size is influenced by perceived distance, a phenomenon explored through various visual stimuli.

Purpose of the Study:

• To investigate how different surface geometries (2D, 3D congruent, 3D reverse perspective) affect the Ponzo illusion.
• To determine the role of perspective gradients and retinal size in modulating illusion strength.

Main Methods:

• Presenting the same 3D scene painted on flat, 3D congruent, and 3D reverse perspective surfaces.
• Observers estimated the size of test probes within these scenes, relying on perspective cues.
• Manipulating retinal size differences between probes across experiments.

Main Results:

• Perspective gradients consistently drove size perception, with 'far' objects judged larger regardless of physical distance.
• Illusion strength was primarily dictated by perspective cues, not the physical surface geometry.
• Retinal size differences played a minor role, with larger differences (Experiment 3) showing a slight effect.

Conclusions:

• The Ponzo illusion is robust across different surface presentations, highlighting the dominance of pictorial depth cues.
• The interplay between perspective, perceived depth, and size constancy is complex and influenced by stimulus properties.
• While perspective is key, retinal size can subtly modulate the strength of visual illusions.