Focusing on an illusion: Accommodating to perceived depth?

Area of Science:

• Visual perception
• Ocular physiology
• Depth perception

Background:

• Ocular accommodation and vergence are depth cues, but their use in perception is debated.
• The hollow-face illusion provides a unique paradigm to study depth perception and accommodation.

Purpose of the Study:

• To investigate the link between ocular accommodation and perceived depth using the hollow-face illusion.
• To determine if accommodation is influenced by perceived depth, even when conflicting visual cues are present.

Main Methods:

• Experiment 1: Measured ocular accommodation and vergence during the hollow-face illusion with upright and inverted masks.
• Experiment 2: Used projected random dot patterns to manipulate perceived depth (convex vs. concave).
• Experiment 3: Assessed the effect of projected dot sharpness on accommodation and perceived depth.

Main Results:

• Accommodation was consistently in front of the physical surface when the hollow-face illusion was perceived.
• Accommodation to the illusory face did not differ from accommodation to the physically convex surface.
• Accommodation was significantly less for the inverted mask (perceived as hollow) and beyond the mid-plane.
• Monocular and binocular viewing yielded similar accommodation effects, suggesting accommodation is not solely driven by vergence.
• Projected dots enhanced accommodation and disambiguated perceived depth, with sharper dots being more effective.

Conclusions:

• Ocular accommodation is closely tied to perceived depth, directly or indirectly, even with competing depth cues.
• Accommodation appears to play a role in disambiguating depth perception, particularly when visual stimuli are sharp.
• Findings suggest accommodation is an active component of the human visual system's depth processing.