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Related Experiment Videos

Phase shifts and the square-wave illusion.

R M Wildzunas1, J G May

  • 1Department of Psychology, University of New Orleans, Lakefront, LA 70148.

Spatial Vision
|January 1, 1992
PubMed
Summary

Phase shifts in visual stimuli create a powerful square-wave illusion, influencing perceived depth and illumination. This illusion

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Area of Science:

  • Visual Perception
  • Computational Neuroscience
  • Psychophysics

Background:

  • Vertical triangle-wave luminance profiles can induce a square-wave illusion.
  • This illusion involves perceived depth and directional illumination, potentially linked to phase-selective mechanisms.
  • Previous research suggests instability in these mechanisms contributes to the illusion.

Purpose of the Study:

  • To investigate the effect of systematic phase shifts on the square-wave illusion.
  • To determine if phase shifts bias the perceived depth and illumination direction.
  • To assess if illusory cues aid phase discrimination.

Main Methods:

  • Experiments 1 and 3: Introduced systematic phase shifts (as small as 9 degrees) between the fundamental and odd harmonics of triangle-wave profiles.
  • Experiment 2: Assessed phase discrimination using phase-shifted profiles with experienced versus naive subjects.

Main Results:

  • A significant bias in the square-wave illusion was observed with even small phase shifts.
  • Phase shifts demonstrated a more powerful bias than previously reported drift-induced biases.
  • Experienced subjects showed significantly better phase discrimination than naive subjects.

Conclusions:

  • Phase plays a critical role in the square-wave illusion, influencing perceived depth and illumination.
  • The direction of phase shift strongly correlates with the perceived direction of illumination.
  • The findings raise questions regarding the influence of local contrast changes on the illusion.

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