Privileged directions for subjective contours: horizontal and vertical versus tilted

Area of Science:

• Visual Perception
• Sensation and Perception
• Psychophysics

Background:

• Subjective contours and brightness enhancement are key phenomena in visual perception.
• The Ehrenstein and Koffka-cross patterns are classic stimuli used to study illusory contours.
• Orientation-dependent effects in visual processing, such as the oblique effect, are well-documented.

Purpose of the Study:

• To investigate the influence of pattern orientation on subjective contours and brightness enhancement in Ehrenstein-like figures.
• To compare perceptual outcomes between upright and tilted Ehrenstein and Koffka-cross patterns.
• To explore the role of basic visual system functioning in orientation-dependent illusory effects.

Main Methods:

• Utilized Ehrenstein and Koffka-cross patterns in upright and 45-degree tilted orientations.
• Employed a magnitude estimation procedure to quantify perceptual responses.
• Conducted two experiments to confirm observed phenomena.

Main Results:

• Upright Ehrenstein patterns produced anomalous illusory patches, while tilted patterns eliminated these, revealing illusory 'streets'.
• In Koffka-cross variants, illusory patches appeared more rounded in the tilted condition compared to the upright.
• These orientation-dependent effects were consistently observed and quantified.

Conclusions:

• Subjective contour formation is facilitated in horizontal and vertical directions compared to oblique directions.
• Orientation-dependent visual perception, including illusory effects, is partly rooted in the fundamental sensory processing of the visual system.
• The findings contribute to understanding the oblique effect and its basis in visual sensation.