Contextual effects on perceived contrast: figure-ground assignment and orientation contrast

Area of Science:

• Neuroscience
• Visual Perception
• Computational Neuroscience

Background:

• Figure-ground segregation is crucial for object recognition, separating visual elements into foreground (figure) and background (ground).
• Previous studies in monkeys showed altered neural firing rates in early visual areas based on figure-ground assignment.
• It remains unclear if similar neural changes influence low-level feature perception in humans.

Purpose of the Study:

• To investigate if figure-ground assignment affects contrast perception in the human visual system.
• To compare the influence of figure-ground assignment on perceived contrast with the effect of orientation contrast.
• To explore potential interactions between figure-ground assignment and orientation contrast in modulating perceived contrast.

Main Methods:

• Used Gabor probes on figures and backgrounds, similar to stimuli in monkey electrophysiology studies.
• Measured contrast discrimination thresholds and perceived contrast for these probes.
• Compared the magnitude and interaction of figure-ground assignment effects with orientation contrast effects.

Main Results:

• Perceived contrast of Gabor probes increased when placed on a figure compared to the background.
• Figure-ground assignment and orientation contrast similarly modulated perceived contrast.
• Significant interactions were observed between figure-ground assignment and orientation contrast effects.

Conclusions:

• Figure-ground assignment demonstrably influences perceived contrast in humans.
• These findings support the hypothesis that figure-ground segregation impacts neural activity in early human visual areas.
• Perceptual effects of figure-ground segregation are comparable in magnitude to orientation contrast effects and interact with them.