Size-contrast illusion induced by unconscious context

Area of Science:

• Visual Perception
• Neuroscience
• Psychology

Background:

• The Ebbinghaus illusion demonstrates how surrounding context influences perceived size.
• Previous research primarily focused on conscious perception of contextual stimuli.

Purpose of the Study:

• To investigate if the Ebbinghaus illusion can be induced by context suppressed from conscious awareness.
• To explore the characteristics and neural underpinnings of unconscious Ebbinghaus illusion induction.

Main Methods:

• Utilizing continuous flash suppression (CFS) to render contextual stimuli invisible.
• Employing a binocular presentation paradigm with interocular suppression.
• Measuring the illusory size effect under conditions of visible and invisible inducers.

Main Results:

• The Ebbinghaus illusion was observed even when context stimuli were invisible via CFS.
• The unconscious illusory size effect was approximately one-third the strength of the visible effect.
• Decay rates of the illusory effect with increasing interstimulus interval were similar for visible and invisible contexts.
• Interocular transfer of the illusory size effect did not occur with suppressed inducers.

Conclusions:

• The size-contrast mechanism of the Ebbinghaus illusion can operate unconsciously.
• The findings suggest involvement of the primary visual cortex (V1) in unconscious size-contrast effects.
• The monocular pathway within V1 appears crucial for mediating this unconscious visual phenomenon.