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See Inside October/November 2008

How Unconscious Mechanisms Affect Thought

Clever experiments root out nooks and crannies in the brain that are hidden from your conscious awareness

Subconsciously Active
Functional brain imaging shows that this angry face still activates a part of your brain that is concerned with fear, the amygdala. That is, at least some sector of your brain knows about the face—as it ought to because an angry male face in front of you might spell big trouble. This brain activity remains unconscious but may influence your behavior or generate a subtle feeling of unease.

Using this technique, psychologist Sheng He, with his student Yi Jiang and their colleagues at the University of Minnesota, made an intriguing discovery. They projected to one eye a photograph of a naked person on one side of the gaze and a scrambled version of the same image on the other side. They then hid both using continuous flash suppression. The paid volunteers who participated in the experiment never saw anything but flashes of color. The psychologists asked the volunteers to guess whether the naked person was in the left or the right part of the image. But they couldn’t. Their guesses were no better than chance.

He and Jiang demonstrated that the observers attended to the naked picture but not to its scrambled counterpart. Even more interesting, straight males attended to pictures of naked women but were slightly repelled by pictures of naked men. Straight women were attracted to pictures of naked men without showing a consistent repulsion for pictures of naked women. Gay men behaved much like straight women; they unconsciously paid attention to the pictures of the naked men but not to those of women. What is disconcerting about this experiment is that this all took place outside the pale of consciousness. Because the observers never actually saw the naked images, they had no idea they were attracted or repelled by them. This experiment is scary because it seems as if people’s sexual orientation could be inferred (statistically) from their unconscious attentional biases. An example of the unconscious mind at work. Freud would have loved it.

What this experiment teaches us is that the mind has many nooks and crannies; some—probably the minority—are consciously accessible, whereas most are hidden from introspection, lost in the vast catacombs of the brain. Yet they can powerfully influence your behavior, making you do things without knowing why. Continuous flash suppression—and other techniques that magicians and psychologists have invented to distract you so you do not see things while looking at them—in combination with functional brain imaging is a delicate tool to map the landscape of the visual unconscious.

Note: This story was originally published with the title, "Rendering the Visible Invisible".

This article was originally published with the title "Consciousness Redux: Rendering the Visible Invisible."

(Further Reading)

  • Continuous Flash Suppression Reduces Negative Afterimages. N. Tsuchiya and C. Koch in Nature Neuroscience, Vol. 8, No. 8, pages 1096–1101; August 2005.
  • A Gender-and Sexual Orientation-Dependent Spatial Attentional Effect of Invisible Images. Y. Jiang, P. Costello, F. Fang, M. Huang and S. He in Proceedings of the National Academy of Sciences USA, Vol. 103, No. 45, pages 17048–17052; November 7, 2006.
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