Study probes the unconscious using subliminal perception

May 22, 1997

Study probes the unconscious using subliminal perception; shows unconscious defenses really do exist.

ANN ARBOR—A University of Michigan study provides strong scientific evidence for the existence of one of the key cornerstones of psychoanalysis: unconscious defense mechanisms.

The study, conducted by U-M researchers Michael Snodgrass and Howard Shevrin, relies on an ingenious experiment using subliminal perception.

Part of a growing body of work using scientific methods and modern technology to illuminate one of the murkiest and most controversial aspects of the mind—the unconscious—the study is being presented May 25 in Washington, D.C., at the annual meeting of the American Psychological Society.

For the study, Snodgrass, a researcher at the U-M Medical School, and Shevrin, a U-M psychology professor, tested 100 subjects using a tachistoscope, a device that flashes words or images at different speeds. Shevrin directs the U-M Hunt Laboratory, where the experiments are part of a program of research on unconscious processes.

Subjects were asked to identify which of four words was being flashed at random for one millisecond (1/1000th of a second), a speed below the threshold of conscious perception.

During a previous practice period, each subject tried two different strategies: 1) say the first of the four words that “pops” into mind and 2) look carefully for any clues, such as letter fragments or shadows, before responding. After trying out both strategies, subjects were asked which strategy they preferred. Then they completed experimental trials.

Researchers compared the accuracy of “lookers” vs. “poppers” while they were using their preferred strategy and while they were using the strategy they felt less comfortable with.

By chance, all subjects would be expected to identify the correct word 25 percent of the time. But when lookers were required to pop, they performed significantly worse than chance.

The results not only reaffirm the existence of subliminal perception but also show that unconscious perception can be unconsciously repressed or inhibited.

“The lookers were uncomfortable relinquishing conscious control, as the pop strategy required,” Snodgrass says. “Thus they unconsciously inhibited the correct answers; they were systematically wrong.

“For many years, the existence of unconscious defense has been regarded as unproven,” notes Snodgrass. “The inhibition effect may well provide a simple, easily replicable demonstration of this phenomenon.”

When lookers were allowed to look—the strategy they preferred—they performed better than chance, even though they were unable to detect the presence of words at all.

“In contrast, poppers performed at chance levels using both strategies. This seems to be because poppers are a more varied group,” says Snodgrass.

“Some poppers really like to pop, some are just frustrated because looking ‘doesn’t work,’ and some just say that the look strategy is ‘too much effort.’ All in all, poppers outnumber lookers two to one.”

As further evidence for the interpretation that the inhibition effect reflects an unconscious defense, Snodgrass points to the results of standard personality tests all the subjects took.

When divided into groups based on their level of defensiveness, high-defense subjects, who tend to deny problems, disavow unseemly feelings and impulses, and avoid threatening ideas, also performed significantly below chance when they used the pop strategy. Those who scored low on these defensive personality characteristics scored at chance levels, similar to the poppers.

According to Snodgrass and Shevrin, these personality differences, as well as the popper vs. looker distinction, seem to point to a general defensive orientation against being unconsciously influenced, that is, against having things “pop” into mind. “On the other hand, the look condition allows these subjects to attribute their responses to the external world, as opposed to spooky unconscious influences, ” says Snodgrass. “Further, they don’t have to relinquish conscious control, so it’s less threatening.”

The current study replicates the findings of four similar studies conducted at the U-M and elsewhere in the last few years, involving 245 subjects in total.

“Our findings not only lend experimental support to the fundamental psychoanalytic concept of repression, but also to the possibility of related phenomena such as repressed memory,” Snodgrass adds.

E-mail: [email protected]

Howard ShevrinAmerican Psychological SocietyMedical School[email protected]