Altered perception

A spider may be a small animal with eight legs, but it can make arachnophobes go crazy. In an experiment, they notice pictures of the animals they fear faster than a control group that does not suffer from the same phobia. And those images also remain in their minds for a longer period of time. That's because their perceptual awareness is altered, according to the findings of a study by psychologists at the University of Mannheim.

"Our study shows that phobia-related stimuli regulate how the brain processes vision," says Georg Alpers, who co-authored the study. "Individual differences between humans influence how they perceive their environment."

Therefore, people suffering from a phobia do not exaggerate their fear, regardless of how irrational their reaction may be.

Two pictures at the same time

In the study, the psychologists showed their sample, which included arachnophobes and non-arachnophobes as a control group, two pictures at the same time, using a mirror stereoscope - one for the left eye and another for the right one.

"It is not possible to permanently see two different pictures simultaneously," Alpers explains. "[The eyes] are competing with each other, and the brain decides in favor of one of them - without us being able to consciously exert influence on that choice."One of the two gray-scale pictures was always a pattern of alternating dark and bright triangles. The other picture, though, showed either a spider or a flower. After eight seconds, the trail ended and the pictures changed.

Spiders trump flowers

The test subjects had to press a button to indicate what they saw: the pattern, the spider (or the flower, respectively) or a combination of the two. Since perception could change during the test, the researchers also measured how long the image remained in the subject's mind.

Arachnophobes recognized the spider almost twice as frequently as the people in the control group. On average, they saw the spider picture for about four seconds per trial - twice as long as the other test subjects.

"With arachnophobes, the spider picture wins sooner and more often the perception contest over the neutral picture," says Antje Gerdes, the second co-author of the study.

An involuntary decision

The test subjects couldn't have said they saw the spider when in reality they perceived a combination of two pictures like the control group tended to, according to the researchers. The psychologists created a control test, which allowed them to measure the truthfulness of their subjects' responses. It showed that if arachnophobes say they saw a spider, they really did.Gerdes and Alpers also rule out the possibility that the arachnophobes in their study could have voluntarily focused on the spiders. "It is not plausible that spider-phobic patients would intentionally expose themselves to their feared objects for longer than necessary," they write in the "Journal of Experimental Psychopathology."

Moreover, in this particular case, people cannot consciously control what they see.

"This study shows was has long been known in psychology," says Dieter Best, deputy chair of the Association of German Psychotherapists (DPtV). "Given the vast quantity of perceivable stimuli, there has to be made a choice."

Emotions and fear in particular seem to play a crucial role in determining the brain's preference for a given image.

An evolutionary curse

There might be "an evolutionary advantage to preferentially process threatening stimuli, but these effects seem to have become dysfunctional in phobic patients," according to Gerdes and Alpers. And people suffering from a phobia may be unable to ignore the cause of their fear.

The researchers of the study suspect that the neural circuits in the brain could be responsible.

The amygdalae, from which fear is triggered in the brain, might be directly linked to the visual cortex, a region of the brain that processes what we see and chooses what we should be aware of.

So that would mean that if your eye catches something you are afraid of, this neural circuit would activate the visual cortex and then make sure that you don't miss it. However, this is something researchers are yet to prove.

Alpers believes the result of the study could improve psychotherapy because it proves that patients do not exaggerate their reactions. As a result, it could enhance a psychotherapist's understanding for his patient. But not everyone agrees.

"Every psychotherapist is already familiar with the underlying principle of selective perception," says psychotherapist Best.