Of course, one has to wonder what sort of images were used. Do images of 'ugly' people have the same effect as images of 'beautiful' people? What degree of violence is necessary to produce the result? What other 'emotionally-charged' stimuli can produce similar results?

Erotic images can turn you blind

18:09 12 August 2005 -- ...

The new study by US psychologists found that people shown erotic or gory images frequently fail to process images they see immediately afterwards.And the researchers say some personality types appear to be affected more than others by the phenomenon, known as “emotion-induced blindness”.

David Zald, from Vanderbilt University in Nashville, Tennessee, and Marvin Chun and colleagues from Yale University in Connecticut, showed hundreds of images to volunteers and asked them to pick a specific image from the rapid sequence. Most of the images were landscape or architectural scenes, but the psychologists included a few emotionally charged images, portraying violent or sexually provocative scenes.

The closer these emotionally charged images occurred prior to the target image, the more frequently people failed to spot the target image, the researchers found.

“We observed that people failed to detect visual images that appeared one-fifth of a second after emotional images, whereas they can detect those images with little problem after neutral images,” Zald says.

Primitive brain

“We think there is essentially a bottleneck for information processing and if a certain type of stimulus captures attention, it can jam up the bottleneck so subsequent information can’t get through,” Zald explains. “It appears to happen involuntarily. The stimulus captures attention and once allocated to that particular stimulus, no other stimuli can get through” for several tenths of a second.

He believes that a primitive part of the brain, known as the amygdala, may play a part. That region is involved in evaluating sensory input according to its emotional relevance and has an autonomic role, influencing heart rate and sweating.

“It is possible that emotionally-charged stimuli produce preferential rapid routing of the impulse that bypasses the slower cortical route via the amygdala," Zald told New Scientist. "Patients with amygdala lesions pick out the target image without reacting to violent images, although they show normal blindness reactions when sexual images are introduced, which suggests another mechanism may also be involved.”

Harm avoiders

The researchers think emotion-induced blindness could lead to drivers simply not seeing another car or pedestrian if they have just witnessed an emotionally charged scene, such as an accident or sexually explicit billboard. The effect could exacerbate the more obvious problem of drivers simply being distracted by large, arresting images....

And some people are more vulnerable than others. The study assessed participants using a personality questionnaire, rating them according to their level of “harm avoidance”. Those scoring highly were more fearful, careful and cautious; those scoring low were more carefree and more comfortable in difficult or dangerous situations.

The researchers found that those with low harm avoidance scores were better able to stay focused on a target image than those with high harm avoidance scores....

Journal reference: Psychonomic Bulletin and Review (August 2005 issue)