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. "It's the responsibility of drivers to ensure that when they are behind the wheel they keep their eyes on the job in hand," says a spokeswoman from Brake, a UK road safety organisation.
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.
?People who are more harm avoidant may not be detecting negative stimuli more than other people, but they have a greater difficulty suppressing that information,? Zald suggests.
The Brake spokeswoman says companies should think about the consequences of placing emotionally charged billboards at dangerous road junctions: ?We should be concerned if drivers are experiencing split-second breaks in concentration, which could result in an accident or death on the roads.?
Journal reference: Psychonomic Bulletin and Review (August 2005 issue)
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