A well-known pheonomenon in psychology has been the ‘inattentional blindness’ principle. In fact, you might know it from experience: it means that people tend to fail seeing things in their visible fields when they have to focus on a task. If you don’t know what this feels like: try this famous experient.
Untill now, it was thought that in order to cause the effect, a cluttered visual field is required. Recent research shows that the effect is present though in many more situations, and that just the act of task-focusing is already a sufficient condition for severe impairment of visual processing. This was revealed during an experiment in which participants were given a visual memory task to complete while their brain activity was measured using functional MRI. The subjects were instructed to pay attention to a flash of light that would come in during their task. It turned out that they didn’t notice the flash, even though there was nothing else to see for the subjects while they were occupied with their task. Participants did notice the flash when they had no particular task. Professor Lavie adds: “The ‘blindness’ seems to be caused by a breakdown in visual messages getting to the brain at the earliest stage in the pathway of information flow, which means that while the eyes ‘see’ the object, the brain does not.”
In other words: while trying to remind something we have just seen, like a route description, our capacity to see our direct environment severely impoverishes. Stated this way, everybody who has ever tried to remember the directions of their navigation system while driving a car now sees the relevance of this new research. Our brain can simply process only a maximum load of information at a time. So when you’re in a situation that needs sharp visual processing: don’t load it with other tasks. Accurate and fast visual processing is already hard enough.
Source: Science Daily
Konstantinou N, Bahrami B, Rees G, & Lavie N (2012). Visual Short-term Memory Load Reduces Retinotopic Cortex Response to Contrast. Journal of cognitive neuroscience, 24 (11), 2199-210 PMID: 22905823