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The famous gorilla experiment conducted by Harvard University when a woman dressed in a gorilla suit ambled across the floor thumping her chest, but 50 % of the audience didn’t notice. The study shows we often err when it comes to concentration and perception. Humans have a limited capacity for attention which in turn means that we have a limited capacity to process information at any given point of time.
When we open our eyes, the whole image gets projected on the retina, but only selective parts of the image are sensed by the brain. This is because as the amount of information in the image was too great to be processed, the brain selectively puts its attention on the most important aspects. Scientists have found that highly prominent events may go unnoticed. 
Researchers now recognize a phenomenon known as “change blindness”, which means that people often fail to detect changes in their field of vision, so long that the change takes place during an eye movement or when the view is somehow interrupted. It has been discovered that our brain tries to construct a meaningful whole out of stimuli that fits in with the scenario of its interest and is capable of discarding majority of other information. This fact can be easily explained by observing a child play the game “spot the difference”. On the first look the child finds the pictures to be similar. Only after careful attention, does he find the differences. The present decade has seen a lot of research into this field. The questions that the scientists are trying to answer are: What is the amount of visual input a brain can consciously and unconsciously encode?
Why do some objects come in the field of observation and not others? What happens to information that is subconsciously perceived?
Arien Mack and Irvin Rock also conducted many experiments and co-authored a book “Inattentional Blindness” in 1998. One of their experiments was very simple. They asked the subjects to observe a cross on the computer screen. The subjects were repetitively asked to judge which arm of the cross was longer. They were in a way made to concentrate on the cross. After some time, unrepentantly, another brightly coloured object was inserted in their field of vision. The researchers reported that the participants often failed to notice the unexpected object on the screen, even when it appeared in the middle of their line of vision. The study gave a conclusive proof that there exists a wide gulf between perception and attention. Some psychologists are of the view that intentional blindness may be in some way related to selective memory instead of selective perception. The cause of the ‘intentional amnesia’ may be organic, functional or circumstantial.
Harvard university researchers have concluded that “we consciously see far less of our world than we think we do. We might well encode much of our visual world without awareness.” We believe that we generally see what is in front of us and by basically looking. But looking and seeing are two different events. It has been observed that we look without seeing during moments of intense concentration. We have all observed that our eyes may be open, the images form on the retina, but still we have limited perception. We all remember these moments of blurred visuals and they come usually when either we are in deep thoughts or involved in an interesting conversation.