A proportion of “sensed” data may be lost without being “perceived”. An example with which most people are familiar is that of failing to perceive something which someone has said to you, when you are concentrating on something else, even though the words would have been received at the ear without any problem. The other side of the coin is the ability of the information processing system to perceive something (such as a picture, sentence, concept, etc.) even though some of the data may be missing. The danger, however, is that people can fill in the gaps with information from their own store of knowledge or experience, and this may lead to the wrong conclusion being drawn.
Once we have formed a mental model of a situation, we often seek information which will confirm this model and, not consciously, reject information which suggests that this model is incorrect.
There are many well-known visual illusions which illustrate the limits of human perception.
The following figure shows how the perceptual system can be misled into believing that one line is longer than the other, even though a ruler will confirm that they are exactly the same.
The image illustrates that we can perceive the same thing quite differently (i.e. the letter “B”? or the number “13”?). This shows the influence of context on our information processing.
In flight operations it is often necessary to refer to checklists or charts, with which the flight crew can become very familiar, especially if they are flying the same route on a regular basis. It is possible that a pilot can scan a checklist or chart and fail to notice that subtle changes have been made. He sees only what he expects to see (expectation). To illustrate how our eyes can deceive us when quickly scanning a sentence, read quickly the sentence below.
At first, most people tend to notice nothing wrong with the sentence. Our perceptual system subconsciously rejects the additional “THE”.
More Visual Illusions
Following is a few sample illusions.
The gray line appears to tilt down to the left, though it is horizontal.
Vertical or horizontal gray lines appear to be distorted.
Circular snakes appear to rotate ‘spontaneously’.