What is a negative hallucination?
A negative hallucination is a common psychological phenomenon which most of us experience several times throughout our lives. Negative hallucinations happen when we find ourselves spending a significant amount of time looking all over the place for something, only to find that it was there in the very first place we looked all along, even though we may have looked there several times.
Rather than seeing something that wasn't really there (hallucination), we didn't see something which was really there and this is why it's called a negative hallucination. Negative hallucinations are actually a very common phenomenon and are the result of selective attention.
What is selective attention?
In order to understand selective attention it's important to understand that, although the human mind is the most powerful tool we know of, it's also true that conscious human perception is generally unreliable. It's also true that no machine or system is 100% reliable and human perception is prone to making many generalizations, distortions and deletions. That is, our mind only filters through information via our five senses which it deems necessary and relevant to our experience.
Much of the mind's subconscious processing is based primarily on visualization, which is why visualization is so often proposed as a useful self-help or self-improvement tool. For example, when driving down a road and considering overtaking the driver in front, the subconscious mind will create an internal mental image of what is likely to happen if we go ahead and carry out that behaviour, based on the information currently available (currently being perceived).
Why do negative hallucinations happen?
As in the above example (overtaking the driver in front) and due to selective attention, our subconscious mind would only consider information which it deems relevant to the experience when creating the internal mental construct of the consequences of overtaking the car in front. Anything not deemed relevant to the experience, even if it may have entered into our peripheral vision, would be ignored and would not be acknowledged by the subconscious and this can sometimes cause us to experience negative hallucinations.
Unfortunately, this flaw in human perception has been known to be the cause of accidents on the roads on multiple occasions and is often the reason that drivers involved in such incidents may go on to make statements such as "I didn't see them" or "they came out of nowhere".
[ Image: BreaW at Pixabay - Public Domain - http://pixabay.com/en/eye-blue-vision-iris-futuristic-491625/ ]