The human senses are not the only things which can influence our internal image of reality. The mind and how it understands and interprets what it sees has a great influence on how we understand what we perceive. A person's concrete understanding of situations is partly due to their personal experiences and information which they have gained throughout their life. This stored information filters one's perceived reality, and can completely change the meaning and value of what an object or occurrence has to them. Thusly, when people interpret the meaning of phenomena, their distinct values twist their perception, and the importance of the phenomena is not the same for all observers (Marvels 129).
An example could be a man whom in his childhood fell down a well filled with spiders and was stuck there for an hour. Understandably, he could have developed arachnophobia and for the rest of his life retained a fear of spiders (and wells). Upon visiting a zoo or similar institution, he may be scared for his life around the exhibits in the insect house, while someone without such an experience in their past would have been completely unconcerned. The past is not the only thing that can convince the mind to interpret information in such a way. Under the affects of a hallucinogenic drug such as LSD, the mind will begin to see shapes and colors which are produced within the drug-addled interior of the person's brain. These images do not exist in anyone else's perception, and are a prime example of neurological bias in perception.