Perception is Selective

Our powers of perception are selective. As stated by Lippman:
We do not first see, then define. We first define, and then see. - Walter Lippmann (1978)
==On the Perception of Incongruity==
Our perceptions are heavily influenced by our expectations. In 1949, Jerome Bruner and Leo Postman published what is now considered a classic experiment entitled "On the Perception of Incongruity: A Paradigm". Bruner and Postman devised a "trick card" experiment to study how people reacted when a stimulus did not match their expectation. They found that "for as long as possible and by whatever means available" a person will continue to see what they expect to see.
The experiment works as follows. Subjects are asked to identify what they see when exposed to playing cards projected rapidly on a screen, such as these:
Notice anything unusual? What do you see?
The deception in the experiment was this: some of the cards presented to the subjects were normal and some were altered, such as the two cards above: a black four of hearts and a red 6 of spades.
The results of the experiment are remarkable:
1. It took subjects up to four times the amount of exposure time to correctly identify trick cards.
2. Once subjects experience incongruity often enough, they come to expect it and can perceive it when it appears.
3. Prior experience with normal cards does not lead to better recognition performance with incongruous cards.
4. Bruner and Postman were able to identify four general kinds of responses to rapidly presented incongruities: 
===Dominance===
--perceptual denial of incongruous elements (subjects continue to insist that a black three of hearts is a red three of hearts despite repeated exposure and failure);
===compromise===
--a blending of incongruous elements (subjects report a black three of hearts as a purple three of hearts);
===disruption===
--a gross failure of the subject to organize the perceptual field at a level of efficiency usually associated with a given viewing condition (after repeated failures to correctly identify a trick card, even when viewed for a considerable duration, one subject reported, "I can't make the suit out, whatever it is. It didn't even look like a card that time. I don't know what color it is now or whether it's a spade or heart. I'm not even sure now what a spade looks like! My God!).
===recognition===
--the subject correctly recognizes incongruity.
5. The greatest single barrier to the recognition of incongruent stimuli is the tendency for perceptual hypotheses to fixate after receiving a minimum of confirmation. (Once subjects make a decision about a perceptual field, they may fixate on their original choice, regardless of whether or not it is correct.)
==Partisan Bias, the "Hostile Media Effect"==
In one study by Vallone, Ross and Lepper (1985) pro-Palestinian and pro-Israeli students at Stanford University were shown the same news filmstrips pertaining to the then-recen Sabra and Shatila massacre of Palestinian refugees by Christian Lebanese militia fighters in Beirut during the Lebanese Civil War. Both sides found that these identical news clips were slanted in favor of the other side. Pro-Israeli students reported seeing more anti-Israel references and fewer favorable references to Israel in the news report and pro-Palestinian students reported seeing more anti-Palestinian references, and fewer favorable referneces to Palestine.. Both sides said a neutral observer would have a more negative view of their side from viewing the clips, and that the media would have excused the other side where it blamed their side. Subjects differed along partisan lines on simple, objective criteria such as the number of references to a given subject. The research suggests the hostile media effect is not just a difference of opinion but a difference of perception.
==Review==
What is the take-away message here? In short, our expectations: our hopes, our dreams, our desires, may dominate interpretation of stimuli. What we see may well be what we hope to see, rather than what really is.
See also: http://psychclassics.yorku.ca/Bruner/Cards/ , which discuses the original experiment in detail.
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Citations:
Bruner, J. S. & Postman, L. (1949). On the perception of incongruity: A paradigm. Journal of Personality, 18, 206-223.
Vallone, R. P., Ross, L., & Lepper, M. R. (1985). The hostile media phenomenon: Biased Perception and Perceptions of Media Bias in Coverage of the "Beirut Massacre". Journal of Personality and Social Psychology, 49, 577-585
Category:Critical Thinking