Wednesday, January 31, 2007

Keep Your Eyes on the Cards

Cognitive psychology is that area of science which is interested in how people think, and it attempts to explain, through the development of models and experimental tests, the inner workings of the mind. Bruner and Postman's (1949) study on the perception of playing cards is one of the most fascinating experiments I have ever heard of, and has stuck with me since hearing about it, many years ago.

Bruner and Postman were interested in the ability to identify an object shown very fast. Using a tachistoscope (an old piece of technology that allows very fast and accurate exposure of images) Bruner and Postman projected pictures of different playing cards at their participants and measured at what speed they could correctly identify them. Beginning very fast (30ms) the presentation speed was slowed at intervals, and the participants responses recorded. The cards that were presented fell into two categories. One group were conventional playing cards (a five of hearts, an ace of hearts etc) and the other were fictional cards (a black three of hearts, a red five of spades etc). What did they find? From Gather.com:

The reader will note that even at the longest exposure used, 1000 ms., only 89.7 per cent of the incongruous cards had been correctly recognized, while 100 per cent of the normal cards had been recognized by 350 milliseconds.
So, people were much better at identifying normal playing cards, and much worse at correctly identifying the fictional cards. Bruner and Postman discovered that their participants would often fixate on one aspect of the card (the colour or suite) and give the correct answer for that aspect. Presented with a black three of hearts, some might consistently identify it as a red card. Others bizarrely reported that the cards were a blend of the two colours, rather than accurately reporting what was actually presented. More from Gather.com
A third reaction may be called disruption. A subject fails to achieve a perceptual organization at the level of coherence normally attained by him at a given exposure level. …”I don’t know what the hell it is now, not even sure whether it’s a playing card,” said one frustrated subject after an exposure well above his normal threshold.
So this experiment is hailed as providing support for the idea that what we perceive as reality is a top-down, bottom-up process. Not only is the information we receive from the senses important (the light from the cards which is relayed into the brain) but that the brain has a framework in place which imposes it's own expectations and beliefs on the information (such that playing cards don't come in a huge variety, so when you are presented with a card it is cheap to come to snap decision about what card it is). A red three of clubs is a rare thing indeed and there are very real evolutionary advantages to making snap decisions like this and sticking to them. Remember the dots, after all.

The difficulty is, like visual illusions, these artificial situations highlight the fact that we did not evolve to identify playing cards. As a species we have achieved more than any other on this planet (and possibly the entire universe). We were not made by a god, and designed to be perfect. Far from it. We are are hodge-podge of evolved predispositions (made by a molecule with the singular purpose to replicate) and we find ourselves lumbered in a modern world. As children we are taught how to think by other humans, who were taught how to think, by other humans before them. Remember Bruner and Postman's work and realise that just like the fictional cards, maybe the reason you're not getting it, is because you're brain isn't letting it in.