Fan effect is a cognitive psychology concept which pertains to the increase of error rate as more related details are acquired.
“Fan” refers to the concept’s multiple associations or network of ideas which seem to form a fan when illustrated through a diagram. This phenomenon was studied by John R. Anderson, a Canadian-born American Psychologist, in 1974. Particularly, Anderson instructed his research participants to memorize 26 sentences. He later asked the participants to identify if certain sentences are indeed part of the original 26 sentences which they were asked to memorize.
The findings showed that it was harder for the participants to distinguish concepts with multiple associations. For instance, the series of phrases “bat and ball”, “yellow and black”, and “green apple” are easier to remember as compared to “ball and ax”, “ax and call”, and “ball and call”. It usually takes more time to recall the differences in the latter series as there are more similar details; hence, multiple associations. The resulting confusion leads to longer processing time or higher probability of committing errors