Processing fluency is the ease with which information is processed in the mind. The ease with which perceptual stimuli are processed is perceptual fluency; the ease with which information can be retrieved from memory is retrieval fluency.[1]
Research in psychology has shown that processing fluency influences different kinds of judgments. For instance, perceptual fluency contributes to the experience of familiarity. A stimulus that has been repeatedly presented before will be processed more fluently. Therefore, people sometimes take fluency as an indication that a stimulus is familiar in cases where fluency does not stem from familiarity.[2] Later research observed that high perceptual fluency increases the experience of positive affect.[3] Research with psychophysiological methods corroborated this positive effect on affective experience: easy-to-perceive stimuli were not only judged more positively but increased activation in the zygomaticus major muscle, the so-called "smiling muscle".[4] The notion that processing fluency is inherently positive led to the processing fluency theory of aesthetic pleasure.[5]
Other studies have shown that when presenting people with a factual statement, manipulations that make the statement easier to mentally process—even totally nonsubstantive changes like writing it in a cleaner font or making it rhyme or simply repeating it—can alter judgment of the truth of the statement, along with evaluation of the intelligence of the statement's author.[6] In one study, people were more likely to judge easy-to-read statements as true.[7] This means that perceived beauty and judged truth have a common underlying experience, namely processing fluency. Indeed, experiments showed that beauty is used as an indication for the correctness of mathematical solutions. This supports the idea that beauty is intuitively seen as truth.[8] Processing fluency may be one of the foundations of intuition.[9]
As high processing fluency indicates that the interaction of a person with the environment goes smoothly,[10], a person does not need to pay particular attention to the environment. By contrast, low processing fluency means that there are problems in the interaction with the environment which requires more attention and an analytical processing style to solve the problem. Indeed, people process information more shallowly when processing fluency is high and employ an analytical thinking style when processing fluency is low.[11][12]
Basic research on processing fluency has been applied to marketing[13] and to finance. For example, psychologists have determined that stocks perform better during the week following their IPO when their names are fluent/easy to pronounce and when their ticker symbols are pronounceable (e.g., KAG) vs. unpronounceable (e.g., KGH).[14] Another recent experiment demonstrated that the long-known effect of illegible handwriting in an essay on grading is mediated by a lack of processing fluency (and not, for example, negative stereotypes related to illegible writing).[15]