Processing fluency is the ease with which information is processed. Perceptual fluency is the ease of processing stimuli based on manipulations to perceptual quality. The ease with which information can be retrieved from memory is retrieval fluency.
Research in cognitive neuroscience and psychology has shown that processing fluency influences different kinds of judgments. For instance, perceptual fluency can contribute to the experience of familiarity when fluent processing is attributed to the past. Repeating the presentation of a stimulus, also known as priming is one method for enhancing fluency. Jacoby and Dallas in 1981 argued that items from past experience are processed more fluently. This becomes a learned experience throughout our lifetime such that fluent items can be attributed to the past. Therefore, people sometimes take fluency as an indication that a stimulus is familiar even though the sense of familiarity is false. Perceptual fluency literature has been dominated with research that posits that fluency leads to familiarity. Behavioral measures of fluency do not have the temporal resolution to properly investigate the interaction between fluency and familiarity. Event-related potentials (ERPs) are a method of averaging brainwaves that has been successful in dissociating different cognitive mechanisms due to small time scale that brainwaves are measured. One study was able to use a manipulation of visual clarity to change perceptual fluency during a recognition task. This manipulation effected ERPs for fluency and familiarity at different times and locations in the brain leading them to believe that these two mechanisms do not come from the same source.
Later research observed that high perceptual fluency increases the experience of positive affect. 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". The notion that processing fluency is inherently positive led to the processing fluency theory of aesthetic pleasure, and it has been used to explain people's negative reactions towards migrants, who appear to be more difficult to process than nonmigrants.
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. This is called the "illusion-of-truth- effect. In one study, people were more likely to judge easy-to-read statements as true. 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. Processing fluency may be one of the foundations of intuition and the "Aha!" experience.
As high processing fluency indicates that the interaction of a person with the environment goes smoothly, 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.
Basic research on processing fluency has been applied to marketing to business names 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). 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).
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