Frequency Illusion: Understanding the Baader-Meinhof Phenomenon

frequency illusion

The frequency illusion (also known as the Baader-Meinhof phenomenon) is a type of cognitive bias, demonstrating how the brain’s filtering system can create a skewed perception of frequency. Once the brain is primed to notice specific information or stimuli, it subconsciously keeps track of subsequent instances, giving a person the impression that the occurrence is unusually high – despite the frequency not having changed objectively.

At the heart of the frequency illusion is selective attention, where the brain’s focus is drawn to relevant stimuli while other data is inadvertently ignored. This influences perception in a way that reinforces the sense of increased frequency; after learning about a new concept, word, or item, one might start noticing it with surprising frequency.

Terry Mullen first used the term “Baader-Meinhof phenomenon” in a letter to the St. Paul Pioneer Press in 1994. The letter tells how he continued noting the name of the German terrorist group Baader-Meinhof after reading about it once. This prompted other readers to share their own encounters with the phenomena, resulting in its widespread recognition. The term “frequency illusion” was coined in 2005, when Stanford linguistics professor Arnold Zwicky talked about it on his blog.


Confirmation bias reinforces frequency illusion by leading individuals to notice evidence that supports their beliefs or recent knowledge while disregarding information that contradicts it.

Once an item or concept catches a person’s attention, every subsequent encounter is registered as a match to the initial observation. This not only strengthens their belief in the increased frequency but also embeds the concept more deeply in their memory, further entrenching the illusion.

Confirmation bias occurs in the later stages of selective attention, after the individual has begun to notice the specific stimuli. By concentrating on this single stimulus, the individual becomes more aware of it, reinforcing their suspicions that it occurs more frequently, even when the frequency has not changed.

Confirmation bias arises when an individual afflicted by frequency illusion seeks reassurance of this increased frequency, believing their hypotheses to be verified since they focus solely on supporting facts.

Selective Attention

Selective attention appears to be the primary cause of frequency illusion and other related illusions and biases. The technique of picking and focusing on specific objects while disregarding distractions is referred to as selective attention. This suggests that people have the unconscious cognitive ability to filter out information that is irrelevant to what they are focusing on.

When frequency illusion arises, selective attention is constantly at work. Because selective attention concentrates on the information they are looking for, their perception of frequency illusion will likewise be focused on the same stimuli.

Because the process of frequency illusion is inextricably linked to selective attention via a cause-and-effect relationship, the “frequent” item, phrase, or thought must be selected.

Recency Illusion

Recency illusion is a type of selective attention effect that often occurs in conjunction with frequency illusion. This illusion arises when a person discovers something recently, prompting them to believe that it also occurred recently.

This effect magnifies frequency illusion since it causes the individual to become more conscious of recent stimuli and increases the likelihood of focusing on it in the near future. Recency illusion, like frequency illusion, is caused by selective attention and can be eliminated by fact-checking.

Split Category Effect

While the split-category effect is more pertinent to frequency estimations, it is still a potential contributor to the frequency delusion. This phenomenon occurs when events are subdivided into smaller subcategories, which can result in an increase in the predicted frequency of occurrence.

This is illustrated by the following question: “Can an individual estimate the quantity of dogs in a given country or provide a count of Beagles, Labradors, Poodles, and French Bulldogs?” The sum of the latter would be greater than the former due to this effect.

Individuals may be susceptible to frequency illusion due to the split-category effect; if they subcategorize an object, phrase, or concept, they may be more likely to observe the subcategories, which would lead them to believe that the frequency of occurrence of the main category has increased.

Impact of Frequency Illusion on Perception and Beliefs

The frequency illusion, sometimes referred to as the Baader-Meinhof phenomenon, significantly shapes individuals’ perceptions and beliefs, often leading to a skewed understanding of reality.  It has been observed that frequency illusion can foster delusions by reinforcing false beliefs through the mechanism of confirmation bias.

For example, someone might hear a rare piece of music and then start noticing it everywhere, leading to the mistaken belief that the song has suddenly surged in popularity. This fallacious reasoning may solidify delusions when further occurrences of the music are overvalued while instances where it is not played are ignored, hence erroneously affirming the belief in its ubiquitous nature.

Randomness and Coincidences

Frequency illusion can also distort one’s understanding of randomness and heighten the propensity to find patterns in coincidences. When someone buys a new red car and subsequently starts to notice red cars more often, they might erroneously conclude that red cars are more prevalent than before.

In truth, their perception has changed, not the actual frequency of red cars. This misconception arises from a heightened awareness, not an objective increase in the observed phenomenon.

Journalists may unintentionally perpetuate frequency illusions by focusing on trending stories or keywords. When a specific event or topic gains traction in journalism, it can appear ubiquitous, leading individuals to believe the occurrence is more prevalent than it actually is. This phenomenon is amplified by the echo chamber effect, where certain narratives are repeated across various media platforms, engraining them further into public awareness.

Frequency Illusion in Everyday Life

In everyday life, individuals encounter a substantial amount of sensory input. The brain, functioning as a filter, uses working memory to identify and prioritize information that seems relevant.

When one learns or notices something new, their brain may label it as important, and suddenly, this new item appears frequently. Linguists often experience frequency illusion when noticing linguistic trends – a word they recently learned seems to pop up in various conversations and readings more than it did before.

Frequency Illusion and Learning

The frequency illusion has implications for learning. When an individual learns a new concept or fact, the recurring recognition of this new information can aid memory retention. For example, after learning about a historical event, one might start noticing references to it in different contexts.

However, the illusion can also lead to a misconception that the frequency of the concept has actually increased in its occurrence when, in fact, it is simply being noticed more due to the individual’s filters paying more attention to it.


Frequency illusion could aid doctors, radiologists, and other medical professionals in detecting disorders. Because of their unfamiliarity with the illness, professionals in the medical field sometimes ignore rare diseases or ailments.

According to medical researchers, based on frequency illusion, medical professionals, particularly those in training, could be primed to recognize rarer patterns and lesions, allowing them to spot rare diseases and ailments with more precision.

Criminal Profiling

Criminal profiling often relies on patterns that help detectives identify likely suspects. However, the frequency illusion can introduce a bias in profiling, leading to overemphasis on specific characteristics that may not be as relevant or indicative of guilt as they seem.

For example, if a criminologist or detective recently dealt with several cases involving a certain profile, they might be more prone to suspect individuals fitting that profile in unrelated cases. Recognizing and mitigating the effects of frequency illusion is critical to maintaining objectivity in the investigation process.

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