Anyone who has moved abroad or across the country can tell you that the process is laborious. Not only are there all the moving boxes to manage, but there are also so many new things to remember: a new address, new street names, sometimes even a new phone number or bank information. When you’ve first moved to a new spot, there’s often an intermediary time period where you need to enter your previous address or contact information into various forms, while simultaneously trying to memorize all the new things being thrown at you. You may find yourself staring at a blank form, struggling to remember your old address, even though you once knew it so well.

Why is this so hard? Well, not only are you likely incredibly overwhelmed, but the psychological concept of retroactive interference may also be at play. This cognitive phenomenon happens when we learn new information that’s similar to previous knowledge, creating a barrier to retrieving the older information. In this case, your old phone number and your new phone number are both just a string of numbers; once you’re focused on memorizing the new number, the digits of your old line may find themselves getting mixed up in your head, as now all you can recall is your current one. 

This cognitive phenomenon has been studied for decades, usually in the context of vocabulary memorization. However, the implications of retroactive interference are relevant for everything from our cognitive wellbeing as we age, to how we structure our education and judicial systems.¹

Proactive Interference: The opposite of retroactive interference, where old memories interfere with the acquisition of new information.¹

Memory Consolidation: The process by which short-term memories are transferred to long-term storage. Retroactive interference disrupts this process, weakening previously learned information.¹

Encoding: The initial learning of new information, which involves transforming perceptual input into a format that can be stored in memory for later retrieval. If encoding is weak, retroactive interference is more likely to occur.¹

Retrieval Failure: When stored information cannot be accessed, sometimes due to interference from new learning.¹

Working Memory: The system in the brain that helps you temporarily retain and manipulate a limited amount of information. Overload in working memory can increase susceptibility to interference.¹

Long-Term Memory: The system that stores learned information for extended periods of time. Retroactive interference disrupts the stability and retrieval of long-term memories.¹

Spacing Effect: The idea that when information is learned through repetition, it is more effectively remembered when spaced over longer, rather than shorter, periods of time. When individuals space out their repetition of information, they can better recall that information in the future.

Cognitive Load Theory: A theory of memory in psychology and instructional design focused on how instructions are processed and learned, considering how information processing capabilities are limited by working memory capacity. A high cognitive load increases the likelihood of interference.

Misinformation Effect: When incorrect or misleading information gathered after an event alters a person’s memory of that event, often due to retroactive interference.

The study of retroactive interference dates back to early experimental psychology research in the late 19th and early 20th centuries. German psychologist Hermann Ebbinghaus was among the first to systematically study memory and forgetting. In 1885, he found that participants’ memories of lists of nonsense syllables could intrude on one another, intervening on either the memory encoding or memory recollection process. His experiments led to the concept of the forgetting curve, which demonstrated how interference contributes to memory loss over time. Later studies on interference confirmed the negative impact of interference on memory.²

In 1900, psychologist John Bergström conducted some of the earliest studies on interference, showing that learning a second list of words impaired recall of a first list. Although this finding underlies the concept of retroactive interference, the term wasn’t formally introduced until researcher Georg Müller and his student Alfons Pilzecker conducted experiments on how new learning disrupts memory consolidation. Their work suggested that fixing learning in memory requires active practice after exposure, meaning that one must be consciously focused on remembering. They defined retroactive interference as "rückwirkende Hemmung,” literally “retroactive inhibition,” which is the cost of subsequent learning on prior learning. Their experiments also used nonsense syllables to investigate consolidation, showing that intervening activity made information vulnerable.^2,3

By the mid-20th century, Donald Hebb proposed the idea that memories are strengthened through repeated neural activation, which became the foundation for understanding why interference weakens memory traces.² Later, cognitive psychologists like Robert and Elizabeth Bjork further refined the study of interference by demonstrating how retrieval-induced forgetting occurs due to competition between old and new information.

More recent research in neuroscience has furthered our understanding of the biological basis of retroactive interference, with studies showing that activity in the brain’s hippocampus is critical in determining whether new information strengthens or disrupts previous memories. Today, interference theory continues to influence the field of psychology, how we structure education, and the artificial intelligence models designed to replicate human memory processes.²

Hermann Ebbinghaus

A German psychologist of the late 1800s and the first person to formally and systematically study memory and forgetting, introducing the concept of the forgetting curve through experiments asking participants to recall nonsense syllables.²  

G. E. Müller

A German experimental psychologist who inspired much of the later work on interference. Prior to his research, forgetting was understood only as being due to the brain’s limited volume and duration of information processing, but Müller observed and conceptualized both proactive and retroactive interference. In 1894, he observed that the learning of a second list of items interfered with recall of the first list.³

John Bergström

One of the first experimental psychologists at Indiana University, Bergström worked in the newly expanded psychology lab in the 1890s and is often credited with conducting the first study on interference.⁴  

Donald Hebb

A Canadian psychologist and neurologist who was particularly interested in understanding how learning occurs and the role of neurons in the process. Hebb was the first to study how memories are strengthened through repeated neural activation; each time a memory is retrieved, the pathway gets stronger, and it becomes easier to remember on future occasions, a concept known as Hebbian learning.

Elizabeth Loftus and John Palmer

Loftus is an American psychologist best known for her research on the misinformation effect, while Palmer’s work has focused on visual attention. Their 1974 study, "Reconstruction of Automobile Destruction," demonstrated that memory can be easily influenced by misleading information.⁵

Robert Bjork and Elizabeth Bjork

The famous memory research husband and wife duo, known for their work on behavioral memory and learning, as well as their longstanding tenure as professors at UCLA. Their 1992 study on students’ memorization of vocabulary lists was a direct investigation into the effects of retroactive interference.⁶ 

Leo Postman

An American cognitive psychologist who studied the role of similarity in proactive interference, showing that distinct material reduced interference. His 1960 study, conducted with researcher Benton Underwood, used lists of paired words to test how the similarity of information impacts recall, the results of which have been used as evidence for the significance of retroactive interference.¹⁴

Retroactive interference affects memory across all stages of life, with significant consequences for aging, education, and workplace performance. As memories compete, older information can be overwritten, leading to challenges in recalling important details, adapting to new knowledge, and maintaining cognitive function. 

Cognitive Decline and Aging 

If you’ve watched your parents or grandparents grow older, you may have seen firsthand that as we age, our memory often declines. In fact, our brain becomes more susceptible to retroactive interference, which can be a significant factor in cognitive decline. This isn’t just because older adults have more memories stored that can potentially get in the way of new information. As we age, the hippocampus, the brain region crucial for memory consolidation, becomes less efficient at distinguishing between similar pieces of information.⁷ When new information is (or appears to be) less distinct, interference occurs more often, and people remember less. 

Imagine your boss or a loved one dictating a huge to-do list. They may start speaking so quickly that you don’t have time to write things down, so you just try to remember as much as you can. When we’re presented with more information than we can remember, younger adults are better at combating interference and recalling the valuable information. This means they may be better at remembering some of those high-priority to-do items, while an older person may struggle more to remember the same amount. Older adults might engage in selective forgetting of prior lists, possibly because their memory is more “present-focused.” Some researchers suspect that this is a result of impaired inhibitory control among older adults.⁷ 

Maybe you’ve also seen the older adults in your life (or seen yourself) struggle to remember past appointments when scheduling new ones, as recent dates interfere with previously stored ones. Perhaps the medication dosages or prescriptions get mixed up, as the appropriate milligrams or drug names often sound similar. Retroactive interference comes into play in many of these everyday situations, but it’s an even bigger concern for individuals with neurodegenerative diseases, like Alzheimer’s. Although everyone’s memory deteriorates during the natural aging process, those with Alzheimer’s and other types of dementia have an even more difficult time retrieving past experiences. Understanding how aging contributes to retroactive interference has helped lead to interventions, with researchers developing more treatments like brain-training exercises and lifestyle modifications that help reinforce older memories.⁷

Educational Challenges and Learning Difficulties

Although proficient memory is important in every situation and stage of life, few tests of our memorization skills are more salient than the experience of school. Retroactive interference plays a critical role in how students retain and retrieve information, and when there is too much interference, this often leads to academic struggles.⁸ Think of a student frantically cramming for a history exam, attempting to remember the names and dates of different events during World War II. Perhaps the last exam covered World War I. The facts they’re looking at now may sound similar to the years or names of the notes they’d previously memorized, and so the new dates might get mixed up with the old ones. Thus, as students acquire new knowledge that closely resembles previous material, the new information can overwrite or distort their earlier understanding.

This also often happens with language. For example, a student studying Spanish may struggle to recall previously learned French vocabulary because the similarities between the two languages cause interference. This issue is especially problematic in fast-paced learning environments where students must absorb multiple subjects or concepts in quick succession.^8,9 To counteract retroactive interference, educational institutions can use strategies like spaced repetition, which involves revisiting information at different intervals, and active recall, which asks students to actively retrieve the information, strengthening the recall process. These techniques have been shown to reinforce memory retention and minimize interference.^8,9

Workplace Performance and Job Training

Even beyond the days of school and exams, those in the workforce often need to update their knowledge and skills frequently, particularly in rapidly evolving fields like technology and healthcare.¹⁰ It’s important that when workers learn new procedures, they don’t forget or confuse them with previously established protocols. It’s easy to understand the importance of this when we think of how often nurses receive training; if the new information they learn about, say, appropriate blood draw protocol interferes with their ability to remember IV protocol, it’s clear that this could lead to not only frustrating inefficiencies, but also dangerous errors. 

The same nurse, as an example, may be trained on a new electronic medical records (EMR) system, and might struggle to recall how to use the previous system, even if it’s still in occasional use. To counteract retroactive interference in the workplace, organizations should emphasize continuous professional development, hands-on training, and knowledge reinforcement techniques to ensure smooth transitions and to support employees.¹⁰

Eyewitness testimony, historical accounts, and even personal memories are all vulnerable to retroactive interference, which can reshape or distort what we remember. Research shows that post-event information can alter witness recollections, while historical revisionism can overwrite societal narratives, sometimes for political or ideological reasons. As neuroscience and AI explore memory modification, the ethical implications of intentionally altering memories, whether for therapeutic purposes or potential misuse, become increasingly urgent.

Eyewitness Testimony and Legal Implications

One of the most concerning consequences of retroactive interference is its role in eyewitness memory distortion, which can lead to wrongful convictions and judicial errors. We often hear of juries in major cases being sequestered, or not allowed to interact with the outside world while the case is going on. This is because studies have shown that post-event information, which can include things like media reports or even general gossip, can not only cause juries to be biased, but even change how they remember the facts they’ve been presented with.⁵ 

The same is true for defendants, prosecutors, and witnesses: studies have shown that law enforcement questioning and conversations with others can interfere with a witness’s original memory, causing them to recall details inaccurately.^5,11 This phenomenon, known as the misinformation effect, has sparked debate over the reliability of eyewitness testimony in court. Critics argue that memory is too malleable and prone to interference to serve as definitive proof, especially in high-stakes situations like criminal cases. 

One of the hallmark studies of memory research is Elizabeth Loftus and John Palmer’s 1974 "Reconstruction of Automobile Destruction” experiment, demonstrating the effects of retroactive interference on memory.⁵ In their experiment, participants watched video clips of car accidents and were then asked questions about what they had seen. The trick was, the wording of the questions varied: some participants were asked how fast the cars were going when they “smashed” into each other, while others were asked the same question but using the words “hit,” “contacted,” “bumped,” or “collided.”

The results revealed that participants’ speed estimates were influenced by the verb used; those who heard the word "smashed" reported significantly higher speeds than those who heard "hit" or "contacted." Even more striking, in a follow-up study, participants who had been asked about cars "smashing" into each other were more likely to falsely recall seeing broken glass at the accident scene, despite none being present in the video.⁵

This experiment highlights two possible explanations for how retroactive interference alters memory. One is the response-bias explanation, which suggests that misleading information influences how individuals answer questions, without actually changing their memory of the event. The other is the memory-alteration or retroactive interference explanation, which proposes that the wording of a question can reshape how an individual remembers an event, effectively rewriting their original memory. Loftus and Palmer’s findings support the latter view, demonstrating that memory is reconstructive rather than a perfect recording of past experiences.⁵

When these insights are applied to the legal world, there are major implications: suggestive questioning can distort eyewitness testimony, potentially leading to false accusations and even wrongful convictions. As a result of this research, the legal system has taken steps to minimize retroactive interference in witness statements. This means that courts and law enforcement agencies now try to emphasize best practices for interviewing witnesses, like avoiding leading questions and informing individuals about the potential for memory distortion. Some jurisdictions have even reduced their reliance on eyewitness testimony or require expert testimony on memory science to ensure fair trials.¹¹ While eyewitness accounts remain a crucial component of the justice system, studies like Loftus and Palmer’s serve as a reminder that human memory is not infallible and must be evaluated with caution.

Historical Revisionism and the Manipulation of Collective Memory

Retroactive interference plays a significant role in how societies remember and reinterpret history, leading to controversies over historical revisionism. Governments, media, and educational institutions may introduce new narratives that overwrite or distort older historical accounts, shaping public perception.¹²

For example, authoritarian regimes have been known to alter historical records to promote nationalistic ideologies, often erasing inconvenient truths or details that may make them look bad. In democratic societies, cultural shifts or new discoveries can also lead to historical reinterpretations, sometimes sparking debates over what should be taught in schools.¹² 

In the United States, heated local and national debates have addressed the question of how we should teach children about the country’s dark past, including things like slavery and the Civil War. While some politicians and parents believe that we should teach future generations about the brutality and violence of these times so that we can learn from our mistakes, others believe that we could inappropriately risk making children feel responsible for the actions of their ancestors. However, we choose to teach history, any new information that we present will interfere with what has previously been learned. 

On a national and even societal level, we are constantly learning new things about the past, which can sometimes reshape how we understand what’s happened throughout history. The challenge is in distinguishing between necessary historical updates and deliberate manipulation. Some argue that revising history based on new evidence is essential, while others fear that such revisions may erase important truths or push political agendas.¹² Because learning new information can retroactively interfere with our understanding of the original events that took place, it’s crucial that we proceed with caution when introducing new perspectives. 

The Ethics of Memory Modification in Neuroscience and AI

Hollywood has had plenty of unrealistic examples of sci-fi scenarios where bad guys can manipulate memories and control minds, but as neuroscience advances, some aspects of memory manipulation have become more of a reality. Researchers are exploring ways to influence memory, raising ethical concerns about whether retroactive interference could be artificially induced to suppress or even alter memories. Some studies have suggested that targeted interventions, including things like pharmaceuticals, brain stimulation, and implantable technologies, could reduce the impact of traumatic memories by weakening their retrieval pathways.¹³

While this could be beneficial for individuals with PTSD or severe anxiety, critics worry that such techniques could be misused. The 2024 film Blink Twice addresses this concern; in the film, an amnesia-inducing drug is used against women as a way to continually assault them while keeping them as willing hostages. Although the technology in the movie was fake, the concern that a memory-manipulation device could get into the wrong hands is a real threat. Could governments or corporations use memory modification to suppress undesirable memories or rewrite the past? Could AI-driven learning systems manipulate human memory by selectively reinforcing or interfering with information? While we know that retroactive interference is powerful in shaping how well we can recall previously learned information, it’s vital that we explore how intentional interference with memory should be pursued, and if so, under what regulations and safeguards.

The Postman Word Pair Study

In the 1960s, cognitive psychologists Brenton Underwood and Leo Postman decided to build on previous memory research to study how retroactive interference affects learning.¹⁴ Like later studies on the subject, their goal was to investigate whether information that someone has recently received interferes with their ability to recall something learned earlier. The two men set up a lab experiment and gathered participants who were split into two groups. Both groups had to remember a list of paired words (e.g. cat – tree, jelly – moss, book – tractor). The experimental group also had to learn another list of words where the second paired word was different (e.g., cat – glass, jelly- time, book – revolver), while the control group was not given a second list. Finally, all participants were asked to recall the words on the first list.

The results showed that the recall of the control group was more accurate than that of the experimental group, meaning they could remember more of the words from the first list. This may have been especially true because the word pairs in the second list were so similar to the word pairs in the first list. Because the same amount of time had passed for both groups, and because both groups had the same number of words to remember, they should theoretically be able to recall the words with equal accuracy.¹⁴ Because the group with exposure to the second list remembered less, this suggested that learning items in the second list interfered with participants’ ability to recall the list. In other words, retroactive interference was at play!

The 1992 Bjork & Bjork Academic Study

In 1992, cognitive psychologists Robert A. Bjork and Elizabeth L. Bjork conducted research on how retroactive interference affects learning and memory retrieval, particularly in educational contexts.⁶ Their work focused on how newly learned information can interfere with students’ recall of previously studied material. Understanding this interference process helped Bjork and Bjork to develop learning strategies that can mitigate this interference.

Over the course of their study, the researchers found that students who studied two similar sets of information in close succession often experienced difficulty recalling the first set because the second set of material interfered with their memory. For instance, if students learned one list of vocabulary words and then immediately studied a second, similar list, they struggled to later accurately recall the first list. Thus, the traditional methods of cramming for an exam, which you may or may not have experienced firsthand, can actually worsen memory retention because of retroactive interference. 

However, the study found that if teachers used spaced repetition and intentional retrieval practices to help students study, they significantly reduced the amount of retroactive interference.⁶ Because these techniques strengthened memory consolidation, they made it easier for students to recall both lists. When students spaced out study sessions, mixed subjects or topics during learning, and employed active recall instead of passive review, they had better results. Hopefully, spreading knowledge of these principles and the effects of interference will encourage educators to apply these techniques to curriculum design. 

Modern CX is Behavioral: How the Peak-End Rule Can Revolutionize Customer Experience 

Understanding the influence of cognitive biases, particularly those that affect our memory, is important when designing the modern consumer experience. The peak-end rule, which describes how we primarily judge an experience based on how we felt at the end and during the highlights, is one such lens we can use to craft a better customer experience. This article delves into the application of the rule in the context of CX design. 

Why do we better remember items at the beginning or end of a list? 

Similar to the peak-end rule, the serial position effect explains why we often remember items from the beginning and end of a list. This cognitive bias is important for understanding how we encode memories and plays a part in explaining why we are subject to retroactive interference. 

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