Key Takeaways
- Interference happens when similar memories make it hard to remember specific events.
- Proactive interference is when old memories make it hard to remember new ones.
- Retroactive interference is when new information makes it hard to remember old information.
Interference is one theory to explain how and why forgetting occurs in long-term memory. Interference is a memory phenomenon in which some memories interfere with the retrieval of other memories.
Here we explore interference in greater detail, including how this theory developed and how it was expanded on with decay theory. We also discuss the two types of interference in psychology: proactive interference and retroactive interference, along with providing examples of each.
What Interference Is
Essentially, interference occurs when some information makes it difficult to recall similar material. Similar memories compete, causing some to be more difficult to remember or even forgotten entirely. Because of this, some long-term memories cannot be retrieved into short-term memory.
With interference, one might confuse the memory of one event with another. This experience can be surprisingly common, especially when faced with a number of very similar memories. If someone is asked to recall what they had for breakfast last Monday, for example, they might struggle to remember because they have so many similar memories of other meals.
There are many different but similar memories encoded in long-term memory, which can make it challenging to recall a specific event and bring it into short-term memory.
History of Interference Theory
Researchers have long been interested in understanding not only how memory works but why people sometimes forget. Interference theory is just one of several proposed explanations, with some important studies contributing to the development of this theory.
In one of the first studies on interference, researcher John A. Bergstrom had participants sort cards into two piles. He found that changing the location of the second pile resulted in slower performance, suggesting that learning the rules for the first task interfered with the memory of rules for the second task.
In 1900, researchers Muller and Pilzecker found that people were less likely to recall nonsense syllables if intervening material was presented 10 minutes or sooner following the original learning task. To them, this indicated that new memories require a period of time to stabilize in memory, a process they dubbed “consolidation.”
Decay Theory
During the late 1950s, psychologist Benton J. Underwood looked at Ebbinghaus’s famous forgetting curve and concluded that forgetting was influenced not only by time but also by previously learned information.
Decay theory elaborates upon Ebbinghaus’s research and suggests that memories decay over time, leading to forgetting. However, a memory may also be susceptible to a number of other influences that affect how well things are recalled and why they are sometimes forgotten.
Many events can take place between the time a memory is encoded and when it is recalled. How rarely (if ever) do we form a memory and then learn nothing new between the formation of that memory and the need to recall that information? Such conditions usually only take place artificially in experimental labs.
While researchers can control for other factors in a lab setting, the real world is filled with a variety of events that may also have an impact memory.
In day-to-day life, any number of events, experiences, and new learning can occur between the actual formation of one memory and the need to recall that memory. When intervening gaps between encoding and recall are filled with other information, there is a corresponding negative impact on memory.
Due to this phenomenon, it can be challenging to determine if forgetting is because of the passing of time or if it is a consequence of one of these intervening factors. Research suggests, for example, that interfering memories are one factor that can also contribute to forgetting.
Two Types of Interference
There are two different types of interference: proactive interference and retroactive interference.
Proactive Interference
Proactive interference is when older memories interfere with the retrieval of newer memories. Because older memories are often better rehearsed and more strongly cemented in long-term memory, it is often easier to recall previously learned information rather than more recent learning.
Proactive interference can sometimes make it more difficult to learn new things. For example, upon moving into a new house, one might find themselves accidentally writing their old address down when filling out forms. The older memory of the previous address makes it more difficult to recall the new one.
Retroactive Interference
Retroactive interference is when newer memories interfere with the retrieval of older memories. Essentially, this type of interference creates a backward effect, making it more difficult to recall things that have been previously learned.
In the case of retroactive interference, learning new things can make it more difficult to recall things that we already know. For example, a musician might learn a new piece, only to find that the new song makes it more difficult to recall an older, previously learned piece.
Research has found that around 70% of information is forgotten within 24 hours of initial learning.
While retroactive interference can have a dramatic impact on the retention of new knowledge, there are some effective strategies that can be implemented to minimize these effects. Overlearning is one effective approach that can be used to reduce retroactive interference, which involves rehearsing new material past the point of acquisition.
Overlearning means studying and practicing what we have learned over and over, even after we’ve achieved sufficient mastery of the subject or skill. This practice helps to ensure that the information will be more stable in long-term memory and improve recollection and performance.
Examples of Interference
There are many different examples of how interference can influence everyday life. Imagine a student preparing for a psychology exam. Between learning the information and taking the actual test, many things can take place. The student may take other classes, work, watch television, read books, engage in conversations, and perform many other activities during this intervening period.
In addition to general decay caused by the time elapsed, other memories might form that could potentially compete with the material the student learned for their exam. So, when the student goes to take their exam, they may find recalling some information quite difficult.
If they’ve learned subsequent material that is very similar to the original information, recalling facts and details for the exam might be harder. They might find themself mixing up different historical figures in psychology or struggling to remember the origins of this field.
The memories formed during the interval between the learning and the test interfere with the older memories, making recall much more difficult.
There are many other examples of interference and its effect on our memories:
- Upon changing one’s mobile phone number, they have a difficult time remembering the new number, so they keep accidentally giving people their old number. The memory of the old number interferes with the ability to recall the new one.
- A person tries to memorize a list of items they need to pick up at the grocery store. During the intervening time, they read a new recipe on their favorite cooking website. Later at the grocery store, they find themselves struggling to remember the items from their shopping list. The competing memory of the new recipe’s ingredients interferes with the memory of what they need at the store.
- Students are often more likely to recall information that they learn shortly before an exam than the material they learned earlier in the term. In this case, newer information competes with the older learning.
- A native English speaker who is trying to learn a new language might find that they keep trying to apply the rules of their native language to the new language they are trying to learn. Older memories interfere with memories of the new information, making it harder to remember the grammar rules for the new language.
- A teacher may struggle to learn the names of new students each year because they keep confusing them with the names of students from previous years.
Interference Research
Researchers have been able to demonstrate the effects of interference in numerous studies. They often do this by increasing the similarity of the information presented.
For example, participants may be presented with the original information and then after a period of time, presented with more information. When tested on what they recall, interference is observed more frequently when the secondary information contains more similarities to the original material.
The more similar two memories are, the more likely it is that interference will occur.
Earlier Research
In one of the earliest studies on the interference theory of forgetting, researchers had subjects memorize a list of two-syllable adjectives. Later, subjects were asked to memorize one of five different lists. Some of these lists were very similar to the original test material, while others were very different.
For example, some lists contained synonyms of the original words, some antonyms, and some were simply nonsense syllables. Later testing showed that recall improved as the differences between the two lists increased. The more similar the lists were, the more interference there was, leading to more difficulty with recall.
Later Research
In one 2018 study, researchers found that retroactive interference had a negative impact on learning and memory consolidation. After a learning task, some participants were presented with a subsequent interference task at various time points. Some had the second learning task three minutes after learning the first information, while others had it nine minutes after.
What the researchers discovered was that the interference task decreased memory performance by as much as 20%. Interestingly, interference tended to have a greater negative impact on those identified as “fast learners” than it did on those identified as “slow learners.”
Interference can play a prominent role in the learning process. Previously learned material can have an impact on future learning and, conversely, newly learning information can affect past learning. One study found that retroactive interference effects were more profound in younger children, but that these effects may diminish as people age.
Applications of Interference Theory
Interference theory can have a number of real-world applications. From a practical, everyday standpoint, interference theory suggests that one of the best ways to improve one’s memory of something is to make it stand out.
If we are trying to remember something and want to avoid the effects of interference, we should look for a way to add novelty. Making up a mnemonic, song, or rhyme is one way to help make what we are studying stand out in our memory.
By making the material memorable and less similar to other memories, it may become easier to recall. Regular practice sessions can also be useful for promoting overlearning and reducing the probability that new memories will interfere with what we are learning now.
