Studies on Interference

Interference Psychology: Definition

Interference is an explanation for long-term memory forgetting. According to this theory, memories similar to the target memory can hinder retrieval.

This is because we often rely on cues associated with a memory to recall it. When multiple similar memories are associated with the same cue, retrieval will be impaired.

Proactive and Retroactive Interference Examples

There are two types of interference: proactive and retroactive interference.

Proactive interference occurs when old memories interfere with recalling a new memory.

Here the old memory (Dutch names) are interfering with the retrieval of new memories (German names). This is likely because they are both associated with similar cues.

On the other hand, retroactive interference occurs when the new memories interfere with what you have learnt earlier.

Contemporary Studies on Interference Theory in Psychology

One of the early studies that aimed to investigate the effect of retroactive interference was conducted by McGeoch & McDonald (1931).

Studies on Interference: McGeoch and McDonald’s (1931) Classical Study

In this study, participants were asked to remember a list of words until they could recall it perfectly. Then, participants had to learn a new, second list. There were six groups, and each learned a different set of words for the second list.

You can see the groups listed in the table below:

Participants then had to recall the original list of words.

Group 1, who learned the list with the most similar material (synonyms), had the worst recall. Group 5, who learned the most irrelevant material (numbers), had the best recall, apart from the control group.

It was concluded that the more similar information is, the more likely it will interfere retroactively with older memories.

Now, let's look at some more recent studies on proactive and retroactive interference.

Retroactive Interference in Psychology

Sosic-Vasic et al. (2018) studied whether the timing at which the new information is learnt will affect the degree of retroactive interference. Their sample consisted of 30 high school students, who were given a list of 12 German-Japanese word pairs and then another list right after, 3, 6 or 9 minutes after the first list. There was also a control condition when no second list was presented. Then, participants were asked to recall the information from the first list.

The study design was within participants, meaning that each participant took part in each condition, with 2-day breaks between them. They also went through the conditions in different orders to prevent order effects.

The researchers found that:

• When participants were presented with the second list (no matter the time), the memory performance on the first list dropped by 20%.
• The time at which the second list was presented affected different students differently.

It was concluded that the period of 12 minutes after learning information is crucial for memory consolidation, and introducing similar information during this time results in retroactive interference.

Proactive Interference in Psychology

Contemporary research on proactive interference has identified that it occurs when memories rely on the same neural circuit. It has also been found that a mnemonic technique called the Method of Loci can reduce Proactive Interference.

Studies on Interference: Crossley et al. (2019): What Leads to Proactive Interference?

Crossley et al. (2019) investigate the time during which memories are sensitive to interference and the role of shared neural circuits between the target and interfering memories. They used conditioning to teach a pond snail to associate a stimulus with a reward (appetitive learning) or punishment (aversive learning).

The authors investigated what would happen if new learning occurred when the old memory was still fresh and vulnerable to disruptions and what would happen if the old memory was already stable.

• When the snail was taught a new association, no matter if it was similar to the first one, when the first memory was still vulnerable, the old one was forgotten due to retroactive interference.

• When the old memory was already stable, and new information was introduced, proactive interference occurred, but only if the new memory engaged the same neural circuit (e.g. both new and old ones were appetitive). When the new memory engaged a different circuit (it was aversive), no interference occurred.

This study shows that in the case of retroactive interference, the time might be more important than shared neural circuits. Even if the new memory doesn't involve the same cues, it can still interfere with the old one.

While proactive interference only occurs if both memories engage the same circuits and can occur even after the new memory has become stable.

Studies on Interference: Bass & Oswald (2014) Overcoming Proactive Interference

The famous Sherlock Holmes often talks about using a mnemonic technique called the mind palace to remember a large amount of complex information. This technique is also called the Method of Loci, and it involves associating each new piece of information you learn with an object that is part of a space you are familiar with (e.g. your house).

Bass & Oswald (2014) aimed to investigate whether the Method of Loci mnemonic can be an effective way to prevent proactive interference.

They divided 94 undergraduate participants into two groups. Both groups were asked to memorise five lists, each containing five words in the fruit category. One group was trained on how to use the Method of Loci to memorise the lists, while the other was just told to memorise the list.

Then the participants were asked to recall as many words from the lists as they could remember in any order.

The study found that:

• The group who wasn't taught the mnemonic had a 38% reduction in recall of words across lists due to proactive interference.
• In contrast, the group taught the Method of Loci technique showed a significant reduction in proactive interference, with only a 25% reduction in recall across lists.

This shows that associating the information with separate cues can help us prevent proactive interference. Keep this technique in mind next time you're memorising a list!

Fig. 2 - The Method of Loci mnemonic uses the representations of spaces which are familiar to you to prevent proactive interference.