Final Paper
The Effects of Retroactive Interference on Amnesia Patients

Abstract
New memories are fragile and vulnerable to interference. Patients who suffer from amnesia can often experience what is referred to as retrograde interference, which is the forgetting of newly learned information due to subsequent interference of additional material given to the subjects. This paper reflects on published articles regarding research about the effects of retroactive interference on the learning and memory retention ability of patients suffering from amnesia. Although research in this topic has not been able to fully answer the mystery that lies beyond the memory storage in the brain, many experiments have been conducted regarding this ailment. Articles on this topic vary in experimentation, yet they all show that interference subsequent to the learning of new information impairs memory consolidation substantially. This idea of retroactive interference dates back to the 1900s and new ideas and theories have been built upon it since. The findings in these articles strongly indicate that patients with anterograde amnesia are better able to form new long-term memory traces than previously presumed. Future research on this topic would lead to a greater variety of discoveries and establish newer memory training methods.

The Effects of Retroactive Interference on
Amnesia Patients Anterograde amnesia is a severe impairment of memory that hinders the ability to build new memories and remember the recent past. This ailment essentially remains a mystery today as the particular mechanism for the brain’s memory storage is not yet well discovered. However, recent research has shown that patients with amnesia are able to retain new knowledge for a lengthier period of time than it was presumed, if the learning is followed by an unfilled interval, devoid of any additional material. The following research articles have explored, in detail, past and future studies on the effects of retroactive and delay interference in the learning of new information in amnesic patients. It also surveys the possibilities of increasing memory retention through the use of a variety of methods that could lower the brain’s susceptibility to such interference.
The research on forgetting, beginning with Herman Ebbinghaus back in 1885, is still notably debated in terms of decay and interference today. The theory of decay explains that forgetting ensues as a function of time, meaning that memory of new learning “decays” with the advancement of time. This leads into the theory of retroactive interference, and whether the occupation of this time period with new material and tasks get in the way of material that is needed to be retained. Another theory of interference led by Underwood (1957), rejected retroactive interference and introduced proactive interference, which is interference from information that was presented before the to-be-retained material (Cowan, 2004). The following works in this paper follow in the footsteps of Müller and Pilzecker (1900), who gave rise to the theory of subsequent interference, that human forgetting is largely impacted by work following the original learning.
To enhance this memory consolidation impacted by interference, Dewar, Cowan, Garcia, & Della Sala (2009) tested a period of delay interference on amnesia patients. Twelve amnesia patients and twelve control subjects were used. The study consisted of four trials with a new 15-word list in each one, presented to the participants through headphones at two-second intervals for each word. Three of the trials consisted of early interference (followed by six minute unfilled interval), mid interference (three minute unfilled interval, interference, then another three minute unfilled interval), and late interference (six minute unfilled interval, followed by the interference). The last trial was a control condition is which there was a nine-minute unfilled interval after the immediate recall. The unfilled periods were when the participants sat alone in a quiet and dark room that was devoid of any distractions. During the interference, the participants were asked to identify drawings on a computer screen while ignoring the superimposed word. Delayed retention and the immediate recall were measured against the four conditions: early, mid, late, unfilled. Participants retained a significantly higher number of words in the last trial with the unfilled delay interval compared to the trials with interference. In all four conditions, the retention rate was considerably higher for the controls than the amnesia patients. The results for the groups differed significantly in the early interference trial, yet were much more similar with the absent or delayed interference. In support of their hypothesis, it was found that the interruption by new information disturbs the consolidation time leading to an inability to retain new learning.
Similar to the previous study, the objective in Dewar, Della Sala, Beschin, & Cowan (2010) was to determine what exactly interfered with the memory consolidation in amnesic patients. This study suggests that the introduction of new material may be more difficult to remember because it differs greatly from the old material that is to be remembered. Ten amnesic patients and ten controls were used to test how well they recalled a given prose following a delay period of ten minutes. One delay period was unfilled, meaning a very minimal interference, and the other was filled, where the participants were to perform a tone detection task by actively listening to piano notes. The proportion of delayed recall was measured across the trials: unfilled and filled conditions. What was unique in this study was the presentation of nonspecific retroactive interference, similar or non-similar material, which was presented in place of item-specific interference, or similar material, that is typically used in clinical practice. A profound impact of interference on retention was found in the data. Even though a majority (7 out of 10) of the amnesic patients could recall the prose after the unfulfilled delay, almost none (1 out of 10) could recall the prose after the interference of the tone detection task. It is hypothesized that these effects of interference take place during distinct memory processes and that they differ qualitatively from each other. Congruent to the previous studies, in Cowan, Beschin, & Della Sala (2004), six patients with amnesia had to listen to a list of words in the first experiment. and stories in the second experiment. Followed by which some participants were asked to recall immediately after learning, and some were given an extended delay that was either activity filled and unfilled. As expected, the amnesiacs that performed a task during the delay period showed severe forgetting, where as significantly less forgetting took place in a majority of the participants spent the delay period in a quiet and dark room. Some patients even appeared to sleep during this interval. Collectively, the data in this research portray the vulnerability of amnesiacs to retroactive interference. Showing a broader scope of this research question, Isaac & Mayes (1999), extended their study to the memory retention of amnesiacs in general. Three experiments studied the rate of forgetting in amnesia patients. The first experiment, the free-recall condition, amnesiacs displayed an increased rate of forgetting than the patients with delays of up to ten minutes. This was replicated into the second experiment, with the cuing condition and the level of cuing that was given in this case impacted the rate of forgetting. In the third experiment, amnesic patients’ sensitivity to interference was an unlikely cause of the accelerated forgetting rate. The researchers interpreted this in terms of the storage deficits encountered by amnesiacs, meaning that amnesiacs are still able to encode new information, yet unable to store it, and hence retrieve it. This study was different from the studies previously mentioned in that it analyzed the encoding and retrieval explanations and damage to the frontal cortex area of patients suffering from amnesia. This is a much more different perspective than the other studies, although experimentation shows great similarity. In addition to the articles mentioned above regarding the effects of retroactive interference and the rate of forgetting, it is important to take into consideration the different kinds of retroactive interference as well as its conditions and factors that could affect memory in non-amnesic patients which could further lead to possible enhancement of retention in amnesia patients. Wichert, Wolf & Schwabe (2011) explored the effects of memory remoteness on consolidation. In this study, participants learned new neutral and emotional pictures following the retrieval of pictures that was learned 1 day, 7 days, or 28 days prior. On the one-day-interval, the results suggested a retroactive interference effect due to the effect of interference being independent of prior retrieval of the originally learned material. On the other hand, the seven-day-interval, the results showed a reconsolidation effect and significant differences could be found between the control group and the retrieval group of both these interval groups. At the twenty-eight-day-interval, the impairing effect of interference weakened and the control group did not differ significantly from the retrieval and interference group. They found that while interference weakens memory performance, the act of retrieval could enhance memory, depending greatly, however, on the age of memories. Studies show that scent improves memory for accompanying information. In Morrin, Krishna & Lwin (2011), scent’s possible immunity to retroactive interference is explored. Their hypotheses were as follows: that unaided and aided consumer memory will be enhanced by the scenting of a product; that being exposed to another scented brand within the same category can create retroactive interference; that the information forgotten by the retroactive interference will be restored when a scent-based cue is used during the retrieval period; and competitive interference will take place in the event that the attributes of two differing brands are mistaken and confused for one another, which would lead to a negative correlation between recall and intrusions. A two-by-two factorial design was used, consisting of the presence or absence of product scent and the exposure to competitive brand or the lack of. Each participant was randomly assigned to one of the categories. Two weeks following their introduction to the first brand of moisturizer, they were exposed to the second brand and two weeks subsequent, they were asked to recall everything that they could about Brand A, then Brand B. Both aided and unaided recall was tested to see if inhibited information due to retroactive interference would be made accessible when the participants were provided with a scented retrieval cue. Morrin, et al. (2011) found that scent is not necessarily immune to interference; however, it does effectively enhance memory, provided that a scented retrieval cue is present at the time of recall. Following additional research, this method could be used by many amnesia patients to aid them in learning basic information that was lost to them before to their high susceptibility to retroactive interference. Another central discovery regarding memory was found in Eakin (2005), where participants experienced a phenomenon known as an illusion of knowing, meaning that they were overconfident in their capability to remember information that they later were not able to recall. These predictions of knowing just before information retrieval, has been shown to vary with the kinds of interference in the studies and have a strong effect on participants’ ability to recall. In Campoy (2011), the length of words was found to affect retroactive interference in short-term memory. This study consisted of two different experiments to show that longer words create a greater retroactive interference than short words. It showed for the first time that the word-length effect might result in the differences of interference levels. An alternative area, which contributes strongly to this topic, is the impact of proactive and retroactive interference in young adults, compared to healthy older adults and adults with amnestic mild cognitive impairment, who show a greater memory difficulty than those adults experiencing normal aging. This was studied in Ebert & Anderson (2009), where it was discovered that healthy older adults were prone to greater susceptibility to interference than younger adults, further confirming previous studies on this topic that the effects of interference seen stronger with aging as the brain gets more vulnerable. Recent research continues to show that memory interference has several different factors involved and subsequently can be controlled in ways to minimize the impact it has on short-term memory. In Rattat & Picard (2012), the modalities of the duration periods in interference showed differences, suggesting that the visual, auditory and auditory-visual intervals are not signified the same way in memory. This provides us with the understanding that there is possible time discrimination involved in memory processes and that dual encoding of information could allow for better accessibility to recall newly learned information. Since amnesia patients’ sensory modalities are intact, using this method could, in the future, allow for greater memory retention. These studies are congruent with other recent findings that reinstate the idea of retroactive interference having a central role as a forgetting mechanism in short-term memory. Having a broader view of such factors that influence interference could help determine ways to enhance memory in amnesiacs.
These findings fit preceding theories and literature, and remain consistent with studies in the past. Overall, minimizing retroactive interference seems to be underlying the improvement of memory consolidation. The data reported in these past and current studies and their interpretations leave significant implications. The aforementioned studies appear to strongly indicate that some amnesic patients are actually able to retain new information, under the condition that they are exposed to as little retroactive interference as possible. It is yet to be established whether this inability to build new memories is unpreventable or if reducing the interference following learning can allow for retrieval. This would indicate that new information is successfully encoded into memory, regardless of how seemingly inaccessible it is. It is important to examine the impact of interference in learning altogether, and developing for techniques to enhance memory consolidation would benefit patients suffering from amnesia. These findings contribute strongly to prospective studies, providing a gateway to a wide variety of directions for further research on this topic and may discover the impact of nominal retroactive interference on the long-term memory of amnesic patients and harvest effective memory training methods. The theoretical implications indicate the need of current and modern technology to integrate a new memory consolidation stage into the standard model of memory.

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