False memories are a prevalent phenomenon that interferes with a variety of important tasks, such as eyewitness testimony. They can occur during the encoding, storing, or recalling phase of the memory-making process. Researchers have discovered that through association, the mind can encode events as authentic memories even though they never occurred. Associative memory illusions can be revealed using an experimental paradigm called the DRM Effect, which presents related word lists to study subjects and tests whether closely associated, but unpresented items become encoded into memory. The ability to discriminate between presented and unpresented items depends on the ability of subjects to monitor the memory task and this can be tested by warning subjects in advance of the possibility of associated memory illusions. Previous studies have shown that the efficacy of monitoring can be increased by an explicit warning, but only modestly and at the expense of recalling presented items. In the present study, undergraduate psychology majors were tested for their associative-monitoring ability using the DRM paradigm. An explicit warning reduced the recall rate of critical unpresented items by approximately 8.8%, thus confirming prior observations. This recall rate though, differs substantially from prior observations and suggests that the efficacy of monitoring could be an unstable characteristic.
Effect of Warning on False Memory Rate
Human memory is prone to making errors (Roediger III and McDermott, 2009). The main forms of error are forgetting and remembering things that did not happen. These errors can occur at any point in the memory-making process, which involves the tasks of encoding, storage, and retrieval. The associative nature of perceptions will affect the encoding process and errors will become stored as if they represent an authentic event. Subsequent events may influence the integrity of stored memories and the retrieval process, for example, the authoritarian presence of a police investigator, resulting in altered retellings of prior events. These types of errors can have dramatic effects on eyewitness testimony and the recovery of so-called suppressed memories, so it is important to understand how memory errors occur.
Roediger and McDermott (1995) modified a memory testing protocol first published by Deese (1959). Termed the DRM Effect, this test consisted of lists of related words that are verbally communicated to test subjects and then recalled in the order heard. The recall ability of subjects indicated that words introduced first or last are recalled more accurately, thus generating a U-shaped curve; however, unmentioned words highly associated with the word list tend to be recalled more often that the words in the middle of the list.
This associative memory illusion is believed to occur because hearing the list involuntarily elicits thoughts about the key word and results in the unpresented word becoming encoded as an authentic memory (Roediger and McDermott, 2009). The process of eliciting the unmentioned key word, which Roediger and McDermott call the 'critical nonstudied' item, is called 'activation. The ability of study subjects to discriminate between a studied and nonstudied item is called 'monitoring'.
The 15 item word lists is intended to activate a key word in the mind of the study subject, which is never actually presented (Roediger and McDermott, 2009). The words on the list are given in a specific order, such that the first words presented are the most highly related to the unstated key word and the last words on the list are only slightly related. The first words on the list are expected to trigger repeated associations with the unstated key word (critical unstudied item), until the summation of these associations or activations become strong enough to be equivalent to having actually heard the word (Reisberg, 2009, p. 238-239). The unstated key word has thus become an integral part of the hypothetical associative network called 'word list'.
The parameters of monitoring can be tested by explicitly by warning study subjects in advance about the possibility of failing to discriminate between studied and nonstudied items (Roediger and McDermott, 2009). Although explicit warnings do reduce the recall rate of critical nonstudied items, the confidence in recalling studied items is reduced as well. This suggests that study subjects become more cautious in general; however, reductions is the recall rate of nonstudied items is reduced slightly more, suggesting that selective monitoring is possible.
This study will test the activation-monitoring model in a population of undergraduate psychology majors. Specifically, the hypothesis being tested is that an explicit warning will significantly reduce the recall rate of critical nonstudied items.
A convenience sample of 341 undergraduate psychology students, enrolled in the HPS203/773 Cognitive Psychology course at Deakin University, volunteered to participate in the study. Student participation was completely voluntary and informed consent was obtained. Demographic information beyond student status was not collected because age and gender were not predicted to be confounding factors.
The effect of a single independent variable (warning) on the rate of recall for critical nonpresented items (dependent variable) was tested.
Materials and Procedure
Participants were instructed to remember lists of words, which the experimenter read out at a rate of approximately one word per second. There were 12 lists of 15 words each. Each list was made up of related words, which were all associated to one common (unpresented) word. For example, the words on the list "queen, England, crown, prince, George, dictator, palace, throne, chess, rule, subject, monarch, royal, leader, reign" were all related to the unpresented word, "king."
After hearing all the words, participants completed a recognition test. This test consisted of 12 critical unpresented words, 36 presented words, and 32 new words. Participants were asked to circle "YES" if they had heard the word presented earlier or "NO" if they had not heard the word. This task had no time limit, but took approximately 2 minutes.
Before hearing the lists of words, participants in the "warning" condition were told that each list was made up of related words. They were told that all the words were associated to one common word. They were instructed to try to figure out the related word and note whether it was presented in the list. As an example, participants were given the "king" list above and told that people often mistakenly remember the word "king" even though it was not presented. They were warned not to make this error. Participants in the "no warning" condition did not receive this warning.
The recall rate of the critical nonstudied items, in the absence of an explicit warning, was 78.50%. The recall rate of the critical unstudied word was reduced to 69.69% if the subjects were given an explicit warning. The difference between these two conditions was statistically significant (students t test: t (339) = 4.42, p < .05, two-tailed).
Percentage of false recognition
We sought to test the activation-monitoring model by measuring the effect of a warning on the rate of recalling critical nonstudied items. We predicted that the independent variable (warning) would significantly lower the recall rate of critical nonstudied items (dependent variable). The results presented here provided significant support for this hypothesis.
Roediger and McDermott (2009) reported an 80% recall rate of critical nonstudied items, which is essentially identical to the 78.50% reported here. This result suggests the false recognition rate of associated items is a stable trait.
McDermott and Roediger (1998) compared the effect of an explicit warning on the recall rate of critical nonpresented items and found that it decreased from 80% to 59%, a reduction of 21% overall. By comparison, an explicit warning had no effect on the recall rate for critical presented items, although the level of confidence in this aspect of the recall exercise was reduced by 6%. The results presented…