Imagination inflation: Imagining a childhood event inflates confidence that it occurred
by Elizabeth Loftus
Page 4
Source: http://faculty.washington.edu/eloftus/Articles/Imagine.htm
As Figure 1 shows, the majority of scores did not change (57% in the imagined condition and 65% in the not-imagined condition). Additionally, when subjects did change their ratings, positive change scores were more likely to occur than were negative ones. But for the purposes of the present experiment, the most interesting result is found by comparing the bars on the extreme right of the figure: There was more positive change in the imagined items (34%) than for the not imagined items (25%). In other words, subjects who initially reported that an event did not happen, but then imagined that it had, were more likely to increase their confidence that it had occurred when asked about it later than were subjects who did not imagine the event. However, because these data were obtained by combining all 1-4 responses from all subjects, individual subjects contributed different numbers of events, so overall statistical comparisons cannot be made at this level. We offer these results only for illustrative purposes, and now direct our attention to each event item.
Would this intriguing pattern repeat for the event items individually? For each of the eight critical items we calculated the percentage of positive change. Figure 2 shows these data displayed according to whether or not the critical event was imagined. For each item, the right hand bar reveals the percentage of subjects with increased confidence after imagining the event. A paired t test treating items as cases showed that the mean difference was 8.2% greater for imagined items than for not imagined items: this difference was significant [t(7) = 5.48, p = .0009, SE = 1.49, two tailed, adjusted power at alpha = .05 was .97]. The effect size, calculated as [mean difference/SDnot imaglned], was a medium to large 0.72. So, for example, in the "Broke window" event. 24% of subjects who imagined the event increased their subjective confidence that it had happened to them, while the corresponding figure for subjects who had not imagined it was only 12%.
Figure 2. Percent of subjects who increased on each item (for subjects who initially responded 1-4; that it, responses indicating that the critical items probably did not happen).
Why does imagining an event lead to more positive changes than not imagining the event? One possible explanation is that the act of imagination simply makes the event seem more familiar at the time the posttest LEI is completed. Another possibility, however, is that the act of imagination reminds some subjects of a true experience from their past. If this "reminder" hypothesis is correct, we might expect to see at least some instances in which subjects initially give a low score indicating that the event probably hadn't happened to them, but the second time jump to a score of 8, indicating that the event definitely did happen to them. On the other hand. if some subjects do make a "big jump" (i.e., they move from an initial score of 1-4 to a final score of 8), it may not be because they remember a genuine experience at all: It may be that imagining the event makes it seem very real, and subjects become quite sure that it happened.
These are highly speculative inferences, and they rest on the assumption that being reminded of a genuine event causes one to be certain. However, to explore the possibilities, we calculated the number of "big jumps," defined as an increase to a score of 8 on the posttest. Such jumps were relatively rare, occurring in only 6 of the 112 imagined items, and in 2 of the 119 not imagined items. These "big jumpers" were found in the following items from Table 1 (cases are in parentheses): "Found $10" (2 imagined); "Lifeguard" (2 imagined); "Emergency room" (1 not imagined); "Stuffed animal" (1 imagined); and "Haircut" (1 imagined, 1 not imagined). When these cases were removed from the analysis and change scores were collapsed across subjects and items, there was still an overall tendency toward imagination inflation. That is, there were still more positive change scores for imagined than not imagined subjects (29.9% vs. 23.4%), and all but the "Lifeguard" item still showed an imagination effect. Over the eight items, the mean difference was 6.55% greater change in imagined items than not imagined items. A paired t test treating items as cases showed that this mean difference was significant [t(7) = 3.02, p = .01, SE = 2.17, two tailed; adjusted power at alpha = .05 was .53]. Effect size was a medium .55.
What kinds of change scores were produced by the subjects who originally did not think an event happened to them, and did not imagine it? Let us return to Figure 2 and examine what happened to these subjects. The left-hand bar for each item shows the percentage of subjects with positive change scores after merely being asked about the event twice, on the pretest and posttest. A paired t test treating items as cases showed that when subjects did change their responses between the first and second LEI tests, the percentage of subjects with positive change scores was significantly greater than the percentage with negative change scores [mean difference = 13.9%, t(7) = 2.67, p = .032, SE = 5.20, two tailed; adjusted power at alpha = .05 was .41]. For instance, 43% of subjects who took only the pretest and posttest became more confident that they had found a $10 bill, and 7% of them became less confident. Thus, even when subjects who did not imagine an event changed their answers, they tended to report greater rather than less confidence that it had occurred. Did these subjects develop false memories because event items were repeated? Of course, there are other explanations for this result. Briefly, it could be regression to the mean. It could be that the second test promotes more accurate recall, or it could be that the second test causes the item to become more plausible, and that increased confidence does not point to completely developed false memories so much as to increased plausibility that they might have occurred. These issues are discussed in more depth later.
We have shown that when subjects imagine an event they do not think happened, they tend to become more confident that it did happen. But what about subjects who initially think an event probably did happen? Would imagination make them even more confident that an event had occurred? Although not the main question in our research, it is worth addressing. To examine the effect of imagination on events thought likely to have happened, we collapsed change scores for them across all subjects and items. We included only items initially judged as 5-7, removing the data for items initially reported as an 8 because these ratings could not increase. The most common outcome among these "probably did happen" subjects in the imagined condition was to stay the same, and the most common change in the not imagined condition was to become less confident. Additionally, positive change occurred more often for not imagined items than for imagined items (36%, or 8/22, vs. 19%, or 4/21). However, because there were so few items, statistical analysis is inappropriate, and we avoid further interpretation.
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