Comparing Direct (Explicit) and Indirect (Implicit) Measures to Study Unconscious Memory
Philip M. Merikle and Eyal M. Reingold
Page 6
Source: http://psych.utoronto.ca/users/reingold/publications/Merikle_&_Reingold_1991/
Figure 2.
Mean sensitivity (A') of the recognition and contrast tasks at each trial block in Experiment 2A and Experiment 2B. (Bars indicate standard errors.)
Inspection of Figure 2 indicates that the same basic pattern of results was found in Experiments 2A and 2B. In both experiments, the indirect contrast measure was more sensitive than the direct recognition measure in the first two block of trials. This greater sensitivity of the indirect measure reflects the influence of unconscious memory. On the other hand, no evidence for unconscious memory was found in the third block of trials in either experiment, as the results of both experiments indicate that the recognition measure was more sensitive than the contrast measure.
The results from Experiments 2A and 2B were evaluated by an overall 2 X 2 X 3 analysis of variance, with experiment (Experiment 2A vs. Experiment 2B), task (Recognition vs. Contrast), and trial block (Block 1, Block 2 and Block 3) as factors. Neither the main effect of experiment nor any interactions involving experiment as a factor were significant sources of variance, all Fs < 1. Thus, the results of the overall analysis are consistent with the conclusion that Experiment 2B was a successful replication of Experiment 2A.
The only significant effect in the overall analysis was the interaction between task and trial block, F (2,376) = 7.65, p < .001. As suggested by Figure 3, which shows the combined result from both experiments, this interaction reflects the greater sensitivity of the contrast relative to the recognition task in Block 1, t (190) = 2.87, p < .01, and in Block 2, t (190) = 2.17, p < .05, coupled with the greater sensitivity of the recognition relative to the contrast task in Block 3, t (190) = 2.44, p < .05.
Figure 3.
Mean sensitivity (A') of the recognition and contrast tasks for the combined data from Experiments 2A and 2B. (Bars indicate standard errors.)
Given the logic underlying the experiments, the most important results are those obtained in Blocks 1 and 2. Even though the absolute sensitivity of the indirect contrast measure was relatively modest, it exhibited greater sensitivity than the direct recognition measure in these blocks of trials. Furthermore, additional analyses of performance indicated that the mean A' for the contrast task was significantly greater than chance in both Block 1 (.539) and Block 2 (.536), both ts (95) > 2.57, p < .025, but that the mean A' for the recognition task did not differ from chance in either Block 1 (.485) or Block 2 (.491). This greater sensitivity of the indirect contrast measure relative to the direct recognition measure provides an unequivocal demonstration of unconscious memory for the uncued words.
An unexpected finding was the increased sensitivity of the recognition task across trial blocks. This hypermnesia was statistically significant, F (2,190) = 4.54, p < .05, as performance on the recognition task, which did not differ from chance in the first two blocks of trials, was significantly greater than chance (.542) in the third block of trials, t (95) = 3.00, p < .01. This improvement in recognition memory differs qualitatively from the significant decrease across trial blocks in the sensitivity of the contrast measure, F (2,190) = 3.19, p < .05. In addition, this hypermnesia in recognition memory for the uncued words also differs qualitatively from the small decrease in recognition memory for the cued words across trial blocks found in Experiment 1.
Even though hypermnesia in recognition memory was unexpected, it is not inconsistent with previous findings. For example, Mandler et al. (1987) conducted an experiment that was very similar to the original Kunst-Wilson and Zajonc (1980) study. They found that recognition memory for geometric forms increased from 46.7% to 52.5% accuracy across two blocks of 10 trials. In addition, a measure of preference indicated that the percentage of old forms selected decreased from 61.7% in the first block trials to 56.7% in the second block of trials. These changes in performance across trial blocks for the direct recognition task and the indirect preference task parallel the changes found in Experiments 2A and 2B for the recognition and contrast tasks.
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