Comparing Direct (Explicit) and Indirect (Implicit) Measures to Study Unconscious Memory
Philip M. Merikle and Eyal M. Reingold
Page 7
Source: http://psych.utoronto.ca/users/reingold/publications/Merikle_&_Reingold_1991/
Taken together, both the results reported by Mandler et al. and the present results suggest that strategies for doing the recognition task may change across trial blocks. During the early trial blocks, it is reasonable to assume that subjects follow the instructions and attempt to decide whether each word is old or new. However, if no conscious information relevant to the old/new decision is available, then subjects may base their decisions on conscious but irrelevant aspects of the task (e.g., the number of letters in a word). Such a strategy would lead to chance performance. Over time, subjects may abandon these ineffective strategies based on consciously available information. As an alternative, many subjects may adopt a more passive strategy and simply base their decisions on general impressions. If this occurred, then the recognition task would in fact become an indirect task. In effect, what is being suggested is that the hypermnesia reflects a release from the interference produced during early trials when irrelevant conscious information is used to guide performance. Once these ineffective strategies are abandoned, the recognition task becomes a sensitive indicator of unconscious influences. This speculative interpretation provides a reasonable account of the hypermnesia found in Experiments 2A and 2B, as well as by Mandler et al. (1987), and it suggests that strategy changes over trial blocks may be an important determinant of the relative sensitivity of different tasks.
General Discussion
According to the logic underlying the approach advocated by Reingold and Merikle (1988), unconscious memory is demonstrated whenever an indirect measure exhibits greater sensitivity than a comparable direct measure of memory. Given this logic, the greater sensitivity of the indirect contrast measure relative to the direct recognition measure in Experiments 2A and 2B necessarily implicates unconscious processes. Likewise, previous findings demonstrating greater sensitivity for indirect than for comparable direct measures of memory (e.g., Eich, 1984; Kunst-Wilson & Zajonc, 1980) also provide strong support for unconscious memory. Thus, both the present results and previous findings provide convincing demonstrations of memory without conscious awareness in normal adults. In addition, given that the results of Experiments 2A and 2B extend the generality of previous findings to another indirect task and another type of encoding manipulation, the present results suggest that greater relative sensitivity of indirect relative to direct measures is a phenomenon that may occur under a wide variety of experimental conditions.
The idea that indirect measures may be more sensitive than direct measures to unconscious influences is certainly not new. One of the earliest proponents of this view was Poetzl (1917) who claimed to demonstrate that unconsciously perceived information tends to emerge later in the content of subjects' dreams. The current widespread interest in comparing direct and indirect measures of memory is also based on the assumption, made either explicitly or implicitly, that indirect tasks are somehow more sensitive than direct tasks to unconscious influences. Consequently, whenever experimental results demonstrate a dissociation between a direct and an indirect task (e.g., Graf & Mandler, 1984; Kunst-Wilson & Zajonc, 1980), it is tempting to interpret such findings as evidence for unconscious processes.
The method for comparing the relative sensitivity of direct and indirect measures of memory illustrated by the present experiments extends and refines these earlier approaches to the study of unconscious processes. As noted previously, one problem complicating many comparisons of direct and indirect measures is that the measures are often quite dissimilar. Thus, interpretation of any observed dissociations is compromised by the fact that differences in performance across tasks may simply reflect task differences and not reflect differences in the underlying processes mediating performance. Matching tasks in terms of the methodological criteria proposed by Reingold and Merikle (1988) ensures comparability of direct and indirect measures and allows for a more straightforward interpretation of any findings indicating greater sensitivity of an indirect measure.
An important advantage of using comparable direct and indirect measures to study unconscious processes is that the methodological requirements are less stringent and the a priori assumptions more minimal than required by many other approaches. Often, when the sensitivity of direct and indirect tasks is compared, it is assumed that the direct measure must indicate null sensitivity if unconscious processes are to be demonstrated convincingly (e.g., Eich, 1984; Holender, 1986; Kunst-Wilson & Zajonc, 1980). Not only is true null sensitivity difficult to demonstrate, but null sensitivity is only meaningful if it is assumed that the direct measure provides an exhaustive index of all relevant conscious experience (Reingold & Merikle, 1988, 1990). If this exhaustiveness assumption is not made, then conscious processes may be involved even when a designated direct measure indicates null sensitivity. By using comparable direct and indirect measures, both the methodological problems associated with demonstrating null sensitivity and logical problems associated with justifying the exhaustiveness assumption are avoided. Rather, with comparable direct and indirect measures, unconscious processes are implicated whenever the indirect measure is more sensitive than the direct measure, even if the direct measure indicates considerable sensitivity.
When direct and indirect measures are comparable, it is also unnecessary to make any assumptions concerning consciousness at the time of initial encoding in order to study unconscious influences at the time of memory retrieval. In previous studies, unnecessary and difficult to justify assumptions have been made, even when the direct and indirect measures have been well matched. For example, both Eich (1984) and Kunst-Wilson and Zajonc (1980) assumed that the stimuli which were later remembered unconsciously were also perceived unconsciously. Eich assumed that the selective attention manipulation ensured that the unattended words were perceived without conscious awareness, and Kunst-Wilson and Zajonc assumed that brief exposures of the random polygons ensured that the subjects were never consciously aware of the stimuli. Without considerable converging evidence, these assumptions are difficult to justify. Fortunately, both assumptions are completely unnecessary. As noted by Reingold and Merikle (1988, 1990), with comparable direct and indirect measures, greater sensitivity of the indirect measure implicates unconscious memory processes, independent of any assumption concerning conscious awareness at the time of initial presentation.
At the empirical level, a consistent picture is beginning to emerge concerning some of the conditions under which it is possible to demonstrate unconscious processes. One empirical generalization is that indirect measures appear to exhibit greater sensitivity than comparable direct measures only when relatively few test trials are administered. Thus, in Experiments 2A and 2B, the indirect contrast measure was more sensitive than the direct recognition measure in the first two blocks of 32 test trials but not in the third block of 32 trials. Similarly, in previous studies involving comparable direct and indirect measures, successful demonstrations of greater relative sensitivity for the indirect measure have been based on as few as 6 test trials (Bornstein et al., 1987), as many as 64 test trials (Eich, 1984), or most frequently, 10 test trials for each task (e.g., Kunst-Wilson & Zajonc, 1980; Mandler et al., 1987; Seamon et al., 1984). A second empirical generalization is that indirect measures are more likely to exhibit greater sensitivity than direct measures when initial processing or encoding is limited. Thus, both brief exposures (e.g, Kunst-Wilson & Zajonc, 1980) and limited allocation of attentional resources, as demonstrated in Experiments 2A and 2B and in Eich's (1984) earlier study, are two conditions leading to greater relative sensitivity for indirect relative to comparable direct measures. Interestingly, Poetzl (1917) suggested that brief exposures and inattention were two equivalent empirical conditions for demonstrating unconscious processes.
The results of the present experiments demonstrate the value of comparing the relative sensitivity of comparable direct and indirect measures to study unconscious processes. When direct and indirect tasks are matched on all characteristics except instructions, greater sensitivity for the indirect measure necessarily implicates unconscious processes, given a minimal a priori assumption. The success of Experiments 2A and 2B suggests that characteristics of unconscious processes in normal adults can be revealed by studying other pairs of comparable direct and indirect tasks. Although we do not suggest that an approach based on comparisons of the relative sensitivity of comparable direct and indirect measures is the only way to investigate unconscious processes, we do suggest that this approach may provide more definitive results than many other approaches because fewer and more minimal a priori assumptions are required to interpret any observed dissociation between measures.
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