Comparing Direct (Explicit) and Indirect (Implicit) Measures to Study Unconscious Memory
Philip M. Merikle and Eyal M. Reingold
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Source: http://psych.utoronto.ca/users/reingold/publications/Merikle_&_Reingold_1991/
Matching direct and indirect memory tasks on these three task characteristics constrains the number of possible interpretations of any observed dissociation between tasks. Furthermore, Reingold and Merikle (1988) suggested that comparisons of the relative sensitivity of comparable direct and indirect measures have the potential to provide definitive evidence for unconscious perception and memory. This alternative approach to the study of unconscious processes is based on the following minimal a priori working assumption: "The sensitivity of a direct discrimination is assumed to be greater than or equal to the sensitivity of a comparable indirect discrimination to conscious, task relevant information." (p. 556, Reingold & Merikle, 1988). In terms of the present context, the rationale underlying this assumption is that conscious information relevant to an old/new discrimination, if it exists, should be used equally or more efficiently when subjects are instructed to make an old/new discrimination (i.e., a direct task) than when subjects are not so instructed (i.e., an indirect task). Conversely, it is difficult to imagine circumstances in which conscious information relevant to an old/new discrimination would enhance performance more when subjects were not instructed to make the old/new discrimination, than when subjects were explicitly instructed to make the old/new discrimination.
Although any a priori assumption can be criticized, the working assumption proposed by Reingold and Merikle (1988) has two distinct advantages relative to the assumptions underlying many other approaches to the study of unconscious processes. First, the assumption is stated explicitly and thus open to evaluation. Second, the assumption is much more minimal than many assumptions which relate direct and indirect tasks to conscious and unconscious processes. In fact, with the proposed working assumption, much of the controversy over the measurement of awareness is bypassed because no constraints are placed on how direct and indirect tasks may be related to conscious and unconscious processes. Rather, given the proposed assumption, both direct and indirect tasks may reflect conscious, unconscious or both conscious and unconscious processes. Thus, even in the absence of a valid measure of awareness (see Erdelyi, 1986, Reingold & Merikle, 1990; Schacter, 1987), the proposed assumption provides a basis for studies of unconscious processes.
The important consequence of this very minimal working assumption is that unconscious memory processes are implicated whenever an indirect measure shows greater sensitivity than a comparable direct measure to an old/new discrimination. This is the case because the assumption rules out the possibility that superior performance on the indirect task is attributable to conscious task relevant information. Therefore, by default, whenever an indirect measure indicates greater sensitivity than a comparable direct measure, it must reflect a greater sensitivity of the indirect measure to unconscious, task relevant information. It is important to emphasize that this interpretation is warranted only if the direct and the indirect measures are truly comparable except for the presence or absence of a reference to the discrimination of interest in the instructions given to subjects. Otherwise, the greater sensitivity of an indirect measure may reflect a methodological artifact rather than an unconscious process.
Empirical support for the possible value of comparing the relative sensitivity of comparable direct and indirect measures in the study of unconscious processes comes from studies of unconscious memory. The results of a number of studies indicate that, at least under certain conditions, indirect measures do in fact exhibit greater sensitivity to an old/new discrimination than comparable direct measures. In one important study, Kunst-Wilson and Zajonc (1980) initially showed subjects ten irregular geometric shapes, with each shape being presented five times for a very brief, 1-msec duration. Following these initial exposures, the subjects were shown 10 pairs of shapes, one old and one new, and they were instructed either to indicate which member of each pair had been presented previously (a direct measure) or to choose the shape they preferred (an indirect measure). With the indirect measure based on preference, the subjects chose the old stimulus in 60% of the pairs. However, with the direct recognition test, old stimuli were selected in only 48% of the pairs, which approximated the chance level of performance. These basic results have been replicated by other investigators (e.g., Bonnano & Stillings, 1986; Seamon, Marsh, & Brody, 1984). In addition, Mandler, Nakamura and Van Zandt (1987) used a similar procedure and found that a variety of tasks requiring indirect discriminations (preference, brightness, darkness) were more sensitive to the old/new discrimination than comparable direct measures of stimulus recognition. According to the logic underlying comparisons between comparable direct and indirect measures, these findings constitute strong evidence for unconscious memory. However, with one exception (Bornstein, Leone, & Galley, 1987), the pattern of results originally reported by Kunst-Wilson and Zajonc (1980) has only been demonstrated with a very specific stimulus set, namely irregular polygons selected from those of Vanderplas and Garvin (1959). Clearly, to establish the generality of these findings, it is necessary to compare the relative sensitivity of comparable direct and indirect measures of memory across other experimental manipulations and sets of stimulus materials.
A study reported by Eich (1984) represents a potentially useful experimental approach. In this study, a version of the dichotic listening paradigm was used. During the study phase, subjects shadowed a prose passage presented on one auditory channel, and concurrently, on the non-shadowed channel, pairs of words were presented. Each word pair consisted of a homophone (e.g., FARE/FAIR) and a context word (e.g., TAXI) which biased interpretation of the homophone toward the less common meaning . In the test phase of the study, subjects were presented auditorily with old and new homophones and they were required either to make an old/new recognition judgement (direct instructions) or to spell the homophone (indirect instructions). The results indicated that the recognition task was completely insensitive to the old/new dimension. However, the homophone spelling task was sensitive to the old/new dimension in that the subjects were biased toward the less common spellings of the homophones.
Eich's study is completely consistent with the approach advocated by Reingold and Merikle (1988) for comparing the relative sensitivity of direct and indirect measures of memory to establish unconscious processes. The direct recognition task and the indirect spelling bias task were comparable except for the instructions given to the subjects. Thus, according to the logic of Reingold and Merikle's approach, the dissociation between recognition memory and spelling bias provides evidence that the non-shadowed words were remembered unconsciously. It is important to emphasize that this conclusion does not require any assumption concerning whether or not the non-shadowed words were truly unattended at the time of encoding. Eich (1984) assumed that the non-shadowed words were perceived without attention, but this difficult, if not impossible, to prove assumption concerning initial encoding is not required to demonstrate unconscious memory. Rather, according to the logic underlying comparisons of comparable direct and indirect measures, Eich's results demonstrate unconscious memory because the indirect homophone spelling task exhibited greater sensitivity than the direct recognition task at the time of retrieval.
This analysis of Eich's results in terms of the logic proposed by Reingold and Merikle (1988) suggests that selective attention may represent a useful experimental manipulation for documenting unconscious memory. Accordingly, in the present experiments, we explored the effects that allocation of visual attention may have on the relative sensitivity of a direct measure of old/new recognition memory and a comparable indirect measure. Each experiment consisted of two phases. During the study phase, subjects were presented with pairs of words and they were required to name one cued word in each pair. During the test phase, new words and either the previously cued words (Experiment 1) or the previously uncued words (Experiments 2A and 2B) were presented against a background mask. The subjects were required to judge whether a word was old or new (direct task) or whether the contrast between a word and the mask was high or low (indirect task).
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