حافظه ضمنی، حافظه آشکار و تصویر اثر عجیب و غریب بودن

The experiments reported here were designed to explore the bizarreness effect in implicit and explicit memory by using simple line drawings of common objects (normal vs. bizarre). Each drawing was presented alone under mixed-list encoding conditions. Results showed that performance on explicit conceptual memory tests (cued recall in Experiments 1 and 2) was higher when material was studied in a bizarre format. No such effect was found with implicit conceptual tests (free association in Experiment 1 and category association in Experiment 2). Experiment 3 showed no effect of bizarreness with word-fragments as perceptual implicit or explicit test cues. These dissociative results have important theoretical implications for the comprehension of memory processes.

There has been a great deal of interest in implicit and explicit memory (Graf and Schacter, 1985) stimulated in particular by the finding of several dissociations between these two hypothesized memory systems (for reviews, see Richardson-Klavehn and Bjork, 1988; Roediger and McDermott, 1993; Schacter, 1987). Whereas in explicit memory tests subjects are instructed to retrieve intentionally previously studied items, in implicit tests the study episode is not mentioned and retention is measured indirectly as performance facilitation on a seemingly unrelated task. This facilitation, called priming effect, is an index of implicit memory (Tulving and Schacter, 1990). This classification was further elaborated by Roediger et al. (1989)in the framework of their processing view of memory (Roediger and Weldon, 1987). The main assumptions of their approach can be summarized as follows. First, performance on memory tests is improved as long as the cognitive operations involved in the test recapitulate or overlap those engaged during learning. Second, implicit memory tests usually require different mental processes than do explicit tests and consequently they differentially benefit from these processes. Third, the most commonly used implicit memory tests draw primarily on perceptual or data-driven processes used in word recognition and object recognition. Such tests are referred to as perceptual implicit tests. One common test is the word-fragment completion, in which subjects are asked to find the missing letters of a word from a fragment such as e_ _ p_ _ n_. Generally subjects are more likely to find the solution if they have been presented with the word “elephant” in a previous stage (see Tulving et al., 1982). Fourth, most explicit memory tests that involve recall and recognition draw largely on conceptual processing (elaboration, organization, meaningful processing and the like), and can therefore be classified as conceptual explicit tests. Fifth, the perceptual/conceptual contrast is not coextensive with the implicit/explicit distinction: conceptual implicit tests and perceptual explicit tests can be implemented. In the case of conceptual implicit tests, subjects are given a cue that is meaningfully related to the target item that was studied beforehand. In the word association test, they are instructed to freely associate to the cue (e.g. tusk for elephant). In the category association test, they are asked to produce members of the relevant category (e.g., animals). In the case of perceptual explicit tests, subjects are instructed to retrieve encoded information with the help of some perceptual display similar to the target. A word-fragment completion test stressing on intentional remembering (word-fragment cued recall) may be considered as a perceptual explicit test (e.g. Weldon et al., 1989; Roediger et al., 1992). In sum, the implicit/explicit and perceptual/conceptual classifications can be combined to yield four kinds of tests: implicit perceptual tests (e.g. word-fragment completion); implicit conceptual tests (e.g., category generation or free association); explicit perceptual tests (e.g., word-fragment cued recall); and explicit conceptual tests (e.g., free recall or semantic cued recall). It is interesting to note that using the same test cues, one can develop an implicit or an explicit test by manipulating the critical instructions used to implement the tests. Thus, using word-fragments as test cues, we can ask subjects to retrieve material from the study episode (perceptual explicit test) or simply to complete spaces with letters in order to produce a word (perceptual implicit test). Moreover, using associates or categories, one can instruct subjects to retrieve material from the study episode (conceptual explicit tests), to produce words meaningfully related to the target, or to produce members of a relevant category (conceptual implicit tests). Schacter et al. (1989)have referred to the retrieval intentionality criterion as the distinguishing feature between explicit and implicit tests. The retrieval intentionality criterion was implemented by several researchers (e.g. Graf and Schacter, 1987 and Graf and Schacter, 1989; Nicolas and Carbonnel, 1996) for the purpose of studying relations between explicit and implicit memory. All of them were looking for variables to dissociate implicit and explicit tests. A potentially interesting variable in this respect is imagery. Pictures are generally better remembered than their corresponding verbal representations on conceptual explicit memory tests such as free recall and recognition (cf., Madigan, 1983; Paivio, 1971, Paivio, 1983 and Paivio, 1986). Pictures are more memorable than words because they engage more of the elaborative encoding processes that are required by conceptual explicit memory tests. When the test cues consist of word-stems or word-fragments (i.e. perceptual tests), studied words produce more priming than did studied pictures (see Roediger et al., 1992). However, a reverse pattern of results is obtained with these variables under explicit test instructions when the same word-fragments or word-stems are used as cues. In the transfer-appropriate framework, it is assumed that priming depends on the degree to which the perceptual and conceptual operations performed during testing match those performed during study. Because the surface features of the words studied are similar to those of the test items, the perceptual analyses of both types of stimuli are similar, leading to stronger priming. The contradictory results obtained with implicit conceptual cues are well illustrated in two recent papers (Nicolas, 1995; Weldon and Coyote, 1996) concerned with picture superiority effect in memory. The logic used in these experiments was based on the assumption that pictures do involve more conceptual processing than words (see Weldon and Roediger, 1987; Weldon et al., 1989). According to the transfer-appropriate processing hypothesis, if pictures initiate more elaborated codes than do words and if a test is sensitive to conceptual processing, then pictures should lead to better performance than words, regardless of the implicit/explicit dimension of the test. However, results failed to show any significant advantage of pictures over words (Weldon and Coyote, 1996; see also Nicolas, 1995, Exp. 2) in implicit conceptual tests. On the other hand, when an explicit test is used, pictures were better recalled than words, producing a functional dissociation. Nicolas (1995)and Weldon and Coyote (1996)concluded that conceptual processing plays a minor role in picture recall superiority and that perceptual distinctiveness might be a more relevant factor in intentional retrieval. Nicolas (1995)assumed that conceptual implicit tests are based mainly on conceptual information or processing, whereas conceptual and perceptual explicit tests are based on additional information provided by pictures (e.g., sensory information). In his sensory-semantic model, Nelson (1979)suggested that even if pictures and words refer to the same semantic units, pictures are more memorable because they have more distinctive sensory codes than words. Thus, the physical distinctiveness of the material seems be a relevant factor in conceptual explicit memory, but not in conceptual implicit memory. It seems that explicit memory tests involve some form of conceptual and perceptual processing and not just an increase in conceptual processing as hypothesized by Weldon et al. (1995). If visual distinctiveness can account for picture superiority effect in explicit memory, it should be possible to test directly this hypothesis using bizarre images that enhance distinctiveness (see Schmidt, 1991). The present series of experiments is intended to test directly whether visual distinctiveness is an important variable in recollective experience from pictures. In the literature it is found that bizarre images are generally perceived as more distinctive than normal ones (see Webber and Marshall, 1978; Einstein and McDaniel, 1987). Empirical evidence supports the mnemonic benefit of bizarre pictures over normal pictures. One critical factor in determining the mnemonic advantage of bizarre pictures is the type of memory test. Indeed, studies have shown positive effects of bizarre pictures in free recall, but not in recognition (Cornoldi et al., 1988; McDaniel and Einstein, 1986; Pra Baldi et al., 1985; Wollen and Cox, 1981). Another important factor in determining the bizarreness effect concerns the structure of the list. Mixed lists, in which both bizarre and common materials are presented lead to a bizarre picture advantage (e.g. McDaniel and Einstein, 1986; O'Brien and Wolford, 1982; Pra Baldi et al., 1985) contrary to what was observed with lists in which all the material presented is bizarre or common (e.g., Collyer et al., 1972; Cox and Wollen, 1981; Marshall et al., 1980). According to Einstein and McDaniel (1987), the distinctiveness view seems to be the most promising for integrating the existing results. For example, distinctive memory traces may be more easily activated under circumstances such as free recall, because of better perceptual discrimination, less susceptibility to the effects of interference, and/or the possibility that they may be more precisely reconstructed from the information available at retrieval time. A recent experiment designed by Nicolas and Marchal (1996)explored for the first time the bizarreness effect in implicit memory. The material used was composed of simple line drawings of common objects (normal or bizarre), with each drawing presented alone under mixed-list conditions. Three different conceptual memory tests were used: free recall, cued recall, and word association (a conceptual implicit memory test). Priming effects in word association test were obtained with normal and bizarre pictures. However, the bizarre picture advantage that was observed using explicit memory tests was absent in the implicit word association test. Thus, the bizarreness effect was not found in a task involving implicit memory. Some researchers (for a review see Einstein and McDaniel, l987) proposed that the bizarreness effect was a conceptual phenomenon. For example, according to Merry (1980)(see also Wollen and Cox, 1981), bizarre images receive extra conceptual processing and are therefore better stored than common images. Other theorists have suggested that the bizarreness effect is based on an enhanced perceptual distinctiveness. If we suppose that the bizarreness effect is a conceptual phenomenon, then according to the transfer-appropriate processing view, priming should be higher for bizarre images than normal ones when implicit conceptual tests are used. Yet results obtained by Nicolas and Marchal (1996)seem to show that it is not the case. But if we assume perceptual distinctiveness (Nicolas, 1995), then the transfer-appropriate processing view predicts no advantage of bizarre images over common ones using conceptual implicit memory tests. By contrast, conceptual explicit tests may benefit from distinctive perceptual and conceptual information. Another possible interpretation of the data collected by Nicolas and Marchal (1996)is that the bizarre images did in fact produce more conceptual processing, but not the type of processing that was useful for this kind of implicit memory test, namely free association. This alternative interpretation suggests that it would be worth developing and testing the bizarreness effect with other conceptual implicit tests. The purpose of the experiments reported here was to further examine the role of distinctiveness in implicit and explicit memory. Distinctiveness was assessed by manipulating the form of the pictures, bizarre versus normal. In the first experiment we manipulated two variables (bizarreness and delay) to compare the pattern of results obtained in word association (a conceptual implicit test) and semantic cued recall (a conceptual explicit test). According to the perceptual hypothesis (Nicolas, 1995; Nicolas and Marchal, 1996), a bizarreness effect was expected only in the explicit version of the test because only conceptual processes are involved in conceptual implicit tests. In contrast, according to the conceptual hypothesis, bizarre images should receive extra conceptual processing and therefore a bizarreness effect would also be expected in the word-association test. The second experiment was designed to extend previous results to another conceptual test, namely category production. The last experiment used word-fragments as test cues; here bizarreness was studied using both an implicit and an explicit perceptual memory test.