Involuntary conscious memory and the method of opposition

The role of involuntary aware memory in the implicit stem and fragment completion tasks: a selective review

In this article I argue that an awareness of the study episode that arises involuntarily during an implicit stem/fragment completion test can under some conditions lead to enhanced repetition priming effects, even though subjects are not engaged in intentional retrieval. I review findings that are consistent with this possibility, which include the effects of depth of processing, and of typography match and new association priming following deep encoding. A theoretical account of involuntary aware memory couched within Moscovitch's (1995b) memory systems framework which suggests that the medial-temporal lobe/hippocampal (MTL/H) complex functions as a memory module is outlined. A putative mechanism is proposed in which involuntary aware memory of a studied item enhances the size of repetition priming effects by guiding its selection in preference to the competitors.

Conscious and unconscious influences of memory: temporal dynamics

Changes in the conscious and unconscious influences of memory over time were assessed in two experiments by using a variant of the process-dissociation procedure. In both experiments, performance on a stem-completion task was measured under both inclusion and exclusion instructions. Across the two experiments, there were four different retention intervals: 2 minutes, 2 days, 2 weeks, and 2 months. The results indicated that conscious influences decreased systematically across retention interval. In contrast, unconscious influences of memory in the absence of conscious influences increased between 2 minutes and 2 days, and then remained relatively stable from 2 days to 2 weeks to 2 months. These results stand in apparent contrast to those of McBride and Dosher (1999), which showed equal rates of forgetting for conscious and unconscious influences of memory on performance. The implications for models of the relation between conscious and unconscious influences of memory on performance are discussed.

A dissociation in infants' memory for stimulus size: evidence for the early development of multiple memory systems

Adults' memory performance on recognition (explicit memory) tests is sensitive to stimulus size, but their performance on priming (implicit memory) tests is not. This memory dissociation is taken as evidence for two, functionally distinct memory systems. Young infants, however, are thought to possess only a single representational system that supports implicit memory; the system that supports explicit memory is thought not to mature before 8-9 months of age. In two experiments with 54 infants, we asked if 3-month-olds exhibit a memory dissociation for stimulus size on recognition and priming tests. All infants learned to move a mobile displaying +s of a given size. In Experiment 1, infants recognized +s in the original size but not 33% smaller or larger. In Experiment 2, +s were effective memory primes in a reactivation task, irrespective of size. The finding that young infants exhibit a memory dissociation for stimulus size adds to growing evidence that two memory systems are functional from early in development.

Primacy and recency in primed free association and associative cued recall

Two experiments compared the serial positions of primed words in an implicit free association test with words recalled in a cued recall test. In both tests, weakly or strongly related word pairs were studied, and the first words of each pair formed the test cues. In the implicit test, weakly related words pairs showed primacy and extended recency effects but strongly related word pairs did not. In the explicit test, both weakly and strongly related word pairs showed primacy and extended recency effects. These functional dissociations between implicit and explicit memory tests indicate that strongly related word pairs are encoded together because they have unitized memory representations that function as integrated units without requiring any additional associative links to be made, but that an additional system or process is required to strengthen weakly related word pairs during encoding. In addition, a further additional system or process is accessed by explicit retrieval.

The effects of levels-of-processing and organization on conceptual implicit memory in the category exemplar production test

The distinction between item-specific and relational information (Hunt & Einstein, 1981) may be relevant to accounts of conceptual priming in the category exemplar production task. In three experiments, the implications of this hypothesis were tested by examining the effects of organization and levels-of-processing (LOP) on this implicit test. Consistent with the hypothesis, the effects of LOP were greater when study lists were organized by category than when they were presented randomly. Furthermore, when subjects claiming test awareness or intentional retrieval were excluded from the analysis, the LOP effect was reduced (and, in fact, eliminated) in the random list condition but remained robust in the categorized condition. Finally, the experimental design of the LOP manipulation (i.e., mixed-list within, blocked-list within, or between subjects) did not moderate the effects of LOP on this priming task.

Manipulation of familiarity reveals a necessary lexical component of the word-stem completion priming effect

These experiments were motivated by the idea that many types of nondeclarative memory are by-products arising from the plasticity that is inherent in much of the nervous system. We hypothesized that two types of repetition priming, word-stem completion (WSC) priming and perceptual identification (PI) priming, rely on different mechanisms because the WSC task and the PI task engage different cognitive and brain processes. We tested this hypothesis by manipulating word familiarity. The results, impaired WSC priming but intact PI priming with unfamiliar words, indicate that WSC priming relies primarily on a modification mechanism, whereas PI priming relies primarily on an acquisition mechanism. Our conclusions are consistent with component processes theories of nondeclarative memory.

Memory, consciousness and neuroimaging

Neuroimaging techniques that allow the assessment of memory performance in healthy human volunteers while simultaneously obtaining measurements of brain activity in vivo may offer new information on the neural correlates of particular forms of memory retrieval and their association with consciousness and intention. We consider evidence from studies with positron emission tomography and functional magnetic resonance imaging indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence concerning the question of whether two components of explicit retrieval--intentional or effortful search and successful conscious recollection--are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively. Last, we consider recent efforts to probe the relation between the phenomenological character of remembering and neural activity. In this instance we broaden our scope to include studies employing event-related potentials and consider evidence concerning the neural correlates of qualitatively different forms of memory, including memory that is specifically associated with a sense of self, and the recollection of particular temporal or perceptual features that might contribute to a rich and vivid experience of the past.

Awareness of remembering achieved through automatic and conscious processes in multiple sclerosis

Fifty multiple sclerosis (MS) and forty-one matched control subjects were administered a word stem completion task and the California Verbal Learning. Test (CVLT). As predicted, priming in a conventional "implicit" task did not differ for MS and control groups, and under "explicit" instructions verbal list recall was significantly lower in the MS group with recognition intact. Application of the process dissociation procedure (Jacoby, Toth, & Yonelinas, 1993) to the word stem task demonstrated that conscious and unconscious processes both contribute to remembering in MS. Exploratory analyses found no group differences in words remembered under inclusion nor exclusion conditions, though preliminary estimates for MS automatic processing exceeded those for controls. As predicted, prospective metamemory judgments reflected subsequent performance for both groups in the inclusion but not the exclusion condition. By contrast, retrospective monitoring for both groups reflected memory performance in both conditions. However post hoc analyses demonstrated that those MS subjects who employed more automatic processing were less aware retrospectively of their successful remembering under exclusion than MS subjects who used less automatic processing.

Levels of processing and single word priming in amnesic and control subjects

This paper describes an experiment which examined how levels of processing (LOP) affected word fragment completion in a group of Wernicke-Korsakoff patients, a group of patients with closed head injury, and matched controls. The data showed that both the memory-impaired groups and the controls showed a LOP effect but that the effect was larger in controls. Data from other studies are reviewed and, in conjunction with the present findings, it is concluded that LOP effects obtained when memory-impaired individuals are tested using implicit memory tasks arise mainly from the contribution of lexical processing of targets and from contamination by explicit recollection.

On the logic of testing the independence assumption in the process-dissociation procedure

The process-dissociation procedure is designed to provide quantitative estimates of the influence of explicit and implicit memory in a variety of tasks. The procedure relies on the assumption that these two forms of memory produce independent influences on performance. Prior investigators have attempted to test this assumption by determining whether the parameter representing the influence of implicit memory (denoted A) is constant across experimental conditions. I argue that the constancy of A cannot provide an appropriate test of the independence assumption, because (1) the prediction of constancy can be generated without the assumption of independence, obviating the need to posit independence; and (2) the constancy of A does not necessarily imply independence, even if one assumes that a dependency hypothesis, supplemented by ancillary assumptions (Curran & Hintzman, 1995), predicts differences in A. I close by emphasizing that we can test the independence assumption by using standard procedures that compare the fit of a model that assumes independence with the fit of a model that assumes dependence.

On the relations among priming, conscious recollection, and intentional retrieval: evidence from neuroimaging research

Neurobiological distinctions among forms of memory have been investigated mainly from the perspective of lesion studies in nonhuman animals and experiments with human neurological patients. We consider recent neuroimaging studies of healthy human volunteers using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) that provide new information concerning the neural correlates of particular forms of memory retrieval. More specifically, we consider evidence indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence suggesting that two components of explicit retrieval-intentional or effortful search and successful conscious recollection-are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively.

Consequences of violating the assumption of independence in the process dissociation procedure: a word fragment completion study

In three experiments that used levels of processing and study time manipulations as independent variables in a word fragment completion task, the validity of the assumption of independence between recollection and automatic influences of memory was assessed. This assumption underlies the use of the process dissociation procedure (Jacoby, 1991), a tool suggested for distinguishing the different contributions of recollection and automatic influences of memory. Overall, it appeared that semantic processing, as compared with physical processing at study, positively affected recollection but negatively affected automatic influences of memory in word fragment completion. This negative effect on the automatic influences was reduced when the available study time decreased. The incompatibility of these results with the assumption of independence between recollection and automatic influences of memory and their impact on the applicability of the process dissociation procedure are discussed.

Impaired word-stem completion priming but intact perceptual identification priming with novel words: evidence from the amnesic patient H.M

We hypothesized that word-stem completion (WSC) priming and perceptual identification (PI) priming, two types of repetition priming, rely on different cognitive and neural mechanisms: WSC priming on a modification mechanism that influences lexical retrieval, and PI priming on plasticity in pre-lexical perceptual systems. We compared the priming performance of the amnesic patient H.M. with words that came into common usage after the onset of his amnesia, and thus were novel to him (post-1965 words), and with familiar (pre-1953) words. We also tested age- and education-matched normal control subjects (NCS) and a patient with anterograde amnesia of recent onset (P.N.). The modification hypothesis predicted that H.M. would fail to show WSC priming with post-1965 words because pre-existing lexical representations of the test stimuli would be necessary for priming to occur. H.M.'s WSC priming score in the post-1965 condition did not differ from 0, and was inferior to the performance of NCS and of P.N. In contrast, H.M. displayed normal WSC priming in the pre-1953 condition. H.M. also showed robust and equivalent levels of PI priming in both conditions. A final experiment demonstrated preserved post-1965 word PI priming in H.M. when his baseline performance was matched with his post-1965 WSC priming baseline score. Our results challenge models that assume that most kinds of verbal repetition priming rely on the same or similar perceptual mechanisms.

Voluntary and involuntary access to autobiographical memory

Involuntary autobiographical memories recorded in a diary study are compared to voluntary autobiographical memories retrieved in response to verbal cues in a laboratory. The verbal cues were generated to be comparable to the cues that were found to elicit the involuntary memories. The findings demonstrate that voluntary and involuntary retrieval may access different samples of autobiographical memories. The voluntary memories were (1) less specific, (2) more frequently rehearsed, and (3) less emotionally positive than the involuntary memories. A reanalysis of the diary study examined conditions of involuntary retrieval. The memories occurred most frequently when attention was diffuse. They were typically triggered by environmental cues matching central features of the remembered event. The findings are discussed in relation to current models of autobiographical memory.

Encapsulation of implicit and explicit memory in sequence learning

Contrasts between implicit and explicit knowledge in the serial reaction time (SJRT) paradigm have been challenged because they have depended on a single dissociation; intact implicit knowledge in the absence of corresponding explicit knowledge. In the SRT task, subjects respond with a corresponding keypress to a cue that appears in one of four locations. The cue follows a repeating sequence of locations, and subjects can exhibit knowledge of the repeating sequence through increasingly rapid performance (an implicit test) or by being able to recognize the sequence (an explicit test). In our study, amnesic patients were given extensive SRT training. Their implicit and explicit test performance was compared to the performance of control subjects who memorized the training sequence. Compared with control subjects, amnesic patients exhibited superior performance on the implicit task and impaired performance on the explicit task. This crossover interaction suggests that implicit and explicit knowledge of the embedded sequence are separate and encapsulated and that they presumably depend on different brain systems.

Full versus divided attention and implicit memory performance

Effects of full and divided attention during study on explicit and implicit memory performance were investigated in two experiments. Study time was manipulated in a third experiment. Experiment 1 showed that both similar and dissociative effects can be found in the two kinds of memory test, depending on the difficulty of the concurrent tasks used in the divided-attention condition. In this experiment, however, standard implicit memory tests were used and contamination by explicit memory influences cannot be ruled out. Therefore, in Experiments 2 and 3 the process dissociation procedure was applied. Manipulations of attention during study and of study time clearly affected the controlled (explicit) memory component, but had no effect on the automatic (implicit) memory component. Theoretical implications of these findings are discussed.

Differences in intentional retrieval during inclusion and exclusion tasks

The process dissociation approach assumes that intentional retrieval processes operate in the same manner during inclusion and exclusion tasks. The present research shows that this assumption is not always tenable. After completing a word stem according to inclusion or exclusion instructions, subjects were asked whether they had recalled a word presented during study while completing the stem. Stem completion latencies were also recorded. When the exclusion task was described as a creativity test (Experiment 2), subjects recalled almost twice as many words during inclusion than during exclusion trials. Also, completion latencies were longer on inclusion trials, suggesting that on these trials subjects tried hard to remember old words. When instructions stressed that recall of old words was as important on exclusion as on inclusion trials (Experiment 1), recall rates did not differ significantly between both kinds of trials. However, completion latencies were significantly longer on inclusion trials, showing that, despite instructions, subjects still invested more effort in trying to remember old words during inclusion trials. The implications of these findings for future process dissociation research are discussed.

Unconscious influences on amnesics' word-stem completion

Amnesic patients and control subjects were asked to complete three-letter word-stems under one of three retrieval conditions. In a direct condition, they were told to use the stems as retrieval cues for words that had just been presented in a study list. In an indirect condition, they were told to use the first word that came to mind with no reference made to the study list. Finally, in an oppositional condition, they were told to use the first word that came to mind unless it had appeared on the study list. During the study list presentation, the patients and controls had analyzed each word according to either semantic (associating to each word) or graphemic (counting letters with enclosed spaces) instructions. The results revealed that the control subjects produced a different number of study words during retrieval as a function of retrieval instructions and encoding condition. The amnesics, however, did not vary their performance as a function of retrieval instructions. Under all conditions, they completed the word-stems far more frequently with words from the study list than would be expected by chance and they consistently produced more semantic than graphemic responses. We concluded that semantic analysis might affect the fluency with which an item occurs for the amnesic, but that the item itself remains independent of the source of that fluency for these patients. Thus, the level of analysis performed on a word during study can affect the unconscious performance of amnesic patients but is unavailable for use during conscious retrieval.

Event-related potentials and the recognition memory exclusion task

Subjects heard words that were presented in either a male or a female voice, and were required to perform one of two encoding tasks according to the gender of the voice. At test studied words were presented visually, along with a set of words new to the experiment. Subjects were required to respond on one key to words belonging to one of the two classes of studied word (targets), and to respond on a different key both to words belonging to the other study class (non-targets), and to words new to the experiment. In comparison to the event-related potentials (ERPs) elicited by new words, the ERPs elicited by correctly detected targets exhibited two temporally and topographically distinct positive going effects: one of these was phasic, showed a parietal maximum, and was larger over the left than the right hemisphere. The second effect was more sustained in time, frontally distributed, and was larger over the right hemisphere. The ERPs elicited by correctly classified non-targets contained the parietal effect only. These findings confirm that retrieval of contextual information in tests of recognition memory (recollection) is associated with two distinct ERP modulations. While one of these may be closely tied to process necessary for recollection, the other may reflect less obligatory processes which operate on the products of successful retrieval.

Implicit memory: what must theories of amnesia explain?

In their target article on explaining functional deficits in amnesia, Mayes and Downes (this issue) discuss the relevance of implicit memory. Our commentary considers a number of implicit memory phenomena that may be especially pertinent to understanding the functional deficits of amnesia. Recent evidence suggests that amnesic patients do not benefit normally from an exact perceptual match of stimuli between study and text. We propose that this impairment may reflect one manifestation of a more general deficit in associative binding of information across different brain subsystems. This idea helps to clarify the distinction between implicit and explicit memory, and suggests that studies of implicit memory can help to elucidate the functional deficits in amnesia.

An event-related potential study of word-stem cued recall

Event-related potentials (ERPs) were recorded from 13 scalp sites while subjects attempted to recall studied words using word-stems. If recall failed, stems were to be completed with the first suitable word to come to mind. To distinguish between correct completions accompanied and unaccompanied by explicit memory, subjects were required to make an overt recognition ("old/new") judgement for each completion. Semantically studied words were associated with higher levels of recall and recognition than were words subjected to non-semantic study. The sole ERP effect was a sustained positive shift in ERPs evoked by stems attracting correct completions that were correctly judged to be old. The shift was anteriorly distributed, and onset was around 300 ms post stimulus. It is interpreted as a reflection of processes either contributing to, or contingent upon, explicit memory retrieval.

Effects of lorazepam and diazepam on conscious and automatic memory processes

Recent studies exploring benzodiazepine memory effects have used the distinction between explicit and implicit tasks. There is now increasing evidence that implicit tasks can be "contaminated" by conscious uses of memory and that unconscious (automatic) use of memory can contaminate explicit tasks, leading to mistaken estimates of their respective influences on memory performance. The aim of the present double-blind, double-placebo study was to assess the memory effects of diazepam and lorazepam using a process-dissociation procedure in a stem-completion task, this procedure providing uncontaminated estimates of conscious and automatic memory processes. The memory task was administrated to 60 healthy volunteers randomly assigned to one of three parallel groups (placebo, diazepam 0.3 mg/kg, lorazepam 0.038 mg/kg). Lorazepam markedly reduced conscious as well as automatic influences of memory. Diazepam also reduced conscious uses of memory, albeit to a lesser extent than lorazepam, but did not decrease the influence of automatic memory. Secondary analyses showed that when the deleterious effect on conscious uses of memory was equated between a diazepam subgroup and the lorazepam group, only lorazepam impaired the automatic use of memory. This study strongly suggests a qualitative difference in the memory effects of the two benzodiazepines. It has some implications regarding the relationships between states of consciousness and memory processes.

Divided attention and indirect memory tests

Attentional state during acquisition is an important determinant of performance on direct memory tests. In two experiments we investigated the effects of dividing attention during acquisition on conceptually driven and data-driven indirect memory tests. Subjects read a list of words with or without distraction. Memory for the words was later tested with an indirect memory test or a direct memory test that differed only in task instructions. In Experiment 1, the indirect test was category-exemplar production (a conceptually driven task) and the direct test was category-cued recall. In Experiment 2, the indirect test was word-fragment completion (a data-driven task) and the direct test was word-fragment cued recall. Dividing attention at encoding decreased performance on both direct memory tests. Of the indirect tests, category-exemplar production but not word-fragment completion was affected. The results indicate that conceptually driven indirect memory tests, like direct memory tests, are affected by divided attention, whereas data-driven indirect tests are not. These results are interpreted within the transfer-appropriate processing framework.

From auditory image to auditory percept: facilitation through common processes?

Two experiments explored implicit memory for auditory stimuli as measured by a test of perceptual identification. The facilitative effect of perceived auditory primes was contrasted with that of imaged auditory primes. In Experiment 1, there was a significant priming effect from imaged spoken-word primes that did not differ significantly from the level of priming due to perceived spoken-word primes, measured by a test of auditory perceptual identification. There was no facilitation of spoken-word identification following creation of an image of a word's referent sound. In Experiment 2, identification of an environmental sound was facilitated by prior processing of an imaged sound from the same category, though there was significantly more transfer following processing of the actual sound.

Interdependence of priming performance and brain-damage

Basically, two hospitalized patient groups were a variety of different learning situations which are subdividable into conventional and experimental tests and which covered so-called implicit and explicit memory tests. Furthermore, data from other cases were used for comparison and for support of the proposed hypotheses. The main sample consisted of 15 focal brain-damaged patients (group N) and 15 patients after surgical interventions outside the nervous system (group O). Aside from affective behavior and intelligence, memory tests were used. These included the WMS-r, picture and face recognition tests, the Tower of Hanoi, the Wisconsin Card Sorting Test (WCST), a Concept Comprehensive Test, and word and picture priming tests. A number of significant differences were obtained between the two age, sex, and education matched groups. Above all, intelligence and memory were reduced in parallel in the cortically damaged compared to the well-matched orthopedic group, while attention and concentration did not differ. Even performance in tests such as the Tower of Hanoi and the WCST differed, perhaps explainable by the proportion of frontal lobe damaged patients and the overall decrease in intelligence in group N. Verbal priming was found to a similar degree in both groups. On the other hand, priming of incomplete pictures was significantly poorer in group N than in group O; furthermore, results from MQ- and IQ-based group splitting (independent of their previous N or O affiliations) suggested a direct relation between mnemonic and other cognitive abilities and success in priming. As perceptual, but not verbal priming differed between groups, and explanation of group N results, based primarily on explicit memory processing, is unlikely. It is concluded that non-brain damaged patients in general are able to use a wider repertoire of information encoding strategies which at least in part is memory and intelligence correlated.

Memory and consciousness: a selective review of issues and data

Methods for dissociating and independently studying conscious (explicit) and unconscious (implicit) memory are discussed. Recent work in the field of amnesia is then briefly reviewed, focusing on the question of how clearly the disorder fractionates according to the implicit-explicit distinction. Finally, evidence supporting dual-process models of recognition memory is reviewed, and data suggesting that amnesic patients have relatively spared familiarity-based recognition memory are critically assessed.

Priming the identification of environmental sounds

Three experiments were conducted using a repetition priming paradigm: Auditory word or environmental sound stimuli were identified by subjects in a pre-test phase, which was followed by a perceptual identification task using either sounds or words in the test phase. Identification of an environmental sound was facilitated by prior presentation of the same sound, but not by prior presentation of a spoken label (Experiments 1 and 2). Similarly, spoken word identification was facilitated by previous presentation of the same word, but not when the word had been used to label an environmental sound (Experiment 1). A degree of abstraction was demonstrated in Experiment 3, which revealed a facilitation effect between similar sounds produced by the same type of source. These results are discussed in terms of the Transfer Appropriate Processing, activation, and systems approaches.

Retrieval volition and memorial awareness in stem completion: an empirical analysis

Facilitation in an incidental test of stem completion shows little influence of depth of processing at study, whereas facilitation in an opposition test (in which subjects give the first word coming to mind, but omit studied words) occurs following graphemic processing, but not following semantic processing. We argue that completions come to mind involuntarily in both tests. Involuntary conscious memory causes studied words to be omitted in an opposition test, but not in an incidental test, so that the difference in priming between tests is a measure of involuntary conscious memory. We obtained data consistent with this hypothesis by making overt the mental activities that occur covertly in an opposition test: (1) an on-line recognition measure in an incidental test showed a strong advantage of semantic over graphemic processing, even though depth of processing exerted little influence on priming; (2) conditionalizing on recognition failure resulted in accurate estimates of opposition performance; and (3) stems were completed much more rapidly in incidental and opposition tests than in an intentional test, in which voluntary retrieval was engaged. The data provide further evidence that retrieval volition (voluntary vs. involuntary) is dissociable from memorial state of awareness (conscious vs. unconscious). We contrast our approach with the process-dissociation approach, which confounds conscious awareness of the past with voluntary retrieval, overlooking involuntary conscious memory.

Input- and output-monitoring in implicit and explicit memory

Previous experiments have shown that the procedure of questioning subjects retrospectively about the input and output status of information (input and output monitoring) is a useful method for assessing the awareness states of subjects during implicit and explicit memory tasks. The main purpose of the present study was to investigate whether the previous findings could be extended to other implicit and explicit memory tasks. We were especially interested in whether differences in input- and output-monitoring performance can be observed when both the implicit and explicit memory tasks are conceptual ones. In a final tet phase, the target items from the study phase and new distractor items were presented. In a recognition-like situation, subjects had to decide whether an item had been presented in the study phase (input status), as well as whether they had produced the item in the memory-test phase (output status). In all three experiments judgments about the input status-but only for those items that had been produced in the implicit or in the explicit memory test--were more precise after explicit than after implicit memory testings. This finding was not influenced by the distinction between perceptual and conceptual-memory tasks (Exp. 1), and was obtained under conditions in which the implicit and the explicit memory tasks were both conceptual and differed only in test instructions (Exps. 2 and 3). These results suggest that not only subjects performing a perceptual test of implicit memory, but also subjects in a conceptual implicit test were less aware of using information from a previous study episode than subjects who received memory instructions. It is concluded that requiring judgments about the input status of information is a good method for assessing subjects' test awareness and is preferable to the use of a questionnaire (Exp. 3). In contrast, in all three experiments no differences were found with the output-monitoring measure between implicit and explicit test conditions.

High-priority event instructions affect implicit and explicit memory tests

Previous work has shown that instructing subjects to give special priority to one target event in a list enhances recall for that event, but impairs recall for the events immediately preceding it (Tulving, 1969). We examined the benefit of high-priority instructions, and the retrograde amnesia for previous items, in three experiments that included two explicit tests of memory (free recall and cued recall with word-stem cues) and an implicit test (word-stem completion). Experiments 1 and 2 revealed a beneficial effect of high-priority instructions on memory for the target events in both free recall and primed word-stem completion. Retrograde amnesia for previous events was either absent (Experiment 1) or modest (Experiment 2) in free recall; however, no evidence for amnesia occurred on the implicit test. In Experiment 3, we asked if the benefit of high-priority instructions on the implicit test was due to contamination from intentional recollection, by employing the logic of the retrieval-intentionality criterion via a levels-of-processing manipulation. The results showed a beneficial effect of high-priority instructions on free recall, word-stem cued recall, and word-stem completion. Level of processing affected the two explicit tests, but not the implicit test, indicating that it induced incidental retrieval. We conclude that the benefit of high-priority instructions occurred on all three tests used in these experiments. In contrast, the phenomenon of retrograde amnesia occurred in free recall, but not in primed word-stem completion.

Intention and awareness in perceptual identification priming

We show that inferences can be made about differences in retrieval intentionality between direct and indirect tests, even when those tests involve different physical cues. When the presence of old items was not mentioned (indirect test condition), we observed a crossed double dissociation between perceptual identification priming and recognition memory as a function of a manipulation of data-driven versus conceptually driven processing at encoding. When subjects were instructed to use their memory to help them identify test items (intentional retrieval condition), priming could be expressed as a monotonically increasing function of recognition memory performance. This reversed association (Dunn & Kirsner, 1988) between priming and recognition memory cannot be accommodated by a model that views intentional retrieval as common to the tests and attributes the crossed double dissociation to an intertest difference in physical cues and associated processes. A posttest questionnaire measure indicated that awareness of the presence of previously encountered items was ubiquitous among indirect test subjects. Crossed double dissociations between direct and indirect measures can therefore be ascribed to differences in retrieval intentionality but not necessarily to differences in subjective awareness of the past.