Effects of imagery instructions on false memories produced on implicit and explicit memory tests

In two experiments, we investigated whether the Deese-Roediger-McDermott paradigm using implicit and explicit memory tests would produce critical lure (CL) words. Participants studied lists of semantic associates (e.g., newspaper, book, write) to induce memories for CL words (e.g., read). Afterwards, participants participated in implicit and explicit memory tests in each experiment. The level of priming of the CL words was quite high and similar to that of the presented words when participants were instructed to image the interword relation on lists during study. Participants explicitly recognized many CL words as having been presented on the lists in Experiment 1 and recalled many CL words in Experiment 2. The results are discussed in light of Underwood's (1965) implicit associative response hypothesis.     

Pupil old/new effects reflect stimulus encoding and decoding in short‐term memory

We conducted five pupil old/new experiments to examine whether pupil old/new effects can be linked to familiarity and/or recollection processes of recognition memory. In Experiments 1–3, we elicited robust pupil old/new effects for legal words and pseudowords (Experiment 1), positive and negative words (Experiment 2), and low‐frequency and high‐frequency words (Experiment 3). Importantly, unlike for old/new effects in ERPs, we failed to find any effects of long‐term memory representations on pupil old/new effects. In Experiment 4, using the words and pseudowords from Experiment 1, participants made lexical decisions instead of old/new decisions. Pupil old/new effects were restricted to legal words. Additionally requiring participants to make speeded responses (Experiment 5) led to a complete absence of old/new effects. Taken together, these data suggest that pupil old/new effects do not map onto familiarity and recollection processes of recognition memory. They rather seem to reflect strength of memory traces in short‐term memory, with little influence of long‐term memory representations. Crucially, weakening the memory trace through manipulations in the experimental task significantly reduces pupil/old new effects.     

Pupil size as a measure of within‐task learning

Pupillometry is commonly used in research to determine how much mental effort an individual is exerting while completing tasks. Traditionally, larger pupils are associated with increased mental effort when completing more difficult tasks. However, little research has investigated how pupils change as individuals learn a new task. In theory, as one repeatedly completes a task, the task demands should reduce, reliance on working memory should decrease, and the task should become more automatic. This should translate to faster completion times and smaller peak pupil dilations. We tested this hypothesis by having participants complete multiple trials of a cognitive task that requires individuals to orient themselves in space relative to a target. We found that trial completion times and maximum pupil size significantly reduced across trials. These data suggest that measuring changes in pupil dilation may help researchers determine whether individuals have shifted from a learned procedure to an automatic processing of information when learning a new task.     

The coupling of emotion and cognition in the eye: introducing the pupil old/new effect

The study presented here investigated the effects of emotional valence on the memory for words by assessing both memory performance and pupillary responses during a recognition memory task. Participants had to make speeded judgments on whether a word presented in the test phase of the experiment had already been presented ("old") or not ("new"). An emotion-induced recognition bias was observed: Words with emotional content not only produced a higher amount of hits, but also elicited more false alarms than neutral words. Further, we found a distinct pupil old/new effect characterized as an elevated pupillary response to hits as opposed to correct rejections. Interestingly, this pupil old/new effect was clearly diminished for emotional words. We therefore argue that the pupil old/new effect is not only able to mirror memory retrieval processes, but also reflects modulation by an emotion-induced recognition bias.     

Implicit memory for emotional words is modulated by cardiac perception

In the present study we investigated the impact of viscero-sensory feedback on memory performance. Participants with good and poor perception of their heart activity were presented with positive, negative and neutral words while heart rate and skin conductance were measured. After a distractor task, participants were asked to complete primed and unprimed wordstems. Implicit memory performance was assessed in terms of accuracy of completion. In our study, participants with good cardiac perception completed significantly more wordstems of previously presented positive and negative words, whereas no group differences were found for wordstems of neutral words and physiological measures during encoding. Our findings document a substantial role of visceral feedback in implicit memory processes. They are in line with Damasio's somatic marker hypothesis stating that access to information about somatic processes facilitates cognitive processing.     

Sleep deprivation impairs binding of information with its context

Binding information to its context in long-term memory is critical for many tasks, including memory tasks and decision making. Failure to associate information to its context could be an important aspect of sleep deprivation effects on cognition, but little is known about binding problems from being sleep-deprived at the time of encoding. We studied how sleep deprivation affects binding using a well-established paradigm testing the ability to remember auditorily presented words (items) and their speakers (source context). In a laboratory study, 68 healthy young adults were randomly assigned to total sleep deprivation or a well-rested control condition. Participants completed an affective item and source memory task twice: once after 7-hour awake during baseline and again 24 hours later, after nearly 31 hours awake in the total sleep deprivation condition or 7 hours awake in the control condition. Participants listened to negative, positive, and neutral words presented by a male or female speaker and were immediately tested for recognition of the words and their respective speakers. Recognition of items declined during sleep deprivation, but even when items were recognized accurately, recognition of their associated sources also declined. Negative items were less bound with their sources than positive or neutral items, but sleep deprivation did not significantly affect this pattern. Our findings indicate that learning while sleep-deprived disrupts the binding of information to its context independent of item valence. Such binding failures may contribute to sleep deprivation effects on tasks requiring the ability to bind new information together in memory.     

Dual-task interference between climbing and a simulated communication task

Climbers often need to maintain communication with other people. Previous research indicates that climbers remember less of the information communicated to them while climbing than when not climbing. In the present research, we investigated at what stage of memory the source of this impairment occurs. Participants were required to respond to words presented to them by saying out loud an associated word. This enforced encoding of the words, and was completed alone, as well as while climbing. Participants then recalled as many words as possible. A separate single-task condition had participants climb without making word associations. Word recall was reduced in the dual-task compared with the single word association task, but there was no difference in the number of word associations made. This indicates that the reduction in word recall was not a result of reduced encoding in the dual-task condition. Concurrent climbing may have reduced word recall by interfering with rehearsal and maintenance of words in memory.     

Impaired implicit memory for gist information in amnesia

In 2 experiments using a converging associates paradigm, the authors evaluated implicit memory for gist information in amnesic patients. In Experiment 1, participants saw multiple sets of associates, each converging on a nonpresented theme word, and were then tested using an implicit word stem completion test and an explicit cued recall test. Amnesic patients showed intact implicit and impaired explicit memory for studied words, but memory for nonpresented lures was impaired, regardless of retrieval instructions. To evaluate whether impaired implicit memory for lures was due to accelerated forgetting of gist information, short study lists were used in Experiment 2, each consisting of a single set of associates. Amnesics' implicit memory for lures was again impaired. These results point to an inability to encode robust gist representations as the cause of impaired gist memory in amnesia.     

Effect of directed forgetting on false recognition: an examination of the activation-monitoring hypothesis

This study examined the influence of directed forgetting on false recognition. Participants studied one of two types of lists consisting of words related to a critical non-presented (CN) word: high or low semantic-associative-strength lists. Thirty-one participants were instructed to forget the Ist list before studying the 2nd list (forget group), another group of 30 participants were instructed to remember both lists (remember group). This was followed by a recognition test and Remember/Know judgments. For CN words, the forget group showed more false recognition than the remember group only for high semantic-associative-strength lists. Moreover, higher proportions of Remember judgments were observed than Know judgments in false recognition responses. These findings are discussed in terms of the activation-monitoring hypothesis of false memories.     

Emotional words impact the mind but not the body: evidence from pupillary responses

Pupillary responses have been shown to be sensitive to both task load and emotional content. We investigated the interplay of these factors in the processing of single words that varied in emotional valence and arousal. Two tasks of different cognitive load, uninstructed reading and a lexical decision task, were employed, followed by an unannounced recognition task. Reaction times were faster and incidental memory performance was better for high-arousing than for low-arousing words. In contrast to previous findings for pictures and sounds, high-arousing words elicited smaller pupillary responses than low-arousing words; these effects were independent of task load, which increased pupil diameter. Therefore, emotional arousal attributed to words does not mandatorily activate the autonomic nervous system, but rather works on a cognitive level, facilitating word processing.     

Study of verbal working memory in patients with Parkinson's disease

The authors examined the nature of the working memory deficit in persons with Parkinson's disease (PD). Three hypotheses were tested: a limited storage capacity, an impaired executive component, and a reduction of psychomotor speed. Verbal working memory was assessed in 14 PD patients without dementia and 14 matched control participants. Participants were administered a classical verbal span test, working memory tasks that required either updating or manipulation capacities, and motor and psychomotor speed tasks. Patients' performance was comparable to that of control participants on the verbal span test. However, results on the working memory tasks indicated a deficit in manipulation with normal updating capacities. Motor and psychomotor slowing were found in the patient group, but slowing could not fully account for the impairment observed in the manipulation task. Results indicated that there is a genuine but selective working memory impairment in patients with PD.     

Feeling of knowing in episodic memory following moderate to severe closed-head injury

The ability to accurately monitor one's memory is a metacognitive process that is important in everyday life. The authors examined episodic memory feeling-of-knowing (FOK) ratings in 21 moderate to severe closed-head injury (CHI) participants (more than 1 year postinjury) and 21 controls. Participants studied 36 critical cue-target word pairs. Following a brief delay, they were asked to recall the target that corresponded to a given cue. Confidence ratings were made for recalled words, and FOK judgments were made for nonrecalled words in terms of the likelihood of recognizing the target word on a subsequent recognition test. CHI participants demonstrated less accurate recall but accurate ability to judge their recall performance (retrospective memory monitoring). They also demonstrated intact FOK judgments when providing binary judgments but demonstrated difficulties making finer discriminations on an ordinal scale (prospective memory monitoring). These findings suggest that memory monitoring is not a unitary construct. It is proposed that CHI participants may display intact memory monitoring when predictions are based on familiarity assessment but not when continued probing for additional episodic information is required.     

WHEN TRUE MEMORIES SUPPRESS FALSE MEMORIES: EFFECTS OF AGEING

After studying a list of words that are all associated to a nonpresented target word, people often falsely recall or recognise the nonpresented target. Previous studies have shown that such false memories are greatly reduced when study lists are presented and tested several times compared to a single study/test trial. We report that older adults, who are sometimes more susceptible to memory distortions than are young adults, failed to exhibit any reduction in false recall or false recognition after five study/test trials compared to a single trial. By contrast, younger adults showed robust suppression of false memories after five study/test trials compared to a single trial. These results are consistent with the idea that older adults rely on memory for the general features or gist of studied materials, but tend not to encode or to retrieve specific details of individual items.     

Pre-learning stress differentially affects long-term memory for emotional words, depending on temporal proximity to the learning experience

Stress exerts a profound, yet complex, influence on learning and memory and can enhance, impair or have no effect on these processes. Here, we have examined how the administration of stress at different times before learning affects long-term (24-hr) memory for neutral and emotional information. Participants submerged their dominant hand into a bath of ice cold water (Stress) or into a bath of warm water (No stress) for 3 min. Either immediately (Exp. 1) or 30 min (Exp. 2) after the water bath manipulation, participants were presented with a list of 30 words varying in emotional valence. The next day, participants' memory for the word list was assessed via free recall and recognition tests. In both experiments, stressed participants exhibited greater blood pressure, salivary cortisol levels, and subjective pain and stress ratings than non-stressed participants in response to the water bath manipulation. Stress applied immediately prior to learning (Exp. 1) enhanced the recognition of positive words, while stress applied 30 min prior to learning (Exp. 2) impaired free recall of negative words. Participants' recognition of positive words in Experiment 1 was positively associated with their heart rate responses to the water bath manipulation, while participants' free recall of negative words in Experiment 2 was negatively associated with their blood pressure and cortisol responses to the water bath manipulation. These findings indicate that the differential effects of pre-learning stress on long-term memory may depend on the temporal proximity of the stressor to the learning experience and the emotional nature of the to-be-learned information.     

Sleep and environmental context: interactive effects for memory

Sleep after learning is often beneficial for memory. Reinstating an environmental context that was present at learning during subsequent retrieval also leads to superior declarative memory performance. This study examined how post-learning sleep, relative to wakefulness, impacts upon context-dependent memory effects. Thirty-two participants encoded word lists in each of two rooms (contexts), which were different in terms of size, odour and background music. Immediately after learning and following a night of sleep or a day of wakefulness, memory for all previously studied words was tested using a category-cued recall task in room one or two alone. Accordingly, a comparison could be made between words retrieved in an environmental context which was the same as, or different to, that of the learning phase. Memory performance was assessed by the difference between the number of words remembered at immediate and delayed retrieval. A 2 × 2 × 2 mixed ANOVA revealed an interaction between retrieval context (same/different to learning) and retention interval (sleep/wakefulness), which was driven by superior memory after sleep than after wake when learning and retrieval took place in different environmental contexts. Our findings suggest a sleep-related reduction in the extent to which context impacts upon retrieval. As such, these data provide initial support for the possibility that sleep dependent processes may promote a decontextualisation of recently formed declarative representations.     

ERP repetition effects in indirect and direct tasks: Effects of age and interitem lag

Event-related potentials (ERPs) were recorded for visually presented words in young and older participants while they performed two tasks. In the indirect task, participants responded to occasional target words. Some of the nontarget words were repeated after a single intervening trial, and others were repeated after a mean of 10 trials. In the direct task participants responded to every item, discriminating between words presented for the first and the second times. Compared with ERPs to unrepeated words, those to words repeated in the indirect task after either lag were more positive in both participant groups. For the short lag, this effect was larger among the older participants. In the direct task, words repeated after either lag elicited a positive shift in the ERPs of the young participants. In the older participants, short lag repeats elicited a repetition effect, but smaller than the equivalent effect among the young participants. Long lag repeats failed to elicit a repetition effect in the direct task in the older participants. The findings show that word repetition in these tasks reflects the modulation of two ERP components, which differ in their sensitivity to age-related changes in memory function.     

Contribution of frontal and temporal lobe function to memory interference from divided attention at retrieval

On the basis of their scores on composite measures of frontal and temporal lobe function, derived from neuropsychological testing, seniors were divided preexperimentally into 4 groups. Participants studied a list of unrelated words under full attention and recalled them while concurrently performing an animacy decision task to words, an odd-digit identification task to numbers, or no distracting task. Large interference effects on memory were produced by the animacy but not by the odd-digit distracting task, and this pattern was not influenced by level of frontal or temporal lobe function. Results show associative retrieval is largely disrupted by competition for common representations, and it is not affected by a reduction in general processing resources, attentional capacity, or competition for memory structures in the temporal lobe.     

What does a patient with semantic dementia remember in verbal short-term memory? Order and sound but not words

In this study, we explored capacities for three different aspects of short-term verbal memory in patients with semantic dementia. As expected, the two patients had poor recall for lexico-semantic item information, as assessed by immediate serial recall of word lists. In contrast, their short-term memory for phonological information was preserved, as evidenced by normal performance for immediate serial recall of nonword lists, with normal or increased nonword phonotactic-frequency effects, and increased sensitivity to phonological lures in a delayed probe recognition task. Furthermore, the patients appeared to have excellent memory for the serial order of the words in a list. These data provide further support for the proposal that language knowledge is a major determining factor of verbal STM capacity, but they also highlight the necessary distinction of processes involved in item and order recall, as proposed by recent models of STM.     

Selective processing of threatening information: effects of attachment representation and anxiety disorder on attention and memory

To investigate the effect of the mental representation of attachment on information processing, 28 anxiety disorder outpatients, as diagnosed by the Anxiety Disorders Interview Schedule-Revised, were administered the Adult Attachment Interview and the State-Trait Anxiety Inventory. They also completed an emotional Stroop task with subliminal and supraliminal exposure conditions, a free recall memory task, and a recognition test. All tasks contained threatening, neutral, and positively valenced stimuli. A nonclinical comparison group of 56 participants completed the same measures. Results on the Stroop task showed color-naming interference for threatening words in the supraliminal condition only. Nonclinical participants with insecure attachment representations showed a global response inhibition to the Stroop task. Clinical participants with secure attachment representations showed the largest Stroop interference of the threatening words compared to the other groups. Results on the free recall task showed superior recall of all types of stimuli by participants with secure attachment representations. In the outpatient group, participants with secure attachment representations showed superior recall of threatening words on the free recall task, compared to insecure participants. Results on the recognition task showed no differences between attachment groups. We conclude that secure attachment representations are characterized by open communication about and processing of threatening information, leading to less defensive exclusion of negative material during the attentional stage of information processing and to better recall of threatening information in a later stage. Attachment insecurity, but not the type of insecurity, seems a decisive factor in attention and memory processes.     

Long-lasting effect of subliminal processes on cardiovascular responses and performance

Students were exposed to a priming task in which subliminal representations of the goal of studying were directly paired (priming-positive group) or not (priming group) to positive words. A control group without subliminal prime of the goal was added. Just after the priming task, students performed an easy or a difficult learning task based on their coursework. Participants in the priming-positive group performed better and had a stronger decrease of pulse transit time and pulse wave amplitude reactivity than participants of the two other groups, but only during the difficult condition. Results suggested that subliminal priming induces effortful behavior extending over twenty five minutes but only when the primes had been associated with visible positive words acting as a reward. These findings provide evidence that subliminal priming can have long-lasting effects on behaviors typical of daily life.