Effects of verbal labeling and exposure duration on implicit memory for visual patterns

The P300, the LPP, context updating, and memory: What is the functional significance of the emotion-related late positive potential?

The emotion-related late positive potential (LPP) of the event-related potential (ERP) has been the topic of many studies over the previous two decades, but the function of this component (the cognitive process that it reflects) is very much an open question. In this paper, I build on frameworks that suggest a close relationship between the LPP and the P300 component of the ERP to argue that the classic context updating account of the P300 may provide insights into the function of the LPP. I then review broader connections between the LPP and memory, and I connect the LPP to research and theory in the area of emotional memory. I argue that while a relationship between the LPP and attention has been widely noted in the literature, connections to memory have been overlooked and that a memory-related process should be considered as one candidate for the function of the LPP.

The unequal variance signal-detection model of recognition memory: Investigating the encoding variability hypothesis

Despite the unequal variance signal-detection (UVSD) model’s prominence as a model of recognition memory, a psychological explanation for the unequal variance assumption has yet to be verified. According to the encoding variability hypothesis, old item memory strength variance (σ_o) is greater than that of new items because items are incremented by variable, rather than fixed, amounts of strength at encoding. Conditions that increase encoding variability should therefore result in greater estimates of σ_o. We conducted three experiments to test this prediction. In Experiment 1, encoding variability was manipulated by presenting items for a fixed or variable (normally distributed) duration at study. In Experiment 2, we used an attentional manipulation whereby participants studied items while performing an auditory one-back task in which distractors were presented at fixed or variable intervals. In Experiment 3, participants studied stimuli with either high or low variance in word frequency. Across experiments, estimates of σ_o were unaffected by our attempts to manipulate encoding variability, even though the manipulations weakly affected subsequent recognition. Instead, estimates of σ_o tended to be positively correlated with estimates of the mean difference in strength between new and studied items (d), as might be expected if σ_o generally scales with d. Our results show that it is surprisingly hard to successfully manipulate encoding variability, and they provide a signpost for others seeking to test the encoding variability hypothesis.

Contextual effects of angry vocal expressions on the encoding and recognition of emotional faces: An event-related potential (ERP) study

It has been shown that stimulus memory (e.g., encoding and recognition) is influenced by emotion. In terms of face memory, event-related potential (ERP) studies have shown that the encoding of emotional faces is influenced by the emotion of concomitant context, when contextual stimuli were input from a visual modality. Behavioral studies also investigated the effect of contextual emotion on subsequent recognition of neutral faces. However, there might be no studies ever investigating the context effect on face encoding and recognition, when contextual stimuli were input from other sensory modalities (e.g., an auditory modality). Additionally, it may be unknown about the neural mechanisms underlying context effects on recognition of emotional faces. Therefore, the present study aimed to use vocal expressions as contexts to investigate whether contextual emotion influences ERP responses during face encoding and recognition. To this end, participants in the present study were asked to memorize angry and neutral faces. The faces were presented concomitant with either angry or neutral vocal expressions. Subsequently, participants were asked to perform an old/new recognition task, in which only faces were presented. In the encoding phase, ERP results showed that compared to neutral vocal expression, angry vocal expressions led to smaller P1 and N170 responses to both angry and neutral faces. For angry faces, however, late positive potential (LPP) responses were increased in the angry voice condition. In the later recognition phase, N170 responses were larger for neutral-encoded faces that had been presented with angry compared to neutral vocal expressions. Preceding angry vocal expression increased FN400 and LPP responses to both neutral-encoded and angry-encoded faces, when the faces showed the encoded expression. Therefore, the present study indicates that contextual emotion with regard to vocal expression influences neural responses during face encoding and subsequent recognition.

Priming and multiple memory systems: perceptual mechanisms of implicit memory

Abstract Research examining the relation between explicit and implicit forms of memory has generated a great deal of evidence concerning the issue of multiple memory systems. This article focuses on an extensively studied implicit memory phenomenon, known as direct or repetition priming, and examines the hypothesis that priming effects on various tasks reflect the operation of a perceptual representation system (PRS)-a class of cortically based subsystems that operate at a presemantic level and support non conscious expressions of memory. Three PRS subsystems are examined: visual word form, structural description, and auditory word form. Pertinent cognitive, neuropsychological, and neurobiological evidence is reviewed, alternative classificatory schemes are discussed, and important conceptual and terminological issues are considered.

Event-Related Potential Correlates of Long-Term Memory for Briefly Presented Faces

Electrophysiological studies have investigated the nature of face recognition in a variety of paradigms; some have contrasted famous and novel faces in explicit memory paradigms, others have repeated faces to examine implicit memory/ priming. If the general finding that implicit memory can last for up to several months also holds for novel faces, a reliable measure of it could have practical application for eyewitness testimony, given that explicit measures of eyewitness memory have at times proven fallible. The current study aimed to determine whether indirect behavioral and electrophysiological measures might yield reliable estimates of face memory over longer intervals than have typically been obtained with priming manipulations. Participants were shown 192 faces and then tested for recognition at four test delays ranging from immediately up to 1 week later. Three event-related brain potential components (e.g., N250r, N400f, and LPC) varied with memory measures although only the N250r varied regardless of explicit recognition, that is, with both repetition and recognition.

The rise and fall of priming: how visual exposure shapes cortical representations of objects

How does the amount of time for which we see an object influence the nature and content of its cortical representation? To address this question, we varied the duration of initial exposure to visual objects and then measured functional magnetic resonance imaging (fMRI) signal and behavioral performance during a subsequent repeated presentation of these objects. We report a novel 'rise-and-fall' pattern relating exposure duration and the corresponding magnitude of fMRI cortical signal. Compared with novel objects, repeated objects elicited maximal cortical response reduction when initially presented for 250 ms. Counter-intuitively, initially seeing an object for a longer duration significantly reduced the magnitude of this effect. This 'rise-and-fall' pattern was also evident for the corresponding behavioral priming. To account for these findings, we propose that the earlier interval of an exposure to a visual stimulus results in a fine-tuning of the cortical response, while additional exposure promotes selection of a subset of key features for continued representation. These two independent mechanisms complement each other in shaping object representations with experience.

Auditory evoked responses and learning and awareness during general anesthesia

BACKGROUND

There is a major distinction between conscious and unconscious learning. Monitoring the mid-latency auditory evoked responses (AER) has been proposed as a measure to ascertain the adequacy of the hypnotic state during surgery. In the present study, we investigated the presence of explicit and implicit memories after anesthesia and examined the relationships of such memories to the AER.

METHODS

We studied 180 patients scheduled for elective surgical procedures. After a thiopental induction, one of four anesthetics were studied: Opioid bolus: 7.5 microg x kg(-1) fentanyl, 70% N2O, with 2.5 microg x kg(-1) supplements as needed (n=100); Opioid infusion: Alfentanil 50 microg x kg(-1) bolus, 1-1.5 microg x kg(-1) x min(-1) infusion, 70% N2O (n=40); Isoflurane 0.3%: Fentanyl 1 microg x kg(-1), 70% N2O, isoflurane 0.3% expired (n=16); Isoflurane 0.7%: Fentanyl 1 microg x kg(-1), 70% N2O, isoflurane 0.7% expired (n=23). AER were recorded before anesthesia, 5 min after surgical incision and then every 30 min until the end of surgery. A tape of either the story of the "Three Little Pigs" or the "Wizard of Oz" was played continuously between the recordings. Explicit memory was assessed postoperatively by tests of recall and recognition, and implicit memory was assessed by the frequency of story-related free associations to target words from the stories, which were solicited twice during a structured interview.

RESULTS

Six patients showed explicit recall of intraoperative events: All received the opioid bolus regimen. About 7% of patients reported dreaming during anesthesia. The incidence of picking the correct story that had been presented during anesthesia averaged 49%, i.e., very close to chance level. Overall, priming occurred only at the second association tests for the opioid bolus regimen, for which the frequency of an association to the presented story among those not giving an association to the control story was 26%, which was double the frequency (13%) of an association to the control story among those not giving an association to the presented story. This was significant by McNemar's test, P=0.02. There were significant associations between awareness, priming and AER, e.g., recall was associated with higher Nb amplitudes during anesthesia and priming was associated with shorter wave latencies.

CONCLUSIONS

The incidence of awareness in patients anesthetized with nitrous oxide and bolus supplementation was 6%. Thus, this anesthetic technique did not reduce the risk of awareness compared with the use of nitrous oxide alone. Implicit memory occurred during nitrous oxide and bolus supplementation. Recording AER during anesthesia may help to predict awareness and implicit memory, particularly the former. The short contents of most of the dreams which were recalled could hamper future studies in this area.

Perceptual implicit memory requires attentional encoding

Perceptual implicit memory for previously attended and unattended words was measured either in a word-stem completion task or in a perceptual fluency (perceptual identification) task. Subjects (N = 144) first engaged in a focused attention task in which they were to identify one of two words presented for 100, 200, or 300 msec. Words were classified as attended if they were reported during the focused attention task and unattended if they were not. Results for both implicit memory tests indicated reliable perceptual implicit memory for attended words but not for unattended words, regardless of focused attention exposure duration. The results indicate that perceptual implicit memory tasks reflect attentional encoding processes; that is, words must undergo attentional encoding if they are to affect performance on a later perceptual implicit memory test.

The role of attention and study time in explicit and implicit memory for unfamiliar visual stimuli

The effects of limited attentional resources and study time on explicit and implicit memory were studied using Schacter and Cooper's possible and impossible objects in their recognition and object decision paradigm. In one experiment, when attention at study was limited by a flanking digits procedure, object recognition was diminished but object decision priming for possible objects was unaffected; in another experiment, limiting attention plus reducing stimulus study time impaired object recognition and eliminated object priming. Recognition memory and perceptual priming for previously unfamiliar visual stimuli were both influenced by attention, although to different degrees. The intervening variable of study time determined the degree to which priming was affected by attentional resources. These results support a limited capacity attentional model for both recognition and perceptual priming of unfamiliar visual stimuli, and they highlight the need for assessing the interaction of attentional resources and study time in explicit and implicit memory tasks.

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.

Do chronic alcoholics have intact implicit memory? An ERP study

In order to investigate whether visual object priming differs from visual word priming and whether the visual repetition priming in chronic alcoholic patients is impaired, we performed an ERP study on 27 male control and 67 male alcoholic subjects. Sixty-one electrodes were employed to record ERPs that were elicited by random presentations of object pictures, words, and scrambles for both pictures and words. We also used an implicit task that required subjects to identify whether each stimulus was recognizable. The current experiment revealed that (1) the reaction times to both recognizable picture and word stimuli were significantly shortened by the prior exposures of the same stimuli, (2) control subjects reflected visual object and word priming in different ERP components with different topographic patterns, (3) alcoholic subjects manifested visual word priming in the same ERP component as controls, and (4) the differences in ERP components, both in amplitude and topographic distribution, between the two groups occurred mainly in the different stimuli. These data suggest that the visual object and word priming have distinctive neural processes. The visual object priming in alcoholic subjects may be impaired while the visual word priming seemed to be intact.

Visual object priming differs from visual word priming: an ERP study

Implicit memory is inferred from repetition priming effects in tasks such as word identification, word fragment completion, and perceptual recognition with masking or brief exposures. In this experiment, we explored whether the visual word and object repetition priming effects can be reflected by features of ERP and whether visual word repetition priming differs from visual object repetition priming. We have observed that (1) pre-exposure to recognizable stimuli (both word and object picture) shortened the response time in identifying their repetitions; (2) repetition of unrecognized scrambles of words or object pictures did not show any effects on ERP patterns; (3) ERPs distinguished recognizable from unrecognizable stimuli; and, (4) repetitions of both words and pictures strongly influenced the patterns of ERPs, though the ERPs to word stimuli differed from the ERPs to picture stimuli.

Memory for words and novel visual patterns: repetition, recognition, and encoding effects in the event-related brain potential

Event-related potentials (ERPs) were recorded during initial study and recognition of words and novel visual patterns. Words and patterns yielded similar recognition results that discriminated correctly recognized old items from correct new items, incorrect old items, and incorrect new items. The study phase data included a number of dissociations between words and patterns. Occasional repeated items yielded faster reaction times for both stimulus types but a late positive ERP repetition effect for words only. The study phase data differentiated words that would later be recognized versus unrecognized, but the patterns did not yield a similar encoding effect. Moreover, the study phase positivity contingent on subsequent recognition was restricted to words that received a positive semantic judgment during study. The functional relationships among the repetition, recognition, and encoding effects are discussed.

Stimulus exposure time and perceptual memory

The recent explosion of research on implicit memory has facilitated the examination of perceptual and conceptual processes in the encoding of information. Nevertheless, stimulus exposure time--the amount of time that a stimulus is physically available to a perceiver's scrutiny--has received little attention. In the present paper, we examine the effect of stimulus exposure time on three implicit memory measures (word-fragment completion, perceptual identification, and general knowledge) and two explicit memory measures (graphemic cued recall and semantic cued recall). In Experiment 1, we demonstrated that increases in exposure time lead to increases in implicit perceptual memory, but not to implicit conceptual memory, when the encoding task focuses on perceptual features of the stimulus. We replicated this effect in Experiment 2 and demonstrated that increases in exposure time lead to increases in perceptual and conceptual memory when the measures are explicit. Thus, the current experiments demonstrate that manipulations of exposure time lead to dissociations in implicit, but not explicit, memory.

A reevaluation of semantic versus nonsemantic processing in implicit memory

A number of investigations have purported to demonstrate that semantic processing does not produce a memorial advantage over nonsemantic processing on implicit tests, as contrasted with the typical advantage of semantic over nonsemantic processing on explicit tests. A review of 166 outcomes from 38 studies that have manipulated processing on implicit tests reveals that on 131 occasions (79%), priming was greater following semantic than it was following nonsemantic processing. This difference was found in both perceptual and conceptual implicit memory tests, as well as in within- and between-subjects designs. It suggests that implicit tests reflect the involvement of both conceptual and perceptual processes. Although explicit contamination may account for some of the processing difference in implicit tests, the pervasiveness of the phenomenon, especially in perceptual implicit tests, makes it an unlikely account for the entire effect.

Nonverbal priming in amnesia

In this experiment, we examined whether a group of well-characterized amnesic patients would exhibit normal priming for novel nonverbal materials after a single exposure. Both amnesic patients and normal control subjects studied line figures and were then given a priming test in which they were asked to reproduce both old (studied) and new (unstudied) figures after a brief exposure. The measure of priming was the number of old patterns drawn correctly relative to the number of new patterns drawn correctly. Both subject groups reproduced more old patterns than new patterns, and the effect was similar in the two groups. In contrast, amnesic patients were significantly impaired on a recognition memory test for the items that had been presented. This study contributes to recent evidence that implicit memory can support the rapid acquisition of novel verbal and nonverbal information. Perceptual priming for such material is independent of the structures damaged in amnesia.