Curran Lab Publications

The ratio of ∆9-tetrahydrocannabinol (THC) to cannabidiol (CBD) varies widely across cannabis strains. CBD has opposite effects to THC on a variety of cognitive functions, including acute THC-induced memory impairments. However, additional data are needed, especially under naturalistic conditions with higher potency forms of cannabis, commonly available in legal markets. The goal of this study was to collect preliminary data on the acute effects of different THC:CBD ratios on memory testing in a brief verbal recognition task under naturalistic conditions, using legal-market Colorado dispensary products. Thirty-two regular cannabis users consumed cannabis of differing THC and CBD levels purchased from a dispensary and were assessed via blood draw and a verbal recognition memory test both before (pretest) and after (posttest) ad libitum home administration in a mobile laboratory. Memory accuracy decreased as post-use THC blood levels increased (n = 29), whereas performance showed no relationship to CBD blood levels. When controlling for post-use THC blood levels as a covariate, participants using primarily THC-based strains showed significantly worse memory accuracy post-use, whereas subjects using strains containing both THC and CBD showed no differences between pre- and post-use memory performance. Using a brief and sensitive verbal recognition task, our study demonstrated that naturalistic, acute THC use impairs memory in a dose dependent manner, whereas the combination of CBD and THC was not associated with impairment.

The current study examined the role of color and spatial frequency on the early acquisition of perceptual expertise after one week of laboratory training with bird stimuli. Participants learned to categorize finches (or warblers) at the subordinate species level (e.g., purple finch) and categorize warblers (or finches) at the more general family level. Training images were presented in their natural colors across 6 sessions. Participants completed a subordinate level species matching task prior to training, one day after training and one week after training while event-related potentials (ERPs) were recorded. Bird images were presented in either their natural congruent color, incongruent color, grayscale, low spatial frequency (LSF<8 cycles per image) or high spatial frequency (HSF>8 cycles per image). Replicating previous training studies, performance benefited more from subordinate- than basic-level training. Before training, any color helped performance, but color congruence effects (congruent>incongruent) only emerged after subordinate-level training. Spatial frequency manipulations did not interact with training. The N170 ERP component was sensitive to spatial frequency manipulations, but not color. N170 spatial frequency effects did not interact with training, and training effects generalized to all manipulations except the LSF images. Like performance, color congruence effects on the N250 were only observed after subordinate level training. These results are consistent with previous reports suggesting that effects of perceptual expertise training on performance are more clearly indexed by N250 than N170 effects. Taken together, our behavioral and ERP results show that color plays an important role in both low- and high- level visual processing, supporting surface-plus-edge–based theories for object processing and recognition.

We used pattern classifiers to extract features related to recognition memory retrieval from the temporal information in single-trial electroencephalography (EEG) data during attempted memory retrieval. Two-class classification was conducted on correctly remembered trials with accurate context (or source) judgments vs. correctly rejected trials. The average accuracy for datasets recorded in a single session was 61% while the average accuracy for datasets recorded in two separate sessions was 56%. To further understand the basis of the classifier’s performance, two other pattern classifiers were trained on different pairs of behavioral conditions. The first of these was designed to use information related to remembering the item and the second to use information related to remembering the contextual information (or source) about the item. Mollison and Curran (2012) had earlier shown that subjects’ familiarity judgments contributed to improved memory of spatial contextual information but not of extrinsic associated color information. These behavioral results were similarly reflected in the event-related potential (ERP) known as the FN400 (an early frontal effect relating to familiarity) which revealed differences between correct and incorrect context memories in the spatial but not color conditions. In our analyses we show that a classifier designed to distinguish between correct and incorrect context memories, more strongly involves early activity (400–500 ms) over the frontal channels for the location distinctions, than for the extrinsic color associations. In contrast, the classifier designed to classify memory for the item (without memory for the context), had more frontal channel involvement for the color associated experiments than for the spatial experiments. Taken together these results argue that location may be bound more tightly with the item than an extrinsic color association. The multivariate classification approach also showed that trial-by-trial variation in EEG corresponding to these ERP components were predictive of subjects’ behavioral responses. Additionally, the multivariate classification approach enabled analysis of error conditions that did not have sufficient trials for standard ERP analyses. These results suggested that false alarms were primarily attributable to item memory (as opposed to memory of associated context), as commonly predicted, but with little previous corroborating EEG evidence.

Multiple mechanisms have been suggested to contribute to the other-race effect on face memory, the phenomenon of better memory performance for own-race than other-race faces. Here, two of these mechanisms, increased attention allocation and greater holistic processing during memory encoding for own-race than other-race faces, were tested in two separate experiments. In these experiments event-related potentials were measured during study (the difference due to memory, Dm) and test phase (old/ new effects) to examine brain activation related to memory encoding and retrieval, allowing for selective investigations of these memory sub-processes. In Experiment 1, participants studied own-race (Caucasian) and other-race (Chinese) faces under focused or divided attention. In Experiment 2, participants studied own-race (Caucasian) and other-race (African American) faces presented upright or upside down (i.e., inverted). Both experiments showed decreases in memory performance when attention allocation or holistic processing was reduced, but these effects were similar for own-race and other-race faces. Manipulations of holistic processing, but not attention allocation, influenced the neural other-race effects during memory encoding. Inverted own- race faces showed similar neural patterns as upright other-race faces, indicating that when holistic processing of own-race faces was reduced, these faces were encoded similarly as upright other-race faces. No influences of the experimental manipulations on other-race effects during memory retrieval were found. The present study provides the first neural evidence that increased holistic processing during memory encoding contributes to the other-race effect on face memory.

 Introduction. As endophenotypes bridge the gap between genetics and phenotypic disease expression, identifying reliable markers is important for fostering understanding of pathophysiology. The present aim was to conduct cur- rent meta-analyses of 3 key auditory event-related poten- tial (ERP) components that have been held as potential endophenotypes for schizophrenia: P50, P300 amplitude and latency, and mismatch negativity (MMN), reflective of sensory gating, attention and classification speed, and perceptual discrimination ability, respectively. In order to assess endophenotype viability, these components were examined in unaffected relatives of patients with schizo- phrenia and healthy controls. Methods: Effect sizes (ES) were examined between relatives and controls for P50 suppression (10 studies, n = 360 relatives, 473 controls), P300 amplitude (20 studies, n = 868 relatives, 961 con- trols), P300 latency (17 studies, n = 674 relatives, 792 controls), and MMN (11 studies, n = 377 relatives, 552 controls). Results: Reliable differences in P50 suppression (ES = 0.86, P < .001), P300 amplitude (ES = −0. 52, P < .001), and P300 latency (ES = 0.44, P < .05) were found between unaffected relatives and controls. A trend was found between relatives and controls for MMN (ES = 0.21, P = 0.06), and the use of extraneous channels was found to be a significant moderator (P = 0.01). When MMN was analyzed using frontocentral channel Fz, a significant dif- ference was found (ES = 0.26, P < 0.01). Discussion The results indicate that P50 suppression, P300 amplitude and P300 latency, and MMN may serve as viable endopheno- types for schizophrenia.

 Introduction. Schizophrenia is associated with deficits in face and affect recognition, which contribute to broader social functioning deficits. The present aim was to conduct a meta-analysis of early face processing in schizophrenia, as indexed by the P100 event-related potential component. Methods. Twelve studies (n = 328 patients with schizo- phrenia, n = 330 healthy controls) of the P100 compo- nent during face processing were evaluated by calculating Cohen’s d for each study and overall weighted mean effect size (ES). In additional exploratory analyses, moderating influences of method and design were investigated, and the P100 component during face processing was evaluated based on valence: 5 studies (n = 225 patients, n = 225 con- trols) included neutral stimuli, 5 studies (n = 225 patients, n = 225 controls) included happy stimuli, and 4 studies (n = 209 patients, n = 209 controls) included fearful stim- uli. Results. The amplitude of the P100 to face stimuli was smaller in patients relative to controls (ES = .41, P < .01). Methodological or design differences did not account for heterogeneity in ES. When split by valence, results indi- cate smaller P100 in patients relative to control subjects in response to neutral (ES = .32, P < .001) and happy (ES = .21, P < .05) stimuli, whereas there was no difference in response to fearful faces (ES = .09, P > .05). Discussion. The results indicate that P100 amplitude in response to faces is smaller in patients with schizophrenia, showing that socially relevant visual processing deficits begin earlier in processing than previously suggested. Additionally, the exploratory analyses suggest emotional specificity in these deficits. Ramifications for our understanding of face pro- cessing deficits and treatment development are discussed.

According to dual-process models, recognition memory depends on two neurocognitive mechanisms: familiarity, which has been linked to the frontal N400 (FN400) effect in studies using ERPs, and recollection, which is reflected by changes in the late positive complex (LPC). Recently, there has been some debate over the relationship between FN400 familiarity effects and N400 semantic effects. According to one view, these effects are one and the same. Proponents of this view have suggested that the frontal distribution of the FN400 could be due to stimulus concreteness: recognition memory experiments commonly use highly imageable or concrete words (or pictures), which elicit semantic ERPs with a frontal distribution. In the present study, we tested this claim using a recognition memory paradigm in which subjects memorized concrete and abstract nouns; half of the words changed font color between study and test. FN400 and LPC old/new effects were observed for abstract as well as concrete words, and were stronger over right hemisphere electrodes for concrete words. However, there was no difference in anteriority of the FN400 effect for the two word types. These findings challenge the notion that the frontal distribution of the FN400 old/new effect is fully explained by stimulus concreteness.

There is a growing debate as to whether frontally distributed FN400 potentials reflect familiarity-based recognition or are functionally identical to centro-parietal N400 reflecting semantic processing. We conducted two experiments in which event-related potentials (ERPs) associated with semantic priming and recognition were recorded, either when priming was embedded within a recognition test (Experiment 1), or when these two phases were separated (Experiment 2). In Experiment 1, we observed 300–500 ms differences between primed and unprimed old words as well as differences between old and new primed words, but these two effects did not differ topographically and both showed midline central maxima. In Experiment 2, the N400 for priming was recorded exclusively during encoding and again showed a midline central distribution. The ERP component of recognition was only found for unrelated words (not primed previously during encoding), and also showed a midline central maximum, but, in addition, was present in the left frontal area of the scalp. Conversely, the priming effect was absent in the left frontal cluster. This pattern of results indicate that FN400 and N400 potentials share similar neural generators; but when priming and recognition are not confounded, these potentials do not entirely overlap in terms of topographical distribution and presumably reflect functionally distinct processes.

Heuristics involve the ability to utilize memory to make quick judgments by exploiting fundamental cognitive abilities. In the current study we investigated the memory processes that contribute to the recognition heuristic and the fluency heuristic, which are both presumed to capitalize on the byproducts of memory to make quick decisions. In Experiment 1, we used a city-size comparison task while recording event-related potentials (ERPs) to investigate the potential contributions of familiarity and recollection to the 2 heuristics. ERPs were markedly different for recognition heuristic-based decisions and fluency heuristic-based decisions, suggesting a role for familiarity in the recognition heuristic and recollection in the fluency heuristic. In Experiment 2, we coupled the same city-size comparison task with measures of subjective preexperimental memory for each stimulus in the task. Although previous literature suggests the fluency heuristic relies on recognition speed alone, our results suggest differential contributions of recognition speed and recollected knowledge to these decisions, whereas the recognition heuristic relies on familiarity. Based on these results, we created a new theoretical framework that explains decisions attributed to both heuristics based on the underlying memory associated with the choice options.

Control processes are critical for both facilitating and suppressing memory retrieval, but these processes are not well understood. The current work, inspired by a similar fMRI design (Detre et al., in press), used a modified Think/No-Think(TNT) paradigm to investigate the neural signatures of volition over enhancing and suppressing memory retrieval. Previous studies have shown memory enhancement when well-learned stimulus pairs are restudied in cued recall (“Recall or think of studied pair item”), and degradation when restudied with cued suppression (“Avoid thinking of studied pair item”). We used category-based (faces vs. scenes) multivariate classification of electroencephalography signals to determine if individual target items were successfully retrieved or suppressed. A logistic regression based on classifier output determined that retrieval activation during the cued recall/suppression period was a predictor for subsequent memory. Labeling trials with this internal measure, as opposed to their nominal Think vs. No-Think condition, revealed the classic TNT pattern of enhanced memory for successful cued-retrieval and degraded memory for cued-suppression. This classification process enabled a more selective investigation into the time-frequency signatures of control over retrieval. Comparing controlled retrieval vs. controlled suppression, results showed more prominent Theta oscillations (3 to 8 Hz) in controlled retrieval. Beta oscillations (12 to 30 Hz) were involved in high levels of both controlled retrieval and suppression, suggesting it may have a more general control-related role. These results suggest unique roles for these frequency bands in retrieval processes.

We show that it is possible to successfully predict subsequent memory performance based on single-trial EEG activity before and during item presentation in the study phase. Two-class classification was conducted to predict subsequently remembered vs. forgotten trials based on subjects' responses in the recognition phase. The overall accuracy across 18 subjects was 59.6% by combining pre- and during- stimulus information. The single-trial classification analysis provides a dimensionality reduction method to project the high-dimensional EEG data onto a discriminative space. These projections revealed novel findings in the pre- and during-stimulus periods related to levels of encoding. It was observed that the pre-stimulus information (specifically oscillatory activity between 25 and 35 Hz) - 300 to 0 ms before stimulus presentation and during-stimulus alpha (7-12 Hz) information between 1000 and 1400 ms after stimulus onset distinguished between recollection and familiarity while the during-stimulus alpha information and temporal information between 400 and 800 ms after stimulus onset mapped these two states to similar values.

People have a memory advantage for faces that belong to the same group, for example, that attend the same university or have the same personality type. Faces from such in-group members are assumed to receive more attention during memory encoding and are therefore recognized more accurately. Here we use event-related potentials related to memory encoding and retrieval to investigate the neural correlates of the in-group memory advantage. Using the minimal group procedure, subjects were classified based on a bogus personality test as belonging to one of two personality types. While the electroencephalogram was recorded, subjects studied and recognized faces supposedly belonging to the subject's own and the other personality type. Subjects recognized in-group faces more accurately than out-group faces but the effect size was small. Using the individual behavioral in-group memory advantage in multivariate analyses of covariance, we determined neural correlates of the in-group advantage. During memory encoding (300 to 1000 ms after stimulus onset), subjects with a high in-group memory advantage elicited more positive amplitudes for subsequently remembered in-group than out-group faces, showing that in-group faces received more attention and elicited more neural activity during initial encoding. Early during memory retrieval (300 to 500 ms), frontal brain areas were more activated for remembered in-group faces indicating an early detection of group membership. Surprisingly, the parietal old/new effect (600 to 900 ms) thought to indicate recollection processes differed between in-group and out-group faces independent from the behavioral in-group memory advantage. This finding suggests that group membership affects memory retrieval independent of memory performance. Comparisons with a previous study on the other-race effect, another memory phenomenon influenced by social classification of faces, suggested that the in-group memory advantage is dominated by top-down processing whereas the other-race effect is also influenced by extensive perceptual experience.

Although investigations of memory and the dynamics of ERP components and neural oscillations as assessed through EEG have been well utilized, little research into the volitional nature of suppression over memory retrieval have used these methods. Oscillation analyses conducted on the Think/No-Think (TNT) task and volitional suppression of retrieval are of interest to broaden our knowledge of neural oscillations associated not only during successful memory retrieval but also when retrieval is unwanted or suppressed. In the current study, we measured EEG during a TNT task and performed ERP and EEG spectral power band analyses. ERP results replicated other researchers’ observations of increases in 500–800 msec parietal effects for items where retrieval was instructed to be elaborated compared with being suppressed. Furthermore, EEG analyses indicated increased alpha (8–12 Hz) and theta (3–8 Hz) oscillations across parietal electrodes for items that were instructed to be suppressed versus those to be elaborated. Additionally, during the second half of the experiment (after repeated attempts at control), increases in theta oscillations were found across both frontal and parietal electrodes for items that were instructed to be suppressed and that were ultimately forgotten versus those ultimately remembered. Increased alpha power for items that were instructed to be suppressed versus elaborated may indicate reductions of retrieval attempts or lack of retrieval success. Increased theta power for items that were instructed to be suppressed versus elaborated may indicate increased or prolonged cognitive control to monitor retrieval events.

Oxytocin has been shown to affect human social information processing including recognition memory for faces. Here we investigated the neural processes underlying the effect of oxytocin on memorizing own-race and other-race faces in men and women. In a placebo controlled, double-blind, between-subject study, participants received either oxytocin or placebo before studying own-race and other-race faces. We recorded event-related potentials (ERPs) during both the study and recognition phase to investigate neural correlates of oxytocin’s effect on memory encoding, memory retrieval, and perception. Oxytocin increased the accuracy of familiarity judgments in the recognition test. Neural correlates for this effect were found in ERPs related to memory encoding and retrieval but not perception. In contrast to its facilitating effects on familiarity, oxytocin impaired recollection judgments, but in men only. Oxytocin did not differentially affect own-race and other-race faces. This study shows that oxytocin influences memory, but not perceptual processes, in a face recognition task and is the first to reveal sex differences in the effect of oxytocin on face memory. Contrary to recent findings in oxytocin and moral decision making, oxytocin did not preferentially improve memory for own-race faces.

Binary choice tasks, such as 2-alternative forced choice, show a complex yet consistent pattern of sequential effects, whereby responses and response times depend on the detailed pattern of prior stimuli going back at least 5 trials. We show this pattern is well explained by simultaneous incremental learning of 2 simple statistics of the trial sequence: the base rate and the repetition rate. Both statistics are learned by the same basic associative mechanism, but they contribute different patterns of sequential effects because they entail different representations of the trial sequence. Subtler aspects of the data that are not explained by these 2 learning processes alone are explained by their interaction, via learning from joint error correction. Specifically, the cue-competition mechanism that has explained classic findings in animal learning (e.g., blocking) appears to operate on learning of sequence statistics. We also find that learning of the base rate and repetition rate are dissociated into response and stimulus processing, respectively, as indicated by event-related potentials, manipulations of stimulus discriminability, and reanalysis of past experiments that eliminated stimuli or prior responses. Thus, sequential effects in these tasks appear to be driven by learning the response base rate and the stimulus repetition rate. Connections are discussed between these findings and previous research attempting to separate stimulus and response-based sequential effects, and research using sequential effects to determine mental representations. We conclude that sequential effects offer a powerful means for uncovering representations and learning mechanisms.

Familiarity and recollection are thought to be separate processes underlying recognition memory. Event-related potentials (ERPs) dissociate these processes, with an early (approximately 300–500 ms) frontal effect relating to familiarity (the FN400) and a later (500–800 ms) parietal old/new effect relating to recollection. It has been debated whether source information for a studied item (i.e., contextual associations from when the item was previously encountered) is only accessible through recollection, or whether familiarity can contribute to successful source recognition. It has been shown that familiarity can assist in perceptual source monitoring when the source attribute is an intrinsic property of the item (e.g., an object’s surface color), but few studies have examined its contribution to recognizing extrinsic source associations. Extrinsic source associations were examined in three experiments involving memory judgments for pictures of common objects. In Experiment 1, source information was spatial and results suggested that familiarity contributed to accurate source recognition: the FN400 ERP component showed a source accuracy effect, and source accuracy was above chance for items judged to only feel familiar. Source information in Experiment 2 was an extrinsic color association; source accuracy was at chance for familiar items and the FN400 did not differ between correct and incorrect source judgments. Experiment 3 replicated the results using a within-subjects manipulation of spatial vs. color source. Overall, the results suggest that familiarity’s contribution to extrinsic source monitoring depends on the type of source information being remembered.

Despite a large body of recognition memory research, its temporal, measured with ERPs, and spatial, measured with fMRI, substrates have never been investigated in the same subjects. In the present study, we obtained this information in parallel sessions, in which subjects studied and recognized images of visual objects and their orientation. The results showed that ERP-familiarity processes between 240 and 440 ms temporally preceded recollection processes and were structurally associated with prefrontal brain regions. Recollection processes were most prominent from 440 to 600 ms and correlated with activation in temporal, parietal, and occipital brain regions. Post-retrieval monitoring, which occurred in the ERP between 600 and 1000 ms as a long-lasting slow-wave over frontal channel groups, showed correlations with activation in the prefrontal and parietal cortex. These ERP/fMRI relationships showed some correspondences to source localizations of the investigated ERP memory effects.

Oxytocin is important to social behavior and emotion regulation in humans. Oxytocin’s role derives in part from its effect on memory performance. More specifically, previous research suggests that oxytocin facilitates recognition of social (e.g., faces), but not of non-social stimuli (e.g., words, visual objects). We conducted the first within-subject study to this hypothesis in a double-blind, placebo-controlled design. We administered oxytocin (24 IU) and placebo (saline) in two separate sessions and in randomized order to healthy men. To obtain a baseline measure for session-dependent memory effects, which are caused by proactive interference, an additional group of male subjects in each session received placebo unbeknownst to them and the experimenter. After administration, participants studied faces and houses. Exactly one day after each study session, participants were asked to make memory judgments of new and old items. In the first study-test session, participants administered with oxytocin showed reduced recollection of previously studied faces and houses. Oxytocin also interacted with proactive-interference effects. By impeding memory in the first session, it reduced proactive interference in the second. But oxytocin contributed additionally to the memory-reducing effect of proactive interference when administered in the second session. These results demonstrate that oxytocin can have a memory-impairing effect on both social and non-social visual objects. The present study also emphasizes the necessity of including a non-treated, baseline group in within-subject designs when investigating oxytocin’s effects on human memory.

Recent progress in the experimental design for event-related fMRI experiments made it possible to find the optimal stimulus sequence for maximum contrast detection power using a genetic algorithm. In this study, a novel algorithm is proposed for optimization of contrast detection power by including probabilistic behavioral information, based on pilot data, in the genetic algorithm. As a particular application, a recognition memory task is studied and the design matrix optimized for contrasts involving the familiarity of individual items (pictures of objects) and the recollection of qualitative information associated with the items (left/right orientation). Optimization of contrast efficiency is a complicated issue whenever subjects' responses are not deterministic but probabilistic. Contrast efficiencies are not predictable unless behavioral responses are included in the design optimization. However, available software for design optimization does not include options for probabilistic behavioral constraints. If the anticipated behavioral responses are included in the optimization algorithm, the design is optimal for the assumed behavioral responses, and the resulting contrast efficiency is greater than what either a block design or a random design can achieve. Furthermore, improvements of contrast detection power depend strongly on the behavioral probabilities, the perceived randomness, and the contrast of interest. The present genetic algorithm can be applied to any case in which fMRI contrasts are dependent on probabilistic responses that can be estimated from pilot data.

Dual process models suggest that recognition memory is supported by familiarity and recollection processes. Previous research administering amnesic drugs and measuring event related potentials (ERPs) during recognition memory have provided evidence for separable neural correlates of familiarity and recollection. The present study examined the effect of midazolam-induced amnesia on memory for details and the proposed ERP correlates of recognition. Midazolam or saline was administered while subjects studied oriented pictures of common objects. ERPs were recorded during a recognition test one day later. Subjects’ discrimination of old and new pictures as well as orientation discrimination was worse when they were administered midazolam than saline. As predicted, the parietal old/new effect was decreased with the administration of midazolam. However, weaker effects on FN400 old/new effects were also observed. These results provide converging pharmacological and electrophysiological evidence that midazolam primarily affects recollection as indexed by parietal ERP old/new effects and memory for orientation, while also exerting some weaker effects on familiarity as indexed by FN400 old/new effects.

Studies employing event-related potentials have shown that when participants are monitoring for a novel target face, the presentation of their own face elicits an enhanced negative brain potential in posterior channels approximately 250 ms after stimulus onset. Here, we investigate whether the own face N250 effect generalizes to other highly familiar objects, specifically, images of the participant’s own dog and own car. In our experiments, participants were asked to monitor for a pre-experimentally unfamiliar target face (Joe), a target dog (Experiment 1: Joe’s Dog) or a target car (Experiment 2: Joe’s Car). The target face and object stimuli were presented with non-target foils that included novel face and object stimuli, the participant’s own face, their own dog (Experiment 1), and their own car (Experiment 2). The consistent findings across the two experiments were the following: (1) the N250 potential differentiated the target faces and objects from the non-target face and object foils and (2) despite being non-targets, the own face and own objects produced an N250 response that was equal in magnitude to the target faces and objects by the end of the experiment. Thus, as indicated by its response to personally familiar and recently familiarized faces and objects, the N250 component is a sensitive index of individuated representations in visual memory.

People are generally better at recognizing faces from their own race than from a different race, as has been shown in numerous behavioral studies. Here we use event-related potentials (ERPs) to investigate how differences between own-race and other-race faces influence the neural correlates of memory encoding and recognition. ERPs of Asian and Caucasian participants were recorded during the study and test phases of a Remember–Know paradigm with Chinese and Caucasian faces. A behavioral other-race effect was apparent in both groups, neither of which recognized other-race faces as well as own-race faces; however, Caucasian subjects showed stronger behavioral other-race effects. In the study phase, memory encoding was assessed with the ERP difference due to memory (Dm). Other-race effects in memory encoding were only found for Caucasian subjects. For subsequently "recollected" items, Caucasian subjects showed less positive mean amplitudes for own-race than other-race faces indicating that less neural activation was required for successful memory encoding of own-race faces. For the comparison of subsequently "recollected" and "familiar" items, Caucasian subjects showed similar brain activation only for ownrace faces suggesting that subsequent familiarity and recollection of own-race faces arose from similar memory encoding processes. Experience with a race also influenced old/new effects, which are ERP correlates of recollection measured during recognition testing. Own-race faces elicited a typical parietal old/new effect, whereas old/new effects for other-race faces were prolonged and dominated by activity in frontal brain regions, suggesting a stronger involvement of post-retrieval monitoring processes. These results indicate that the other-race effect is a memory encoding- and recognition-based phenomenon.

This study examined how perceptual expertise facilitates encoding and recognition. The electroencephalogram of car experts and car novices was recorded in the study as well as test phases of a remember/know task with car and bird stimuli. Car expertise influenced performance and eventrelated potentials (ERPs) for cars but not birds. Experts recognized and "recollected" cars more accurately, while novices had more false alarms. The ERPs provided neural evidence for theoretical assumptions about expert memory. Memory encoding in the study phase was less effortful and more elaborate for experts than novices, as indicated by lower mean amplitudes for subsequently "recollected" cars and by indistinguishable differences due to memory for recollection and familiarity. The parietal old/new effect, a correlate of recollection measured during recognition testing, was only found for experts. The results show that refined perceptual and semantic processing, characteristics of perceptual expertise, facilitate both memory encoding and recognition memory.

Two experiments investigated the processes underlying the picture superiority effect on recognition memory. Studied pictures were associated with higher accuracy than studied words, regardless of whether test stimuli were words (Experiment 1) or pictures (Experiment 2). Event-related brain potentials (ERPs) recorded during test suggested that the 300–500msec FN400 old/ new effect, hypothesized to be related to familiarity-based recognition, benefited from study/test congruity, such that it was larger when study and test format remained constant than when they differed. The 500–800 msec parietal old/new effect, hypothesized to be related to recollection, benefited from studying pictures, regardless of test format. The parallel between the accuracy and parietal ERP results suggests that picture superiority may arise from encoding the distinctive attributes of pictures in a manner that enhances their later recollection. Furthermore, when words were tested, opposite effects of studying words versus studying pictures were observed on the FN400 (word > picture) versus parietal (picture > word) old/new effects—providing strong evidence for a crossover interaction between these components that is consistent with a dual-process perspective.

In their seminal study Diamond and Carey (1986, Journal of Experimental Psychology: General 115 107-117) found a larger inversion effect for dog pictures in dog experts than novices, supporting a role of visual expertise in the observation of particularly large inversion effects for faces. However, subsequent studies have provided mixed results, and very few have compared the inversion effects for faces and familiar non-face object categories. Here we tested the effect of inversion on faces and cars in car experts and novices, using a delayed matching task across viewpoint changes. Inversion affected accuracy much more for pictures of faces than of cars for both groups, with no interaction between expertise and category. However, for car experts only there was a significant correlation between the magnitude of the inversion cost in RT for car pictures and the level of expertise as measured in an independent task. These observations support the view that the particularly large inversion effect found for faces is related to expert visual processes which can be at least partially recruited to process other non-face object categories.

The primary aim of this review is to examine evidence for a functional role of gamma and theta oscillations in human episodic memory. It is proposed here that gamma and theta oscillations allow for the transient interaction between cortical structures and the hippocampus for the encoding and retrieval of episodic memories as described by the hippocampal memory indexing theory (Teyler and DiScenna, 1986). Gamma rhythms can act in the cortex to bind perceptual features and in the hippocampus to bind the rich perceptual and contextual information from diverse brain regions into episodic representations. Theta oscillations act to temporally order these individual episodic memory representations. Through feedback projections from the hippocampus to the cortex these gamma and theta patterns could cause the reinstatement of the entire episodic memory representation in the cortex. In addition, theta oscillations could allow for top-down control from the frontal cortex to the hippocampus modulating the encoding and retrieval of episodic memories.

The present experiments examined how semantic vs. perceptual encoding and perceptual match affect the processes involved in recognition memory. Experiment 1 examined the effects of encoding task and perceptual match between study and test fonts on recognition discrimination for words. Font fan was used to determine the effect of distinctiveness on perceptual match. The semantic encoding task and perceptual match for distinctive items led to better recognition memory. Event-related brain potentials (ERPs) recorded from the human scalp during recognition memory experiments have revealed differences between old (studied) and new (not studied) items that are thought to reflect the activity of memory related brain processes. In Experiment 2, the semantic encoding task and perceptual match for distinctive words led to better recognition memory by acting on both familiarity and recollection processes, as purportedly indexed by the FN400 and parietal old/new effects. Combined these results suggest that the semantic encoding task and perceptual match for distinctive items aid recognition memory by acting on both familiarity and recollection processes.

The neural mechanisms underlying the processing of conventional and novel conceptual metaphorical sentences were examined with event-related potentials (ERPs). Conventional metaphors were created based on the Contemporary Theory of Metaphor and were operationally defined as familiar and readily interpretable. Novel metaphors were unfamiliar and harder to interpret. Using a sensicality judgment task, we compared ERPs elicited by the same target word when it was used to end anomalous, novel metaphorical, conventional metaphorical and literal sentences. Amplitudes of the N400 ERP component (320–440 ms) were more negative for anomalous sentences, novel metaphors, and conventional metaphors compared with literal sentences. Within a later window (440– 560 ms), ERPs associated with conventional metaphors converged to the same level as literal sentences while the novel metaphors stayed anomalous throughout. The reported results were compatible with models assuming an initial stage for metaphor mappings from one concept to another and that these mappings are cognitively taxing.

Expertise facilitates change detection performance, but the neural underpinnings of these benefits are unknown. Expert image analysts showed larger change-related ERP effects between about 100–200 msec after stimulus onset than did novices, which correlated with both accuracy and years of analysis experience. These results demonstrate that years of visual experience can induce fundamental changes in early visual processing which are related to change detection abilities.

This article presents data and theory concerning the fundamental question of how the brain achieves a balance between integrating and separating perceptual information over time. This theory was tested in the domain of word reading by examining brain responses to briefly presented words that were either new or immediate repetitions. Critically, the prime that immediately preceded the target was presented either for 150 ms or 2,000 ms, thus examining a situation of perceptual integration versus one of perceptual separation. Electrophysiological responses during the first 200 ms following presentation of the target word were assessed using electroencephalography (EEG) and magnetoencephalography (MEG) recordings. As predicted by a dynamic neural network model with habituation, repeated words produced less of a perceptual response, and this effect diminished with increased prime duration. Using dynamics that best accounted for the behavioral transition from positive to negative priming with increasing prime duration, the model correctly predicted the time course of the event-related potential (ERP) repetition effects under the assumption that letter processing is the source of observed P100 repetition effects and word processing is the source of observed N170 repetition effects.

Five experiments explored the effects of immediate repetition priming on episodic recognition (the "Jacoby–Whitehouse effect") as measured with forced-choice testing. These experiments confirmed key predictions of a model adapted from D. E. Huber and R. C. O’Reilly’s (2003) dynamic neural network of perception. In this model, short prime durations pre-activate primed items, enhancing perceptual fluency and familiarity, whereas long prime durations result in habituation, causing perceptual disfluency and less familiarity. Short duration primes produced a recognition preference for primed words (Experiments 1, 2, and 5), whereas long duration primes produced a preference against primed words (Experiments 3, 4, and 5). Experiment 2 found prime duration effects even when participants accurately identified short duration primes. A cued-recall task included in Experiments 3, 4, and 5 found priming effects only for recognition trials that were followed by cued-recall failure. These results suggest that priming can enhance as well as lower familiarity, without affecting recollection. Experiment 4 provided a manipulation check on this procedure through a delay manipulation that preferentially affected recognition followed by cued-recall success.

People usually categorize objects more quickly at the basic level (e.g., "dog") than at the subordinate (e.g., "collie") or superordinate (e.g., "animal") levels. Notable exceptions to this rule include objects of expertise, faces, or atypical objects (e.g., "penguin", "poodle"), all of which show faster than normal subordinate-level categorization. We hypothesize that the subordinate-level reaction time advantage for faces is influenced by their discriminability relative to other faces in the stimulus set. First, we replicated the subordinate-level advantage for faces (Experiment 1) and then showed that a basic-level advantage for faces can be elicited by increasing the perceptual similarity of the face stimuli, making discrimination more difficult (Experiment 2). Finally, we repeated both effects within subjects, showing that individual faces were slower to be categorized in the context of similar faces and more quickly categorized among diverse faces (Experiment 3).

This study examined the neural mechanisms underlying perceptual categorization and expertise. Participants were either exposed to or learned to classify three categories of cars (sedans, SUVs, antiques) at either the basic or subordinate level. Event-Related Potentials (ERPs) as well as accuracy and reaction time were recorded before, immediately after, and 1- week after training. Behavioral results showed that only subordinate-level training led to better discrimination of trained cars, and this ability was retained a week after training. ERPs showed an equivalent increase in the N170 across all three training conditions whereas the N250 was only enhanced in response to subordinate-level training. The behavioral and electrophysiological results distinguish category learning at the subordinate level from category learning occurring at the basic level or from simple exposure. Together with data from previous investigations, the current results suggest that subordinate-level training, but not basic-level or exposure training, leads to expert-like improvements in categorization accuracy. These improvements are mirrored by changes in the N250 rather than the N170 component, and these effects persist at least a week after training, so are conceivably related to long-term learning processes supporting perceptual expertise.

The question of interference (how new learning affects previously acquired knowledge and vice versa) is a central theoretical issue in episodic memory research, but very few human neuroimaging studies have addressed this question. Here, we used event-related potentials (ERPs) to test the predictions of the complementary learning systems (CLS) model regarding how list strength manipulations (strengthening some, but not all, items on a study list) affect recognition memory. Our analysis focused on the FN400 old–new effect, a hypothesized ERP correlate of familiarity-based recognition, and the parietal old–new effect, a hypothesized ERP correlate of recollection-based recognition. As is predicted by the CLS model, increasing list strength selectively reduced the ERP correlate of recollection-based discrimination, leaving the ERP correlate of familiarity-based discrimination intact. In a second experiment, we obtained converging evidence for the CLS model’s predictions, using a remember/know test: Increasing list strength reduced recollection-based discrimination but did not reduce familiarity-based discrimination.

Recognition memory requires both retrieval processes and control processes such as criterion setting. Decision criteria were manipulated by offering different payoffs for correct "old" versus "new" responses. Criterion setting influenced the following late-occurring (1,000+ ms), conflict-sensitive eventrelated brain potential (ERP) components: the stimulus-locked late posterior negativity (LPN) and the response-locked error-related negativity (ERN). The LPN–ERN were most negative to hits under conservative payoff conditions involving conflict between the correct old response and the payoff for new responses. This same conservative– hit condition was most frequently associated with response reversals when fast initial judgments were followed by slower judgments. Postresponse ERP activity may index conflict-sensitive processes underlying postretrieval cognitive control mechanisms involved with assessing responses to current items and updating response criteria on later trials.

Separate event-related brain potential (ERP) components have been hypothesized to index familiarity and recollection processes that support recognition memory. A 300- to 500-ms mid-frontal FN400 old/new difference has been related to familiarity, whereas a 500- to 800-ms parietal old/new difference has been related to recollection. Other recent work has cast doubt on the FN400 familiarity hypothesis, especially its application to familiarity-based recognition of conceptually impoverished stimuli such as novel faces. Here we show that FN400 old/new differences can be observed with novel faces, and as predicted by the familiarity hypothesis, these differences are observed regardless of whether or not recognition is accompanied by the recollection of specific details from the study episode. Furthermore, FN400 differentiation between hits and misses is more consistent with an explicit familiarity process than an implicit memory process.

Whether memories can be suppressed has been a controversial issue in psychology and cognitive neuroscience for decades. We found evidence that emotional memories are suppressed via two time-differentiated neural mechanisms: (i) an initial suppression by the right inferior frontal gyrus over regions supporting sensory components of the memory representation (visual cortex, thalamus), followed by (ii) right medial frontal gyrus control over regions supporting multimodal and emotional components of the memory representation (hippocampus, amygdala), both of which are influenced by fronto-polar regions. These results indicate that memory suppression does occur and, at least in nonpsychiatric populations, is under the control of prefrontal regions.

The error-related negativity (ERN) and error positivity (Pe) are electrophysiological markers of error processing thought to originate in the medial frontal cortex. Previous studies using probabilistic reinforcement showed that individuals who learn more from negative than from positive feedback (negative learners) had larger ERNs than did positive learners. These findings support the dopamine (DA) reinforcement-learning hypothesis of the ERN and associated computational models. However, it remains unclear (1) to what extent these effects generalize to tasks outside the restricted probabilistic reinforcement-learning domain and (2) whether there is a dopaminergic source of these effects. To address these issues, we tested subject’s reinforcement-learning biases behaviorally and recorded EEG during an unrelated recognition memory experiment. Initial recognition responses were speeded, but the subjects were subsequently allowed to self-correct their responses. We found that negative learners, as assessed via probabilistic learning, had larger ERNs in the recognition memory task, suggestive of a common underlying enhanced error-processing mechanism. Negative learners also had enhanced Pes when selfcorrecting errors than did positive learners. Moreover, the ERN and Pe components contributed independently to negative learning. We also tested for a dopaminergic genetic basis of these ERP components. We analyzed the COMT val/met polymorphism, which has been linked to frontal DA levels. The COMT genotype affected Pe (but not ERN) magnitude; met/met homozygotes showed enhanced Pes to self-corrected errors, as compared with val carriers. These results are consistent with a role for the Pe and frontal monoamines in error awareness.

Associative recognition memory often is thought to rely primarily on recollection processes, but opinions differ regarding the possible contribution of familiarity. The current experiments capitalized on hypothesized event-related potential (ERP) measures of familiarity and recollection to assess the contribution of each process to associative recognition. In two ERP experiments, participants studied pairs of fractals and were later tested on their ability to recognize the studied pairs. Early (100–175 ms) visual ERP components were sensitive to the novelty of individual fractals, but later components hypothesized to be indicative of familiarity and recollection were sensitive to the novelty of the association between fractals. These relationships suggest that accurate memory for visual associations may be dependent on both familiarity and recollection processes.

The degree of commonality between the perceptual mechanisms involved in processing faces and objects of expertise is intensely debated. To clarify this issue, we recorded occipitotemporal event-related potentials in response to faces when concurrently processing visual objects of expertise. In car experts fixating pictures of cars, we observed a large decrease of an evoked potential elicited by face stimuli between 130 and 200 msec, the N170. This sensory suppression was much lower when the car and face stimuli were separated by a 200-msec blank interval. With and without this delay, there was a strong correlation between the face-evoked N170 amplitude decrease and the subject’s level of car expertise as measured in an independent behavioral task. Together, these results show that neural representations of faces and nonface objects in a domain of expertise compete for visual processes in the occipito-temporal cortex as early as 130–200 msec following stimulus onset.

According to dual-process models, recognition memory is supported by distinct retrieval processes known as familiarity and recollection. Important evidence supporting the dual-process framework has come from studies using event-related brain potentials (ERPs). These studies have identified two topographically distinct ERP correlates of recognition memory –the "parietal" and "mid-frontal" old/new effects – that are dissociated by variables that selectively modulate recollection and familiarity, respectively. We evaluate the extent to which ERP data support dual-process models in light of the proposal that recollection is a continuous rather than a discrete memory process. We also examine the claim that the putative ERP index of familiarity is a reflection of implicit rather than explicit memory. We conclude that ERP findings continue to offer strong support for the dual-process perspective.

In this chapter we will review recent event-related potential (ERP) work relevant to the dual-process perspective and examine the implications of this work for understanding binding in human memory. More comprehensive reviews of ERP memory research, each addressing the dual-process perspective to some extent, are available elsewhere (Johnson 1995; Rugg 1995; Allan et al. 1998; Friedman and Johnson 2000; Mecklinger 2000; Wilding and Sharpe 2003). In particular, we will review evidence relevant to the hypothesis that the 300–500 ms FN400 ERP old–new effect is related to familiarity, and the 400–800 ms parietal ERP old–new effect is related to recollection.

Dual-process theories of recognition memory hypothesize separate underlying familiarity and recollection processes, but the necessity of multiple processes is debated. Previous research has suggested that scalp-recorded event-related brain potentials (ERPs) may index the activity of separate familiarity and recollection processes. Other research indicates that the amnestic drug midazolam impairs recollection more than familiarity. Here, we used a convergent pharmacological and electrophysiological approach to manipulate and monitor human brain activity and provide evidence for separate processes. Midazolam selectively influenced the putative ERP-correlate of recollection but not the putative ERP-correlate of familiarity. Under control conditions (saline), subjects’ accuracy correlated with the recollection-related but not the familiarity-related ERP component, suggesting that recollection was dominant in driving memory. The opposite pattern was observed under midazolam administration, suggesting that when recollection fails, subjects may leverage familiarity to compensate. Thus, in contrast to perspectives holding that familiarity represents the default process, these results suggest that recollection was dominant until its impairment unveiled the influence of familiarity.

Two experiments utilized a think/no-think paradigm to examine whether cognitive control of memories differs depending on whether they contain information with negative or neutral emotional content. During a training phase, participants learned face-word pairs (Experiment 1) or face-picture pairs (Experiment 2). In a subsequent experimental phase, participants were shown faces and told to think of the items paired with some of the faces and to try not to think of the items paired with other faces. Finally, in a test phase, participants were again shown each face and asked to recall the item with which it had been paired previously. Results for both verbal (Experiment 1) and nonverbal (Experiment 2) items indicated that the facilitatory and inhibitory influences of cognitive control were larger for negative than neutral items.

Studies of memory retrieval have identified electroencephalographic (EEG) correlates of a test item’s old–new status, reaction time, and memory load. In the current study, we used a multivariate analysis to disentangle the effects of these correlated variables. During retrieval, power of left-parietal theta (4 – 8 Hz) oscillations increased in proportion to how well a test item was remembered, and theta in central regions correlated with decision making. We also studied how these oscillatory dynamics complemented event-related potentials. These findings are the first to demonstrate that distinct patterns of theta oscillations can simultaneously relate to different aspects of behavior.

Subordinate-level object processing is regarded as a hallmark of perceptual expertise. However, the relative contribution of subordinate- and basic-level category experience in the acquisition of perceptual expertise has not been clearly delineated. In this study, participants learned to classify wading birds and owls at either the basic (e.g., wading bird, owl) or the subordinate (e.g., egret, snowy owl) level. After 6 days of training, behavioral results showed that subordinate-level but not basic-level training improved subordinate discrimination of trained exemplars, novel exemplars, and exemplars from novel species. Eventrelated potentials indicated that both basic- and subordinatelevel training enhanced the early N170 component, but only subordinate-level training amplified the later N250 component. These results are consistent with models positing separate basic and subordinate learning mechanisms, and, contrary to perspectives attempting to explain visual expertise solely in terms of subordinate-level processing, suggest that expertise enhances neural responses of both basic and subordinate processing.

Electrophysiological studies using event-related potentials have demonstrated that face stimuli elicit a greater negative brain potential in right posterior recording sites 170 msec after stimulus onset (N170) relative to nonface stimuli. Results from repetition priming paradigms have shown that repeated exposures of familiar faces elicit a larger negative brainwave (N250r) at inferior temporal sites compared to repetitions of unfamiliar faces. However, less is known about the time course and learning conditions under which the N250 face representation is acquired. In the familiarization phase of the Joe/no Joe task, subjects studied a target "Joe" face "Jane" for female subjects) and, during the course of the experiment, identified a series of sequentially presented faces as either Joe or not Joe. The critical stimulus conditions included the subject’s own face, a same-sex Joe (Jane) face and a same-sex "other" face. The main finding was that the subject’s own face produced a focal negative deflection (N250) in posterior channels relative to nontarget faces. The task-relevant Joe target face was not differentiated from other nontarget faces in the first half of the experiment. However, in the second half, the Joe face produced an N250 response that was similar in magnitude to the own face. These findings suggest that the N250 indexes two types of face memories: a preexperimentally familiar face representation (i.e., the "own face") and a newly acquired face representation (i.e., the Joe/Jane face) that was formed during the course of the experiment.

Expertise with print is likely to optimize visual processes for recognizing characters of a familiar writing system. Although brain activations have been identified for words and letter strings in contrast with other stimuli, relatively little work has focused on the neural basis of single-letter perception. English readers and Chinese–English bilinguals participated in an ERP study and performed a 1-back identity judgment on Roman letters, Chinese characters, pseudofonts, and their string versions. The Chinese– English bilinguals showed an enhanced N170 for both Roman letters and Chinese characters relative to pseudofonts. For the non-Chinese readers, the N170 amplitude was larger for Roman letters relative to Chinese characters and pseudofonts. Our results suggest that changes in relatively early visual processes underlie expert letter perception.

The error-related negativity (ERN) is an electrophysiological marker thought to reflect changes in dopamine when participants make errors in cognitive tasks. Our computational model further predicts that larger ERNs should be associated with better learning to avoid maladaptive responses. Here we show that participants who avoided negative events had larger ERNs than those who were biased to learn more from positive outcomes. We also tested for effects of response conflict on ERN magnitude. While there was no overall effect of conflict, positive learners had larger ERNs when having to choose among two good options (win/win decisions) compared with two bad options (lose/lose decisions), whereas negative learners exhibited the opposite pattern. These results demonstrate that the ERN predicts the degree to which participants are biased to learn more from their mistakes than their correct choices and clarify the extent to which it indexes decision conflict.

 A hallmark of perceptual expertise is that experts classify objects at a more specific, subordinate level of abstraction than novices. To what extent does subordinate- level learning contribute to the transfer of perceptual expertise to novel exemplars and novel categories? In this study, participants learned to classify 10 varieties of wading birds and 10 varieties of owls at either the subordinate, species (e.g., "great blue crown heron", "eastern screech owl") or the family ("wading bird", "owl") level of abstraction. During training, the amount of visual exposure was equated such that participants received an equal number of learning trials for wading birds and owls. Pre- and posttraining performance was measured in a same/different discrimination task in which participants judged whether pairs of bird stimuli belonged to the same or different species. Participants trained in species-level discrimination demonstrated greater transfer to novel exemplars and novel species categories than participants trained in family-level discrimination. These findings suggest that perceptual categorization, not perceptual exposure per se, is important for the development and generalization of visual expertise.

Dual-process theories suggest that recognition memory is determined by two separate processes: familiarity and recollection. Experiment 1 behaviorally replicated past studies using the remember/know procedure to indicate that the amount of attention devoted to study influences both recollection and familiarity, but recollection more strongly. Experiments 1 and 2 assessed the effects of attention on two ERP components that have been hypothesized to be related to familiarity (FN400 old/new effect, 300–500 ms, anterior) and recollection (parietal old/new effect, 400–800 ms, posterior). Parietal old/new effects were reduced by divided attention, but FN400 old/new effects were not. Parietal ERPs (400–800 ms) in experiment 2 increased with confidence in recognizing old items, but not new items. These results support the hypothesis that the parietal old/new effect is related to recollection.

Recognition memory studies have suggested that event-related brain potentials (ERPs) may tap into several different memory processes. In particular, two ERP components have been hypothesized as related to familiarity (FN400 old/new effect, 300–500 ms, anterior) and recollection processes (parietal old/new effect, 400–800 ms, posterior). The functional significance of the FN400 old/new effect is uncertain because similar old/new differences have been shown to disappear at moderately long retention intervals. The present study investigated the effects of retention interval (34 min, 39 min, or 1 day) on the FN400 and parietal old/new effects in two different recency discrimination tasks. The results suggest that the FN400 old/new effect can be maintained across 1-day retention intervals, so it may index brain processes capable of contributing to long-term memory.

Dual process theories posit that separate recollection and familiarity processes contribute to recognition memory. Previous research, testing recognition memory for words, indicates that event-related brain potentials (ERPs) can be used to dissociate recollection from familiarity. It has been hypothesized that the FN400 ERP old /new effect (300–500 ms) varies with stimulus familiarity, but the parietal ERP old /new effect (400–800 ms) varies with recollection. The results reported here are consistent with this hypothesis, extending it to the recognition of pictures when subjects had to discriminate between studied pictures, highly familiar lures (mirror-reversals of studied pictures), and new pictures. Furthermore, the parietal old /new effect showed significant recollection-related differences only for subjects with good behavioral discrimination between studied items and similar lures.

Distinct event-related potential effects have been related to familiarity and recollection processes underlying recognition memory. Familiarity has been conceptualized as similar either to perceptual priming mechanisms supporting implicit memory or to amodal global-matching processes that should show little sensitivity to perceptual variables. The present experiment manipulated the study modality of words (auditory, visual) that were visually tested for recognition memory. The mid-frontal (300–500 ms) old/new effect often attributed to familiarity was not affected by studymodality, so it appears related to an amodal familiarity process. An earlier (176–260ms) fronto-polar old/new effect was perceptually specific in that it was observed only following visual study. The parietal old/new effect (400–800 ms), often attributed to recollection, was similar following both visual and auditory study. Temporal-spatial PCA clarified the separability of these effects.

Memory for the time of events may benefit from reconstructive, location-based, and distance-based processes, but these processes are difficult to dissociate with behavioral methods. Neuropsychological research has emphasized the contribution of prefrontal brain mechanisms to memory for time but has not clearly differentiated location- from distance-based processing. The present experiment recorded event-related brain potentials (ERPs) while subjects completed two different temporal memory tests, designed to emphasize either location- or distance-based processing. The subjects’ reports of locationbased versus distance-based strategies and the reaction time pattern validated our experimental manipulation. Late (800–1,800 msec) frontal ERP effects were related to location-based processing. The results provide support for a two-process theory of memory for time and suggest that frontal memory mechanisms are specifically related to reconstructive, location-based processing.

The perception of faces and of nonface objects share common early visual processing stages. Some argue, however, that the brain eventually processes faces separately from other objects, within a domain-specific module dedicated to face perception. This apparent specialization for faces could, alternatively, result from people's expertise with this category of stimuli. Here we used behavioral and electrophysiological measures of interference to address the functional independence of face and object processing. If the expert processing of faces and cars depend on common mechanisms related to holistic perception (obligatory processing of all parts), then for human subjects who are presumed to be face experts, car perception should interfere with concurrent face perception. Furthermore, such interference should increase with greater expertise in car identification, and indeed this is what we found. Event-related potentials (ERPs) suggest that this interference arose from perceptual processes contributing to the holistic processing of both objects of expertise and faces.

Object categorization emphasizes the similarities that bind exemplars into categories, whereas recognition memory emphasizes the specific identification of previously encountered exemplars. Mathematical modeling has highlighted similarities in the computational requirements of these tasks, but neuropsychological research has suggested that categorization and recognition may depend on separate brain systems. Following training with families of novel visual shapes (blobs), event-related brain potentials (ERPs) were recorded during both categorization and recognition tasks. ERPs related to early visual processing (N1, 156–200 msec) were sensitive to category membership. Middle latency ERPs (FN400 effects, 300–500 msec) were sensitive to both category membership and old/new differences. Later ERPs (parietal effects, 400–800 msec) were primarily affected by old/new differences. Thus, there was a temporal transition so that earlier processes were more sensitive to categorical discrimination and later processes were more sensitive to recognition-related discrimination. Aspects of these results are consistent with both mathematical modeling and neuropsychological perspectives.

A recent paper in this journal reports two event-related potential (ERP) experiments interpreted as supporting the domain specificity of the visual mechanisms implicated in processing faces (Cognition 83 (2002) 1). The authors argue that because a large neurophysiological response to faces (N170) is less influenced by the task than the response to objects, and because the response for human faces extends to ape faces (for which we are not expert), we should reject the hypothesis that the face-sensitivity reflected by the N170 can be accounted for by the subordinate-level expertise model of object recognition (Nature Neuroscience 3 (2000) 764). In this commentary, we question this conclusion based on some of our own ERP work on expert object recognition as well as the work of others.

Complex information, such as that required for motor skills, can be learned implicitly, without awareness.Much debate has centered on the appropriate methods for proving that implicit learning is not influenced by explicit awareness. A recent study by Destrebecqz and Cleeremans has provided compelling evidence for implicit sequence learning without awareness by using the "method of opposition".

People often falsely recognize nonstudied lures that are semantically similar to previously studied words. Behavioral research suggests that such false recognition is based on high semantic overlap between studied items and lures that yield a feeling of familiarity, whereas true recognition is more often associated with the recollection of details. Despite this behavioral evidence for differences between true and false recognition, research measuring brain activity (PET, fMRI, ERP) has not clearly differentiated corresponding differences in brain activity. A median split was used to separate subjects into Good and Poor performers based on their discrimination of studied targets from similar lures. Only Good performers showed late (1000-1500 msec), right frontal event-related brain potentials (ERPs) that were more positive for targets and lures compared with new items. The right frontal differences are interpreted as reflecting postretrieval evaluation processes that were more likely to be engaged by Good than Poor performers. Both Good and Poor performers showed a parietal ERP old/new effect (400-800 msec), but only Poor performers showed a parietal old/lure difference. These results are consistent with the view that the parietal and frontal ERP old/new effects reflect dissociable processes related to recollection.

The effects of aging on visuospatial attention were investigated with event-related brain potentials (ERPs). A central arrow pointed towards (75% valid cues) or away from (25% invalid cues) the location of upcoming visual targets to which subjects made two choice discriminations. Young and older adults responded faster following valid than invalid cues. The absolute magnitude of the cueing effect was larger for older than young subjects, but cueing effects were similar between groups when estimated proportionally to overall response time. Under the present conditions, the electrophysiological manifestations of visuospatial attention were similar for young and older adults. Early ERP components following the target stimulus (P1, N1, Nd1) were slower for older than young subjects, but amplitude was similarly affected by cueing in each group. The temporal correspondence between component latencies and the observed cueing effects are consistent with theories positing that attention amplifies the sensory gain of early perceptual processes. The observation that aging slowed latency of the ipsilateral but not the contralateral P1, is consistent with age differences in interhemispheric transfer times. A broadly distributed 200–400 ms validity effect on ERP amplitude was similar between groups in timing, spatial distribution, and magnitude. The 200–400 ms attention effect appeared to be a modulation of the P3 in younger subjects, as earlier observed. However, the present study dissociated the 200–400 ms attention effects from the P3 component because the P3 did not peak until 526 ms in older subjects.

The effects of aging on visuospatial attention were investigated with event-related brain potentials (ERPs). A central arrow pointed towards (75% valid cues) or away from (25% invalid cues) the location of upcoming visual targets to which subjects made two choice discriminations. Young and older adults responded faster following valid than invalid cues. The absolute magnitude of the cueing effect was larger for older than young subjects, but cueing effects were similar between groups when estimated proportionally to overall response time. Under the present conditions, the electrophysiological manifestations of visuospatial attention were similar for young and older adults. Early ERP components following the target stimulus (P1, N1, Nd1) were slower for older than young subjects, but amplitude was similarly affected by cueing in each group. The temporal correspondence between component latencies and the observed cueing effects are consistent with theories positing that attention amplifies the sensory gain of early perceptual processes. The observation that aging slowed latency of the ipsilateral but not the contralateral P1, is consistent with age differences in interhemispheric transfer times. A broadly distributed 200–400 ms validity effect on ERP amplitude was similar between groups in timing, spatial distribution, and magnitude. The 200–400 ms attention effect appeared to be a modulation of the P3 in younger subjects, as earlier observed. However, the present study dissociated the 200–400 ms attention effects from the P3 component because the P3 did not peak until 526 ms in older subjects.

It is widely hypothesized that separate recollection and familiarity processes contribute to recognition memory. The present research measured event-related brain potentials (ERPs) from 128 head locations to identify patterns of brain activity related to recollection and familiarity. In two experiments, subjects performed a recognition memory task requiring discrimination between previously studied words, similar words that changed plurality between study and test, and new words (following Hintzman & Curran, 1994). The FN400 ERP component (300–500 msec) varied with the familiarity of words (new > studied = similar). The parietal component (400–800 msec) was associated with the recollection of plurality (studied > similar = new). Differences in the timing and spatial topography of the FN400 and parietal effects support the view that familiarity and recollection arise from distinct neurocognitive processes.

Event-related brain potentials (ERPs) recorded from a 128-sensor array were used to differentiate brain processes associated with intentional vs incidental memory retrieval. Two experiments examined ERP differences between old (studied) and new (non-studied) words and pseudowords while subjects performed either a recognition memory task or lexical decision task. Previous research has related a P600 old/new e}ect to the recollection of details, and the present experiments show that this effect was not amplified by intentional retrieval. The P600 effect was larger for words than pseudowords. An earlier (300 to 500 ms) frontally maximal, N400-like old/new effect ("FN400")was similar for words and pseudowords. A third, previously unidentified, mid-frontal, old/new effect was associated with only pseudoword recognition from 300 to 500 ms. Results are discussed with respect to dual-process theories of recognition memory.

Implicit memory is often thought to reflect an influence of past experience on perceptual processes, yet priming effects are found when the perceptual format of stimuli changes between study and test episodes. Such cross-modal priming effects have been hypothesized to depend upon stimulus recoding processes whereby a stimulus presented in one modality is converted to other perceptual formats. The present research examined recoding accounts of cross-modal priming by testing patients with verbal production deficits that presumably impair the conversion of visual words into auditory/phonological forms. The patients showed normal priming in a visual stem completion task following visual study (Experiment 1), but showed impairments following auditory study in both implicit (Experiment 2) and explicit (Experiment 3) stem completion. The results are consistent with the hypothesis that verbal production processes contribute to the recoding of visual stimuli and support cross-modal priming. The results also indicate that shared processes contribute to both explicit memory and cross-modal implicit memory.

Recent neuroimaging studies have obtained evidence of activation in the medial temporal lobe (MTL) during episodic encoding and retrieval. On the basis of a meta-analysis of MTL activations in studies that used positron emission tomography (PET), Lepage et al. (Hippocampus 1998;8:313–322) suggested that episodic encoding tends to involve the anterior MTL, whereas episodic retrieval tends to involve the posterior MTL. In a meta-analysis of studies that used PET and functional magnetic resonance imaging, Schacter and Wagner (Hippocampus 1999;9:7–24) reported weaker evidence for such a rostrocaudal distribution of encoding and retrieval activations. However, these meta-analyses were based largely on studies that examined encoding or retrieval separately. Here, we report a direct, within-subjects comparison of MTL activation during episodic encoding and retrieval by using PET. Results indicated that both encoding and retrieval were associated with blood flow increases in similar MTL regions with little indication that encoding and retrieval are preferentially associated with activity in the anterior versus the posterior MTL. Direct comparisons revealed greater blood flow increases in posterior MTL during encoding than retrieval.

We previously reported a case study of a man with right frontal lobe damage, BG, who showed extraordinarily high false alarm rates on remembe~know recognition tests (Schacter, D. L. et al., Neuropsychologia, 1996, Vol. 34, pp. 793-808). Experiment 1 extends his high false alarm rate to yes-no recognition tests. BG typically gives false "remember" responses on remember-know tests, and this pattern was uninfluenced when he was asked to explain the basis for his "remember" responses (Experiments 2 and 3). When BG was given a semantic encoding task, he stopped giving "remember"-based false alarms (Experiment 4). Signal detection analyses revealed that BG had a discrimination deficit and an abnormally liberal response bias (especially for "remember" responses) in most conditions. Overall, BG’s high false alarm rate is interpreted as reflecting an over-reliance on the general similarity between a test item and the study episode.

Patients with anterograde amnesia are commonly believed to exhibit normal implicit learning. Research with the serial reaction time (SRT) task suggests that normal subjects can implicitly learn visuospatial sequences through a process that is sensitive to higher-order information that is more complex than pairwise associations between adjacent stimuli. The present research reexamined SRT learning in a group of amnesic patients with a design intended to specifically address the learning of higher-order information. Despite seemingly normal learning effects on average, the results suggest that amnesic patients do not learn higher-order information as well as control subjects. These results suggest that amnesic patients have an associative learning impairment, even when learning is implicit, and that the medial temporal lobe and/or diencephalic brain areas typically damaged in cases of amnesia normally contribute to implicit sequence learning.

Prior research has repeatedly implicated the striatum in implicit sequence learning; however, imaging findings have been inconclusive with respect to the sub-territories and laterality involved. Using functional magnetic resonance imaging (fMRI), we studied brain activation profiles associated with performance of the serial reaction time task (SRT) in 10 normal right-handed males. Behavioral results indicate that significant implicit learning occurred, uncontaminated by significant explicit knowledge. Concatenated fMRI data from the entire cohort revealed significant right-lateralized activation in both the caudate and putamen. Analysis of fMRI data from individual subjects showed inter-individual variability as to the precise territories involved, including right as well as left caudate and putamen. Interestingly, all seven subjects who manifested robust learning effects exhibited significant activation within the putamen. Moreover, among those seven subjects, the magnitude of signal intensity change within the putamen correlated significantly with the magnitude of reaction time advantage achieved. These findings demonstrate right-sided striatal activation across subjects during implicit sequence learning, but also highlight interindividual variability with respect to the laterality and striatal subterritories involved. In particular, results from individual subjects suggest that, during the SRT, the reaction time advantage garnered via implicit sequence learning might be predominantly associated with activity within the putamen.

We described a patient, BG, who exhibited a striking pattern of false recognition after an infarction of the right frontal lobe. Seven experiments document the existence of the phenomenon, explore its characteristics, and demonstrate how it can be eliminated. BG showed pathologically high false alarm rates when stimuli were visual words (experiments 1 and 4), auditory words (experiment 2), environmental sounds (experiment 3), pseudowords (experiment 5), and pictures (experiment 7). His false alarms were not merely attributable to the semantic or physical similarity of studied and non-studied items (experiments 4 and 5). However, BG’s false recognitions were virtually eliminated by presenting him with categorized stimuli and testing him with new stimuli from non-studied categories (experiments 6 and 7). The results suggest that BG’s false alarms may be attributable to an over-reliance on memory for general characteristics of the study episode, along with impaired memory for specific items. The damaged right frontal lobe mechanisms may normally support the monitoring and/or retrieval processes that are necessary for item-specific recognition.

When subjects read an semantically unexpected word, the brain electrical activity shows a negative deflection at about 400 msec in comparison with the response to an expected word. In order to study the brain systems related to this effect we mapped it with a dense (64-channel) electrode array and two reference-independent measures, one estimating the average potential gradients and the other radial current density. With these measures, the event-related brain potential (ERP) begins at about 70 msec with the P1, reflecting bilateral current sources over occipitoparietal areas. A strongly left-lateralized N1 then follows, peaking at about 180 msec, accompanied by an anterior positivity, the P2. A separate posterior positive pattern then emerges that seems to repeat the topography of the P1. Next, at about 350 msec, the ERP for the congruous word develops a P300 or LPC, characterized by a diffuse positivity over the superior surface of the head and several negativities over inferior regions. This superior source/inferior sink pattern of the LPC is greater over the left hemisphere. In contrast, the ERP for the incongruous word in this interval displays the N400 as a period in which topographic features are absent. At about 400 msec the ERP for the incongruous word begins to develop an LPC, which then remains relatively symmetric over the two hemispheres.