Distinct FN400/N400 memory effects for perceptually fluent and disfluent words.

Recognition memory studies have shown that increased perceptual fluency results in more "old" responses and, presumably, increases familiarity. However, the exact neural mechanisms of these effects remain unresolved. We conducted two ERP experiments in which participants encoded words and performed a recognition test where fluency was manipulated by changing clarity of test words (half of them were clear or blurry). In the more demanding Experiment 1, we found a reversed effect of fluency on recognition (more hits for blurry words), which was accompanied by larger N400 and LPC old/new effects for blurry words. For high confidence responses, the topography of N400 shifted towards frontal electrodes (the FN400 for blurry words). In the less demanding Experiment 2, no behavioral differences between clear and blurry words were observed. However, there was a discrepancy in the ERP results, with the frontal FN400 for blurry words and the parietal N400 for clear words, suggesting that distinct neural pathways can support familiarity-based recognition for clear and blurry items. In both experiments, early perceptual fluency ERP effects were also observed. The results indicate that both semantic processing and familiarity can be enhanced by perceptual fluency and contribute to recognition judgments, depending on the interpretations of fluency.

Context influences the FN400 recognition event-related potential.

Recognition of studied items often elicit more positive event-related potentials (ERPs) than unstudied items at mid-frontal electrodes about 300-500 ms (i.e., the FN400). The debate over the psychological processes associated with the FN400 has led to two competing hypotheses. One hypothesis is that the FN400 reflects familiarity, whereas another hypothesis is that it reflects conceptual implicit memory (i.e., conceptual fluency). The present experiment tested these hypotheses by presenting meaningless images that lack familiarity and conceptual fluency, off-brand products that lack pre-experimental familiarity, and name-brand products that have both pre-experimental familiarity and conceptual fluency. ERPs were recorded during judgments of lifetime and recent recognition. During both forms of recognition, ERPs in the FN400 window were greater for meaningless images than name- or off-brand products. Because this evidence is difficult to reconcile with either the familiarity or conceptual fluency hypotheses, the results are interpreted within a broader theoretical framework that includes top-down psychological (i.e., context) influences on the FN400.

Encoding focus does not affect recollection of action memories: Event related potential (ERP) and modeling evidence.

Prior work using word stimuli has uncovered evidence that encoding focus (i.e., self-focus or other-focus) alters non-diagnostic recollection and the putative ERP correlate of recollection (i.e., the Late Positive Component or LPC; Leynes and Mok, 2017, Brain & Cognition). The present study examined the generality of these effects by testing memory for actions. Participants viewed videos of either a male actor or female actor completing simple actions (e.g., Ride the Elevator; Climb the Stairs). Participants judged how much fun it would be to personally perform the action under the self-focus encoding condition, whereas they rated how much fun the actor had while performing the action in the other-focus encoding condition. At test, participants made source judgments regarding who (i.e., male or female) performed the action. Self- and other-focus encoding had similar effects on all behavioral measures including parameters from Dual Process Signal Detection and Unequal Variance Signal Detection models. Experiment 2 recorded brain activity (event-related potentials) and found that self- and other-focus encoding produced similar recognition and LPC amplitudes. These results suggest that encoding focus did not affect the amount of non-diagnostic recollection because both action types promoted strong recollection. Such results are additional evidence that action memory creates more complex traces as compared with typical lab-based stimuli (i.e., pictures or words) and identifies an important boundary condition for encoding focus effects on recollection.

Event-related potential (ERP) evidence that encoding focus alters recollected features.

Event-related potential (ERP) evidence suggests that encoding focus alters the quality of information bound in memory, which can affect source memory. In the present study, participants studied product images with blue or and yellow filters while focusing either on the self (self-focus) or on the color of the filtered image (other-focus). Self-focus encoding produced more positive encoding ERPs, greater recognition for old/new judgments, and a greater Late Positive Component (LPC; the putative neural correlate for recollection). Other-focus encoding led to a greater FN400 component suggesting that features (i.e., filter color and product image) were unitized and increased the familiarity used to make memory judgments. The results indicate that encoding focus can alter the balance of features bound in memory. Some features support a specific memory query (diagnostic recollection), whereas other features are from the past do not necessarily inform the memory query (non-diagnostic recollection). Thus, recollection is a complex process that depends on interactions between encoding processes, characteristics of the encountered information, and the broad context of the memory probe.

Event-Related Potential Measures of Smartphone Distraction.

The effect of smartphone use on cognitive function was quantified using measures of neural activity called event-related potentials (ERPs). Participants engaged in a primary task ( Exp. 1a : executive function; Exp. 1b : gambling) with no distraction and while using their smartphone to read online news articles. Smartphone use slowed behavioral responses and reduced the P300 ERP amplitudes by ∼50 percent and provides evidence that smartphones have a large distracting effect. Experiment 2 compared executive function ERPs from smartphone-experienced users ( Exp. 1a ) with those collected on smartphone-naive subjects (collected in late 2006 and early 2007; Scisco et al.). This comparison provides preliminary evidence that smartphone use may be improving visual spatial attention. Collectively, the data highlight some costs and benefits of smartphone use.

Encoding focus alters diagnostic recollection and event-related potentials (ERPs).

The influence of encoding focus on source memory was investigated using event-related potentials (ERPs). Encoding was focused on the self (self-focus) or on the speaker (other-focus) while hearing words spoken in a male or female voice. Examination of the behavioral and ERP evidence suggests that encoding focus alters the amount of diagnostic recollection. Self-focus encoding produced more positive encoding ERPs, led to greater old/new recognition, and elicited a greater Late Positive Component (LPC; the putative neural correlate of recollection) during the source test. Other-focus encoding led to greater source memory and a smaller LPC amplitude. Collectively, the results suggest that encoding focus alters the information bound in the memory trace that leads to varying levels of source-diagnostic features. Drawing attention to the speaker facilitates binding of source-diagnostic features (i.e., voice), whereas self-focus encoding facilitates binding a host of non-diagnostic features. The results have important implications for situations that depend on encoding processes, such as false memory or classroom learning, and they provide evidence that the LPC tracks recollected details but not necessarily diagnostic recollection.

What psychological process is reflected in the FN400 event-related potential component?

During many recognition contexts, old items elicit a more positive event-related potentials (ERPs) than new items at mid-frontal electrodes about 300-500ms. The psychological processes that are reflected in is ERP component (i.e., the FN400) has been vigorously debated. Some argue that the FN400 reflects familiarity, whereas others argue that it reflects conceptual implicit memory. Three experiments contrasted these two hypotheses by presenting pre-experimentally familiar (i.e., name-brand) products and novel, off-brand products. In addition, some of the off-brand products were conceptually primed by the name-brand product to determine how FN400 amplitude would be affected by conceptually primed, but novel, products. The results provided mixed support for both theoretical views, and it is integrated with a broader theoretical framework to characterize the psychological processes captured by the FN400.

Visual perspective during remembering: ERP evidence of familiarity-based source monitoring.

Autobiographical recollections are accompanied by visual perspectives that can be either a view through the person's own eyes (first-person) or a view that integrates visual characteristics of the rememberer into the reconstructed scene (third-person). Some have argued that a third-person perspective serves as a coping mechanism allowing the person to distance themselves from details of painful memories. The study reported here created first- and third-person memories in a novel experimental paradigm. Later, participants discriminated between these perspectives on a source memory test while event-related potentials (ERPs) were recorded. Experimental evidence from the current study suggests that memories from different perspectives can be effectively modeled in the lab. Directly comparing first-person and third-person memories revealed no strong source memory or ERP differences; however, more first-person memories were recognized. Surprisingly, the modeling of the behavioral data using ROC curves and Dual Process Signal Detection (DPSD) measures of recollection and familiarity suggest that familiarity contributed to source judgments of both first- and third-person memories. The ERP data support this claim because the putative ERP correlate of familiarity (i.e., FN400) was observed during the source test. Because source monitoring tends to draw on recollection, evidence of familiarity-based source monitoring has been elusive, and these results support a key prediction of the Source Monitoring Framework (SMF) - that source decisions can be based on familiarity in some contexts (Johnson, Hashtroudi, & Lindsay, 1993; Mitchell & Johnson, 2009).

Neurophysiological evidence that perceptions of fluency produce mere exposure effects.

Recent exposure to people or objects increases liking ratings, the "mere exposure effect" (Zajonc in American Psychologist, 35, 117-123, 1968), and an increase in processing fluency has been identified as a potential mechanism for producing this effect. This fluency hypothesis was directly tested by altering the trial-by-trial image clarity (i.e., fluency) while Event-Related Potentials (ERPs) were recorded. In Experiment 1, clarity was altered across two trial blocks that each had homogenous trial-by-trial clarity, whereas clarity varied randomly across trials in Experiment 2. Blocking or randomizing image clarity across trials was expected to produce different levels of relative fluency and alter mere exposure effects. The mere exposure effect (i.e., old products liked more than new products) was observed when stimulus clarity remained constant across trials, and clear image ERPs were more positive than blurry image ERPs. Importantly, these patterns were reversed when clarity varied randomly across test trials, such that participants liked clear images more than blurry (i.e., no mere exposure effect) and clear image ERPs were more negative than blurry image ERPs. The findings provide direct experimental support from both behavioral and electrophysiological measures that, in some contexts, mere exposure is the product of top-down interpretations of fluency.

Influence of encoding focus and stereotypes on source monitoring event-related-potentials.

Source memory, memory for the origin of a memory, can be influenced by stereotypes and the information of focus during encoding processes. Participants studied words from two different speakers (male or female) using self-focus or other-focus encoding. Source judgments for the speaker׳s voice and Event-Related Potentials (ERPs) were recorded during test. Self-focus encoding increased dependence on stereotype information and the Late Posterior Negativity (LPN). The results link the LPN with an increase in systematic decision processes such as consulting prior knowledge to support an episodic memory judgment. In addition, other-focus encoding increased conditional source judgments and resulted in weaker old/new recognition relative to the self-focus encoding. The putative correlate of recollection (LPC) was absent during this condition and this was taken as evidence that recollection of partial information supported source judgments. Collectively, the results suggest that other-focus encoding changes source monitoring processing by altering the weight of specific memory features.

Event-related potentials indicate that fluency can be interpreted as familiarity.

Recent evidence suggests that fluency may be capable of supporting recognition independently of familiarity. This hypothesis was further tested in the present study. 29 participants encoded name-brand and off-brand products in an incidental task. Participants then judged whether the product was old or new during two tests with products from one category (i.e., only name-brand or only off-brand products) and a mixed test (where both name-brand and off-brand products were shown). The ERP data elicited by off-brand products varied as a function of test format. During the mixed test, off-brand products were correlated with a FN400 effect, whereas a fluency ERP (old ERPs were more negative than new at parietal electrodes 225-400ms) was observed during the other test. Importantly, no FN400 was detected during this test. The ERP results suggest that viewing the off-brand products during the mixed test produced a familiarity experience; however, fluency supported recognition when viewing off-brand products on the other test. The results are strong evidence that top-down processing of visual features during recognition interprets the information relative to the context. This process results in either fluency or, in other contexts, it is interpreted as familiarity as the Discrepancy-Attribution Hypothesis (Whittlesea and Williams, 2001a, 2001b) contends.

Variations in retrieval monitoring during action memory judgments: evidence from event-related potentials (ERPs).

The present study investigated the neuroscience of memory for actions using event-related potentials (ERPs). Actions were performed, initiated but not completed (i.e., interrupted), or watched while the experimenter performed the action during encoding. Memory was assessed in a reality monitoring (RM) test (performed vs. watched actions), as well as in an internal source monitoring (ISM) test (performed vs. interrupted) while ERPs were recorded. Behavioral measures provided evidence of robust old/new recognition for all actions, but the analysis of source errors revealed that interrupted actions were often confused with performed actions. The ERP correlate of recollection, the parietal "old/new" effect (700-900ms), was observed for all actions. The right frontal "old/new" effect (1500-1800ms) that correlates with general memory monitoring was observed in RM but not in ISM. Instead, ISM was associated with the late posterior negativity (LPN) that has been connected to more specific memory monitoring. This pattern of ERP findings suggest that, in this context, general monitoring was used to discriminate self- versus other-performed actions, whereas more specific monitoring was required to support the discrimination of completed and interrupted actions. We argue that the mix of general/specific monitoring processes is shaped by the global retrieval context, which includes the number of memory features that overlap and the combination of sources being considered among other factors.

Event-related potential evidence of accessing gender stereotypes to aid source monitoring.

Source memory for the speaker's voice (male or female) was investigated when semantic knowledge (gender stereotypes) could and could not inform the episodic source judgment while event-related potentials (ERPs) were recorded. Source accuracy was greater and response times were faster when stereotypes could predict the speaker's voice at test. Recollection supported source judgments in both conditions as indicated by significant parietal "old/new" ERP effects (500-800ms). Prototypical late ERP effects (the right frontal "old/new" effect and the late posterior negativity, LPN) were evident when source judgment was based solely on episodic memory. However, these two late ERP effects were diminished and a novel, frontal-negative ERP with left-central topography was observed when stereotypes aided source judgments. This pattern of ERP activity likely reflects activation of left frontal or left temporal lobes when semantic knowledge, in the form of a gender stereotype, is accessed to inform the episodic source judgment.

Event-related potential (ERP) evidence for source-monitoring based on the absence of information.

Event-related potentials (ERPs) were recorded during a reality monitoring (RM) task (i.e., discriminating between seen and imagined words) and during an internal source monitoring (ISM) task (i.e., discriminating between self-generated and imagined words). Behavioral measures indicated robust recollection during both tests with greater recollection during ISM. The ERP correlate of recollection, the parietal old/new effect, was observed for both seen and imagined words during RM but only for self-generated words during ISM. This evidence indicates that self-generated information was diagnostic of source and that recollection of imagined words was based on the absence of self-generated information during ISM. The late posterior negativity (LPN) ERP old/new effects were observed for all conditions; however, the generated word LPN was attenuated during ISM. This pattern is consistent with the hypothesis that it reflects continued evaluation of trace information and suggests that recovery of self-generated information does not initiate an extensive evaluation of memory characteristics.

Memory blocking in schizophrenia reflects deficient retrieval control mechanisms.

Retrieval interference and orthographic processing were evaluated in schizophrenia, schizotypal personality disorder, and non-psychiatric control participants using a word fragment completion paradigm. Participants studied solutions and later completed corresponding fragments preceded by solutions, orthographically similar blocking words, or ampersands. Although schizophrenia patients completed fewest fragments, they showed equivalent repetition priming and blocking magnitude, supporting intact orthographic processing. Schizophrenia patients were more likely to commit intrusions in the blocking condition, whereas control participants displayed better mental control because they were more likely to withhold the response. These results suggest schizophrenia patients show abnormal functioning of control mechanisms responsible for selection and inhibition of competitors.

Objective and subjective measures indicate that orthographically similar words produce a blocking experience.

Memory blocks are a common experience characterised by inappropriate retrieval of information that impairs memory search processes. In five studies, memory blocks were induced via exposure to orthographically similar words (Smith & Tindell, 1997) while participants reported their subjective experiences to determine whether the memory block effect (MBE) paradigm produces a feeling of being blocked. Experiments 1 and 3 provided evidence that the MBE is associated with more blocked experiences. In Experiments 2 and 4 increased blocking experiences correlated with blocked fragments when the experimental manipulation was disguised, which demonstrates that ratings were not contaminated by demand characteristics. Experiment 5 demonstrated that blocking happens even when there is no study list. Collectively, the subjective retrieval ratings and the objective response data provide converging evidence that exposure to orthographically similar words induces a memory block characterised by an ineffective memory search that perseverates on interfering information.

Event-related potential (ERP) correlates of memory blocking and priming during a word fragment test.

Exposure to orthographically similar words impairs the ability to complete word fragments (e.g., Smith and Tindell, 1997), providing evidence that retrieval has been blocked (the Memory Block Effect or MBE). Two studies measured event-related potentials (ERPs) to explore the neural correlates of priming and blocking. The behavioral data in both experiments revealed that exposure to blocking words decreased fragment completions, increased intrusions (i.e., attempts to complete fragments using a blocking word), and slowed response times relative to control fragments. The ERPs in Experiment 1 indicate that priming and blocking begin during the early stages of lexical processing because lexical-related ERP amplitudes (N200) were larger than the control condition. A negative, frontal ERP emerged approximately 500ms after fragment onset and was attenuated for blocking and primed fragments, which suggests that it reflects executive processes that govern solving fragments. Experiment 2 replicated these effects and revealed that both N200 and the late, negative ERP amplitudes varied according to whether or not the fragments were completed, which indicates that these ERPs reflect lexical activation and blocking processes. Collectively, the data suggest that blocking and priming begin to influence word fragment completion during early lexical processing and blocking impedes a normal memory search.

Eliminating the memory blocking effect.

Six experiments investigated the memory blocking effect (MBE) in which exposure to orthographically similar words (e.g., BALLOON) impairs one's ability to complete a similar fragment (e.g., BAL_ON_, solution is BALCONY). Experiments 1 and 2 demonstrated that blocking is not observed after a 72-hour delay; however, repetition priming was observed after the same delay. Experiments 3 and 4 showed that presenting unrelated semantic information during the fragment completion test eliminates blocking. Experiment 5 demonstrated that the MBE persists despite directed-forgetting instructions, and Experiments 5 and 6 demonstrated that activating both the solutions and blocking words for a particular fragment at study eliminates blocking. Collectively, the data demonstrate that reading orthographically similar primes automatically triggers retrieval of the blocking word and an executive control process works to manage this interference. A working framework that describes how an executive control mechanism could govern memory retrieval in the memory-blocking paradigm is presented to stimulate development of more advanced theoretical models that can explain blocking.

Event-related potential (ERP) evidence for varied recollection during source monitoring.

The source monitoring framework (SMF; M. K. Johnson, S. Hashtroudi, & D. S. Lindsay, 1993) posits that source monitoring can be supported by varying degrees of recollection. Source judgments were made for words heard at study (male or female voice) followed by remember/know (RK) judgments in order to assess differences in degrees of recollection during source monitoring (J. L. Hicks, R. L. Marsh, & L. Ritschel, 2002). The neural correlate of recollection was examined by contrasting event-related potentials (ERPs) for R and K responses that followed accurate source judgments. The recollection ERP effect was greater for R than K responses but greater for K responses than correct rejections, which reinforces the behavioral evidence that indicates source monitoring can be supported by varying degrees of recollection. A robust late posterior negativity ERP effect was present and began earlier for accurate source judgments given subsequent R than K responses. This is interpreted as reflecting systematic decision processes that are described by the SMF.