Event-related Potentials Repetition Effect Research Articles

Categorical ERP repetition effects for human and furniture items in 7‐month‐old infants

AbstractBehavioural and recent neural evidence indicates that young infants discriminate broad stimulus categories. However, little is known about the categorical perception of humans represented as full bodies with heads and their discrimination from inanimate objects. This study compares infants' brain processing of human and furniture pictures, probing infants' categorization skills with an event‐related potential (ERP) paradigm. Seven‐month‐old infants (n = 23) were tested in a rapid repetition ERP paradigm. Trials consisted of two consecutive stimuli: prime and target. Different ERP parameters (Nc, PSW) were compared across human and furniture items and for repeated and unrepeated categories. The PSW was consistently enhanced for unrepeated compared to repeated categories, thus indicating category discrimination. Nc amplitude was enhanced for furniture primes compared to human primes, but not for corresponding targets. In sum, these findings suggest that ERP rapid repetition studies are suitable for probing perceptual category discrimination in infancy. 7‐month‐olds discriminated between humans, presented as full body pictures, and furniture exemplars, but did not seem to prefer either of these categories.Highlights 7‐month‐olds' ability to categorize humans and furniture items was tested using rapid repetition ERPs. The PSW was enhanced for unrepeated categories, indicating broad categorization. The Nc, indicating neural attention, was not enhanced for humans compared to furniture items.

The Ground Side of an Object

Traditional theories of perception posit that only objects access semantics; abutting, patently shapeless grounds do not. Surprisingly, this assumption has been untested until now. In two experiments, participants classified silhouettes as depicting meaningful real-world or meaningless novel objects while event-related potentials (ERPs) were recorded. The borders of half of the novel objects suggested portions of meaningful objects on the ground side. Participants were unaware of these meaningful objects because grounds are perceived as shapeless. In Experiment 1, in which silhouettes were presented twice, N400 ERP repetition effects indicated that semantics were accessed for novel silhouettes that suggested meaningful objects in the ground and for silhouettes that depicted real-world objects, but not for novel silhouettes that did not suggest meaningful objects in the ground. In Experiment 2, repetition was manipulated via matching prime words. This experiment replicated the effect observed in Experiment 1. These experiments provide the first neurophysiological evidence that semantic access can occur for the apparently shapeless ground side of a border.

The time course of repetition effects for familiar faces and objects: An ERP study

Face and object priming has been extensively studied, but less is known about the repetition processes which are specific to each material and those which are common to both types of material. In order to track the time course of these repetition processes, EEG was recorded while 12 healthy young subjects performed a long-term perceptual repetition priming task using faces and object drawings. Item repetition induced early (N170) and late (P300 and 400–600 ms time-window) event-related potential (ERP) modulations. The N170 component was reduced in response to primed stimuli even with several hundred intervening items and this repetition effect was larger for objects than for faces. This early repetition effect may reflect the implicit retrieval of perceptual features. The late repetition effects showed enhanced positivity for primed items at centro-parietal, central and frontal sites. During this later time-window (400 and 600 ms at central and frontal sites), ERP repetition effects were more obvious at the left side for objects and at the right side for faces. ERP repetition effects were also larger for famous faces during this time-window. These later repetition effects may reflect deeper semantic processing and/or greater involvement of involuntary explicit retrieval processes for the famous faces. Taken together, these results suggest that among the implicit and explicit memory processes elicited by a perceptual priming task, some of them are modulated by the type of item which is repeated.

Brain potentials and repetition effects during encoding and retrieval of words

Using event-related potentials (ERPs), this study utilized a study-test paradigm to investigate the existence of a common mechanism underlying repeated learning effects during encoding and retrieval. Results showed repeated learning effects occurred in both encoding and retrieval. The effect of encoding, however, appeared earlier and lasted longer than that of retrieval. Furthermore, the effect of implicit retrieval appeared earlier than that of explicit retrieval. The main scalp distributions of the repetition effects related to both encoding and retrieval occurred at parietal and central sites. Both ERP repetition effects manifested significantly larger and positive-going ERP response of repeated words compared with the words' first appearance. The ERP repetition effects support the hypothesis that there is common learning-related automatic processing during encoding and retrieval.

Event-related potential repetition effects at encoding predict memory performance at test

The present study used multiple repetitions of meaningless pictorial stimuli to examine the electrophysiological correlates of the creation of a new stimulus representation. Study participants judged whether preexperimentally unfamiliar figures (meaningless line drawings) that were repeated up to four times contained a crossover in their contour. Stimulus repetition thereby led to a reduction of the visual N1 component in event-related potentials as well as to a late (430-600 ms), successively increasing positivity over posterior electrodes. In particular, the size of this latter event-related potential effect highly correlated with and thus predicted participants' performance in a subsequent recognition memory test. It can therefore be interpreted as neural correlate of the creation of a new memory-effective stimulus representation.

Recognition memory for unfamiliar faces in Parkinson's disease: Behavioral and electrophysiologic measures

We analyzed event-related potentials (ERPs) and behavioral measurements during a recognition memory task in 15 normal elderly subjects and 15 patients with Parkinson's disease (PD). To elicit ERPs unfamiliar faces were repeated immediately after initial presentation (at lag 0), after one intervening face (at lag 1) or at lag 3. Compared to normal controls, PD patients showed decreased accuracy in recognizing new unfamiliar faces. P170 latency and amplitude were similar between both groups. ERP amplitude between 300 and 500 ms after the stimulus in control subjects showed a positive shift (ERP repetition effect) for lag 0 at all sites and for lag 1 and 3 repetitions at the Fz site, while effects in the PD group were not noted at any site, even for the lag 0 repetition. ERP waveforms for the first presentation of faces in PD patients showed a significant positive shift compared to normal controls. These data suggest intact perception but impaired recognition memory for unfamiliar faces in PD. In addition, recognition memory deficits in PD may result from impairment of comparison of structural representations of presented faces with stored representations of faces known to the observer.

Evaluating models of object-decision priming: Evidence from event-related potential repetition effects.

This study was designed to differentiate between structural description and bias accounts of performance in the possible/impossible object-decision test. Two event-related potential (ERP) studies examined how the visual system processes structurally possible and impossible objects. Specifically, the authors investigated the effects of object repetition on a series of early posterior components during structural (Experiment 1) and functional (Experiment 2) encoding and the relationship of these effects to behavioral measures of priming. In both experiments, the authors found repetition enhancement of the posterior N1 and N2 for possible objects only. In addition, the magnitude of the N1 repetition effect for possible objects was correlated with priming for possible objects. Although the behavioral results were more ambiguous, these ERP results fail to support bias models that hold that both possible and impossible objects are processed similarly in the visual system. Instead, they support the view that priming is supported by a structural description system that encodes the global 3-dimensional structure of an object.

Lateralization of repetition effects in event-related potentials to words in left- and right-handed women

In our previous event-related potential (ERP) study [A. Nowicka, I. Szatkowska, Memory-induced modulation of event-related potentials in frontal cortex of human subjects: a divided visual field study, Neurosci. Lett. 359 (2004) 171–174], word repetition effects in right-handed males were observed only in case of the direct stimulation of the left (competent) hemisphere. Since the left-handedness and the factor of female gender may determine the lateralization of verbal functions, the goal of the present study was to test the sensitivity of the ERP repetition effects to the visual field of word presentation in the group of left- and right-handed women. ERPs were recorded from symmetrical sites over the left and right hemisphere. Target words were presented in the left (LVF) or right (RVF) visual hemifield. Subjects’ were instructed to recognize the target word on a response card. A substantial portion of words was repeated twice. Words elicited different ERPs at frontal sites when presented the first and second times: ERPs were more positive to the repeated stimulus than to its first occurrence. However, in right-handed participants, repetition effects were only observed when target words were presented to the RVF whereas in left-handed participants, repetition effects were only observed when target words were presented to the LVF. These findings are indicative of the asymmetrical involvement of the two hemispheres in memory-induced modulation of brain activity related to verbal processing in left- and right-handed women.

Reduced word-repetition effect in the event-related potentials of thought-disordered patients with schizophrenia

Repetition effect in event-related potentials (ERPs) was studied in 10 non-thought-disordered (non-TD) patients with schizophrenia, 8 thought-disordered (TD) patients with schizophrenia, and 10 normal control subjects while they performed a semantic categorization task with incidental word repetitions. All patients were in a stable or partially remitted stage. Although both healthy control and non-TD groups produced more positive ERPs to the repeated words than to the new words (ERP repetition effect) for 250–500 ms, the TD group did not show the ERP repetition effect. These findings suggest that the abnormal attenuation of the ERP repetition effect during semantic processing may be more prominent in schizophrenic patients with thought disorder than in those without the symptom.

Repetition-priming Modulates Category-related Effects on Event-related Potentials: Further Evidence for Multiple Cortical Semantic Systems

In the present study, the significance of category-related brain activations as an index of semantic memory structure was assessed within a repetition-priming paradigm during a lexical decision task. The interpretation of category-related effects has been debated since previous studies observed category-related brain activity mainly in tasks requiring explicit semantic categorization. Furthermore, categories were frequently associated with behavioral performance differences, which could have influenced the pattern of brain activation. Event-related potentials (ERPs) to words denoting objects from artifactual (e.g., tools) and natural categories (e.g., animals) were recorded while subjects were presented with words and pseudowords as distracters, which were repeatedly presented. Category-related ERP differences emerged in the time window of the N400, an electrophysiological index of semantic processing, over occipito-parietal and fronto-central regions as well as in the following window of a late positive potential. Repetition priming modulated these category-related ERP effects whereas behavioral repetition priming (faster reactions to repeated words) was comparable for both categories. Differences in ERP repetition effects were specifically due to diminished category-related activity at repeated presentation. The present results show that category-related brain activation is not confined to tasks requiring explicit semantic categorization. Most importantly, the study demonstrates that category-related brain activation can be specifically modulated by repetition priming in the absence of corresponding behavioral performance differences. These findings therefore substantiate the significance of category-related brain activations as reflections of semantic memory structure and support the notion of multiple cortical semantic systems.

Memory-induced modulation of event-related potentials in frontal cortex of human subjects: a divided visual field study

The aim of the present study was to test whether memory processes depend on which hemisphere initiates processing of visual information. Event-related potentials (ERPs) to laterally displayed stimuli (words and Kanji) were recorded from symmetrical sites over the left (LH) and right hemisphere (RH), i.e. the hemisphere contralateral and ipsilateral to the visual field of stimulus presentation. ERP recordings for the new and repeated stimuli were compared. A memory-related modulation of ERPs was found for frontal recording sites. The late ERP repetition effect, however, was present in the ERP data only in the case of the direct stimulation of the competent hemisphere, i.e. the LH for words and RH for Kanji. Stimulation of the incompetent hemisphere resulted in lack of the repetition effect in either hemisphere.

Modulation of oscillatory brain activity and evoked potentials in a repetition priming task in the human EEG.

Cortical object representations seem to require the formation of neural cell assemblies. The physiological correlate of cell assembly activity may be seen in synchronized neural activity in the gamma band range. The improvement in perceiving and identifying an object by experience is commonly referred to as repetition priming. One possible neural mechanism for repetition priming is 'repetition suppression' within a cell assembly coding the stimulus. The present electroencephalogram study was designed to investigate oscillatory brain activity when line drawings of concrete objects were repeated either immediately after a first presentation or after intervening a number of different stimuli. Results showed a broad posterior distribution of induced gamma band responses (GBRs) after the initial picture presentation. Repeated presentations of the same picture led to a significant decrease of induced gamma power. Furthermore, repeated presentations of the same object resulted in a decrease in phase synchrony between distant electrode sites. No significant repetition effects were found in the alpha or beta frequency range. The event-related potential (ERP), which was also modulated by priming, showed a different scalp distribution compared with induced GBRs. In addition, ERP repetition effects decayed at larger intervals between initial and repeated presentations, whereas induced GBRs were not modulated as a function of stimulus lag. We concluded that the decrease in amplitude of induced GBRs and the reduction of gamma phase synchrony between pairs of electrodes after repeated picture presentations might be linked to a 'sharpening' mechanism within a cell assembly representing an object.

Dissociating memory processes involved in direct and indirect tests with ERPs to unfamiliar faces

Event-related potentials (ERPs) were recorded during indirect and direct memory tests for unfamiliar faces. In both tests, ERPs displayed the usual positive shift known as the ERP repetition effect. In the indirect test, this effect includes parietal effect (the usual N400 effect) and a right fronto-central effect. Both effects are also present in the direct test. Two additional effects are present only in the direct test. These effects are an early fronto-polar effect and a late posterior effect (the usual P600 effect). These findings are taken as support for the distinction between ‘associative’ processes elicited in both the direct and indirect tests, and ‘episodic’ processes elicited only in the direct test. This task dissociation could well provide a scalp correlate of the distinction between the neocortical and cortico-limbic systems that have been shown to contribute respectively to associative and episodic processing. In addition, it is proposed that the dissociation between the two frontal effects could be accounted for by a distinction between the processing of intrinsic vs. extrinsic contextual attributes as a function of the task requirements.

Modality-specific effects of immediate word repetition

Event-related potentials (ERPs) elicited by visually presented words were employed to investigate whether the neural correlates of repetition within- and across-modality differ when repetition is immediate, and the influence of explicit memory maximal. Relative to the ERPs elicited by first presentations, ERPs elicited by immediate, within-modality repetitions began to differ from approximately 200 ms post-stimulus onset. ERP repetition effects elicited by across-modality repetition did not onset until approximately 150 ms later. Within- and across-modality repetition effects were also dissociable neuroanatomically, exhibiting different scalp distributions. The findings support the proposal that the modality-sensitive component of visual word repetition effects operates at an early, pre-semantic processing stage.

Event-related potentials differentiate the effects of aging on word and nonword repetition in explicit and implicit memory tasks.

Explicit memory declines with age while implicit memory remains largely intact. These experiments extended behavioral findings by recording event-related potentials (ERPs) in young and elderly adults during repetition priming and recognition memory paradigms. Words and pronounceable nonwords repeated after 1 of 3 delays. Stimuli were categorized as either word-nonword or old-new. Repeated items elicited more positive-going potentials in both tasks. Hemispheric asymmetries for word and nonword processing were observed during lexical decision: Repetition effects were larger over the left hemisphere for words and over the right hemisphere for nonwords. For the young, ERP repetition effects were larger during recognition memory. For old adults, conversely, repetition produced more positive-going waveforms during lexical decision. The elderly had ERP and behavioral deficits at long recognition delays. ERP repetition effects in the elderly, like behavioral performance, were preserved in an implicit task but impaired in an explicit memory task.

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

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

Modulation of event-related potentials by the repetition of drawings of novel objects

In experiment 1, event-related potentials (ERPs) were recorded from 13 scalp sites while subjects viewed a series of line drawings of novel objects. Most of the drawings were of objects that were structurally possible, while the remainder were of structurally impossible objects; the task was to respond to each presentation of an impossible object. Approximately one third of the possible objects were repetitions of the immediately preceding drawing. Compared to the ERPs elicited by first presentations, the ERPs elicited by repetitions were more negative-going. This negative repetition effect comprised two temporally and topographically distinct components. In experiment 2, subjects monitored drawings of unstructured patterns, so as to detect occasional ‘targets’ containing a pair of parallel lines. Repetitions of ‘non-target’ patterns elicited ERPs which were largely indistinguishable from those elicited by first presentations. Thus, the negative repetition effects found in experiment 1 are not merely a consequence of repeating visual patterns in a demanding discrimination task. Possible reasons why novel objects should elicit ERP repetition effects opposite in polarity to those observed in tasks employing verbal or meaningful pictorial stimuli are discussed.

Word repetition effects on event-related potentials in healthy young and old subjects, and in patients with alzheimer-type dementia

Event-related potentials (ERPs) were recorded from 16 healthy young (mean age 21 years) and 16 healthy old subjects (mean age 64 years), and from 11 subjects with a diagnosis of Dementia of Alzheimer Type (DAT). The task requirement was to attend to a series of visually presented words so as to respond to occasional animal names. Non-animal names repeated after either a single or six intervening items. In the young subjects ERPs evoked by repeated words dislayed a widespread, sustained positive-going shift relative to ERPs evoked by first presentations (the ERP repetition effect). This effect onset around 220 msec and did not differ as a function of inter-item lag. Other than for a delay in onset of approximately 80 msec, the ERP repetition effect in the healthy old group was in all respects equivalent to that of the young subjects. The ERP repetition effects in the DAT patients were statistically indistinguishable from those of an appropriately matched sub-set of the healthy old subjects. These results indicate that the ERP repetition effect remains robust in subjects in whom explicit memory has declined as a result of normal aging or DAT. Thus they suggest that the effect reflects processes independent of those underlying explicit memory, and that it may index a form of memory relatively unaffected by the pathology underlying DAT.

Modulation of event-related potentials by word repetition: the role of visual selective attention.

Event-related potentials (ERPs) were recorded while subjects viewed visually presented words, some of which occurred twice. Each trial consisted of two colored letter strings, the requirement being to attend to and make a word/nonword discrimination for one of the strings. Attention was manipulated by color in Experiment 1, and color and a precue were used in Experiment 2. As in previous ERP studies of word repetition, a positive offset to repeated words developed when both first and second presentations were the focus of attention. In Experiment 2, ERPs showed evidence of positive-going repetition effects in all conditions in which at least one of the two presentations of the repeated word was attended. In the visual modality, the positive-going ERP repetition effect occurs only when at least one of the two presentations of a repeated item is the object of attention, which suggests that one or more of the processes reflected by the effect is capacity limited.

Event-related potentials and repetition priming in young, middle-aged and elderly normal subjects

Although the structure of semantic memory appears to be unaffected with increasing age, there is evidence that older adults are less efficient at accessing stored memory representations. Aging also results in a decline in the ability to use contextual information effectively, suggesting a deficit in episodic memory processes. The present experiment examines the effects of age on memory retrieval of stored representations and the use of contextual information. Event-related potentials (ERP) were recorded to immediate and delayed word repetition during a lexical decision task. Three groups of subjects were tested: young (mean = 27.3 years), middle (mean = 46.7 years) and old (mean = 67.4 years). Behavioral facilitation due to repetition did not significantly differ across groups. With increasing age, the ERP waveform showed a positive shift which began around 300–400 ms post-stimulus and was apparent across all stimulus types and response conditions. This positive shift may reflect an age-related decrease in cortical excitation. Although the onset of the ERP repetition effect was not affected by age, its duration for both immediate and delayed repetition was significantly prolonged. In the light of recent models of ERP word repetition effects, these results suggest that processes related to accessing stored representations in memory are unaffected by age. The extended duration of the repetition effect and the increase in the magnitude of the effect of delayed repetition with age suggest that aging effects processes related to the retrieval and use of contextual information in integrating a stimulus with its context.