An electrophysiological investigation of indirect semantic priming

In two experiments, direct and indirect semantic priming were measured using event-related potentials. In Experiment 1, participants rated the relatedness between prime and target on a seven-point scale. In Experiment 2, participants simply read the primes and targets as they monitored for a semantic category in probe filler items. Significant direct and indirect N400 priming effects were observed in both experiments. In Experiment 1, the indirect N400 priming effect remained significant when indirectly related and unrelated word pairs were matched for participants' explicit relatedness judgments. In both experiments, the indirect N400 priming effects were preserved when indirectly related and unrelated word pairs were matched on more global and objective measures of semantic similarity. These findings are discussed in the context of current theoretical models of semantic memory and semantic priming.     

Electrophysiological evidence for task effects on semantic priming in auditory word processing

Event-related brain potentials (ERPs) associated with semantic relatedness were recorded in two auditory word recognition tasks. In the Memorize task, subjects listened to a list of words in anticipation of a subsequent recognition test. In the Count Nonwords task, subjects silently counted the number of nonwords occurring within a list of words. Within each list, target words were either semantically related or unrelated to the immediately preceding word. As in comparable visual tasks, the amplitude of a negative ERP component (N400) was significantly attenuated when targets were preceded by semantically related primes. This attenuation was greater in the Memorize than in the Count Nonwords task. These data are consistent with the view that the sensitivity of N400 amplitude to semantic relatedness is modulated by task variables that manipulate depth of processing.     

Semantic transparency and masked morphological priming: an ERP investigation

The role of semantics in the segmentation of morphologically complex words was examined using event-related potentials (ERPs) recorded to target words primed by semantically transparent (hunter-hunt,) opaque (corner-corn), and orthographically related (scandal-scan) masked primes. Behavioral data showed that only transparent items gave rise to priming. The ERP data showed both N250 and the N400 effects with transparent items generating greater priming than orthographic or opaque. Furthermore, priming effects across conditions revealed the existence of a significant linear trend, with transparent items showing the greatest effects and orthographic items the smallest, suggesting that these priming effects vary as a function of morphological structure and semantic transparency. The results are discussed in terms of a model of morphological processing.     

Auditory and visual semantic priming using different stimulus onset asynchronies: An event-related brain potential study

Semantic priming effects (behavioral and electrophysiological) were compared in the visual and auditory modalities across three stimulus onset asynchronies (SOAs; 0, 200, and 800 ms). When both prime and target were presented in the visual modality (the prime just to the left of a fixation point and the target to the right) there were N400 priming effects present across the three SOAs. However, the N400 in the 0-ms SOA condition extended longer in time (800 vs. 500 ms) than in the other SOAs. When both the prime and target were presented in the auditory modality (the prime to the right ear and the target to the left), the largest priming effects were found for the 800-ms SOA. Moreover, there was a relatively early priming effect present in the 0- and 800-ms SOA conditions but not in the 200-ms condition. The results are discussed in terms of modality differences in the time course of word comprehension processes.     

Emotionally positive stimuli facilitate lexical decisions-an ERP study

The influence of briefly presented positive and negative emotional pictures on lexical decisions on positive, negative and neutral words or pseudowords was investigated. Behavioural reactions were the fastest following all positive stimuli and most accurate for positive words. Stimulus-locked ERPs revealed enhanced early posterior and late parietal attention effects following positive pictures. A small neural affective priming effect was reflected by P3 modulation, indicating more attention allocation to affectively incongruent prime-target pairs. N400 was insensitive to emotion. Response-locked ERPs revealed an early fronto-central negativity from 480 ms before reactions to positive words. It was generated in both fronto-central and extra-striate visual areas, demonstrating a contribution of perceptual and, notably, motor preparation processes. Thus, no behavioural and little neural evidence for congruency-driven affective priming with emotional pictures was found, but positive stimuli generally facilitated lexical decisions, not only enhancing perception, but also acting rapidly on response preparation and by-passing full semantic analysis.     

The interdependence of spatial attention and lexical access as revealed by early asymmetries in occipito-parietal ERP activity

A test of the possible functional interaction between mechanisms subserving spatial attention and lexical access was devised by displaying one green and one red string of letters, one to the left and one to the right of fixation, and having participants attend to a target string defined by color while ignoring the other distractor string. The target string for a delayed lexical decision task could be a word or a nonword. The distractor was always a word. When the target was a word, target and distractor were associatively related on half of the trials and not related in the other trials. The event-related potential time-locked to the onset of the letter strings produced an N2pc (a greater negativity at scalp sites contralateral to the target relative to the ipsilateral sites arising at about 170 ms poststimulus). N2pc amplitude was reduced when the words were related relative to when they were not related. The results provide direct, online evidence that the rapid activation of meaning by visual words can influence the efficiency of the deployment of spatial attention.     

Relatedness proportion effects on masked associative priming: an ERP study

Abstract The effect of relatedness proportion (the percentage of related words in a list) on associative priming was investigated in two masked priming experiments. In Experiment 1, subjects were randomly assigned to either a high (80%) or low (20%) relatedness proportion condition and performed a lexical decision task. Semantically related and unrelated primes were briefly flashed (50 ms) before the targets and were preceded by a mask that prevented their overt identification. In Experiment 2, subjects were tested in both relatedness proportion conditions in a categorization task; the N400, an electrophysiological index of lexical and semantic priming, was measured in trials that did not require a button press. Behavioral and electrophysiological priming effects were observed in both high and low relatedness proportion conditions. The observed priming effects were not modulated by relatedness proportion. The results are discussed in terms of current theories of associative priming.     

Event-related brain potentials evoked by verbs and nouns in a primed lexical decision task

We investigated whether verbs and nouns evoke comparable behavioral and N400 effects in a primed lexical decision task. Twenty-nine students were tested, 13 in a pilot study in which only response times and error rates were collected and 16 in a study in which ERPs were recorded from 124 scalp electrodes. Stimuli were noun-noun and verb-verb pairs with the targets bearing either a strong, a moderate, or no semantic association to the prime or being a pseudoword. Behavioral data revealed comparable priming effects for both word categories. These proved to be independent from the SOA (250 and 800 ms) and they followed the well-known pattern of decreasing response times and error rates with increasing relatedness between target and prime. ERPs revealed pronounced N400 effects for both word categories with a larger amplitude for noun than for verb pairs. A systematic analysis of topographic differences between noun- and verb-evoked ERPs and N400 effects, respectively, gave no convincing support to the hypothesis that the two word categories activate distinct neuronal networks.     

An electrophysiological investigation of semantic priming with pictures of real objects

Event-related potentials were recorded using color pictures of real objects. Participants made relatedness judgments for pictures that were highly, moderately, or unrelated to a picture of a preceding prime object (Experiment 1) or object identification decisions for related/easily identified, unrelated/easily identified, and unrelated/unidentifiable objects preceded by prime objects (Experiment 2). Unrelated pictures elicited larger event-related potential negativities between 225 and 500 ms than did related pictures, although the first portion of this epoch had a more frontal distribution than did the later portion. The later epoch differentiated the unrelated from the moderately related and the moderately related from the highly related pictures (Experiment 1), but the early epoch produced differences only between the unrelated and related pictures (Experiments 1 and 2). This pattern supports the existence of two separate components, an anterior, image-specific N300 and a later, central/parietal amodal N400.     

Concreteness of positive word contributions to affective priming: An ERP study

Recent behavioral data suggest that the concreteness of positive words modulates subsequent cognitive processing; however, the underlying physiological processes of this influence are not well understood. To explore this process, positive-abstract words or positive-concrete words were used as primes when participants performed a lexical decision task during the measurement of event-related potentials (ERPs). The behavioral data revealed a significant affective priming effect (i.e., incongruent > congruent) only for abstract word pairs. The N400 amplitude was larger for affectively incongruent pairs compared to affectively congruent pairs, independent of the prime concreteness. The amplitude of the late positive component (LPC) was modulated by prime concreteness. The processing of positive-abstract targets was facilitated by previous exposure to a congruent prime, as reflected by the reduced LPC, which has been thought to reflect attentional and memory processes. However, no differences in the LPC amplitude were found between congruent and incongruent-concrete pairs. These findings suggest that the influence of the concreteness of positive words mainly occurs during the decision-making processing and memory-related stages.     

Automatic word form processing in masked priming: an ERP study

Five prime types (unrelated words, pronounceable nonwords, illegal strings of letters, false fonts, or neutral strings of Xs) preceded word and nonword targets in a masked priming study designed to investigate word form processing as indexed by event-related potentials (ERPs). Participants performed a lexical decision task on targets. In the 150-250-ms epoch at fronto-central, central, and temporo-parietal sites ERPs were smallest to targets preceded by words and nonwords, followed by letter strings, false fonts, and finally neutral primes. This refractory pattern sensitive to orthography supports the view that ERPs in the 150-250-ms epoch index activation of neural systems involved in word form processing and suggests that such activation may be graded, being maximal with word-like stimuli and relatively reduced with alphabet-like stimuli. Further, these results from a masked priming paradigm confirm the automatic nature of word form processing.     

An electrophysiological study of cross-modal repetition priming

Few studies have focused on language processing across modalities. Two experiments examined between-modality interactions across three prime-target intervals (0, 200, and 800 ms) in a cross-modal repetition priming paradigm. Event-related potentials were recorded to auditory targets following visual primes (Experiment 1) or visual targets following auditory primes (Experiment 2). In Experiment 1 robust repetition effects were found for auditory targets as early as 100 ms, and continued through the N400 epoch. Moreover, these visual-auditory repetition effects were large across all three prime-target intervals although they onset 200 ms later at the shortest interval. In Experiment 2 repetition effects to visual targets started later (at 200 ms), but also offset relatively later (approximately 1000 ms). These auditory-visual repetition effects were both smaller overall and absent for the two shortest prime-target intervals during the typical N400 window.     

Missed prime words within the attentional blink evoke an N400 semantic priming effect

When subjects identified a target among distractors in a rapid serial visual presentation task, the detection of a subsequent target is impaired (attentional blink). By measuring event-related potentials (ERPs) we investigated if the processing of an unidentified prime word elicits the N400 semantic priming effect. Subjects (N = 12) had to identify three target words among distractors in a rapid serial visual presentation task. We varied the association strength between a prime (second target) and a probe (third target). The detection of the prime was impaired. Missed primes did not elicit a P300, indicating that they were not explicitly recognized. Despite this difference between recognized and missed primes, the N400 effect was present in both cases. This result suggests that automatic spread of activation (ASA) can be evoked by missed primes within the attentional blink. It furthermore demonstrates that ASA is sufficient to evoke the N400 effect.     

Modulation of the attentional span by foveal and parafoveal task load: An ERP study using attentional probes

Due to capacity limitation, visual attention must be focused to a limited region of the visual field. Nevertheless, it is assumed that the size of that region may vary with task demands. We aimed to obtain direct evidence for the modulation of visuospatial attention as a function of foveal and parafoveal task load. Participants were required to fixate the center word of word triplets. In separate task blocks, either just the fixated word or both the fixated and the parafoveal word to the right should be semantically classified. The spatiotemporal distribution of attention was assessed with task‐irrelevant probes flashed briefly at center or parafoveal positions, during or in between word presentation trials. The N1 component of the ERP elicited by intertrial probes at possible target positions increased with task demands within a block. These results suggest the recruitment of additional attentional resources rather than a redistribution of a fixed resource pool, which persists across trials.     

Intentional forgetting reduces the semantic processing of to‐be‐forgotten items: An ERP study of item‐method directed forgetting

In two ERP experiments, we examined whether active inhibition is involved in intentional forgetting. Both experiments consisted of a nondirected‐forgetting (nDF) and a directed‐forgetting (DF) block. Participants were sequentially presented with a prime, an R/F (remember/forget) cue, and a target. Participants made lexical decisions to both the primes and targets (Experiment 1) or only to the targets (Experiment 2). They were also instructed to remember or to forget the primes in response to the R/F cues in the DF block but to ignore these cues in the nDF block. The N400 semantic priming effect was observed when comparing the ERPs elicited by semantically unrelated and related targets in the DF block. In comparison to the nDF block, the N400 effect was greatly reduced for targets preceded by F cues in the DF block. These findings suggest that semantic processing is reduced by the instruction to forget and active inhibition is involved in intentional forgetting.     

Measurement of ERP latency differences: a comparison of single-participant and jackknife-based scoring methods

We used computer simulations to evaluate different procedures for measuring changes in the onset latency of a representative range of event-related components (the auditory and visual N1, P3, N2pc, and the frequency-related P3 difference wave). These procedures included several techniques to determine onset latencies combined with approaches using both single-participant average waveforms and jackknife-subsample average waveforms. In general, the jackknife-based approach combined with the relative criterion technique or combined with the fractional area technique (J.C. Hansen & S.A. Hillyard, 1980; S.J. Luck, 2005) provided the most accurate method and the greatest statistical power, with no inflation of Type I error rate.     

Neural mechanisms of subliminal priming for traumatic episodic memory: An ERP study

Event-related brain potentials (ERPs) were measured to study the electrophysiological mechanisms of subliminal priming of traumatic episodic memory. Twenty-four Chinese subjects who had experienced the great Sichuan earthquake in 2008 were classified either as normal control or as post-traumatic stress disorder (PTSD) subjects. Results showed that subliminally presented earthquake-related words elicited two significantly more positive ERP deflections (P2 and P300) than did earthquake-unrelated words between 250–300 ms and 340–400 ms post-stimulus periods for the PTSD group, but not for the control group. Dipole source analysis showed that the P2 was mainly generated in the posterior cingulate cortex (PCC), which appeared to be related to unconscious attentional resource allocation to the earthquake-related words. In addition, the P300 was found to be generated in the parahippocampal gyrus, which seemed to be related to the involuntary activation of traumatic episodic memory. These results indicated that catastrophic earthquake experiences made some subjects extremely sensitive and hyper-responsive to trauma-related information.     

Influence of acute stress on response inhibition in healthy men: An ERP study

The current study investigated the influence of acute stress and the resulting cortisol increase on response inhibition and its underlying cortical processes, using EEG. Before and after an acute stressor or a control condition, 39 healthy men performed a go/no‐go task while ERPs (N2, P3), reaction times, errors, and salivary cortisol were measured. Acute stress impaired neither accuracy nor reaction times, but differentially affected the neural correlates of response inhibition; namely, stress led to enhanced amplitudes of the N2 difference waves (N2d, no‐go minus go), indicating enhanced response inhibition and conflict monitoring. Moreover, participants responding to the stressor with an acute substantial rise in cortisol (high cortisol responders) showed reduced amplitudes of the P3 of the difference waves (P3d, no‐go minus go) after the stressor, indicating an impaired evaluation and finalization of the inhibitory process. Our findings indicate that stress leads to a reallocation of cognitive resources to the neural subprocesses of inhibitory control, strengthening premotor response inhibition and the detection of response conflict, while concurrently diminishing the subsequent finalization process within the stream of processing.     

Interactions of age of acquisition and lexical frequency effects with phonological regularity: An ERP study

Across languages, lexical frequency and age of acquisition (AoA) are important predictors of word reading that are naturally correlated, and both variables have been shown to interact with phonological regularity. Previous behavioral findings in Chinese have shown stronger regularity effects in low frequency relative to high frequency characters. Meanwhile, the arbitrary mapping hypothesis predicts stronger interference effects in late‐acquired irregular words. This study examined the neural bases of these phenomena in Chinese using a delayed naming task with 480 single characters. Single‐trial ERP analyses were conducted to contrast the interactions of frequency or AoA effects with phonological regularity, while controlling for the other factor. Results showed differential and significant effects of AoA and frequency at the N400 and late positive component (LPC), respectively, indicating their independence. ERP interaction patterns of frequency and regularity in Chinese were observed for the first time in the LPC time window and suggested semantic interference from sublexical units during character reading. Interaction of AoA and regularity at the N400 could be explained by the semantic hypothesis but appeared inconsistent with the arbitrary mapping hypothesis.     

Semantic priming and stimulus degradation: Implications for the role of the N400 in language processing

Two experiments explored the effects of stimulus degradation on behavioral and event-related potential (ERP) measures of semantic priming. The primary goal was to help elucidate the psychological processes that underlie the N400 component. In both experiments, subjects made speeded lexical decisions to words and pseudowords preceded by either semantically related or unrelated prime words. In one block of trials, the target stimuli were intact, and in a second block they were degraded by removing a random 33% of the elements making up each letter of the target (Experiment 1) or by overlaying a matrix of dots on the target (Experiment 2). In both experiments, subjects responded faster and more accurately to related targets than to unrelated targets (behavioral semantic priming effect), and this priming effect was greater when the target was degraded. However, although the N400 component was larger for unrelated than related targets (ERP semantic priming effect), there was no evidence that this difference was larger in the degraded block of either experiment. These results indicate that the behavioral and ERP measures reported here appear to be tapping into different components of the process(es) involved in semantic priming. The implication of the results for the linguistic processes underlying the N400 are discussed.