Evidence from partially valid cueing that words are processed serially

There has been a longstanding debate about whether lexical and semantic processing of words is serial or parallel. We addressed this debate using partially valid cueing, where one of two words is cued. The cue was valid on 80% and invalid on the other 20% of the trials. The task was semantic categorization, and performance was measured by accuracy. The new feature was to limit attentional switching using a postmask of consonants that closely followed the presentation of words. We found a large effect of cueing and, most importantly, performance for the uncued word was at chance. This chance performance was consistent with serial processing, but not with typical parallel processing. This result adds to the evidence from other recent studies that the lexical and semantic processing of words is serial.

Neutral and threatening distracter word stimuli are unnecessarily stored in working memory but do not differ in their degree of working memory storage

Evidence suggests that threatening stimuli induce attentional biases compared to neutral stimuli, leading to subsequent storage in working memory. The current study examined how threatening versus neutral word distracters influence attention, and how this affects the unnecessary storage of these task-irrelevant stimuli in working memory. We measured the N2pc and contralateral delay activity (CDA), two event-related potentials (ERPs) that index attentional selection and the number of items maintained in WM, respectively, as participants completed a lateralized change detection task using word stimuli. Our results replicated work demonstrating a CDA effect for word stimuli, and found that distracter words are unnecessarily stored in working memory. However, we observed non-significant differences in attentional bias and working memory storage between distracter word conditions, and individual variation in anxiety was not associated with these processes. Bayes Factor analyses supported these null effects, suggesting that differences between neutral and threatening distracter words are unlikely.

Dividing attention influences contextual facilitation and revision during language comprehension

Although we often seem to successfully comprehend language in the face of distraction, few studies have examined the role of sustained attention in critical components of sentence processing, such as integrating information over a sentence and revising predictions when unexpected information is encountered. The current study investigated the impact of attention on sentence processing using a novel dual-task paradigm. Participants read weakly and strongly constraining sentences with expected or unexpected endings while also tracking the motion of dots in the background, and their EEG was recorded. Under full attention, the amplitude of the N400 component of the ERP, a measure of semantic access, was reduced (facilitated) in a graded fashion by contextual strength and fit. This context-based facilitation was attenuated when attention was divided, suggesting that sustained attention is important for building up message-level representations. In contrast, the post-N400 frontal positivity that has been observed to prediction violations and associated with revision processes was unaffected by dividing attention. However, under divided attention, participants also elicited posteriorly-distributed effects to these violations. Thus, predictive processes seem to be engaged even when attention is divided, but additional resources may then be required to process unexpected information.

Reward supports flexible orienting of attention to category information and influences subsequent memory

Preparatory control of attention facilitates the efficient processing and encoding of an expected stimulus. However, this can occur at the expense of increasing the processing cost of unexpected stimuli. Preparatory control can be influenced by motivational factors, such as the expectation of a reward. Interestingly, expectation of a high reward can increase target processing, as well as reduce the cost associated with reorienting. Using a semantic cueing paradigm, we examined the interaction of reward expectation and cue-validity on semantic judgment performance and subsequent memory. Preparatory attention was assessed with pupillometry. Valid category cueing was associated with better semantic judgment performance and better subsequent memory compared to invalidly cued items. Higher reward also resulted in a larger pre-target pupil diameter, which could be indicative of increased preparatory task engagement or arousal. Critically, higher reward also reduced reorienting cost in both semantic judgment and subsequent memory performance. Our findings suggest that reward expectation can facilitate the effective control of preparatory attention for semantic information, and can support optimal goal-directed behavior based on changing task demands.

Modulation of parafoveal word processing by cognitive load during modified visual search tasks

During visual search for simple items, the amount of information that can be processed in parafoveal vision depends on the cognitive resources that are available. However, whether this applies to the semantic processing of words remains controversial. This work was designed to manipulate simultaneously two sources of cognitive load to study their impact on the depth of parafoveal word processing during a modified visual search task. The participants had to search for target words among parafoveally presented semantic, orthographic or target-unrelated distractor words while their electroencephalogram was recorded. The task-related load was manipulated by either giving target words in advance (literal task) or giving only a semantic clue to define them (categorical task). The foveal load was manipulated by displaying either a word or hash symbols at the centre of the screen. Parafoveal orthographic and semantic distractors had an impact on the early event-related potential component P2a only in the literal task and when hash symbols were displayed at the fovea, i.e., when both the task-related and foveal loads were low. The data show that all sources of cognitive load must be considered to understand how parafoveal words are processed in visual search contexts.

Effects of Task Difficulty on Neural Processes Underlying Semantics: An Event-Related Potentials Study

Purpose Improving the ability to listen efficiently in noisy environments is a critical goal for hearing rehabilitation. However, understanding of the impact of difficult listening conditions on language processing is limited. The current study evaluated the neural processes underlying semantics in challenging listening conditions. Method Thirty adults with normal hearing completed an auditory sentence processing task in 4-talker babble. Event-related brain potentials were elicited by the final word in high- or low-context sentences, where the final word was either highly expected or not expected, followed by a 4-alternative forced-choice response with either longer (1,000 ms), middle (700 ms), or shorter (400 ms) response time deadlines (RTDs). Results Behavioral accuracy was reduced, and reactions times were faster for shorter RTDs. N400 amplitudes, reflecting ease of lexical access, were larger when elicited by target words in low-context sentences followed by shorter compared with longer RTDs. Conclusions These results reveal that more neural resources are allocated for semantic processing/lexical access when listening difficulty increases. Differences between RTDs may reflect increased attentional allocation for shorter RTDs. These findings suggest that situational listening demands can impact the demands for cognitive resources engaged in language processing, which could significantly impact listener experiences across environments.

Auditory attention enhances processing of positive and negative words in inferior and superior prefrontal cortex

Visually presented emotional words are processed preferentially and effects of emotional content are similar to those of explicit attention deployment in that both amplify visual processing. However, auditory processing of emotional words is less well characterized and interactions between emotional content and task-induced attention have not been fully understood. Here, we investigate auditory processing of emotional words, focussing on how auditory attention to positive and negative words impacts their cerebral processing. A Functional magnetic resonance imaging (fMRI) study manipulating word valence and attention allocation was performed. Participants heard negative, positive and neutral words to which they either listened passively or attended by counting negative or positive words, respectively. Regardless of valence, active processing compared to passive listening increased activity in primary auditory cortex, left intraparietal sulcus, and right superior frontal gyrus (SFG). The attended valence elicited stronger activity in left inferior frontal gyrus (IFG) and left SFG, in line with these regions' role in semantic retrieval and evaluative processing. No evidence for valence-specific attentional modulation in auditory regions or distinct valence-specific regional activations (i.e., negative > positive or positive > negative) was obtained. Thus, allocation of auditory attention to positive and negative words can substantially increase their processing in higher-order language and evaluative brain areas without modulating early stages of auditory processing. Inferior and superior frontal brain structures mediate interactions between emotional content, attention, and working memory when prosodically neutral speech is processed.

The Fixation Distance to the Stimulus Influences ERP Quality: An EEG and Eye Tracking N400 Study

In a typical visual Event Related Potential (ERP) study, the stimulus is presented centrally on the screen. Normally an ERP response will be measured provided that the participant directs their gaze towards the stimulus. The aim of this study was to assess how the N400 component of an ERP was affected when the stimulus was presented in the foveal, parafoveal or peripheral vision of the participant's visual field. Utilizing stimuli that have previously produced an N400 response to action incongruities, the same stimuli sequences were presented at 0°, 4°, 8° and 12° of visual angle from a fixation location. In addition to the EEG data, eye tracking data were recorded to act as a fixation control method and to allow for eye artifact detection. The results show a significant N400 effect in the right parieto-temporal electrodes within the 0° visual angle condition. For the other conditions, the N400 effect was reduced (4°) or not present (8° and 12°). Our results suggest that the disappearance of the N400 effect with eccentricity is due to the fixation distance to the stimulus. However, variables like attentional allocation could have also had an impact on the results. This study highlights the importance of presenting a stimulus within the foveal vision of the participant in order to maximize ERP effects related to higher order cognitive processes.

Task-dependent modulation of word processing mechanisms during modified visual search tasks

During visual search for words, the impact of the visual and semantic features of words varies as a function of the search task. This event-related potential (ERP) study focused on the way these features of words are used to detect similarities between the distractor words that are glanced at and the target word, as well as to then reject the distractor words. The participants had to search for a target word that was either given literally or defined by a semantic clue among words presented sequentially. The distractor words included words that resembled the target and words that were semantically related to the target. The P2a component was the first component to be modulated by the visual and/or semantic similarity of distractors to the target word, and these modulations varied according to the task. The same held true for the later N300 and N400 components, which confirms that, depending on the task, distinct processing pathways were sensitized through attentional modulation. Hence, the process that matches what is perceived with the target acts during the first 200 ms after word presentation, and both early detection and late rejection processes of words depend on the search task and on the representation of the target stored in memory.

ERP correlates of letter identity and letter position are modulated by lexical frequency

The encoding of letter position is a key aspect in all recently proposed models of visual-word recognition. We analyzed the impact of lexical frequency on letter position assignment by examining the temporal dynamics of lexical activation induced by pseudowords extracted from words of different frequencies. For each word (e.g., BRIDGE), we created two pseudowords: A transposed-letter (TL: BRIGDE) and a replaced-letter pseudoword (RL: BRITGE). ERPs were recorded while participants read words and pseudowords in two tasks: Semantic categorization (experiment 1) and lexical decision (experiment 2). For high-frequency stimuli, similar ERPs were obtained for words and TL-pseudowords, but the N400 component to words was reduced relative to RL-pseudowords, indicating less lexical/semantic activation. In contrast, TL- and RL-pseudowords created from low-frequency stimuli elicited similar ERPs. Behavioral responses in the lexical decision task paralleled this asymmetry. The present findings impose constraints on computational and neural models of visual-word recognition.

The context-object-manipulation triad: cross talk during action perception revealed by fMRI

To recognize an action, an observer exploits information about the applied manipulation, the involved objects, and the context where the action occurs. Context, object, and manipulation information are hence expected to be tightly coupled in a triadic relationship (the COM triad hereafter). The current fMRI study investigated the hemodynamic signatures of reciprocal modulation in the COM triad. Participants watched short video clips of pantomime actions, that is, actions performed with inappropriate objects, taking place at compatible or incompatible contexts. The usage of pantomime actions enabled the disentanglement of the neural substrates of context-manipulation (CM) and context-object (CO) associations. There were trials in which (1) both manipulation and objects, (2) only manipulation, (3) only objects, or (4) neither manipulation nor objects were compatible with the context. CM compatibility effects were found in an action-related network comprising ventral premotor cortex, SMA, left anterior intraparietal sulcus, and bilateral occipito-temporal cortex. Conversely, CO compatibility effects were found bilaterally in lateral occipital complex. These effects interacted in subregions of the lateral occipital complex. An overlap of CM and CO effects was observed in the occipito-temporal cortex and the dorsal attention network, that is, superior frontal sulcus/dorsal premotor cortex and superior parietal lobe. Results indicate that contextual information is integrated into the analysis of actions. Manipulation and object information is linked by contextual associations as a function of co-occurrence in specific contexts. Activation of either CM or CO associations shifts attention to either action- or object-related relevant information.

Are depictive gestures like pictures? commonalities and differences in semantic processing

Conversation is multi-modal, involving both talk and gesture. Does understanding depictive gestures engage processes similar to those recruited in the comprehension of drawings or photographs? Event-related brain potentials (ERPs) were recorded from neurotypical adults as they viewed spontaneously produced depictive gestures preceded by congruent and incongruent contexts. Gestures were presented either dynamically in short, soundless video-clips, or statically as freeze frames extracted from gesture videos. In a separate ERP experiment, the same participants viewed related or unrelated pairs of photographs depicting common real-world objects. Both object photos and gesture stimuli elicited less negative ERPs from 400 to 600ms post-stimulus when preceded by matching versus mismatching contexts (dN450). Object photos and static gesture stills also elicited less negative ERPs between 300 and 400ms post-stimulus (dN300). Findings demonstrate commonalities between the conceptual integration processes underlying the interpretation of iconic gestures and other types of image-based representations of the visual world.

Evoked alpha and early access to the knowledge system: the P1 inhibition timing hypothesis

In this article, a theory is presented which assumes that the visual P1 reflects the same cognitive and physiological functionality as alpha (with a frequency of about 10 Hz).Whereas alpha is an ongoing process, the P1 is the manifestation of an event-related process. It is suggested that alpha and the P1 reflect inhibition that is effective during early access to a complex knowledge system (KS). Most importantly, inhibition operates in two different ways. In potentially competing and task irrelevant networks, inhibition is used to block information processing. In task relevant neural networks, however, inhibition is used to increase the signal to noise ratio (SNR) by enabling precisely timed activity in neurons with a high level of excitation but silencing neurons with a comparatively low level of excitation. Inhibition is increased to modulate the SNR when processing complexity and network excitation increases and when certain types of attentional demands - such as top-down control, expectancy or reflexive attention - increase. A variety of findings are reviewed to demonstrate that they can well be interpreted on the basis of the suggested theory. One interesting aspect thereby is that attentional benefits (reflected e.g., by a larger P1 for attended as compared to unattended items at contralateral sites) and costs (reflected e.g., by a larger P1 at ipsilateral sites) can both be interpreted in terms of inhibition. In the former case an increased P1 is associated with a more effective processing of the presented item (due to an inhibition modulated increase in SNR), in the latter case, however, with a suppression of item processing (due to inhibition that blocks information processing).

Effects of attention on what is known and what is not: MEG evidence for functionally discrete memory circuits

Recent results obtained with a neural-network model of the language cortex suggest that the memory circuits developing for words are both distributed and functionally discrete. This model makes testable predictions about brain responses to words and pseudowords under variable availability of attentional resources. In particular, due to their strong internal connections, the action-perception circuits for words that the network spontaneously developed exhibit functionally discrete activation dynamics, which are only marginally affected by attentional variations. At the same time, network responses to unfamiliar items - pseudowords - that have not been previously learned (and, therefore, lack corresponding memory representations) exhibit (and predict) strong attention dependence, explained by the different amounts of attentional resources available and, therefore, different degrees of competition between multiple memory circuits partially activated by items lacking lexical traces. We tested these predictions in a novel magnetoencephalography experiment and presented subjects with familiar words and matched unfamiliar pseudowords during attention demanding tasks and under distraction. The magnetic mismatch negativity (MMN) response to words showed relative immunity to attention variations, whereas the MMN to pseudowords exhibited profound variability: when subjects attended the stimuli, the brain response to pseudowords was larger than that to words (as typically observed in the N400); when attention was withdrawn, the opposite pattern emerged, with the response to pseudowords reduced below the response to words. Main cortical sources of these activations were localized to superior-temporal cortex. These results confirm the model's predictions and provide evidence in support of the hypothesis that words are represented in the brain as action-perception circuits that are both discrete and distributed.