W. Caroline West

Imaginal, Semantic, and Surface-Level Processing of Concrete and Abstract Words: An Electrophysiological Investigation

Words representing concrete concepts are processed more quickly and efficiently than words representing abstract concepts. Concreteness effects have also been observed in studies using event-related brain potentials (ERPs). The aim of this study was to examine concrete and abstract words using both reaction time (RT) and ERP measurements to determine (1) at what point in the stream of cognitive processing concreteness effects emerge and (2) how different types of cognitive operations influence these concreteness effects. Three groups of subjects performed a sentence verification task in which the final word of each sentence was concrete or abstract. For each group the truthfulness judgment required either (1) image generation, (2) a semantic decision, or (3) evaluation of surface characteristics. Concrete and abstract words produced similar RTs and ERPs in the surface task, suggesting that postlexical semantic processing is necessary to elicit concreteness effects. In both the semantic and imagery tasks, RTs were shorter for concrete than for abstract words. This difference was greatest in the imagery task. Also, in both of these tasks concrete words elicited more negative ERPs than abstract words between 300 and 550 msec (N400). This effect was widespread across the scalp and may reflect activation in a linguistic semantic system common to both concrete and abstract words. ERPs were also more negative for concrete than abstract words between 550 and 800 msec. This effect was more frontally distributed and was most evident in the imagery task. We propose that this later anterior effect represents a distinct ERP component (N700) that is sensitive to the use of mental imagery. The N700 may reflect the access of specific characteristics of the imaged item or activation in a working memory system specific to mental imagery. These results also support the extended dual-coding hypothesis that superior associative connections and the use of mental imagery both contribute to processing advantages for concrete words over abstract words.

Event-related potentials during discourse-level semantic integration of complex pictures

This study examined event-related potentials (ERPs) elicited in response to semantic processing of non-verbal stories. ERPs were recorded from 29 scalp electrodes on 16 participants while they viewed series of complex gray-scale pictures, each of which relayed a simple story. The final picture of each story was either congruous or incongruous with the preceding context. Participants made delayed meaningfulness judgments for each story. Averaged ERPs time-locked to the onset of the final picture were more negative for incongruous than congruous pictures. Two distinct components were sensitive to congruency. The first component peaked at approximately 325 ms (N300) and was distributed over central and frontal sites. The second component peaked at approximately 500 ms and also had a centro-frontal maximum but was more widespread than the earlier component (anterior N400). The distinct scalp topographies of these two negativities provide strong evidence that the N300 and N400 are separate and distinguishable components. Furthermore, the presence of the N300 in this exclusively pictorial task suggests that the N300 is specific to the semantic processing of non-verbal stimuli and is not due to linguistic mediation. This study also revealed that the N400 can be modulated by discourse-level coherence manipulations with pictures. Finally, the different patterns of ERP effects observed during the semantic processing of verbal and non-verbal information suggest that non-identical neuronal sources, and thus non-identical representational systems, are accessed by these different types of materials. These findings strongly support at least partial modularity of semantic representations and processing mechanisms in the human brain.

Determinants of Bold Signal Correlates of Processing Object-Extracted Relative Clauses

Event-related functional magnetic resonance imaging (fMRI) was used to investigate the determinants of blood oxygenation level-dependent (BOLD) signal correlates of processing relative clauses. Matched pairs of sentences that differed in their processing demands were compared. One member of the pair consisted of a syntactically simpler object-subject (OS) sentence, containing a subject-relativized clause attached to the object noun phrase. The second member of the pair consisted of a syntactically more complex subject-object (SO) sentence, containing an object-relativized clause attached to the subject noun phrase. Participants made plausibility judgments about the sentences in whole sentence visual presentation. Voxel-wise statistical activation maps showed increased BOLD signal in multiple cortical regions for complex compared to simple syntactic structures. This pattern was found for plausible sentences only and, within the set of plausible sentences, for SO sentences in which the head noun of the relative clause was animate and the subject noun of the relative clause was inanimate. These results require a re-interpretation of previous results with the same materials using positron emission tomography.

The Influence of Stimulus Deviance on Electrophysiologic and Behavioral Responses to Novel Events

This study investigated the role of stimulus deviance in determining electrophysiologic and behavioral responses to novelty. Stimulus deviance was defined in terms of differences either from the immediately preceding context or from long-term experience. Subjects participated in a visual event-related potential (ERP) experiment, in which they controlled the duration of stimulus viewing with a button press, which served as a measure of exploratory behavior. Each of the three experimental conditions included a frequent repetitive background stimulus and infrequent stimuli that deviated from the background stimulus. In one condition, both background and deviant stimuli were simple, easily recognizable geometric figures. In another condition, both background and deviant stimuli were unusual/unfamiliar figures, and in a third condition, the background stimulus was a highly unusual figure, and the deviant stimuli were simple, geometric shapes. Deviant stimuli elicited larger N2-P3 amplitudes and longer viewing durations than the repetitive background stimulus, even when the deviant stimuli were simple, familiar shapes and the background stimulus was a highly unusual figure. Compared to simple, familiar deviant stimuli, unusual deviant stimuli elicited larger N2-P3 amplitudes and longer viewing times. Within subjects, the deviant stimuli that evoked the largest N2-P3 responses also elicited the longest viewing durations. We conclude that deviance from both immediate context and long-term prior experience contribute to the response to novelty, with the combination generating the largest N2-P3 amplitude and the most sustained attention. The amplitude of the N2-P3 may reflect how much uncertainty is evoked by a novel visual stimulus and signal the need for further exploration and cognitive processing.

The neural organization of semantic memory: Electrophysiological activity suggests feature-based segregation

Despite decades of research, it remains controversial whether semantic knowledge is anatomically segregated in the human brain. To address this question, we recorded event-related potentials (ERPs) while participants viewed pictures of animals and tools. Within the 200-600-ms epoch after stimulus presentation, animals (relative to tools) elicited an increased anterior negativity that, based on previous ERP studies, we interpret as associated with semantic processing of visual object attributes. In contrast, tools (relative to animals) evoked an enhanced posterior left-lateralized negativity that, according to prior research, might reflect accessing knowledge of characteristic motion and/or more general functional properties of objects. These results support the hypothesis of the neuroanatomical knowledge organization at the level of object features: the observed neurophysiological activity was modulated by the features that were most salient for object recognition. The high temporal resolution of ERPs allowed us to demonstrate that differences in processing animals and tools occurred specifically within the time-window encompassing semantic analysis.

Functional Magnetic Resonance Imaging Reveals Neuroanatomical Dissociations During Semantic Integration in Schizophrenia

BACKGROUND Schizophrenia symptoms can be conceptualized in terms of a breakdown of a balance between 1) activating, retrieving, and matching stored representations to incoming information (semantic memory-based processing) and 2) fully integrating activated semantic representations with one another and with other types of representations to form a gestalt representation of meaning (semantic integration). Semantic memory-based processes are relatively more dependent on inferior frontal and temporal cortices, whereas particularly demanding integrative processes additionally recruit the dorsolateral prefrontal cortex (DLPFC) and sometimes parietal cortices. We used functional magnetic resonance imaging (fMRI) to determine whether the modulation of temporal/inferior frontal cortices and the DLPFC can be neuroanatomically dissociated in schizophrenia, as semantic integration demands increase. Integration demands were manipulated by varying the nature (concrete vs. abstract) and the congruity (incongruous vs. congruous) of words within sentences. METHODS Sixteen right-handed schizophrenia patients and 16 healthy volunteers, matched on age and parental socioeconomic status, underwent event-related fMRI scanning while they read sentences. Blood oxygen level dependent (BOLD) effects were contrasted to words within sentences that were 1) concrete versus abstract and 2) semantically incongruous versus congruous with their preceding contexts. RESULTS In both contrasts, large networks mediating the activation and retrieval of verbal and imagistic representations were normally modulated in patients. However, unlike control subjects, patients failed to recruit the DLPFC, medial frontal and parietal cortices to incongruous (relative to congruous) sentences, and failed to recruit the DLPFC to concrete (relative to abstract) sentences. CONCLUSIONS As meaning is built from language, schizophrenia patients demonstrate a neuroanatomical dissociation in the modulation of temporal/inferior frontal cortices and the DLPFC.

Task and semantic relationship influence both the polarity and localization of hemodynamic modulation during lexico-semantic processing

This study examined how task (implicit vs. explicit) and semantic relationship (direct vs. indirect) modulated hemodynamic activity during lexico‐semantic processing. Participants viewed directly related, indirectly related, and unrelated prime‐target word‐pairs as they performed (a) an implicit lexical decision (LD) task in which they decided whether each target was a real word or a nonword, and (b) an explicit relatedness judgment (RJ) task in which they determined whether each word‐pair was related or unrelated in meaning. Task influenced both the polarity and neuroanatomical localization of hemodynamic modulation. Semantic relationship influenced the neuroanatomical localization of hemodynamic modulation. The implicit LD task was primarily associated with inferior prefrontal and ventral inferior temporal/fusiform hemodynamic response suppression to directly related (relative to unrelated) word‐pairs, and with more widespread temporal–occipital response suppression to indirectly related (relative to unrelated) word‐pairs. In contrast, the explicit RJ task was primarily associated with left inferior parietal hemodynamic response enhancement to both directly and indirectly related (relative to unrelated) word‐pairs, as well as with additional left inferior prefrontal hemodynamic response enhancement to indirectly related (relative to unrelated) word‐pairs. These findings are discussed in relation to the specific neurocognitive processes thought to underlie implicit and explicit semantic processes. Hum Brain Mapp, 2008.

Question/statement judgments: an fMRI study of intonation processing.

We examined changes in fMRI BOLD signal associated with question/statement judgments in an event‐related paradigm to investigate the neural basis of processing one aspect of intonation. Subjects made judgments about digitized recordings of three types of utterances: questions with rising intonation (RQ; e.g., “She was talking to her father?”), statements with a falling intonation (FS; e.g., “She was talking to her father.”), and questions with a falling intonation and a word order change (FQ; e.g., “Was she talking to her father?”). Functional echo planar imaging (EPI) scans were collected from 11 normal subjects. There was increased BOLD activity in bilateral inferior frontal and temporal regions for RQ over either FQ or FS stimuli. The study provides data relevant to the location of regions responsive to intonationally marked illocutionary differences between questions and statements. Hum Brain Mapping 23:85–98, 2004.

Understanding human original actions directed at real-world goals: The role of the lateral prefrontal cortex

Adaptive, original actions, which can succeed in multiple contextual situations, require understanding of what is relevant to a goal. Recognizing what is relevant may also help in predicting kinematics of observed, original actions. During action observation, comparisons between sensory input and expected action kinematics have been argued critical to accurate goal inference. Experimental studies with laboratory tasks, both in humans and nonhuman primates, demonstrated that the lateral prefrontal cortex (LPFC) can learn, hierarchically organize, and use goal-relevant information. To determine whether this LPFC capacity is generalizable to real-world cognition, we recorded functional magnetic resonance imaging (fMRI) data in the human brain during comprehension of original and usual object-directed actions embedded in video-depictions of real-life behaviors. We hypothesized that LPFC will contribute to forming goal-relevant representations necessary for kinematic predictions of original actions. Additionally, resting-state fMRI was employed to examine functional connectivity between the brain regions delineated in the video fMRI experiment. According to behavioral data, original videos could be understood by identifying elements relevant to real-life goals at different levels of abstraction. Patterns of enhanced activity in four regions in the left LPFC, evoked by original, relative to usual, video scenes, were consistent with previous neuroimaging findings on representing abstract and concrete stimuli dimensions relevant to laboratory goals. In the anterior left LPFC, the activity increased selectively when representations of broad classes of objects and actions, which could achieve the perceived overall behavioral goal, were likely to bias kinematic predictions of original actions. In contrast, in the more posterior regions, the activity increased even when concrete properties of the target object were more likely to bias the kinematic prediction. Functional connectivity was observed between contiguous regions along the rostro-caudal LPFC axis, but not between the regions that were not immediately adjacent. These findings generalize the representational hierarchy account of LPFC function to diverse core principles that can govern both production and comprehension of flexible real-life behavior.

Cortical activation during a semantic priming lexical decision task as revealed by event-related fMRI

Previous studies using event-related brain potentials (ERPs) have shown an increase in the amplitude of the N400 component m response to words or pseudowords preceded by unrelated prime words than to words preceded by semantically related prime words (e.g., Holcomb, 1988). We report here an fMRI study aimed at identifying the cortical regions underlying this effect. More generally, the goal of this study was to localize the neuroanatomical substrates of semantic information processing.