Bihua Cao

Automatic processing of taxonomic and thematic relations in semantic priming - Differentiation by early N400 and late frontal negativity.

Most current models of knowledge organization are based on hierarchical (plant-pine) or taxonomic categories (animal-plant). Another important organizational pattern is thematic categories, which performs external or complementary roles in the same scenario or event (bee-honey). The goal of this study was to explore the processing of hierarchical categories and thematic categories under automatic processing conditions that minimize strategic influences. The Evoked response potential (ERP) procedure was used to examine the time course of semantic priming for category members with a short stimulus onset asynchrony (SOA) of 300ms as participants performed a lexical decision task. Six experimental conditions were compared: hierarchical relations (offspring-grandson), internal features (gold-golden), productive relations (bee-honey), script relations (room-tenant), unrelated (star-spoon), and non-word trials (star-derf). We found faster reaction times for related prime-target pairs than unrelated pairs except for productive relations. The ERP data showed that an early N400 effect (200-400ms) was more negative for unrelated words than for all related words. Furthermore, a frontal negativity (400-550ms) elicited by productive relations was smaller (more positive) than other related words. We suggest that the smaller frontal negativity in the processing of productive relations indicates their increased salience in knowledge structure compared to less prominent hierarchical relations. Indeed, the allocation of attentional resources and subsequent recruitment of additional memory processing might be two of the hallmarks of thematic relations.

Functional imaging of brain responses to different outcomes of hypothesis testing: revealed in a category induction task

Functional magnetic resonance imaging (fMRI) was used to examine differences in brain activation that occur when a person receives the different outcomes of hypothesis testing (HT). Participants were provided with a series of images of batteries and were asked to learn a rule governing what kinds of batteries were charged. Within each trial, the first two charged batteries were sequentially displayed, and participants would generate a preliminary hypothesis based on the perceptual comparison. Next, a third battery that served to strengthen, reject, or was irrelevant to the preliminary hypothesis was displayed. The fMRI results revealed that (1) no significant differences in brain activation were found between the 2 hypothesis-maintain conditions (i.e., strengthen and irrelevant conditions); and (2) compared with the hypothesis-maintain conditions, the hypothesis-reject condition activated the left medial frontal cortex, bilateral putamen, left parietal cortex, and right cerebellum. These findings are discussed in terms of the neural correlates of the subcomponents of HT and working memory manipulation.

Electrophysiological difference between mental state decoding and mental state reasoning.

Previous studies have explored the neural mechanism of Theory of Mind (ToM), but the neural correlates of its two components, mental state decoding and mental state reasoning, remain unclear. In the present study, participants were presented with various photographs, showing an actor looking at 1 of 2 objects, either with a happy or an unhappy expression. They were asked to either decode the emotion of the actor (mental state decoding task), predict which object would be chosen by the actor (mental state reasoning task), or judge at which object the actor was gazing (physical task), while scalp potentials were recorded. Results showed that (1) the reasoning task elicited an earlier N2 peak than the decoding task did over the prefrontal scalp sites; and (2) during the late positive component (240-440 ms), the reasoning task elicited a more positive deflection than the other two tasks did at the prefrontal scalp sites. In addition, neither the decoding task nor the reasoning task has no left/right hemisphere difference. These findings imply that mental state reasoning differs from mental state decoding early (210 ms) after stimulus onset, and that the prefrontal lobe is the neural basis of mental state reasoning.

Electrophysiological correlates of hypothesis testing.

Where and how the cortical areas are activated when a person receives the result of hypothesis testing is still unclear. By using a category induction task, this study provided participants with various batteries and asked them to learn which kind of batteries were charged. After learning, they were required to give a response to the probe stimuli. In each trial, two batteries were displayed sequentially, and a preliminary hypothesis could be formed based on the perceptual analysis of the batteries. Then, a third battery served to strengthen, reject, or maintain the former hypothesis was presented. The electrophysiological results revealed an increased late positive complexes when the hypothesis was rejected, reflecting a process of hypothesis evaluation and memory-context updating.

Different brain potentials evoked at distinct phases of rule learning

The neural mechanisms of rule learning are of interest to cognitive neuroscientists, but the time course of rule induction and the related brain potential remain unclear. In this study, event-related brain potentials (ERPs) were measured during the distinct phases of rule induction. Participants in two experiments were presented with a series of Arabic numbers and were asked to detect the hidden rules. The ERP results revealed that (a) the rule-discovery trials elicited a larger P3 component than the nondiscovery trials, reflecting the initial identification of the regularity of number series, and (b) when a new instance was incongruent with the previously acquired rule, a larger N2 and enhanced late positive component were elicited, reflecting the process of mismatch detection and the updating of working memory context.

Electrophysiological evidence of separate pathways for the perception of depth and 3D objects

Previous studies have investigated the neural mechanism of 3D perception, but the neural distinction between 3D-objects and depth processing remains unclear. In the present study, participants viewed three types of graphics (planar graphics, perspective drawings, and 3D objects) while event-related potentials (ERP) were recorded. The ERP results revealed the following: (1) 3D objects elicited a larger and delayed N1 component than the other two types of stimuli; (2) during the P2 time window, significant differences between 3D objects and the perspective drawings were found mainly over a group of electrode sites in the left lateral occipital region; and (3) during the N2 complex, differences between planar graphics and perspective drawings were found over a group of electrode sites in the right hemisphere, whereas differences between perspective drawings and 3D objects were observed at another group of electrode sites in the left hemisphere. These findings support the claim that depth processing and object identification might be processed by separate pathways and at different latencies.

The neural basis of desire reasoning for self and others: an event-related potential study.

Theory of mind refers to the ability to attribute mental states to self and others, and predict actions in terms of mental states. It is still unclear how certain kinds of processing occur in theory of mind operation. The present study compared neural activities elicited by desire reasoning for self and for others under consistent or inconsistent conditions using the event-related potential method. The results showed that the late positive component (LPC) associated with desire reasoning was larger during the 450–550u2009ms time period in the condition of reasoning for self than that for others when desires were inconsistent. A left hemisphere effect on the scalp distribution was observed for the LPC component. The present study showed that a left frontal LPC component might reflect the subjective categorization process in desire reasoning.

Hierarchical effects on target detection and conflict monitoring

Previous neuroimaging studies have demonstrated a hierarchical functional structure of the frontal cortices of the human brain, but the temporal course and the electrophysiological signature of the hierarchical representation remains unaddressed. In the present study, twenty-one volunteers were asked to perform a nested cue-target task, while their scalp potentials were recorded. The results showed that: (1) in comparison with the lower-level hierarchical targets, the higher-level targets elicited a larger N2 component (220–350u2009ms) at the frontal sites, and a smaller P3 component (350–500u2009ms) across the frontal and parietal sites; (2) conflict-related negativity (non-target minus target) was greater for the lower-level hierarchy than the higher-level, reflecting a more intensive process of conflict monitoring at the final step of target detection. These results imply that decision making, context updating, and conflict monitoring differ among different hierarchical levels of abstraction.

Hybrid model of price pair comparisons: evidence from an event-related potential study.

It remains unclear whether number and unit are represented holistically (i.e. number and unit were processed as a whole) or compositionally (number and unit were processed separately) in the brain. The current study asked participants to compare price pairs with different monetary units that were presented serially. The close and far distances were defined in terms of the overall magnitude between two prices. Electrophysiological results showed that the distance effects were observed on the N2 component at the frontal regions, with far distances eliciting more negativity than close distances. This result suggests that participants compute the holistic price magnitudes before comparing them. Furthermore, a congruence effect was observed in the parietal regions. Incongruent prices elicited more negative amplitude than congruent prices on the N2 component, which implied that numbers and monetary units were processed separately over the same time course. Taken together, these findings suggest that numbers and monetary units are represented holistically and compositionally, which supports the hybrid model.

Real-life experience modifies early electrophysiological responses in the visual system

To examine whether experience can alter the sensitivity of the visual system to particular aspects of visual processing, 17 earthquake survivors and 17 controls were exposed to pictures of objects, and were required to identify the unbroken ones by checking for flaws on the surface. The electrophysiological results indicated that approximately 150 ms after presentation of a visual stimulus, the earthquake survivors showed an enhanced negativity (N1) as compared with the controls. This finding supports the claim that the pattern of neural activity associated with the early stages of object perception can be modified by real-world experiences.