Neural correlates of theory-of-mind reasoning: an event-related potential study

Everyday understanding of human behavior rests on having a theory of mind—the ability to relate people's actions to underlying mental states such as beliefs and desires. It has been suggested that an impaired theory of mind may lie at the heart of psychological disorders that are characterized by deficits in social understanding, such as autism. In this study, we employed the event-related potential methodology to index the activity of neural systems that are engaged during theory-of-mind reasoning in adults. Specifically, neural activity elicited by tasks that required thinking about mental as compared with nonmental representations (i.e., beliefs vs. photographs) was characterized by a focally enhanced positivity over left frontal areas, which was diminished over left parietal areas. These findings provide an important perspective on both children's theory-of-mind development and the neurobiology of disorders in which theory of mind seems to be impaired.     

Methodological issues in event-related brain potential research

Event-related brain potential (ERP) measures have become increasingly popular in experimental psychology and are often employed by researchers who are not formally trained in electrophysiology. A proper application of these measures requires knowledge about the methodological principles and practical issues that are relevant to ERP measurement, analysis, and interpretation. A brief introductory survey of different aspects of ERP methodology (recording, data processing and signal extraction, statistical analysis and interpretation of ERP effects) is presented, and the contributions collected in this special issue on ERP methodology are introduced.     

Response-monitoring dysfunction in schizophrenia: an event-related brain potential study

Error-monitoring abnormalities may underlie positive symptoms of schizophrenia. Response-synchronized event-related potentials during picture-word matching yielded error- and correct-response-related negativity (ERN, CRN) and positivity (Pe, Pc) and preresponse lateralized readiness potentials (LRP) from 18 schizophrenic patients and 18 controls. Both groups responded faster to matches than nonmatches, although patients were generally slower and made more errors to nonmatches. Compared with controls, patients, particularly with paranoid subtype, had smaller ERNs and larger CRNs, which were indistinguishable. LRPs showed evidence of more response conflict before errors than before correct responses in controls but not patients. Despite ERN/CRN abnormalities, post-error slowing and Pe were normal in patients, suggesting a dissociation of ERN and error awareness. Anterior cingulate and dorsolateral prefrontal cortical dysfunction in schizophrenia are implicated.     

The effects of direction similarity in visual working memory: Behavioural and event-related potential studies

Object similarity can improve visual working memory (VWM) performance in the change-detection task, but impair the recognition performance when it occurs at retrieval of VWM in the recognition task. The effect of direction similarity is an issue that has not been well resolved. Furthermore, electrophysiological evidence in support of the mechanisms that underlie the effects of similarity is still scarce. In the current study, we conducted three behavioural experiments to examine the effects of direction similarity on memory performance with regard to both the encoding and retrieval phases of VWM and one event-related potential (ERP) experiment to explore the neural signatures of direction similarity in VWM. Our behavioural studies indicated that direction similarity improved performance when it occurred at the encoding phase but impaired performance when it occurred at the retrieval phase. Moreover, the ERP experiment showed that the amplitude of the contralateral delay activity (CDA) increased with the increasing set size for similar but not dissimilar directions. In addition, the CDA amplitude for similar directions was lower than that for dissimilar directions at set size 2. Taken together, these findings suggest that direction similarity at encoding has a positive effect on VWM performance and at retrieval has a negative effect. Given that VWM capacity depends on information load and the number of objects, the positive effect of similarity may be attributed to reduced information load of memory objects.     

Unitization,similarity, and overt attention in categorization and exposure

Unitization, the creation of new stimulus features by the fusion of preexisting features, is one of the hypothesized processes of perceptual learning (Goldstone Annual Review of Psychology, 49:585–612, 1998). Some argue that unitization occurs to the extent that it is required for successful task performance (e.g., Shiffrin & Lightfoot, 1997), while others argue that unitization is largely independent of functionality (e.g., McLaren & Mackintosh Animal Learning & Behavior, 30:177–200, 2000). Across three experiments, employing supervised category learning and unsupervised exposure, we investigated three predictions of the McLaren and Mackintosh (Animal Learning & Behavior, 30:177–200, 2000) model: (1) Unitization is accompanied by an initial increase in the subjective similarity of stimuli sharing a unitized component; (2) unitization of a configuration occurs through exposure to its components, even when the task does not require it; (3) as unitization approaches completion, salience of the unitized component may be reduced. Our data supported these predictions. We also found that unitization is associated with increases in overt attention to the unitized component, as measured through eye tracking.     

Social categorization and similarity in intergroup behaviour

The present study is one of a series exploring the role of social categorization in intergroup behaviour. It has been found in our previous studies that in ?minimal' situations, in which the subjects were categorized into groups on the basis of visual judgments they had made or of their esthetic preferences, they clearly discriminated against members of an outgroup although this gave them no personal advantage. However, in these previous studies division into groups was still made on the basis of certain criteria of ?real' similarity between subjects who were assigned to the same category. Therefore, the present study established social categories on an explicitly random basis without any reference to any such real similarity. It was found that, as soon as the notion of ?group' was introduced into the situation, the subjects still discriminated against those assigned to another random category. This discrimination was considerably more marked than the one based on a division of subjects in terms of interindividual similarities in which the notion of ?group' was never explicitly introduced. In addition, it was found that fairness was also a determinant of the subjects' decisions. The results are discussed from the point of view of their relevance to a social-cognitive theory of intergroup behaviour.     

Social feedback interferes with implicit rule learning: Evidence from event-related brain potentials

The human brain can learn contingencies built into stimulus sequences unconsciously. The quality of such implicit learning has been connected to stimulus social relevance, but results so far are inconsistent. We engaged participants in an implicit-intentional learning task in which they learned to discriminate between legal and illegal card triads on the sole basis of feedback provided within a staircase procedure. Half of the participants received feedback from pictures of faces with a happy or sad expression (social group) and the other half based on traffic light icons (symbolic group). We hypothesised that feedback from faces would have a greater impact on learning than that from traffic lights. Although performance during learning did not differ between groups, the feedback error-related negativity (fERN) was delayed by ~20 ms for social relative to symbolic feedback, and the P3b modulation elicited by infrequent legal card triads within a stream of illegal ones during the test phase was significantly larger in the symbolic than the social feedback group. Furthermore, the P3b mean amplitude recorded at test negatively correlated with the latency of the fERN recorded during learning. These results counterintuitively suggest that, relative to symbolic feedback, socially salient feedback interferes with implicit learning.     

Neural correlates of inference-driven attention in perceptual and symbolic tasks: An event-related potential study

The inferential system anticipates the external environment by building up internal representations of its regularities. To that purpose, two sources of information are especially important and attract attentional resources: expected and unexpected events, which are useful for checking the accuracy of internal representations. In the present study, we investigated the behavioural properties and the neural mechanisms underlying the strategic allocation of attention triggered by those events. To that end, event-related potentials (ERPs) were recorded during the performance of two tasks requiring detection of predictable and unpredictable response events embedded in a visuospatial or numeric sequence. The behavioural results in the two tasks mirror each other, suggesting the recruitment of similar attentional allocation processes between the two domains. The ERPs showed partially similar effects. In both tasks, a P3a-like component signalled the capture of attention by events clashing with previous expectations, whilst a P3b-like component marked the focusing of attention on predicted events and its redistribution among all possible response events occurring after the detection of an unexpected event.     

Distractibility after frontal lobe lesions: behavioral and event-related brain potential evidence

The authors used a semantic priming paradigm to investigate the distractibility phenomenon of patients with frontal lobe lesions (FLPs). They tested two distractibility categories: an inhibition category requiring inhibition of an automatic response and a distraction category caused by irrelevant, unexpected stimuli. Fifteen FLPs were compared with 2 matched control groups: 14 posterior-lesion patients and 15 normal controls. Both behavioral and event-related brain potential (ERP) measures were used. The results suggest that, although there were differences in performance between the FLP group and the control groups, there was no evidence that the FLPs had difficulty specifically with the inhibition category. The most consistent ERP result was that the FLP group had longer N100 latencies than either control group. On the basis of these results, the authors hypothesize that FLPs have difficulty focusing on and starting to process a new stimulus. The authors also discuss the unique contribution ERP evidence has made to cognitive studies.     

Alcoholism risk and the P300 event-related brain potential: modality, task, and gender effects

The P300 event related potential (ERP) was elicited from young adults at low- (LR) and high-risk (HR) for alcoholism (n = 24/risk group), with equal numbers of male and female subjects employed. The effects of stimulus modality, task difficulty, and gender were assessed with analogous auditory and visual paradigms (tone location/head rotation and tone matching/shape matching). Although task performance was generally comparable across risk groups, LR subjects produced smaller P300 amplitudes than HR subjects for the visual matching tasks. No consistent risk group P300 latency effects were obtained. Gender, task difficulty, and scalp topography differentially modulated the risk group outcomes across paradigms. These findings suggest that P300 amplitude reflects risk-for-alcoholism in male and female young adults, but the specific task conditions and electrode location affect the strength of risk group differences.     

Choice and response time processes in the identification and categorization of unidimensional stimuli

Lacouture and Marley (1991, 1995, 2001) have successfully modeled the probabilities of correct responses and the mean correct response times (RTs) in unidimensional absolute identification tasks for various stimulus ranges and stimulus/response set sizes, for individual and group data. These fits include those to a set of phenomena often referred to as end-anchor effects. A revised model, with the independent accumulator decision process replaced by a leaky competing accumulator decision process, fits the probabilities of correct responses and the full distributions of RTs in unidimensional absolute identification. The revised model is also applied successfully to a particular class of unidimensional categorization tasks. We discuss possible extensions for handling sequential effects in unidimensional absolute identification, and other extensions of the given class of categorization tasks that are of potential empirical and theoretical importance as a supplement to the study of multidimensional absolute identification tasks.     

The negativity bias is eliminated in older adults: age-related reduction in event-related brain potentials associated with evaluative categorization

Studies of younger adults have found that negative information has a stronger influence than positive information across a wide range of domains. T. A. Ito, J. T. Larsen, N. K. Smith, and J. T. Cacioppo (1998) reported that during evaluative categorization, extreme negative images produced greater brain activity than did equally extreme positive images in younger adults. Older adults have been reported to optimize affect and attend less to negative information. In this article, the negativity bias was examined in 20 older versus 20 younger adults during evaluative categorization, with a focus on brain activity occurring roughly 500 ms after presentation of visual stimuli. Results demonstrated a significant decrease in brain activity to both positive and negative stimuli (p < .05) and an elimination of the negativity bias in older adults.     

Dealing with artifacts: The EOG contamination of the event-related brain potential

Eye movements and blinks represent a major source of artifacts in the electroencephalogram (EEG) and event-related brain potentials (ERPs). The origin of this artifact is the large difference in potential that exists between the cornea and the retina. Eye movements and blinks produce shifts of the electric fields that propagate across the whole head and that can be several times larger than the activity generated by the brain. Ocular activity can be monitored by electrodes located near the eyes (electrooculogram, or EOG). The electric fields associated with eye movements and blinks are somewhat different. The simplest procedure for dealing with ocular artifacts is to eliminate trials on which EOG activity is detected (rejection). However, this technique may result in data loss and biased data samples, especially when one is comparing clinical populations or tasks involving large amounts of eye movements. Another approach involves estimation and correction of the ocular artifact on the EEG and ERP traces. Several techniques have been proposed. Some of them are reviewed in the present paper. Issues related to the accuracy of the various techniques, as well as other advantages and limitations, are also discussed. Finally, general guidelines for how to deal with ocular artifacts are proposed.     

Neural correlates of belief- and desire-reasoning in 7- and 8-year-old children: an event-related potential study

Theory of mind requires belief‐ and desire‐understanding. Event‐related brain potential (ERP) research on belief‐ and desire‐reasoning in adults found mid‐frontal activations for both desires and beliefs, and selective right‐posterior activations only for beliefs. Developmentally, children understand desires before beliefs; thus, a critical question concerns whether neural specialization for belief‐reasoning exists in childhood or develops later. Neural activity was recorded as 7‐ and 8‐year‐olds (N = 18) performed the same diverse‐desires, diverse‐beliefs, and physical control tasks used in a previous adult ERP study. Like adults, mid‐frontal scalp activations were found for belief‐ and desire‐reasoning. Moreover, analyses using correct trials alone yielded selective right‐posterior activations for belief‐reasoning. Results suggest developmental links between increasingly accurate understanding of complex mental states and neural specialization supporting this understanding.     

Enemies and friends in the neighborhood: orthographic similarity effects in semantic categorization

Studies investigating orthographic similarity effects in semantic tasks have produced inconsistent results. The authors investigated orthographic similarity effects in animacy decision and in contrast with previous studies, they took semantic congruency into account. In Experiments 1 and 2, performance to a target (cat) was better if a previously studied neighbor (rat) was congruent (i.e., belonged to the same animate-inanimate category) than it was if it was incongruent (e.g., mat). In Experiments 3 and 4, performance was better for targets with more preexisting congruent neighbors than for targets with more preexisting incongruent neighbors. These results demonstrate that orthographic similarity effects in semantic categorization are conditional on semantic congruency. This strongly suggests that semantic information becomes available before orthographic processing has been completed.     

Effects of additional tasks on language perception: an event-related brain potential investigation

The authors investigated effects of task and overlapping processing load on semantic processing. In 3 experiments the brain potential component N400 was elicited by synonymous and nonsynonymous spoken noun pairs that were to be classified according to semantic relatedness. The time course of the N400 component to the nouns was delayed, and its amplitude was reduced when additional tasks had to be performed. The delay increased with temporal overlap and was more pronounced for language-related than for spatial additional tasks. Delays of N400 were also caused by a compatibility manipulation in the additional tasks. Theoretical accounts of the observed interference of overlapping tasks with language perception in terms of attentional shifts were discarded. Explanations in terms of resource sharing and single channel processing are discussed.     

An event-related brain potential investigation of PTSD and PTSD symptoms in abused children

We tested 186 children ranging in age from 6 years, 10 months to 13 years, 7 months; 174 suffered either physical and/or sexual abuse, and 12 were nonabused children. Abused subjects were grouped in four different ways. The primary grouping was based on whether subjects satisfied the DSM III-R criteria for posttraumatic stress disorder (PTSD). Secondary groupings were based upon the three symptom clusters used to make the PTSD diagnosis (arousal, avaidance, and reexperiencing). In each of these groupings three separate subgroups were formed with approximately 25 percent in the high and low symptom count subgroups and the remaining 50 percent in the middle symptom count subgroup. Subjects listened to four different intensity levels (65, 80, 95, and 102 dB) of a 1 KHz tone, pseudo-randomly ordered, while event-related brain potentials (ERPs) were recorded. Two separate blocks were used, one with short intervals (4±1 sec) between tones and the other with longer intervals (17±2 sec). PTSD subjects presented a greater P2-N2 ERP intensity gradient (i.e., a larger increase in the P2-N2 ERP component as tone intensity increased) than did abused subjects without PTSD. Abused subjects with the highest number of reexperiencing symptoms showed a similar P2-N2 augmenting effect when compared to those with the lowest number of reexperiencing symptoms. Subjects with the highest number of arousal symptoms showed a shallower intensity gradient for the N1-P2 ERP component than did those with fewer arousal symptoms. The results are discussed in relation to previous results reported on adults with PTSD and in terms of CNS processing of stimulus intensity information.     

Causal knowledge and categories: the effects of causal beliefs on categorization, induction, and similarity

Despite the recent interest in the theoretical knowledge embedded in human representations of categories, little research has systematically manipulated the structure of such knowledge. Across four experiments this study assessed the effects of interattribute causal laws on a number of category-based judgments. The authors found that (a) any attribute occupying a central position in a network of causal relationships comes to dominate category membership, (b) combinations of attribute values are important to category membership to the extent they jointly confirm or violate the causal laws, and (c) the presence of causal knowledge affects the induction of new properties to the category. These effects were a result of the causal laws, rather than the empirical correlations produced by those laws. Implications for the doctrine of psychological essentialism, similarity-based models of categorization, and the representation of causal knowledge are discussed.