Francisco J. Rubia

Attentional set shifting modulates the target P3b Response in the Wisconsin card sorting test

For years the Wisconsin card sorting test (WCST) has been used as a test of frontal lobe function. Recent event-related potential (ERP) research has shown large differences in the amplitude of P3b responses evoked by early and late trials within each WCST series ([8]: Barceló F., Sanz M., Molina V., Rubia FJ. The Wisconsin Card Sorting Test and the assessment of frontal function: A validation study with event-related potentials. Neuropsychologia 1997;35:399-408). In this study, 16 normal subjects performed a WCST adaptation to investigate the role of attentional set shifting in these WCST P3b effects. Two control tasks were designed to examine whether early-late WCST P3b changes reflect category selection (attention) or category storage (memory) operations. Results suggest both a sharp P3b attenuation during shift WCST trials, followed by a gradual P3b build-up during post-shift trials. This P3b modulation could not be attributed to selection or storage of simple sensory stimulus dimensions, nor was it observed when the new rule was externally prompted by the first card in the WCST series. Instead, WCST P3b changes seem related to the endogenously generated shift in the perceptual rule used to sort the cards (i.e., the shift in set). The gradual build-up in P3b amplitude paralleled a progressive improvement in sorting efficiency over several post-shift WCST trials. A model based on formal theories of visual attention and attentional set shifting is proposed to account for these effects. The model offers firm grounds for prediction and bridges the gap between related clinical and experimental evidence.

The Wisconsin Card Sorting Test and the assessment of frontal function: A validation study with event-related potentials

The Wisconsin Card Sorting Test (WCST) is generally regarded as the prototype of abstract reasoning task and has been routinely used to assess frontal lobe function in a variety of clinical and research contexts. However, there are growing concerns that the WCST fails to discriminate frontal patients from those with lesions in other brain regions or from normals. Event-related potentials (ERP) from frontal, fronto-temporal, temporal, parietal and occipital areas were recorded during the performance of a computerized version of the WCST in order to explore frontal versus non-frontal ERP indexes during WCST activation. The task protocol was contrived to focus on the differences between early and late trials of each WCST series. Cognitive processes underlying these two task conditions have been described as extradimensional and intradimensional shifts in attention, respectively. Differences between early and late WCST trials appeared as soon as 120 msec poststimulus and were associated with a negative field potential centred at the fronto-temporal region of the left hemisphere. Significantly larger amplitudes of the posterior P3b wave for late as compared with early WCST trials also lent support to claims of a strong involvement of working memory mechanisms during WCST performance. Results are discussed in terms of the implications for the utility of ERP measures in clinical neuropsychology.

The Recognition Potential: An ERP Index of Lexical Access ☆

Recognition potential (RP) is a brain electrical response that appears when a subject views recognizable images of words. However, it has yet to be determined whether the processes reflected by RP are related to orthographic or to semantic analysis. This study aimed to resolve this question by studying the RP evoked by orthographically correct stimuli that were devoid of meaning. Results showed RP not only to this type of stimuli, but also to others achieving lower levels in the reading process. Strikingly, however, the RP amplitude significantly differed in parallel with the levels of the reading processes attained by the stimuli, the amplitude of the RP progressively increasing as the level approached the semantic one, which showed the highest amplitude. These results not only confirm the replicability of RP, but also its promise of potential usefulness in the study and assessment of language perception.

Event-Related Potentials and Semantics: An Overview and an Integrative Proposal ☆

Event-related potentials have shown to be a valuable tool when studying language processing. In this review we focus on the literature that deals with semantic processing. Thus, we review studies concerning the classic semantic-related ERP component, the N400, those concerning the recently described recognition potential (RP), and studies that have attempted to identify brain activations related to semantic processing without focusing on specific ERP components. From the available data we provide an integrative proposal. According to this proposal, ERPs are clear indexes of the three subprocesses presumably involved in semantic comprehension. ERPs would provide, additionally, information about the time course of such subprocesses.

Functional differences in the semantic processing of concrete and abstract words

There is considerable debate as to whether the semantic system is a unitary one in which meanings are available in a peculiar, perceptual-free format, or whether it is functionally segregated into anatomically discrete, modality-specific but semantic regions. In the former case, concrete and abstract words should not differ in the amount of activation of semantic areas. Neuroimaging studies in this field are, however, far from conclusive, and one reason for this may be that the degree of imageability of the stimuli - probably a crucial variable - has not been considered. Recognition Potential (RP) reflects semantic processing and appears to originate in basal extrastriate regions involved in semantic processing. In this study, we compared the RP of concrete and abstract words that actually differ in their degree of imageability. Results indicate that the semantic processing areas in which the RP originates display a higher activation for concrete (more imageable) material, but that abstract material also evokes a notably larger RP component compared with pseudowords or unpronounceable letter strings. Accordingly, the study appears to suggest that there is no full functional segregation of the semantic systems. Rather, our data support the existence of a semantic system that is specialised in concrete, imageable material, and that is also activated, though to a lower extent, by abstract material.

Common basal extrastriate areas for the semantic processing of words and pictures.

OBJECTIVE The recognition potential (RP) is an electrophysiological brain response which is sensitive to the semantic processing of meaningful stimuli. In this study we attempt to elucidate the topography and neural origin of the RP evoked by pictures and to compare it with the RP evoked by words. METHODS Words, pictures, Chinese characters and control stimuli were presented to 20 subjects following the rapid stream stimulation procedure. The activity was recorded using 60 cephalic electrodes. RESULTS We found a RP displaying its maximal amplitude at the left inferior parieto-occipital electrode (PO7) for words and at the right homologue electrode (PO8) for pictures and Chinese characters. Both the amplitude and the latency of the RP were larger in the case of words. A profile analysis indicated that the neural generators of the RP were common regardless of the type of stimulus, and a dipole analysis placed them about the lingual gyrus. CONCLUSIONS Words and pictures share the same neural generators for the RP despite of subtle differences in lateralization. This is interpreted as an index of a multimodal semantic processing in basal extrastriate areas.

Non-frontal P3b-like activity evoked by the Wisconsin Card Sorting Test

EVENT related potentials (ERP) were recorded from 29 electrode positions in 10 normal subjects while they performed a simplified version of the Wisconsin Card Sorting Test (WCST). The design focused on ERP differences between early and late trials within each WCST series. Topographic and dipole analyses confirmed the reliability of two ERP signs: one conspicuous mid-parietal P3b wave and one asymmetrical frontal-temporal component. A three-dipole model accounted for these ERP signs with > 90% accuracy even in individual subjects, and suggests a sub-second activation of temporal-parietal and medial temporal association areas during card sorting. The WCST-related P3b wave is proposed to reflect working memory operations such as template matching and template formation during card sorting.

Topographic maps of brain electrical activity in primary degenerative dementia of the Alzheimer type and multiinfarct dementia

The topography of the electroencephalographic (EEG) pattern of ten patients with primary degenerative dementia of the Alzheimer type, ten multiinfarct dementia patients, and ten age-matched controls was compared during three different behavioral conditions: resting condition with eyes open (EO), memorizing a list of words (M), and recalling the same list of words (R). Results indicate that the alpha frequency band does not show significant changes. On the other hand, the theta band could be considered an important factor in the differential diagnosis of the primary degenerative dementia of the Alzheimer type, showing a higher power over right posterior regions in this group of patients compared with the multiinfarct dementia patients under different behavioral conditions.

Insights from event-related potentials into the temporal and hierarchical organization of the ventral and dorsal streams of the visual system in selective attention

The temporal and hierarchical relationships between the dorsal and the ventral streams in selective attention are known only in relation to the use of spatial location as the attentional cue mediated by the dorsal stream. To improve this state of affairs, event-related brain potentials were recorded while subjects attended simultaneously to motion direction (mediated by the dorsal stream) and to a property mediated by the ventral stream (color or shape). At about the same time, a selection positivity (SP) started for attention mediated by both streams. However, the SP for color and shape peaked about 60 ms later than motion SP. Subsequently, a selection negativity (SN) followed by a late positive component (LPC) were found simultaneously for attention mediated by both streams. A hierarchical relationship between the two streams was not observed, but neither SN nor LPC for one property was completely insensitive to the values of the other property.

Similarities and differences between phrase structure and morphosyntactic violations in Spanish: An event-related potentials study

Event-related potentials (ERPs) were employed to compare word category and verb inflection violations in Spanish. A similar frontal negativity was found between 250-400 ms for both violation types, suggesting that they equally disrupt initial syntactic analyses. Also, word category violations elicited a negativity at posterior electrodes larger than verb inflection anomalies and correct sentences within this time window, probably reflecting difficulties to semantically analyse phrase structure violations. Finally, a centroparietal positivity in the 500-700 ms interval was found for both error types. Both violations did not differ along the first half of this interval (500-600 ms), but larger effects for verb inflection violations were reported along the second half of this period (600-700 ms). These findings suggest that whereas processes dealing with the reanalyses of sentence structure are equally triggered by both anomaly types, further attempts of repairing the structure of sentences occur only with verb inflection violations.