Distinctive conflict processes associated with different stimulus presentation patterns: an event-related potential study

Enhancing links between visual short term memory, visual attention and cognitive control processes through practice: An electrophysiological insight

The operation of attention on visible objects involves a sequence of cognitive processes. The current study firstly aimed to elucidate the effects of practice on neural mechanisms underlying attentional processes as measured with both behavioural and electrophysiological measures. Secondly, it aimed to identify any pattern in the relationship between Event-Related Potential (ERP) components which play a role in the operation of attention in vision. Twenty-seven participants took part in two recording sessions one week apart, performing an experimental paradigm which combined a match-to-sample task with a memory-guided efficient visual-search task within one trial sequence. Overall, practice decreased behavioural response times, increased accuracy, and modulated several ERP components that represent cognitive and neural processing stages. This neuromodulation through practice was also associated with an enhanced link between behavioural measures and ERP components and with an enhanced cortico-cortical interaction of functionally interconnected ERP components. Principal component analysis (PCA) of the ERP amplitude data revealed three components, having different rostro-caudal topographic representations. The first component included both the centro-parietal and parieto-occipital mismatch triggered negativity - involved in integration of visual representations of the target with current task-relevant representations stored in visual working memory - loaded with second negative posterior-bilateral (N2pb) component, involved in categorising specific pop-out target features. The second component comprised the amplitude of bilateral anterior P2 - related to detection of a specific pop-out feature - loaded with bilateral anterior N2, related to detection of conflicting features, and fronto-central mismatch triggered negativity. The third component included the parieto-occipital N1 - related to early neural responses to the stimulus array - which loaded with the second negative posterior-contralateral (N2pc) component, mediating the process of orienting and focusing covert attention on peripheral target features. We discussed these three components as representing different neurocognitive systems modulated with practice within which the input selection process operates.

Cognitive impairment in generalized anxiety disorder revealed by event-related potential N270

BACKGROUND

Cognitive function in anxiety disorders has been the subject of limited investigation, especially in generalized anxiety disorder (GAD). The purpose of this study was to investigate the cognitive function in subjects with GAD using mismatch-triggered negativity N270.

METHODS

Fifteen medication-free patients with a DSM-IV diagnosis of GAD, and 15 well-matched healthy controls performed a dual-feature delayed matching task while event-related potentials were recorded from their scalp.

RESULTS

The GAD group was characterized by the decreased N270 amplitude in the left hemisphere. The smaller N270 amplitude was associated with greater symptoms of anxiety and depression.

CONCLUSION

Since N270 is thought to index cognitive function in different domains, including attention and memory, our results suggest that individuals with GAD have an impaired cognitive function, particularly in selective attention and working memory. These cognitive deficits may have clinical significance in subjects with GAD and should be considered in treatment planning.

Spatio-temporal Patterns of Brain Activity Distinguish Strategies of Multiple-object Tracking

Human observers can readily track up to four independently moving items simultaneously, even in the presence of moving distractors. Here we combined EEG and magnetoencephalography recordings to investigate the neural processes underlying this remarkable capability. Participants were instructed to track four of eight independently moving items for 3 sec. When the movement ceased a probe stimulus consisting of four items with a higher luminance was presented. The location of the probe items could correspond fully, partly, or not at all with the tracked items. Participants reported whether the probe items fully matched the tracked items or not. About half of the participants showed slower RTs and higher error rates with increasing correspondence between tracked items and the probe. The other half, however, showed faster RTs and lower error rates when the probe fully matched the tracked items. This latter behavioral pattern was associated with enhanced probe-evoked neural activity that was localized to the lateral occipital cortex in the time range 170–210 msec. This enhanced response in the object-selective lateral occipital cortex suggested that these participants performed the tracking task by visualizing the overall shape configuration defined by the vertices of the tracked items, thereby producing a behavioral advantage on full-match trials. In a later time range (270–310 msec) probe-evoked neural activity increased monotonically as a function of decreasing target–probe correspondence in all participants. This later modulation, localized to superior parietal cortex, was proposed to reflect the degree of mismatch between the probe and the automatically formed visual STM representation of the tracked items.

Effects of discrepancy between imagined and perceived sounds on the N2 component of the event-related potential

Two experiments were conducted to examine whether the N2 component of the event-related potential (ERP), typically elicited in a S1-S2 matching task and considered to reflect mismatch process, can still be elicited when the S1 was imagined instead of perceived and to investigate how N2 amplitude varied with the degree of S1-S2 discrepancy. Three levels of discrepancy were defined by the degree of separation between the heard (S2) and imagined (S1) sounds. It was found that the N2 was reliably elicited when the perceived S2 differed from the imagined S1, but whether N2 amplitude increased with the degree of discrepancy depended in part on the S1-S2 discriminability (as evidenced by reaction time). Specifically, the effect of increasing discrepancy was attenuated as discriminability increased from hard to easy. These results, together with the dynamic ERP topography observed within the N2 window, suggest that the N2 effect reflects two sequential but overlapping processes: automatic mismatch and controlled detection.