Shujuan Tian

Event-related potentials evoked by multi-feature conflict under different attentive conditions

Abstract. Event-related potentials (ERPs) were recorded in subjects while they were performing a matching task. The focus of the present study was on the contributions made by ERP recording to revealing the time-course of multi-conflict information processing in the brain during visual attention. Participants were instructed to discriminate whether the attributes of the first stimulus (S1) were the same as those of the second one (S2) of a pair. Stimuli were defined by three features: color, global shape, and local shape. In condition 1, all attributes of the two stimuli of the pair were constant (no conflict); in condition2, S2 was different from S1 in all attributes (conflict). The experiment comprised three tasks. In task 1, subjects attended to the color of the stimuli and ignored the other attributes. In task 2, they were asked to attend to both color and global shape of stimuli and disregard the local shape. In task 3, all attributes were attended to. An ERP component N270 was elicited by attending to the color conflict in session one. In task 2, attending to color and global shape induced two ERP effects in the conflict condition: N270 and N400. The results suggest that the attended different conflicts of the two visual attributes of the stimuli were processed in series. However, in task 3, only one apparent negative component, N270, was observed in the conflict condition. The difference between data from task 2 and 3 showed that more than one processing model exists in the human brain for processing multiple visual attribute conflicts.

Enhancement of conflict processing activity in human brain under task relevant condition

To investigate the working mechanism of the conflict processing system, pairs of colored numbers were sequentially presented on a screen to subjects. They were asked to determine if the magnitude or the color of the two numbers was identical. Event-related potentials (ERPs) were recorded at the same time. A negative potential peaking at 270 ms (N270) after the onset of the second number (S2) was elicited when S2 conflicted with the first number (S1) in task-relevant and (or) irrelevant attribute conflicts. The mean amplitude of the N270 was more negative in task relevant conflict than in irrelevant conflict. Therefore, the conflict processing activity can be initiated independently of the task, but is enhanced in task relevant conflict.

Human brain sub-systems for discrimination of visual shapes.

To investigate whether stereo and plane visual shapes are processed in the same brain system, participants were instructed to discriminate whether two visual stimuli presented in sequence were identical and event-related potential (ERP) was recorded from their scalp. The first (S1) and the second stimuli (S2) were the same stereo shapes in condition 1, but were different in condition 3. They were the same plane shapes in condition 2, but different in condition 4. A negative component (N270) was recorded in condition 3 and 4, which showed the maximal amplitude in the right posterior scalp in condition 3 and in the anterior scalp in condition 4. A different cognition mechanism is involved in the processing of non-matched stereo and plane visual shapes.

The N270 component of the event-related potential reflects supramodal conflict processing in humans

It is unclear whether crossmodal information conflict can initiate the conflict processing system indexed by a component of the event-related potential (ERP) called the N270, which previously has been observed only for visual conflict. ERPs were recorded in ten subjects, while they were engaged in a visual-auditory discrimination task. A visual stimulus of a facial photograph was followed by an auditory stimulus of Chinese syllable [a] or [i], which might be sounded by the same gender of its preceding photograph (gender match) or by different gender (gender conflict). Subjects pressed a button for gender match and another for gender conflict. A prominent N270, similar to that evoked by visual conflicts, was elicited by the auditory stimuli in gender conflict condition. It is likely that N270 reflects the brain activity of a supra-modal conflict processing system.

Different processes are involved in human brain for shape and face comparisons.

Fifteen subjects participated in a matching task of visual stimuli. Two sequentially presented stimuli in a pair were the same shape (shape match), different shapes (shape mismatch), same human face (face match) or different faces (face mismatch). All four kinds of stimulus pairs were of equal probability. The shape mismatch pairs elicited a negative event-related potential component N270 (Peak latency: 262.1+/-16.5 ms, P4) after the second stimulus onset, while the face mismatch evoked N270 with longer peak latency (301.2+/-19.8 ms, P4) and N450. There exists a specific system for mismatch processing of a complex stimulus (face) in the human brain.

Interstimulus Interval Effect on Event-Related Potential N270 in a Color Matching Task

Event-related brain potentials were recorded in a matching task, in which subjects were asked to discriminate if the color of the second stimulus (S2) was the same as the first stimulus (S1). The interstimulus interval between the two stimuli of a pair was of three levels (150 ms, 500 ms and 1000 ms). A negative component about 270 ms after the presentation of S2 was elicited when the color of the two stimuli was not identical for the interstimulus interval of 500 ms and 1000 ms, but not for the interval of 150 ms. This may suggest that N270 represented the response of the brain to conflicting information between different cortical levels.

Cognitive impairment in Parkinson's disease revealed by event-related potential N270

Disturbed cognitive function is a well-recognized feature of idiopathic Parkinsons disease (PD). The aim of this study was to find a susceptive index to reveal the minor cognitive impairment in PD patients. Thirty PD patients without clinical dementia and thirty-four age-matched normal controls performed a matching task while event-related potentials (ERPs) were recorded from their scalp. There were two kinds of stimulus pairs in this study: match condition, the second stimulus (S2) in a pair was identical to the first one (S1); conflict condition, S2 conflicted with S1 in the color attribute. Subjects were required to press a button in the match condition and another button in the conflict condition. A negative ERP component, N270, which was considered to reflect the conflict processing activity in human brain, was evoked by the S2 of the conflict condition. The patient group showed a delayed and smaller N270 than the control group. The prolongation of its peak latency was significant at P3 and P4 electrodes and the reduction of its mean amplitude was significant at P3 electrode. The amplitude of P300 elicited in the match condition was decreased in the patient group at P4 electrode but its latency did not differ from the control group. These results indicate that PD patients as a group showed cognitive decline even in the absence of clinical dementia. N270 is a sensitive index in revealing this minor cognitive impairment.

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

Twelve subjects were asked to perform visual stimulus presentation tasks. Two figures were presented either simultaneously or sequentially. They were either in congruity (same shapes) or in conflict (different shapes) with each other. Conflicting stimulus pairs presented sequentially evoked a negative event-related component with a fronto–central and bilateral posterior scalp distribution, referred to as N270. In contrast, stimuli displayed simultaneously elicited a N220 with fronto–central prominence, irrespective of whether they were in conflict or in congruity. The results suggest that the N270 may be associated with the processing of a conflict with working memory information whereas the N220 might reflect the detection and evaluation of attention to visual information in the human brain.

Brain potentials elicited by matching global and occluded 3-dimensional contours

Subjects were instructed to match 3-dimensional forms while event-related potentials (ERPs) were recorded to explore the relationship between visual completion and conflict processing. Sequentially presented paired stimuli (S1 and S2) were identical in condition I, while in condition II the images were of the same contour, but S2 contained an invisible portion, and in condition III S1 and S2 were of different contours. Subjects indicated if stimuli were physically identical or contour similar in two separate sessions. Following the onset of S2, ERP components P100, N150, and LPC were recorded in all conditions. N150 was enhanced in condition II in both sessions, and N270 was elicited in conditions II and III. N150 is related to visual completion, while N270 is related to the evaluation of information discrepancy, belonging to independent systems.

Event-Related Potentials in a No-Go Task Involving Response-Tendency Conflict:

Event-related potentials (ERPs) were recorded while 13 subjects completed a color discrimination task. In task one, subjects were asked to press a button when the presented stimulus was a red or a green spot (Go stimulus), and inhibited any motor response when the stimulus was a yellow or a white spot (No-go stimulus). In task two, subjects were instructed to count the number of the Go stimuli, not to count the No-go stimuli. In order to investigate the influence of probability on ERP components, two sessions were designed in each task. In session one, the probability of the four kinds of stimuli was equal. In session two, the probability of red, green, yellow, and white were 10%, 10%, 10%, and 70% respectively. An enhanced negative potential in the frontal area was recorded in the 200–400 ms range both following No-go stimuli and following No-count stimuli, which was not influenced by the stimulus probability. The result cast doubt on the interpretation of the frontal negative potential enhancement as reflecting response-inhibition processes. The potential might be related to the information processing of response-tendency conflict rather than the suppression of motor execution.