| ObjectiveVisual attention control is usually divided into goal-directed attention and stimulus-driven attention:the former is also known as top-down attentional control, means that the subjects’ selection only relevant to current target; latter is also known as bottom-up attentional control, refers to shifting the subjects’attention to certain sensations outside the subjects. Visual attention can be automatically directed to a specific target (goal-driven attention control mechanism); it can also be captured by a significant non-target stimulus (stimulus-driven control mechanisms). For example, when we concentrate on our work in front of the computer, our attention is focused on the contents of the current work, it’s the goal-oriented attentional control; but if a colleague called your name suddenly, our attention will leave the current work, shifting to the next colleague, and this time the attention is stimulus-oriented.Functional magnetic resonance imaging studies suggest that the dorsal attention network (DAN) which include bilateral cortical frontal eye field (FEF) and intraparietal sulcus/superior parietal lobule (SPL/IPS), is the carrier of top-down attention control mechanism mentioned by biased competition model and related theories; and the ventral attention network (VAN), which can not be activated by expectations or task preparation, but can be activated by the reorienting of behavior stimulation. Mainly includes the ventral frontal cortex/anterior insula (VFC/AI) and the temporal-parietal junction cortex (TPJ).The manner of top-down and bottom-up attentional control process interact to determine overall attentional priority has long been the subject of considerable controversy. Some have argued that the bottom-up component induced by significant stimulus exerts dominance in determining overall attentional reorienting, which supported by additional singleton paradigm. Studies have shown that less than150ms after the onset of attentional processing completely stimulus-driven, free from the impact of a top-down mechanism; whereas others have assigned dominance to the top-down component.Leber consider that the key to solve the problem as above-mentioned is to reconciliate the opposing bodies of viewpoints. He proposes subjects’behavior was sometimes affected by the stimulus-driven attentional processing, sometimes by the impact of the goal-driven attentional processing. In other words, subjects’effort to prevent attention been captured fluctuated from moment-to-moment, and this volatility can be predicted by measuring activity of certain brain regions, his research employed a searching paradigm which requires observer looking for a ring (target stimulus) in a number of squares (unrelated stimulus), during the whole experiment, an irrelevant color singleton distractor appeared on50%of trials. The experiment require subject to exclude the interference of distractor test, functional imaging results showed that the left middle frontal gyrus (left middle frontal gyrus) activity stronger the subsequent retries behavior credits, the smaller the effect of heart. Functional magnetic resonance imaging results confirmed that the higher BLOD signal of pretrial activity in middle frontal gyrus, the less distraction effect of next trial.Functional imaging research of Fockert et al.(2004) and Weissman et al.(2006) also suggest that top-down attention mechanism impact on the bottom-up is an important source of attention to controlling the level of attentional fluctuations. But all these fMRI studies only researches by space, functional neuroimaging studies could neither tell the exact time of attentional capture, nor tell the behavioral performance (attentional fluctuations) occurred in the perception stage or implementation stage; and historical neurophysiological research only focuses on the nerve potential change of individual lead, lack of the network (space) point of view.Our study draw top-down factors into additional paradigm which normally focused on the bottom-up factors, we divided the subjects into two groups based on the speed of respond time, slower respond time confers greater distraction, faster respond time confers less distraction. We hope we can find out the brain regions and time course mediate the top-down and bottom-up forms of attention by surveying interaction effect of salient distractor and attentional fluctuation with the same multichannel phase time series of ERP,MethodExperimental subjects take the form of recruiting volunteers, the inclusion criteria is healthy, right-handed, no neurological mental disease and no family history of mental illness, normal vision or vision correction, no color blindness, no color weakness, not previously participated in a similar experiment, were well informed and participated in exchange for monetary compensation. All18participators were postgraduate students or resident physician, three of whom were excluded because of too much eye movement. The rest fifteen (six females) people are between the ages of22-30years (25.73±1.87years).Each present image is composed by eight distributed stimulus visual.search sequence, every graphic contains7hollow square (1.6×1.6°) and a hollow diamond (1.5×1.5°), all eight shapes were arranged circular uniformly distributed around a central fixation, transverse the longitudinal axis of symmetry, the distance from the center of each graphic is4.5°and draw by0.2°width line. A white number randomly distributed within the eight graphics number "2" and "5", and these two numbers were half and half. All numbers are located in the center of the figure with width of0.2°. The background of the display is black. In half of the trials, the square diamond were drawn in green; in the other half of the trials, all but one of the squares were randomly drawn in red, and the remaining item was drawn in green.The experimental stimuli were presented on a LCD located100cm from the observer’s eyes. Subjects comfortable sitting in the slightly dusky room (relative soundproof room, temperature about24℃) face the computer screen, the horizontal viewing angle and vertical viewing angle is7.0°. The computer screen refresh rate was75Hz. The subjects reacted by left and right buttons, system automatically records the reaction time and right or wrong. Participant’s response based on the numbers within each hollow diamond singleton."2" were reported via a button press by the left index finger and "5" by right index finger. Before each experimental trial began, a fixation point will be presented for duration of600ms, then search arrays were added to the display, for about1000ms display disappeared, leaving only fixation. The total experiment consists of600test times, after every75trial (for120seconds) subject rest for30seconds, everyone Exercise4minutes before the formal experiment.EEG was recorded by an ERP system with19recording electrodes installed in accordance with the international10-20standard lead system (FP1, FP2, F3, F4, C3, C4, P3, P4,01,02, F7, F8, T3, T4, T5, T6, FZ, CZ, PZ) developed in our lab, which could record behavior performance and EEG data at the same time. Filter bandwidth is0.5-100Hz, the impedance between scalp and electrode was smaller than10kΩ.The on-set of the search sequence recorded as0ms, The ERP epochs were averaged off-line and included pre-stimulus activity of100ms and post-stimulus activity of1000ms. Classification superimposed processing EEG fragments, automatically reject pseudo-differential threshold is set to70μV and artifact above70μV and other artifact were eliminated manually. Under various conditions involved in the ERP superimposed EEG fragment is not less than30. Only response correctly, artifact rejected and100-1550ms after onset EEG fragment involved in superposition.Statistical analyzes were performed by using within-subject design, Paired t test was carried, both response time and correct rates were analyzed using SPSS13.0software. We divided all single ERPs into fast, medium and slow groups evenly by reaction time, and eliminate the middle group. We carried out a two-factor repeated-measure ANOVA for ERPs:(response speed:fastest/slowest)*(salient distractor:yes/no). All ERP data were analyzed by using statistical parametric mapping of F-values [SPM (F)] technique. The significant level was0.05.Result 1. Behavioral indicatorA total of10.1%error trials are excluded,3.0%of which due to the reaction time exceeded the effective range (100-1550ms),7.1%due to wrong response.Reaction time:reaction time in the interference condition (791.20±62.22ms) significantly longer than the non-interference condition (772.40±53.77ms):t (14)=4.26,P<0.001.Accuracy:Accuracy in the interference condition (90.96±3.53%) lower than under the condition of non-interference (88.84±6.64%) with a significant trend:t (14)=1.81, P=0.09. Confirming color distractor lead to effective attentional capture effect.We divide every subject’s ERPs into groups by Reaction time, The mean reaction time of two group under non-interference condition were646.8±40.1ms and909.7±75.5ms; while the mean reaction time of two group under interference condition were649.9±42.5ms and940.6±89.1ms.2. ERP and SPMThe ERP statistical parametric mapping SPM (t) results suggest that the significant distraction effect located at the bilateral frontal-parietal area (360-410ms) under fast response speed; and the significant distraction effect is located at the left frontal region (260-385ms;435-735ms) under slow response speed.Under2(salient distractor:yes/no)×2(response speed:fastest/slowest) conditions, the ERP statistical parametric mapping SPM (F) results revealed the significant interaction effect between the two factors:the medial prefrontal cortex (mPFC)(340-380ms) and left frontal area (340-860ms); the main effect of attentional levels: bilateral frontoparietal area(380-580ms;780-860ms), central frontoparietal area (460-540ms) and left temporaloccipital area(500-660ms); the main effect of salient distractor interference:the central frontoparietal area (360-460ms;580-660ms)and occipital region(500-660ms).Conclusion In this experiment, reaction time in the interference condition significantly longer than the non-interference condition, and statistically significant, and accurate rate under interference condition is also lower than the non-interference conditions (although not reach statistical significance). Confirming random red distractor is the major factor causes observers’ attentional capture.SPM (F) result revealed that the significant interference main effect appears in the frontoparietal central area, where no interaction effect with the speed of response factors has existed in the area. Indicate that the central area of the frontal and parietal ERP spatiotemporal patterns of activated in tasks is related with attentional capture result by significant no-task-relevant distractor. This result is similar with Fockert and his colleagues’ conclusion about whether a no-task-relevant distractor present or not is be bound up with activation of superior parietal cortex and frontal cortex. Most of the functional neuroscience research focused on the brain response to stimulus or task. However, even the lack of task and stimulus conditions, activation of our brain can still fluctuated from time-to-time. And brain activity in the resting fixation generated affect with behavior, fMRI research found ongoing fluctuations in intrinsic activity under the resting state largely (74%) affected the left somatic motor cortex and trial-by-trial fluctuation. Therefore, the reaction speed main effect as displayed at the ERP spatiotemporal patterns, the significant activation of bilateral frontoparietal region, the central area of the frontal and parietal and left temporal occipital region is in fact a comprehensive reflection of the resting state of the brain’s activity fluctuations and attentional level of volatility caused by exogenous significant interference.Further analysis compared interference and no-interference group by fast reaction speed condition and slow reaction speed condition respectively, SPM (t) results explained why the level of attentional control sometimes higher and more capable resistant to strong interference in the presence of interference. The reason has been show in Figure3-3A:compared with the non-interference term conditions, ERP spatiotemporal patterns of bilateral frontal-parietal area (360-410ms) under fast reaction speed condition activated successively, where hadn’t activated under slow reaction speed condition, indicating the presence of interference terms, bilateral frontal-parietal area for the360-410ms activation may effectively plays an important role in avoiding attention capture by significant interference items. This is not coincident with Leber’s findings about left middle frontal gyrus is crucial to avoid attention being captured by irrelevant distractor, and our results indicate the occurring time may be230-300ms. The experimental results show that the right frontal areas may come together with left frontal region is involved in the regulation of attentional control, and has put an emphasis on the left frontal gyrus, can not tell left frontal gyrus interact with which brain regions during attentional capture, And figure3-3B is further prompted that the left frontal and occipital region activation is related to the distractor effect.Limited processing capacity of the dorsal attention network may be involved in internal and external information processing. Attentional gateway hypothesis proposed rostral prefrontal cortex (rPFC) control the switching of external and internal information processing systems. rPFC interacting with anterior frontoparietal network, the basal ganglia, the IFJ and other brain regions work together in the processing of shifting attentional control. The fMRI study revealed that lateral aspects of the rPFC are activated when attention is directed to internal information, whereas anterior medial aspects of the rPFC are activated when attention is directed to environmental information. Among them, the left middle frontal gyrus may have significant effect in avoiding subject’s attention being captured by salient task-irrelevant distractor. Variation of attentional control may be the result of the interaction of the gateway system and the default mode network. Attentional gateway system may lead to attentional fluctuation together with the default mode network. The ERP interaction effects identified presently provide two type framework of information processing and switching time, which is consistent with former fMRI studies, which is, the early enhanced activity(340-380ms) in the left frontal area and the medial prefrontal cortex (mPFC) may indicate that attentional gateway system acts as gateway between the internal and external information processing systems, and left frontal subsequent enhanced activity (340-900ms) may mediate the supervisor of BU/TD mechanism in external information processing.In summary, reaction time in the interference condition significantly longer than the non-interference condition, confirming random red distractor is the major factor causes observers’ attentional capture. Our results demonstrate that attentional gateway system is not only involved in the regulation of the internal and external attention system (left frontal area and the medial prefrontal cortex), also mediated the BU/TD Regulation (left frontal area). Attentional fluctuation reflected by behavioral performance mainly derived from the execution stage, may be the result of DMN and the prefrontal cortex working in concert, salient distractor lead early (140-180ms) reorienting response in the right ventral attention network. |
PDF Full Text Request