Gunter T C, Wijers A A, Jackson J L, Mulder G
Institute for Experimental and Occupational Psychology, Groningen, The Netherlands.
Psychophysiology. 1994 Mar;31(2):140-53. doi: 10.1111/j.1469-8986.1994.tb01034.x.
In the first experiment, 48 subjects carried out a visual spatial attention task. Stimuli were presented at the vertical meridian, either above or below a fixation dot, and the subjects were instructed to attend to one of these stimulus positions and ignore the other position. In three different conditions, the distances between stimulus positions and fixation were 0.5 degrees, 0.9 degrees, and 1.3 degrees. Subjects searched for the presence of prememorized target letters at the attended location: memory load was one or four items in different conditions. The P1/N1 enhancement typically found on the horizontal dimension was not observed on the vertical dimension. Instead, a positive shift of the attended compared with the unattended stimuli was found, which was most prominent at anterior electrodes. This positivity showed effects of the distance manipulation. The N2b-P3a effects of attention and the effect of memory load (search negativity) normally present in this kind of selective search task were also found. Reaction times were faster when attention was directed above fixation than when it was directed below fixation. The event-related potential data suggested that this difference could be attributed to a more efficient neglecting of irrelevant stimuli presented below fixation. In Experiment 2, we examined whether the absence of the P1/N1 enhancement as the result of spatial attention in Experiment 1 could be attributed to (a) the presentation of stimuli along the vertical meridian instead of along the horizontal meridian, (b) the use of midline electrodes instead of lateralized electrodes, and (c) the relatively small spatial separation between the relevant and irrelevant stimuli. Twelve subjects searched for the presence of a single target letter at an attended position in three different conditions. In two of the conditions the letters were presented to the left or right of fixation. The distance between fixation and the stimulus positions was 1.3 degrees in one of these conditions and 3 degrees in the other condition. In the third condition, the stimuli were presented at 3 degrees above or below fixation. In all three conditions effects similar to those in Experiment 1 were observed. In addition, in all three conditions an enhancement of the P1 and N1 components was found at two lateral occipitotemporal electrodes.
在第一个实验中，48名受试者执行了一项视觉空间注意力任务。刺激物呈现在垂直子午线上，要么在注视点上方，要么在注视点下方，受试者被指示关注其中一个刺激位置而忽略另一个位置。在三种不同条件下，刺激位置与注视点之间的距离分别为0.5度、0.9度和1.3度。受试者在被关注的位置搜索预先记忆的目标字母：在不同条件下记忆负荷为一个或四个项目。通常在水平维度上发现的P1/N1增强在垂直维度上未被观察到。相反，发现与未被关注的刺激相比，被关注的刺激有正向偏移，这在前部电极处最为明显。这种正向偏移显示出距离操纵的效果。在这种选择性搜索任务中通常存在的注意力的N2b - P3a效应和记忆负荷效应（搜索负性）也被发现。当注意力指向注视点上方时的反应时间比指向注视点下方时更快。事件相关电位数据表明，这种差异可能归因于对呈现于注视点下方的无关刺激的更有效忽略。在实验2中，我们研究了实验1中由于空间注意力导致的P1/N1增强缺失是否可归因于：(a) 沿着垂直子午线而非水平子午线呈现刺激；(b) 使用中线电极而非侧化电极；以及(c) 相关刺激和无关刺激之间相对较小的空间间隔。12名受试者在三种不同条件下在被关注的位置搜索单个目标字母。在其中两种条件下，字母呈现在注视点的左侧或右侧。在其中一种条件下，注视点与刺激位置之间的距离为1.3度，在另一种条件下为3度。在第三种条件下，刺激呈现在注视点上方或下方3度处。在所有三种条件下都观察到了与实验1中类似的效应。此外，在所有三种条件下，在两个外侧枕颞电极处发现了P1和N1成分的增强。
