Heinze H J, Hinrichs H, Scholz M, Burchert W, Mangun G R
Otto-von-Guericke-Universität Magdeburg, Magdeburg, Germany.
J Cogn Neurosci. 1998 Jul;10(4):485-98. doi: 10.1162/089892998562898.
The neural mechanisms of hierarchical stimulus processing were investigated using a combined event-related potentials (ERPs) and positron emission tomography (PET) approach. Healthy subjects were tested under two conditions that involved selective or divided attention between local and global levels of hierarchical letter stimuli in order to determine whether and where hemispheric differences might exist in the processing of local versus global information. When attention was divided between global and local levels, the N2 component of the ERPs (260- to 360-msec latency) elicited by the target stimuli showed asymmetries in amplitude over the two hemispheres. The N2 to local targets was larger over the left hemisphere, but the N2 to global targets tended to be slightly larger over the right hemisphere. However, the shorter-latency, sensory-evoked P1 component (90- to 150-msec latency) was not different for global versus local targets under conditions of divided attention. In contrast, during selective attention to either global or local targets, asymmetries in the N2 component were not observed. But under selective attention conditions, the sensory-evoked P1 components in the extrastriate cortex were enlarged for global versus local attention. Increased regional cerebral blood flow in the posterior fusiform gyrus bilaterally was observed in the PET data during selective attention to either global or local targets, but neither these nor the P1 component showed any tendency toward hemispheric difference for global versus local attention. Neither were there any activations observed in the parietal lobe during selective attention to global versus local targets. Together these data indicate that early sensory inputs are not modulated to gate global versus local information differentially into the two hemispheres. Rather, later stages of processing that may be asymmetrically organized in the left and right hemispheres operate in parallel to process global and local aspects of complex stimuli (i.e., the N2 effect of the ERPs). This pattern of results supports models proposing that spatial frequency analysis is only asymmetric at higher stages of perceptual processing and not at the earliest stages of visual cortical analysis.
采用事件相关电位（ERP）和正电子发射断层扫描（PET）相结合的方法，研究了分层刺激处理的神经机制。健康受试者在两种条件下接受测试，这两种条件涉及在分层字母刺激的局部和全局水平之间进行选择性或分散性注意，以确定在处理局部与全局信息时，半球差异是否存在以及存在于何处。当在全局和局部水平之间分散注意时，目标刺激诱发的ERP的N2成分（潜伏期为260至360毫秒）在两个半球上的振幅表现出不对称性。左侧半球上对局部目标的N2更大，但右侧半球上对全局目标的N2往往略大。然而，在分散注意条件下，全局目标与局部目标的潜伏期较短的感觉诱发P1成分（潜伏期为90至150毫秒）并无差异。相反，在选择性注意全局或局部目标期间，未观察到N2成分的不对称性。但在选择性注意条件下，对于全局与局部注意，纹外皮层中的感觉诱发P1成分在全局注意时会增大。在PET数据中，当选择性注意全局或局部目标时，双侧后梭状回的局部脑血流增加，但这些以及P1成分在全局与局部注意方面均未表现出任何半球差异倾向。在选择性注意全局与局部目标期间，顶叶也未观察到任何激活。这些数据共同表明，早期感觉输入不会被调节以将全局与局部信息差异性地传入两个半球。相反，可能在左右半球不对称组织的后期处理阶段并行运作，以处理复杂刺激的全局和局部方面（即ERP的N2效应）。这种结果模式支持了这样的模型，即空间频率分析仅在知觉处理的较高阶段是不对称的，而在视觉皮层分析的最早阶段并非如此。
