Jeong Su Keun, Xu Yaoda
J Vis. 2016 Aug 1;16(10):2. doi: 10.1167/16.10.2.
The human parietal cortex exhibits a preference to contralaterally presented visual stimuli (i.e., laterality) as well as an asymmetry between the two hemispheres with the left parietal cortex showing greater laterality than the right. Using visual short-term memory and perceptual tasks and varying target location predictability, this study examined whether hemispheric laterality and asymmetry are fixed characteristics of the human parietal cortex or whether they are dynamic and modulated by the deployment of top-down attention to the target present hemifield. Two parietal regions were examined here that have previously been shown to be involved in visual object individuation and identification and are located in the inferior and superior intraparietal sulcus (IPS), respectively. Across three experiments, significant laterality was found in both parietal regions regardless of attentional modulation with laterality being greater in the inferior than superior IPS, consistent with their roles in object individuation and identification, respectively. Although the deployment of top-down attention had no effect on the superior IPS, it significantly increased laterality in the inferior IPS. The deployment of top-down spatial attention can thus amplify the strength of laterality in the inferior IPS. Hemispheric asymmetry, on the other hand, was absent in both brain regions and only emerged in the inferior but not the superior IPS with the deployment of top-down attention. Interestingly, the strength of hemispheric asymmetry significantly correlated with the strength of laterality in the inferior IPS. Hemispheric asymmetry thus seems to only emerge when there is a sufficient amount of laterality present in a brain region.
人类顶叶皮层对向对侧呈现的视觉刺激表现出偏好（即偏侧性），并且两个半球之间存在不对称性，左侧顶叶皮层的偏侧性比右侧更强。本研究通过视觉短期记忆和感知任务，并改变目标位置的可预测性，来探究半球偏侧性和不对称性是人类顶叶皮层的固定特征，还是动态的，并受自上而下对目标所在半视野的注意力分配的调节。这里研究了两个顶叶区域，先前的研究表明它们分别参与视觉对象的个体化和识别，且分别位于顶内沟（IPS）的下部和上部。在三个实验中，无论注意力调节如何，在两个顶叶区域均发现了显著的偏侧性，下部IPS的偏侧性大于上部IPS，这分别与其在对象个体化和识别中的作用一致。尽管自上而下的注意力分配对上部IPS没有影响，但它显著增加了下部IPS的偏侧性。因此，自上而下的空间注意力分配可以增强下部IPS的偏侧性强度。另一方面，两个脑区均不存在半球不对称性，只有在自上而下的注意力分配时，下部IPS而非上部IPS才出现半球不对称性。有趣的是，半球不对称性的强度与下部IPS的偏侧性强度显著相关。因此，半球不对称性似乎只有在一个脑区存在足够程度的偏侧性时才会出现。
