Centre de Neuroscience Cognitive, Centre National de la Recherche Scientifique, Université Claude Bernard Lyon Bron, France.
Front Integr Neurosci. 2012 Jun 29;6:39. doi: 10.3389/fnint.2012.00039. eCollection 2012.
The posterior parietal cortex participates to numerous cognitive functions, from perceptual to attentional and decisional processes. However, the same functions have also been attributed to the frontal cortex. We previously conducted a series of reversible inactivations of the lateral intraparietal area (LIP) and of the frontal eye field (FEF) in the monkey which showed impairments in covert visual search performance, characterized mainly by an increase in the mean reaction time (RT) necessary to detect a contralesional target. Only subtle differences were observed between the inactivation effects in both areas. In particular, the magnitude of the deficit was dependant of search task difficulty for LIP, but not for FEF. In the present study, we re-examine these data in order to try to dissociate the specific involvement of these two regions, by considering the entire RT distribution instead of mean RT. We use the LATER model to help us interpret the effects of the inactivations with regard to information accumulation rate and decision processes. We show that: (1) different search strategies can be used by monkeys to perform visual search, either by processing the visual scene in parallel, or by combining parallel and serial processes; (2) LIP and FEF inactivations have very different effects on the RT distributions in the two monkeys. Although our results are not conclusive with regards to the exact functional mechanisms affected by the inactivations, the effects we observe on RT distributions could be accounted by an involvement of LIP in saliency representation or decision-making, and an involvement of FEF in attentional shifts and perception. Finally, we observe that the use of the LATER model is limited in the context of a visual search as it cannot fit all the behavioral strategies encountered. We propose that the diversity in search strategies observed in our monkeys also exists in individual human subjects and should be considered in future experiments.
顶叶后皮质参与了众多认知功能，从感知到注意和决策过程。然而，同样的功能也归因于额叶皮质。我们之前在猴子中进行了一系列外侧顶内区（LIP）和额眼区（FEF）的可逆失活实验，结果表明，在隐蔽视觉搜索表现中存在损伤，主要表现为检测对侧目标所需的平均反应时间（RT）增加。在这两个区域的失活效应之间观察到只有细微的差异。特别是，LIP 的缺陷程度取决于搜索任务的难度，但 FEF 则不然。在本研究中，我们重新检查这些数据，试图通过考虑整个 RT 分布而不是平均 RT，来区分这两个区域的特定参与。我们使用 LATER 模型来帮助我们解释失活对信息积累率和决策过程的影响。我们表明：（1）猴子可以使用不同的搜索策略来执行视觉搜索，要么通过并行处理视觉场景，要么通过并行和串行过程的组合；（2）LIP 和 FEF 的失活对两只猴子的 RT 分布有非常不同的影响。尽管我们的结果对于失活所影响的确切功能机制没有定论，但我们在 RT 分布上观察到的影响可以通过 LIP 参与显著度表示或决策，以及 FEF 参与注意力转移和感知来解释。最后，我们观察到，在视觉搜索的背景下，LATER 模型的使用受到限制，因为它不能适应所有遇到的行为策略。我们提出，我们的猴子中观察到的搜索策略的多样性也存在于个体人类受试者中，应该在未来的实验中考虑。
