Functional Anatomy Of Perceptual and Attentional Systems in the Primate Brain

由于视觉系统的处理能力有限，一个典型的场景包含许多不同的对象，这些对象竞争神经表征。在神经水平上，多个刺激之间的竞争通过它们的视觉诱发反应的相互抑制来证明，并且在感受野水平上发生得最强烈。多个对象之间的竞争既可能受到自下而上的感觉驱动机制（如刺激显著性）的影响，也可能受到自上而下的影响（如选择性注意）的影响。 虽然表征刺激之间的竞争最终在视觉皮层内解决，但自上而下的偏置信号的来源可能来自额叶和顶叶皮层的分布式网络。 最近，我们报道了前额叶皮层（PFC）病变的猴子在他们的自上而下控制切换能力选择性受损。 在过去的一年里，我们询问了后顶叶皮层（PPC）损伤的猴子是否会表现出相似或不同的行为效应。 我们的研究结果表明，与PFC病变的猴子不同，PPC病变的猴子在切换自上而下控制的能力方面没有选择性受损。 相反，它们在空间定位它们需要区分的目标方面具有选择性损害。 因此，PFC在改变任务需求的基础上切换注意力控制的能力中起着至关重要的作用，而PPC在将注意力资源分配到行为相关的空间位置中起着至关重要的作用。 这些调查结果正在准备出版。 在过去的一年中，我们还旨在通过测试关于注意力分散是否来自增加的感官驱动的干扰或低效的自上而下的控制的假设，更好地表征ADHD中注意力分散的性质。 我们采用了一个注意过滤范式，其中的歧视难度和分心物显着性参数操纵。增加辨别困难应该会增加自上而下过程的负荷，而增加干扰物的显著性应该会导致更强的感官干扰。我们发现了一个显着的相互作用的歧视困难和分心物的显着性：对于困难的歧视，ADHD儿童过滤干扰一样有效的健康儿童和成年人，所有群体都慢于响应高与低显着性分心物。相比之下，对于简单的区分，ADHD儿童比健康儿童和成人慢得多，犯的错误也更多。为了便于辨别，健康儿童和成人可以像过滤低显著性干扰物一样容易地过滤掉高显著性干扰物，但ADHD儿童对低显著性干扰物的反应要比对高显著性干扰物的反应慢。 事实上，ADHD儿童表现出有效的注意力过滤时，任务要求高，但显示不足和非典型的干扰过滤低任务要求下，表明过滤机制保持完好，在这些儿童，但触发激活注意力是选择性受损。 关于注意力在知觉学习中所起的作用，文献中有相互矛盾的证据。 为了进一步研究这个问题，我们独立地操纵外源性（非自愿）和内源性（自愿）的注意力，并测量在不同象限的视野中呈现的定向刺激的感知学习率。 通过这种方式，我们可以在有人值守、分开值守和无人值守的位置跟踪学习。 我们还测量了训练前后刺激的对比度阈值。 我们的研究结果表明，外源性和内源性的注意，在执行方向歧视的准确性提高到更大的程度在有人值守的位置比在无人值守的位置。 然而，重要的是，只有外源性的注意力导致对比度阈值的提高。 这些发现表明，外源性和内源性的注意促进知觉学习，但这两种类型的注意可能是由不同的神经机制介导的。 目前正在编写一份报告这些调查结果的文件。 视网膜定位选择性，通过功能磁共振成像活动模式，与视觉刺激的位置一致的变化，已被证明在许多人类大脑区域，特别是枕叶视觉皮层和额叶和顶叶区域与内源性（自愿）的注意。我们假设，retinotopic的选择性也存在于活跃的区域在外源性（非自愿）的注意。为了验证这一假设，我们获得了功能磁共振成像数据，而受试者保持被动固定在中央十字架。在不可预测的时间间隔，刺激组成的阵列迅速扩大的圆圈出现在六个空间位置之一。积极的功能磁共振成像激活的刺激介绍被确定在多个大脑区域，包括颞顶交界处（TPJ），一个区域以前牵连外源性注意。TPJ激活似乎没有被组织为整个皮质表面的地图。然而，多体素模式识别分析成功地预测了fMRI的反应，每一个的15个刺激位置对，表明在TPJ的活动模式依赖于retinotopic刺激位置。 这是第一次证明空间位置是在与外源性注意力相关的大脑区域中表示的。

A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the mutual suppression of their visually evoked responses and occurs most strongly at the level of the receptive field. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms, such as stimulus salience, and top-down influences, such as selective attention. Although the competition among stimuli for representation is ultimately resolved within visual cortex, the source of top-down biasing signals likely derives from a distributed network of areas in frontal and parietal cortex. Recently, we reported that monkeys with lesions of prefrontal cortex (PFC) are selectively impaired in their ability to switch top-down control. In the past year, we asked whether monkeys with lesions of posterior parietal cortex (PPC) would show similar or different behavioral effects. Our results showed that, unlike monkeys with PFC lesions, those with PPC lesions are not selectively impaired in their ability to switch top-down control. Rather, they have a selective impairment in spatially locating targets they are required to discriminate. Thus, the PFC plays a critical role in the ability to switch attentional control on the basis of changing task demands, whereas the PPC plays a critical role in allocating attentional resources to behaviorally relevant spatial locations. These findings are being prepared for publication. During the past year, we also aimed to better characterize the nature of distractibility in ADHD by testing hypotheses about whether distractibility arises from increased sensory-driven interference or from inefficient top-down control. We employed an attentional filtering paradigm in which discrimination difficulty and distractor salience were parametrically manipulated. Increased discrimination difficulty should add to the load of top-down processes, whereas increased distractor salience should result in stronger sensory interference. We found a striking interaction of discrimination difficulty and distractor salience: For difficult discriminations, ADHD children filtered distractors as efficiently as healthy children and adults, and all groups were slower to respond with high vs. low salience distractors. In contrast, for easy discriminations, ADHD children were much slower and made more errors than healthy children and adults. For easy discriminations, healthy children and adults filtered out high salience distractors as easily as low salience distractors, but ADHD children were slower to respond on trials with low salience distractors than they did on trials with high salience distractors. The fact that ADHD children exhibit efficient attentional filtering when task demands are high, but show deficient and atypical distractor filtering under low task demands suggests that filtering mechanisms remain intact in these children but the trigger for activating attention is selectively impaired. There is conflicting evidence in the literature regarding the role played by attention in perceptual learning. To further examine this issue, we independently manipulated exogenous (involuntary) and endogenous (voluntary) attention and measured the rate of perceptual learning of oriented stimuli presented in different quadrants of the visual field. In this way, we could track learning at attended, divided-attended, and unattended locations. We also measured contrast thresholds of the stimuli before and after training. Our results showed that, for both exogenous and endogenous attention, accuracy in performing the orientation discrimination improved to a greater extent at attended than at unattended locations. Importantly, however, only exogenous attention resulted in improved contrast thresholds. These findings suggest that both exogenous and endogenous attention facilitate perceptual learning, but that these two types of attention may be mediated by different neural mechanisms. A paper reporting these findings is currently in preparation. Retinotopic selectivity, as measured by fMRI activity patterns that vary consistently with the location of visual stimuli, has been documented in many human brain regions, notably occipital visual cortex and frontal and parietal regions associated with endogenous (voluntary) attention. We hypothesized that retinotopic selectivity also exists in regions active during exogenous (involuntary) attention. To test this hypothesis, we acquired fMRI data while subjects maintained passive fixation on a central cross. At unpredictable time intervals, stimuli consisting of an array of rapidly expanding circles appeared at one of six spatial locations. Positive fMRI activations to the stimulus presentations were identified in multiple brain regions including the temporoparietal junction (TPJ), a region previously implicated in exogenous attention. The TPJ activations did not appear to be organized as a map across the cortical surface. However, multivoxel pattern recognition analysis successfully predicted fMRI responses to every one of the fifteen stimulus location pairs, demonstrating that patterns of activity in TPJ depend on the retinotopic stimulus location. This is the first demonstration that spatial locations are represented in a brain region associated with exogenous attention.