Department of Psychology and Neuroscience Graduate Program, University of California, San Diego, La Jolla, CA 92093, USA.
J Neurosci. 2012 May 30;32(22):7723-33. doi: 10.1523/JNEUROSCI.5558-11.2012.
Most models assume that top-down attention enhances the gain of sensory neurons tuned to behaviorally relevant stimuli (on-target gain). However, theoretical work suggests that when targets and distracters are highly similar, attention should enhance the gain of neurons that are tuned away from the target, because these neurons better discriminate neighboring features (off-target gain). While it is established that off-target neurons support difficult fine discriminations, it is unclear if top-down attentional gain can be optimally applied to informative off-target sensory neurons or if gain is always applied to on-target neurons, regardless of task demands. To test the optimality of attentional gain in human visual cortex, we used functional magnetic resonance imaging and an encoding model to estimate the response profile across a set of hypothetical orientation-selective channels during a difficult discrimination task. The results suggest that top-down attention can adaptively modulate off-target neural populations, but only when the discriminanda are precisely specified in advance. Furthermore, logistic regression revealed that activation levels in off-target orientation channels predicted behavioral accuracy on a trial-by-trial basis. Overall, these data suggest that attention does not only increase the gain of sensory-evoked responses, but may bias population response profiles in an optimal manner that respects both the tuning properties of sensory neurons and the physical characteristics of the stimulus array.
大多数模型假设自上而下的注意力增强了对行为相关刺激（目标增益）敏感的感觉神经元的增益。然而，理论工作表明，当目标和分心物高度相似时，注意力应该增强与目标偏离的神经元的增益，因为这些神经元可以更好地区分相邻的特征（离目标增益）。虽然已经确定离目标神经元支持困难的精细辨别，但尚不清楚自上而下的注意力增益是否可以最佳地应用于信息丰富的离目标感觉神经元，或者是否无论任务需求如何，增益始终应用于目标神经元。为了测试人类视觉皮层注意力增益的最优性，我们使用功能磁共振成像和编码模型来估计在困难辨别任务期间一组假设的方向选择性通道中的响应分布。结果表明，自上而下的注意力可以自适应地调节离目标的神经元群体，但仅当判别标准在预先精确指定时才如此。此外，逻辑回归表明，离目标方向通道中的激活水平可以根据每次试验的基础预测行为准确性。总的来说，这些数据表明，注意力不仅会增加感觉诱发反应的增益，而且可能以一种尊重感觉神经元的调谐特性和刺激阵列的物理特性的最佳方式偏向群体反应分布。
