Section Biophysics, Department of Cognitive Neuroscience, Doders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Medical Centre, 6500 HB Nijmegen, The Netherlands.
J Neurosci. 2013 Jul 17;33(29):12077-89. doi: 10.1523/JNEUROSCI.2613-12.2013.
It is often assumed that decision making involves neural competition, accumulation of evidence "scores" over time, and commitment to a particular alternative once its scores reach a critical decision threshold first. So far, however, neither the first-to-threshold rule nor the nature of competition (feedforward or feedback inhibition) has been revealed by experiments. Here, we presented two simultaneously flashed targets that reversed their intensity difference during each presentation and instructed human subjects to make a saccade toward the brightest target. All subjects preferentially chose the target that was brightest during the first stimulus phase. Unless this first phase lasted only 40 ms, this primacy effect persisted even if the second, reversed-intensity phase lasted longer. This effect did not result from premature commitment to the initially dominant target, because a strong target imbalance in the opposite direction later drove nearly all responses toward that location. Moreover, there was a nonmonotonic relation between target imbalance and primacy: increasing the target imbalance beyond 40 cd/m(2) caused an attenuation of primacy. These are the hallmarks of hysteresis, predicted by models in which target representations compete through strong feedback. Reaction times were independent of the choice probability. This dissociation suggests that target selection and movement initiation are distinct phenomena.
人们通常认为决策涉及神经竞争，即随着时间的推移“分数”的积累，并在某个分数达到关键决策阈值时，就会做出特定的选择。然而，到目前为止，实验既没有揭示出先到阈值规则，也没有揭示竞争的性质（前馈或反馈抑制）。在这里，我们呈现了两个同时闪烁的目标，在每个呈现过程中改变它们之间的强度差异，并指导人类被试朝着最亮的目标进行扫视。所有被试都优先选择在第一个刺激阶段最亮的目标。除非这个第一阶段持续时间仅为 40 毫秒，否则这种优先效应会一直持续，即使第二个强度反转阶段持续时间更长。这种效应不是由于过早地对最初占主导地位的目标做出承诺，因为后来一个强烈的、相反方向的目标不平衡几乎导致所有反应都指向那个位置。此外，目标不平衡与优先性之间存在非单调关系：将目标不平衡增加到 40 cd/m(2)以上会导致优先性衰减。这些都是滞后的特征，这是通过强反馈竞争的模型所预测的。反应时间与选择概率无关。这种分离表明目标选择和运动启动是两个不同的现象。
