Dmochowski Jacek P, Norcia Anthony M
Department of Psychology, Stanford University, Stanford, CA, United States of America.
PLoS One. 2015 Nov 23;10(11):e0143339. doi: 10.1371/journal.pone.0143339. eCollection 2015.
The mechanisms of perceptual decision-making are frequently studied through measurements of reaction time (RT). Classical sequential-sampling models (SSMs) of decision-making posit RT as the sum of non-overlapping sensory, evidence accumulation, and motor delays. In contrast, recent empirical evidence hints at a continuous-flow paradigm in which multiple motor plans evolve concurrently with the accumulation of sensory evidence. Here we employ a trial-to-trial reliability-based component analysis of encephalographic data acquired during a random-dot motion task to directly image continuous flow in the human brain. We identify three topographically distinct neural sources whose dynamics exhibit contemporaneous ramping to time-of-response, with the rate and duration of ramping discriminating fast and slow responses. Only one of these sources, a parietal component, exhibits dependence on strength-of-evidence. The remaining two components possess topographies consistent with origins in the motor system, and their covariation with RT overlaps in time with the evidence accumulation process. After fitting the behavioral data to a popular SSM, we find that the model decision variable is more closely matched to the combined activity of the three components than to their individual activity. Our results emphasize the role of motor variability in shaping RT distributions on perceptual decision tasks, suggesting that physiologically plausible computational accounts of perceptual decision-making must model the concurrent nature of evidence accumulation and motor planning.
感知决策机制常通过反应时间（RT）测量来研究。经典的决策序列采样模型（SSMs）将RT视为非重叠的感官、证据积累和运动延迟之和。相比之下，最近的经验证据暗示了一种连续流范式，其中多个运动计划与感官证据的积累同时演变。在这里，我们采用基于逐次试验可靠性的成分分析方法，对在随机点运动任务中获取的脑电图数据进行分析，以直接描绘人脑中的连续流。我们识别出三个在地形上不同的神经源，其动态变化在反应时刻呈现同步上升，上升的速率和持续时间区分快速和慢速反应。这些源中只有一个，即顶叶成分，表现出对证据强度的依赖性。其余两个成分的地形与运动系统的起源一致，它们与RT的协变在时间上与证据积累过程重叠。在将行为数据拟合到一个流行的SSM后，我们发现模型决策变量与这三个成分的联合活动比与它们的个体活动更紧密匹配。我们的结果强调了运动变异性在塑造感知决策任务中RT分布方面的作用，表明感知决策的生理上合理的计算解释必须对证据积累和运动计划的并发性质进行建模。
