Togoli Irene, Collignon Olivier, Bueti Domenica, Fornaciai Michele
Université catholique de Louvain, Louvain-la-Neuve, Belgium.
International School for Advanced Studies (SISSA), Trieste, Italy.
J Cogn Neurosci. 2025 Feb 1;37(2):498-514. doi: 10.1162/jocn_a_02263.
The animal brain is endowed with an innate sense of number allowing to intuitively perceive the approximate quantity of items in a scene, or "numerosity." This ability is not limited to items distributed in space, but also to events unfolding in time and to the average numerosity of dynamic scenes. How the brain computes and represents the average numerosity over time, however, remains unclear. Here, we investigate the mechanisms and EEG signature of the perception of average numerosity over time. To do so, we used stimuli composed of a variable number (3-12) of briefly presented dot arrays (50 msec each) and asked participants to judge the average numerosity of the sequence. We first show that the weight of different portions of the stimuli in determining the judgment depends on how many arrays are included in the sequence itself: the longer the sequence, the lower the weight of the latest arrays. Second, we show systematic adaptation effects across stimuli in consecutive trials. Importantly, the EEG results highlight two processing stages whereby the amplitude of occipital ERPs reflects the adaptation effect (∼300 msec after stimulus onset) and the accuracy and precision of average numerosity judgments (∼450-700 msec). These two stages are consistent with processes involved with the representation of perceived average numerosity and with perceptual decision-making, respectively. Overall, our findings provide new evidence showing how the visual system computes the average numerosity of dynamic visual stimuli, and support the existence of a dedicated, relatively low-level perceptual mechanism mediating this process.
动物大脑具有一种天生的数字感，使其能够直观地感知场景中物品的大致数量，即“数量”。这种能力不仅限于空间中分布的物品，还适用于时间上展开的事件以及动态场景的平均数量。然而，大脑如何计算并表征随时间变化的平均数量仍不清楚。在此，我们研究随时间感知平均数量的机制和脑电图特征。为此，我们使用由可变数量（3至12个）的短暂呈现的点阵列（每个50毫秒）组成的刺激，并要求参与者判断序列的平均数量。我们首先表明，刺激的不同部分在决定判断时的权重取决于序列本身包含的阵列数量：序列越长，最新阵列的权重越低。其次，我们展示了连续试验中不同刺激间的系统性适应效应。重要的是，脑电图结果突出了两个处理阶段，其中枕叶事件相关电位的幅度反映了适应效应（刺激开始后约300毫秒）以及平均数量判断的准确性和精确性（约450至700毫秒）。这两个阶段分别与感知到的平均数量的表征过程和感知决策过程一致。总体而言，我们的研究结果提供了新的证据，表明视觉系统如何计算动态视觉刺激的平均数量，并支持存在一种专门的、相对低级的感知机制来介导这一过程。
