Center for Mind/Brain Sciences-CIMeC, University of Trento, Rovereto, Italy.
Eur J Neurosci. 2021 Aug;54(3):4971-4984. doi: 10.1111/ejn.15352. Epub 2021 Jul 13.
Extracting the number of objects in perceived scenes is a fundamental cognitive ability. Number processing is proposed to rely on two consecutive stages: an early object location map that captures individuated objects in a location-specific way and a subsequent location-invariant representation that captures numerosity at an abstract level. However, it is unclear whether this framework applies to small numerosities that can be individuated at once ("subitized"). Here, we reanalyzed data from two electroencephalography (EEG) experiments using multivariate pattern decoding to identify location-specific and location-invariant stages of numerosity processing in the subitizing range. In these experiments, one to three targets were presented in the left or right hemifield, which allowed for decoding target numerosity within each hemifield separately (location specific) or across hemifields (location invariant). Experiment 1 indicated the presence of a location-specific stage (180-200 ms after stimulus), followed by a location-invariant stage (300 ms after stimulus). A time-by-channel searchlight analysis revealed that the early location-specific stage is most evident at occipital channels, whereas the late location-invariant stage is most evident at parietal channels. Experiment 2 showed that both location-specific and location-invariant components are engaged only during tasks that explicitly require numerosity processing, ruling out automatic, and passive recording of numerosity. These results suggest that numerosity coding in subitizing is strongly grounded on an attention-based, location-specific stage. This stage overlaps with the subsequent activation of a location-invariant stage, where a full representation of numerosity is finalized. Taken together, our findings provide clear evidence for a temporal and spatial segregation of location-specific and location-invariant numerosity coding of small object numerosities.
提取感知场景中的物体数量是一种基本的认知能力。有人提出，数量处理依赖于两个连续的阶段：一个早期的物体位置图，以特定位置的方式捕获个体物体，以及随后的位置不变表示，以抽象的水平捕获数量。然而，目前尚不清楚该框架是否适用于可以一次识别的小数量（“瞬间识别”）。在这里，我们使用多变量模式解码重新分析了两项脑电图 (EEG) 实验的数据，以确定在瞬间识别范围内数量处理的位置特定和位置不变阶段。在这些实验中，一个到三个目标出现在左或右视野中，这允许分别在每个视野内（位置特定）或在视野之间（位置不变）解码目标数量。实验 1 表明存在一个位置特定的阶段（刺激后 180-200 毫秒），随后是一个位置不变的阶段（刺激后 300 毫秒）。时间-通道搜索灯分析表明，早期的位置特定阶段在枕部通道最为明显，而晚期的位置不变阶段在顶叶通道最为明显。实验 2 表明，只有在明确要求数量处理的任务中，位置特定和位置不变的成分才会被激活，排除了数量的自动和被动记录。这些结果表明，在瞬间识别中，数量编码强烈基于基于注意力的位置特定阶段。该阶段与随后位置不变阶段的激活重叠，在该阶段中完成了数量的完整表示。总之，我们的研究结果为小物体数量的位置特定和位置不变数量编码的时间和空间分离提供了明确的证据。
