How Your Brain Processes Quantities

This piece, by Onno Berkan, was published on 03/04/25. The original text, by Togoli et al., was published by the Journal of Cognitive Neuroscience on 02/01/25.

This joint European study focused on numerosity (the process of number perception), investigating how our brains process and understand the average number of objects we see over time. The researchers investigated how crowded a street is based on people walking in and out of view. 

The researchers conducted experiments in which participants watched quick sequences of dot patterns displayed on a computer screen. These sequences showed different numbers of dots that changed rapidly, and participants had to judge whether the average number of dots they saw was higher or lower than a reference number they had memorized. The sequences varied in the number of dots shown and the length of time they lasted.

The results revealed several significant findings. First, people could accurately judge the average number of dots, even though it was challenging. When looking at how people processed the information, the experimenter found that the way people weighted different parts of the sequence depended on how long it was. People gave more importance to the dots shown at the end for shorter sequences, while for longer sequences, they paid more attention to what they saw at the beginning.

Interestingly, the study found that what people saw in previous trials affected how they perceived the current display, showing a phenomenon called "adaptation". This means that after seeing a sequence with many dots, people tended to perceive the following sequence as having fewer dots, and vice versa.

The researchers also recorded brain activity using EEG and found patterns corresponding to how people processed these numerical sequences. They identified two main processing stages in the brain: an early spike (around 300 milliseconds) that represented the initial perception of the average number, and a later spike related to making decisions about what was seen.

This research is particularly relevant because in real life, we often need to estimate changing quantities over time rather than just static amounts. When we judge how crowded a street is, we're not just taking a single snapshot but averaging what we see over time. The study suggests that our brains have specialized mechanisms for these kinds of dynamic numerical information.

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