50 apples in a row. Is the brain immediately able to distinguish, when seeing these apples, whether it is indeed 50 apples and not 49, or 51?
Our brain has an instinctive ability to approximate the numerosity of the apples at a glance. This so-called ‘approximate number system’ is an important and basic skill. Both humans and animals possess this skill. Even human babies have this skill. For instance, this skill allows us to determine which plate contains more biscuits. It is an old evolutionary skill that is thought to be at the foundation of our mathematical abilities. There is a small area in our brain, the size of a postage stamp, which is involved in the perception of numerosity. The lower the number of items, the more brain cells will be involved. If the number is 4 or 5, more brain cells will respond than when the number is 49, 50 or 51. Consequently, we can determine the difference between 4 or 5 apples at a glance, but we cannot directly estimate whether we see 49, 50, or 51 apples.